EMBE i/IAEA D RICULTURE

i L U ^ j

EM BE

i/IA E A D

RICULTURE

1 1 И

I N T E R N A T I O N A L A T O M I C E N E R G Y A G E N C Y , V I E N N A , 1971

DISINFESTATION OF FRUIT BY IRRADIATION

P A N E L PROCEEDINGS SERIES

DISINFESTATION OF FRUIT BY IRRADIATION

PROCEEDINGS OF A P A N E L ON TH E USE OF IR R AD IAT IO N TO SOLVE

Q U AR AN TIN E PR O B LE M S IN THE IN T E R N A T IO N A L F R U IT TR AD E ,

O RGANIZED B Y THE JO INT F A O / IA E A DIVISION OF ATO M IC ENERG Y

IN FOOD AND A G R IC U LTU R E , AND H E LD IN HONOLULU, H AW AII, U N ITED STATES OF A M E R IC A

7-11 DECEM BER 1970

IN T E R N A T IO N A L A TO M IC ENERG Y AG EN C Y V IEN N A , 1971

D IS IN FESTATIO N OF F R U IT B Y IR R A D IA T IO N IA E A , V IE N N A , 1971

STI/PUB/299

Printed by the IAEA in Austria October 1971

FOREWORD

The exchange o f products in international trade in creases the r isk o f tran s fe rr in g a pest from one country to another and, th ere fo re , most governm ents have introduced plant quarantine laws defin ing the conditions under which produce may be im ported. Such laws requ iring the d is in festation o f trop ica l fru its before im portation is perm itted are particu la r ly im portant when considering the expansion o f m arkets fo r trop ica l fru its . Because current p rescrib ed methods fo r the d isin festation o f fru its have lim itations and the fact that health hazards m ay arise from chem ical residues, it is evident that other methods must be developed. The e ffec tiven ess o f using ion izing radiation fo r the d isin festation o f fru its to com ply with quarantine regulations has been sa tis fa c to r ily dem onstrated and fu rtherm ore, fo r some fru its an additional benefit from this treatm ent is the delaying o f the ripen ing p rocess.

A Panel on the Use o f Irrad ia tion to Solve Quarantine P rob lem s in the International F ru it T rade was convened in Hawaii by the Joint FAO /IAE A D iv is ion o f A tom ic E nergy in Food and Agricu ltu re from 7 to 11 D ecem ber 1970, at the invitation o f the U .S . A tom ic E nergy Com m ission and the State o f Hawaii, to advise the D irec to rs G enera l o f the Food and Agricu ltu re O rgan ization o f the United Nations and o f the International A tom ic E nergy Agency on how these organ izations can best fu lf il l th e ir ro le s in prom oting the use o f irrad ia tion in so lving quarantine prob lem s which ham per the international fru it trade.

The Panel m em bers w ere 16 experts from six countries. A detailed evaluation was made o f the prospects fo r the industria l application o f irrad ia tion in the d isin festation o f trop ica l fru its . These P roceed ings contain the contributions from the m em bers o f the Panel, together with the genera l conclusions, considerations and recom m endations fo r fu rther ac tiv ities in this fie ld .

CONTENTS

O verv iew o f USAEC In terest in Food Irrad ia tion (P L 422/1) ............... 1E. E. F o w l e r

Hawaii Developm ent Irrad ia to r — A Tool in T rop ica l Fru itP ro cess in g (P L 4 2 2 /2 ).................................................................................. 7K .K . O t a g a k i

Quarantine Regulations and R estrictions and the ir E ffec t on Im port and Export o f P lan t M ateria l and Com m odities(P L 422/3) ....................................................................................................... 1 1E . W. J a c k s o n

USDA R esearch on Irrad ia tion to Solve Quarantine P rob lem sin F ru it (P L 422/4) ...................................................................................... 23H. C. C o x

Basis fo r D eveloping Quarantine Treatm ents fo r F ru it F lie s(P L 422/5) ....................................................................................................... 27A .K . B u r d i t t , J r . , S . T . S e o a n d J .W . B a l o c k

Dose Requ irem ents fo r Quarantine Treatm ent o f F ru it F lie swith Gamma Radiation (P L -4 2 2 / 6 )............................................................ 33A .K . B u r d i t t , Jr. a n d S . T . S e o

D osim etry, T o leran ce and S h e lf-L ife Extension Related to D isin festation o f T ro p ica l F ru its by Gamma Irrad ia tion(P L 422/7) ....................................................................................................... 43

. J . H . M o y , E .K . A k a m i n e , J .L . B r e w b a k e r ,I .W . B u d d e n h a g e n , E. R o s s , H. S p i e l m a n n ,M .D . U p a d h y a , N. W e n k a m , D. H e l b e r , A .M . D o l l a r ,M. H a n a o k a a n d G. A. M c C l i s h

Radiation Techniques and the Export o f Mangoes from thePh ilipp ines (P L 4 2 2 /8 )................................................................................. 59I. D. C l a r k e

P h ys io lo g ica l E ffec ts o f Gamma Radiation on Some T ro p ica l F ru its(P L 422/9) ....................................................................................................... 65A . S r e e n i v a s a n , P . T h o m a s a n d S .D . D h a r k a r

Chem ical, Econom ic, P h ys ica l and P h ys io lo g ica l L im ita tionsto Irrad ia tion o f F ru its (P L 422/10) ........................................................ 93E . C . M a x i e , N. F. S o m m e r a n d F . G . M i t c h e l l

Sensory, Chem ical and Nutritional Evaluation on the E ffec t o f Ion iz ing Radiation on Mangoes ( M angifera ind ica, Linn),Carabao V a rie ty (P L 422/11) ..................................................................... 101I .S. P a b l o , Juanita A . M a n a l o , V ic to r ia A . C a r d e ñ o

Recent R esearch on the Influence o f Irrad ia tion o f Certain T rop ica lF ru its in Thailand (P L 422/12) ................................................................ 113P . L o a h a r a n u

Extension o f Storage L ife o f Bananas by Gamma Irrad ia tion(P L 422/13) ..................................................................................................... 125Hung-yen K a o

S em i-C om m erc ia l-S ca le Studies on Irrad ia ted Papaya (P L 422/14) . . 137A . M . D o l l a r , M. H a n a o k a , G .A . M c C l i s h a n d J .H . M o y

B en efit-C ost Ana lys is fo r Export Papaya D isin fested byIon izing Radiation (P L 422/15) ................................................................ 157A .M . D o l l a r , M. H a n a o k a a n d G .A . M c C l i s h

Sum m aries, Conclusions, Considerations andRecom m endations o f the Panel .................................................................. 167L is t o f Panel M em bers ................................................................................... 175

PL-422/1

OVERVIEW OF USAEC INTEREST IN FOOD IRRADIATION

E.E. F O WLER

Division of Isotopes Development, U.S. Atomic Energy Commission,

Washington, D . C . ,

United States of America

Abstract

OVERVIEW OF USAEC INTEREST IN FOOD IRRADIATION.This paper contains a summary progress statement on the U. S. Atomic Energy Commission's program

on food irradiation. Detailed information on the work supported by the USAEC on the disinfestation by irradiation of papayas is given and also the actual status of research and the economic prospects of this treatment.

M ost o f you are fa m ilia r with the goals and ob jectives of the U .S .A tom ic E nergy C om m ission 1 s p rogram on radiation p reserva tion of foods.Our m iss ion is to develop technology leading to the com m erc ia liza tion of low -dose radiation p rocess ing of perishable foods fo r gen era l consum er use. Th is is distinguished from the Departm ent of the A rm y program on radiation s te r iliza tion of foods fo r m ilita ry purposes.

A t f ir s t glance, food would appear to be a highly unusual area toward which the A tom ic E nergy Com m ission would d irec t its attention. H ow ever, the atom can, and is contributing in many ways in helping to, a llev ia te w orld food prob lem s.

In our current concern o ve r the w o r ld 's food supply, emphasis is p laced on the production o f m ore food. H ow ever, much m ore food would be ava ilab le , if we could cut down on the loss of food a lready in production. The United Nations' Food and A gricu ltu re O rganization (FA O ) estim ates that one-fifth o f the w o r ld 's entire food crop (many tim es the production of the United States) is destroyed by insects, m icroorgan ism s and other pests.In some spec ific areas, losses m ay run as high as 50 per cent of the entire annual production. F o r exam ple, in India annual crop loss o f fru it and vegetab les in transport and storage runs to about f iv e m illion tons annually.In A fr ic a , up to 50 per cent o f the Continent's dried fish is lost through insect in festation . It is estim ated that about 50 m illion people could be fed each yea r by the gra in lost through pest destruction. In one of the most advanced countries in Latin A m er ica n early a th ird of the food harvested spoils b e fo re reaching the consum er.

Radioisotopes can be e ffe c tiv e in helping to reduce such staggering losses in s e ve ra l ways: in decreasing the p erishab ility of some foods during tim es when they m ight be in storage, in transport o r in the m arket p lace; in delaying the ripen ing of fru its and vegetab les so they can reach the consum er in edib le condition; in k illing many pests, parasites and bacteria that destroy crops and cattle; and, in helping to breed health ier strains of lives tock and crops - lives tock that produce m ore and b etter m eat and crops that have a h igher y ie ld and can re s is t certa in d iseases and adverse weather conditions.

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2 FOWLER

Let me mention b r ie f ly som e of the work being ca rr ied out in these fie ld s . F ir s t l e t 's look at the use of radiation to d isin fest gra in . Th is application could prove to be ex trem e ly im portant. It has been indicated that in term s of w orld production o f c e rea l grain , a 50 per cent decrease in losses would resu lt in annual protein savings of nine m illion tons, enough to feed nearly 300 m illion people. A s many of you m ay know, through one of the U S A E C 's food irrad ia tion p rogram s, a dem onstration gra in irrad ia to r is in operation at the U .S . Departm ent o f A g r icu ltu re ' s (USDA) Stored- Products Insect R esearch and Developm ent Labora tory , Savannah, G eorg ia . Th is unit, which uses the rad io isotope cob a lt-60 as its source, can d isin fest 5000 lb o f bulk grain per hour. We have made irrad ia to rs available on loan to countries overseas that want to conduct s im ila r work.

It is in terestin g to observe here that there is g rea t in terest abroad in food irrad ia tion . Today m ore than 50 countries a lready have active research and developm ent p rogram s in the fie ld .

In addition to using rad io isotopes to d isin fest and p rese rve food, we are using them to reduce losses in production and to grow better food, both lives to ck and crops.

The sc rew worm scourge that attacked cattle in the Southeastern part of the United States was v ir tu a lly elim inated by a campaign that used the rad ia tion -s te r iliza tion technique. This same technique, the s te r ile m ale re lea se method, is being applied in many areas of the w orld , in p ro gram s invo lv ing in ternational co-operation through the IA E A .

F in a lly , in this gen era l area o f rad io isotopes and food, we continue to make p rogress in developing and applying those techniques that use rad io isotope tra ce rs and radiation to help us produce hea lth ier strains o f crops and livestock . These include crop plants that have la rg e r y ie lds , r e s is t certa in d iseases and weather conditions, and even lend them selves to m ore e ffic ien t methods o f harvesting.

Since the in itia tion o f the U SA E C 's food irrad ia tion p rogram in 1960, we have screened som e 50 products. The purpose o f the screen ing p rocess was to identify those foods dem onstrating the grea test technical and econom ic feas ib ility fo r ultim ate com m erc ia l developm ent and m arket acceptance. Em phasis in the screen ing process was on m a rk e t- life extension o f fresh foods. Th is search led to the se lection o f s ix foods fo r fu ll-s ca le research and developm ent, wholesom eness and safety testing and preparation of petitions fo r submission to the Food and Drug Adm in istration (FD A ) during the period 1970 to 1975. The products se lected w ere papayas, s traw berries , fin fish , shrim p, m ushroom s, and fresh red m eats.

A s many o f you know, our e ffo rts w ere disrupted because o f fis ca l res tra in ts and because o f esca lating Food and Drug Adm in istration requ irem en ts fo r c learance o f foods p rocessed using ion izing radiation. As a consequence, the USAEC 1 s p rogram is currently lim ited to seeking FD A approval fo r three products:

( 1 ) papayas fo r quarantine disin festation and delayed ripening;( 2 ) fresh s traw b err ies to reduce and control decay and rot; and(3 ) fin fish to extend fresh m arket life by reduction of spoilage flo ra .

These products w ere chosen because o f technologica l and econom ic considerations. I f it had becom e necessary to reduce the program to one product, we would have chosen papayas. The reason fo r this is s tra igh t

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forw ard ; we fe e l s trongly that the irrad ia tion d isin festation process can gain quick acceptance in the trop ica l fru it trade once clearance fo r genera l consum er use is obtained from the Food and Drug Adm in istration . The product is good, the econom ics look reasonable and the m arket appears p rom ising.

Th ere is good prospect that the p rocess could be used com m erc ia lly as ea r ly as 1972. Our current plans a re to com plete a ll work on papayas by June 1971 and to submit a petition to the Food and Drug Adm in istration fo r clearance during the fo llow ing 1 2 months.

The USAEC has been sponsoring resea rch work in the State o f Hawaii s ince 1964. At that tim e, the U n ivers ity o f Hawaii began p re lim in a ry studies on the radiation p rocess in g o f agricu ltu ra l products indigenous to the State. Favourab le resu lts w ere obtained fo r papayas, mangoes, bananas, and other trop ica l fru it. H ow ever, the m ost a ttractive from a technolog ica l and econom ic standpoint w ere papayas. The resu lts o f the work conducted at the U n ivers ity o f Hawaii indicated a th ree- to four-day m a rk e t- life extension fo r papayas when they w ere subjected to irrad ia tion at a dose le v e l o f 75 to 100 k ilo rad a fte r the standard hot-w ater treatm ent. A t this dose le v e l, the Hawaiian F ru it F ly is e ffe c t iv e ly controlled , and the irrad ia tion p rocess would enable papayas to m eet the U SD A 's quarantine regulation .In fact, the USDA lifted its quarantine requ irem ent, perm itting us to com m erc ia lly ship experim enta l lots o f rad ia tion -d is in fested papayas to the mainland to co llec t data requ ired fo r the petition to be submitted to the FD A . We established, th ere fo re , that the chem ical fumigant, ethylene d ibrom ide, could be rep laced by irrad ia tion fo r con trolling the Hawaiian F ru it F ly . In addition, the radiation p rocess a lso delays m aturation, provid ing a sligh tly lon ger m arket life .

The next lo g ica l step was to build a p ilo t plant to dem onstrate if the labora tory resu lts could be con firm ed on a n ea r-com m erc ia l sca le . To provide fo r this, we contracted with the State o f Hawaii Department o f A gricu ltu re fo r the construction and operation o f the Hawaiian Developm ent Irra d ia to r (HD I). I w ish to recogn ize that the State o f Hawaii co-financed the construction o f the ir ra d ia to r with the U.S. A tom ic E nergy Com m ission. The ultim ate ob jec tive o f the work being ca rr ied out by Dr. Otagaki and his a ssocia tes using the HDI is to establish p rocess conditions and to develop econom ic in form ation which w ill fo s te r ea rly com m erc ia liza tion o f the p rocess once Food and Drug Adm in istration approval is obtained fo r the products involved. In addition, the HDI is used to provide irrad ia tion s e rv ic e s to the U n ivers ity o f Hawaii, the U SD A 's A gricu ltu re R esearch S e rv ice F ru it F ly Labora tory , and other agencies and industries in Hawaii. F o r exam ple, the Hawaiian M illin g Company in Honolulu was awarded a Defense Supply Agency contract to provide the U .S. A rm ed F o rces with 100 000 lb o f wheat flou r irrad ia tion fo r d isin festation purposes. The irrad ia tion was perfo rm ed using the HDI.

The Hawaiian Developm ent Irra d ia to r in itia lly contained 200 000 C i of cob a lt-60. Th is provided a capability fo r p rocessing m ore than 4000 lb of papayas per hour at the s h e lf- life extension dose le v e l o f 75 to 100 k ilorad . Since the HDI becam e fu lly operational in m id-1967, the irrad ia tion p ro cess ing o f papayas has been o f prim e concern.

In 1967, the USAEC com pleted a cost-benefit analysis o f se lected products in its food irrad ia tion p rogram . Papaya was one o f the products evaluated. Some o f the m ore in terestin g conclusions fo llow .

4 FOWLER

Assum ing the mainland m arket would expand at a ra te equal to the 1967 le v e l, demand would increase from 5 m illion to 45 m illion lb fo r papayas by 1980.

I f a s ix - to eight-day sh e lf- life extension could be obtained by ir r a d iation shipping costs by surface v e s s e l ra ther than a ir c a r r ie r could resu lt in transportation savings o f 8 . 5 £/lb. Chem ical d isin festation costs also w ill be elim inated.

Adding the net y e a r ly benefits between 1970 to i 980, and discounting these at a 10 p er cent ra te , the sum o f the annual benefits is n early $9- m illion .

I f one w ere to assume that the growth of the papaya industry would p a ra lle l that of avocado and fresh pineapple in th e ir f ir s t 15 to 20 years , the papaya m arket would reach annual va lues, discounted at 1 0 per cent, o f $22-m illion . The estim ates w ere based on an FD A approval o f papayas by late 1967. These estim ates w ere recen tly reca lcu lated using present-day data and the same genera l trend was indicated.

I w ish to conclude m y rem arks by sum m arizing the current status o f our studies on the wholesom eness and safety o f irrad ia ted papayas. Two- y ea r anim al feed ing studies w ere in itiated som e 18 months ago. Data obtained to date look v e ry encouraging with no adverse e ffec ts being observed.

The anim al feeding studies are being conducted under a protoco l developed in co-operation with our Food and Drug Adm in istration . You may be in terested in knowing that our Food and Drug authorities have characte r iz e d the p ro toco l as being genera lly excellen t.

F o r the papaya feed ing study, we w ere successfu l in breaking a longstanding a rb itra ry ru le by the Food and Drug Adm in istration that ir r a d iated foods must be fed to anim als at a le v e l o f 35 per cent o f the tota l diet on a d ry-w eigh t basis . As a ll o f you recogn ize , this feed ing le v e l presents an unusual insult to the anim al. W ith respect to papayas, the FD A agreed to a le v e l o f 15 per cent wet weight o f the to ta l diet fed as a fresh puree.The 15-per cent le v e l was a rr iv ed at a fte r the USAEC ca rr ied out a 30-day p re lim in a ry study to determ ine the maximum to le rab le le v e l fo r this product in the tota l diet fo r the th ree species o f anim als to be used, rats, m ice, and dogs.

The papaya diets consist o f a standard labora tory ration, an unirradiated, unfumigated control, and two irrad ia ted products using doses o f 75 k ilorad and 200 k ilorad . Th ese diets a re fed fo r two y ea rs through th ree gen erations of anim als, where appropriate. The number o f anim als used at the beginning o f each feed study includes 400 rats, 600 m ice , and 32 dogs with the sex d istribution being equal fo r each spec ies . The tota l population o f anim als fo r the 2 -y ea r feed ing studies is approxim ately 3000. Based upon our experience in the United States the cost to com plete a wholesom eness and safety study is approxim ately $ 250 000.

The protoco l is v e ry sp ec ific with respect to physio log ica l and patholog ica l fac tors which must be evaluated. O f prin c ipa l in terest a re data re la ted to ra te o f growth, reproduction, longevity and tum or production.The data co llec ted are subjected to appropriate s ta tis tica l analyses and if s ign ificant d iffe ren ces a re found, it is n ecessary to evaluate these d ifferences in term s o f th e ir im portance in rega rd to safety o f the food fo r unlim ited human consumption.

I am p leased to report that a fte r 12 months o f feeding no adverse e ffects have been observed fo r any o f the fac tors investigated in the th ree species

PL-422/1 5

o f anim als being used. Regard ing the reproduction studies, data obtained so fa r fo r the Fx and F2 generations o f both rats and m ice show no s ig n ificant adverse e ffec ts . T h ird generation data a re not yet ava ilab le fo r analysis. A t present, the m ating o f the dogs is s t ill in p rogress to com plete the lit te rs fo r a ll experim enta l diet groups.

I f Food and Drug Adm in istration approval is forthcom ing fo r irrad ia tion o f papayas, it w il l rep resen t the f ir s t food so p rocessed and introduced into in ternational trade.

PL-422/2

HAWAII DEVELOPM ENT IRRADIATOR - A TOOL IN TROPICAL FRUIT PROCESSING

K.K. O T A G A K I

Department of Agriculture,

Honolulu, Hawaii,


Abstract

HAWAII DEVELOPMENT IRRADIATOR - A TOOL IN TROPICAL FRUIT PROCESSING.The state of Hawaii has embarked on a development program to further the marketing potential of

tropical fruits through the application of nuclear energy as a disinfestation process. The quasi-commercial Hawaii Development Irradiator (HDI) serves as a forerunner to the establishment of full-scale commercial irradiation facilities in the Pacific rim countries.

1. O V E R A L L GOALS

The Hawaii Developm ent Irrad ia to r (HDI) provides fo r the treatm ent o f s em i-com m erc ia l quantities o f trop ica l fru its and other com m odities, shipping tr ia ls fo r consum er-acceptance studies, and re a lis t ic evaluation o f the cost-benefit ra tio o f radiation versus other com petitive, com m erc ia l methods. Such data are needed to generate industry in terest and its early adoption and use o f the irrad ia tion p rocess.

F acto rs em phasized in the developm ent program s a re production methods, including package and storage conditions, p rocessing and product distribution procedures, management considerations, and m arket testing.

The prospect fo r the com m erc ia l u tilization o f irrad ia tion to achieve sh e lf- life extension and e ffec tive disin festation o f trop ica l fru its appears encouraging. The developm ent program is based upon the research program at the U n ivers ity o f Hawaii and by the F ru it F ly laboratory, A gricu ltu ra l R esearch S erv ice , United States Department o f A gricu ltu re . These studies have dem onstrated that radiation dosages o f m ore than 2 1 krad prevent the developm ent of f l ie s and add to the sh e lf- life o f papayas, m angoes and other trop ica l fru its . Mango seed w eev ils , not a ffected by the com m erc ia l le v e l o f fum igation .for papayas, a re con tro lled by radiation dosages o f m ore than 25 krad. F lavour, odour, texture, and appearance o f m ost fru its, with the notable exception o f avocados, are unaffected by radiation dosages o f up to about 100 to 150 krad. U ltim ately, these resu lts must be applied to com m erc ia l p ractices b e fo re the radiation p rocess can be w idely adopted, and to this end, some accom m odations in m arketing must be im plem ented .Thus, the s ign ificance o f the irrad ia tion program .

Recent cost-benefit studies have shown low -dose irrad ia tion to be o f s ign ificant econom ic value to the papaya industry, a year-rou nd product.The rep o rt points out the advantages o f low -dose irrad ia tion o f papayas through the extension o f s h e lf- life fo r g rea te r m arket potential. The p ro spects fo r mango and pineapple a re less prom ising, but a re encouraging.

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8 O T A G A K I

With fa s te r and m ore econom ic means o f transportation by container ships and jumbo je ts , m arketing of fresh fru its , vegetab les , and flo ra l products w ill gain an e v e r widening distribution throughout the world.

The Hawaii Developm ent Irrad ia to r is a h ighly flex ib le sem i-com m erc ia l unit. Construction was com pleted in D ecem ber 1966 through the joint e ffo rt o f the U .S . A tom ic Energy Com m ission and the State of Hawaii. Shakedown operation o f the fa c ility was com pleted by the sum m er o f 1967.

2. R A D IA T IO N PROCESSING

The fa c ility consists o f a cobalt-60 source o f 220 000 Ci with a throughput o f 4000 lb o f packaged papaya per hour, but is designed fo r a 500 000-Ci capacity with maximum potential throughput o f 1 2 000 lb per hour.

The irrad ia tion system consists p r im a r ily o f (1) source modules and e leva to r, (2) p rocess conveyor, (3) transport conveyor, (4) package-loading station, and (5) w ater-treatm en t system . The system can trea t s em icom m erc ia l quantities at doses ranging from 5 krad to m ore than 500 krad, dosages suitable fo r pasteurization o r d isin festation.

The conveyor system norm ally handles packaged products in c a r r ie rs , up to 180 c a r r ie rs per hour, with each c a r r ie r load weighing less than 50 lb with dim ension lim ita tions of 14 in. X 18 in. X 42 in. The dose pattern can be a lte red quickly by changing the position and number o f source modules.

The maximum dose rate im m ediately above o r below a source module is 1 to 1/2 M rad per hour, depending on the distance o f the package surface from the source module. The processing speed determ ines the total accummulated dose, with the greatest exposure im m ed iate ly above o r below a source.

The minimum absorbed-dose position is at both ends o f the package, as orien ted across the line o f tra ve l. The m axim um -to-m inim um dose ra tio is between 1. 7 and 1.2 with tw o-, fou r-, and e igh t-sou rce m odules, depending on the bulk density and dim ensions o f the packaged unit.

3. C O N TR O L OF DOSE

The dw ell tim e, a dose-con tro l factor, is the accumulated elapsed tim e fo r each "s tep " that the individual c a r r ie r must go through as it tra v e rs e s o ve r and under the source. Th ere a re 18 c a r r ie rs , equivalent to the 18 steps, on the conveyor at a ll tim es. Each c a r r ie r is pushed onto the p rocess conveyor by an a ir-opera ted piston tr ig g e red by an e le c tr ica l tim er.

4. M E ASU REM EN T O F R AD IAT IO N DOSE

The absorbed dose is m easured d irec tly by means o f dos im eter v ia ls p laced at p re-determ in ed areas in the fru it carton. The radiation dose is m easured spectrophotom etrica lly on the basis o f oxidation o f fe rrou s iron (F r ick e dos im eter).

Operation o f the p rocess conveyor is m onitored by an event re co rd e r with the speed chosen to allow in terpretation o f the tim ing cyc le at an

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accuracy o f better than 1%. Chem ical dosim etry reco rd s can be checked and iden tified with process ing records provid ing a permanent re co rd of p rocess in g param eters .

5. SOURCE STORAGE

The coba lt-sou rce storage consists o f a c ircu la ting 19-ft pool system , two ca rtr id ge-type fi lte r s , a heat exchanger and a ca rtr id ge-type dem in e ra liz e r .

M ake-up w ater, supplied to the sou rce-s to rage pool a fter process ing through the s e rv ic e dem in era lize r, can be regenera ted as needed.

6 . R A D IO LO G IC A L S A F E T Y

An underground holding system is connected to the pool overflow , c e ll- f lo o r drain, and a flo o r drain in the m echanical room . Th is system allows retention o f a ll w ater from potentia lly contaminated areas fo r rad io log ica l sa fety testing b e fo re d ischarge into the sew er system .

E le c tr ic a l in terlocks, radiation detectors and a larm system s provide adequate safety m easures in work areas.

7. B IO LO G IC A L S A F E T Y

T es ts a re being p rogram m ed by the U .S. A tom ic E nergy Com m ission fo r irrad ia ted papayas to evaluate wholesom eness on the basis o f animal tes ts which w ill include studies o f te ra to log ic , carcinogen ic, and tox ic e ffec ts to com ply with Food and Drug Adm in istra tion (FD A ) requ irem ents. F eed ing t r ia ls are program m ed o v e r a 2 -yea r period with physical, chem ical, and h is to log ica l exam inations o f each o f the test animals and th e ir progeny, including thousands o f c lin ica l, te ra to log ic , and h isto-patho log ica l exam inations. The 2-y ea r feed ing study is scheduled fo r com pletion in A p r il 1971. Th is w ill be fo llow ed by subm ission o f data to FD A fo r its rev iew and study.

8 . EX PAN D E D D E V E LO PM E N T PROGRAM S

Although grea t e ffo rts have been and continue to be expended on econom ic fe a s ib ility studies and achievem ents in irrad ia tion technology, the extent to which com m erc ia liza tion develops depends h eav ily on the food industry its e lf. Sufficient in teres t must be generated within the industry fo r p a r t ic ipation in shipping and storage tests on a co -opera tive basis. Emphasis should a lso be placed on a concerted educational p rogram .

M ayor prob lem s which must be reso lved to perm it com m erc ia liza tion include:

(1) Food and Drug Adm in istra tion clearance requ irem ents o f 2-y ea r anim al feed testing;

( 2 ) econom ic relationsh ip of costs versu s benefits; and(3) consum er acceptance o f irrad ia ted foods.

10 O T A G A K I

The change by the U .S . Department o f Health, Education and W e lfa re in the period o f testing from 90 days to 2 yea rs has been a serious deterrent to sustaining the in teres t o f industry.

The fa c ility w ill be ava ilab le to s e rv ic e the needs o f our neighbouring P a c ific r im countries.

9. SU M M ARY

1. The HDI se rves as a developm ent unit o f the USAEC to gather fea s ib ility data on costs fo r la rg e -s c a le food p rocess ing through irrad ia tion .

2. F ru its can be d isin fested by low -dose irrad ia tion which im proves s h e lf- life by delaying ripening and senescence.

3. Radiation makes low -cos t transportation o f trop ica l fru its feas ib le , encouraging expansion o f m arkets.

4. The v e rsa tility o f the HDI encourages its use in areas other than food processing.

PL-422/3

QUARANTINE REGULATIONS AND RESTRICTIONS AND THEIR EFFECT ON IMPORT AND EXPORT OF PLA N T MATERIAL AND COMMODITIES

E.W. J A C K S O N

U. S. Department of Agriculture,

Agricultural Research Service,

Plant Quarantine Division,

Honolulu, Hawaii,


Abstract

QUARANTINE REGULATIONS AND RESTRICTIONS AND THEIR EFFECT ON IMPORT AND EXPORT OF PLANT MATERIAL AND COMMODITIES.

The paper discusses the various ways in which agricultural pests can be spread by man in his travels through the world and how quarantine regulations and their enforcement in the United States of America operate to minimize possible infestation. Specific problems are illustrated by reference to recent large increases in the numbers of travellers and the corresponding large numbers of interceptions at points of entry. The effect of quarantine restrictions on international trade in agricultural produce is discussed and examples of various treatments used to eliminate pests are quoted.

1. INTRO D U C TIO N

Ideal quarantine approaches must furnish the maximum protection fo r agricu ltu re with the least in terferen ce in w orld trade.

Quarantine regulations and their en forcem ent invo lve the inspection and c learance of:

(a) A ir c ra ft , m a rit im e vesse ls , surface veh ic les , including ra ilw ay cars.(b) C argo , including non-plant m ateria l, com m odities manufactured or

o r p rocessed from plant m a ter ia l and fresh plant m a ter ia l fo r propagation or consumption.

(c ) P assen gers and th e ir baggage, including m ilita ry personnel.

Th is paper covers the broad p ictu re of quarantine en forcem ent and how certa in pests im pede or stop the im ports into and/or exports to areas f r e e of these pests.

P eop le m ay be c ity fo lks, nomads of the desert, urban d w elle rs , keepers o f animals o r t i l le r s o f the so il. R egard less o f the l i f e s ty le they a ll r e fle c t the in fluence of the ir environment. Some m ore than others. Ind ividuals with "g re en thumbs" r e v e l in the surrounding flow ers , ornamental plants, fru its and vegetab le gardens. Herb doctors p resc r ib e rem ed ies o f lo ca l herbs and plant parts (d ried o r fresh ) to r e lie v e d iscom fort and cure illn esses . Ethnic groups and geographic sections have certa in p r e fe r r e d d ieta ry elem ents and use plant products pecu lia r to th e ir reg iona l situation.

11

12 JA C K SO N

Because of reluctance to fo rego our l i fe sty le , a portion of the environ ment m ay be taken with us when we trave l. Once underway, we co llec t exotic item s fo r the return trip home. Some o f these intentionally ca rr ied item s harbour agricu ltu ra l pests. Unintentionally, we c a rry pests in packing m a ter ia ls , in curios made from plant m ateria l, in so il adhering to shoes, etc. Additionally , hitchhiking pests m ay stow away on c a r r ie rs transporting passengers, passenger baggage or ca rgo to a ll parts o f the w orld . Hence, the avenues o f invasion a re numerous and speedy fo r the entry o f agricu ltu ra l pests to com pete with mankind fo r food and fib re .

The w ide se lection of a irc ra ft types, a ir lin e schedules and the speed w ith which you assem bled here illu stra tes som e of today 's quarantine prob lem s.

2. A G R IC U L T U R A L PESTS

Th e lis t of known, sign ificant, agricu ltu ra l pests damaging agricu ltu ra l m a ter ia l in various parts of the w orld is voluminous. T h ere is an even g rea te r number o f m inor pests and pests of undeterm ined destructive potential. A g r icu ltu ra l pests include insects, m ites, nematodes, snails, slugs, pa ras itic plants and plant d iseases o r pathogens. You may recogn ize a few from the fo llow ing abbreviated lis t of com m only known, sign ificant pests: red -legged earth m ite , grape phylloxera, Colorado potato beetle , cotton bo ll w eev il, pink bollw orm , European corn borer, Andean potato w eev il, cockchafers, Japanese b eetle , San Jose sca le , c itrus black fly , Southern green stink bug, khapra b eetle , fru it flies (m any kinds; we have th ree in Hawaii - O rienta l, M editerranean and M e lo n ), golden nematode, soybean cyst nematode, giant A fr ican snail, w itchweed, scab d iseases of c itrus, citrus canker, phony peach d isease, potato w art and Dutch elm d isease.

3. PE ST ESTAB LISH M EN T IN NEW AREAS

Pes ts can be introduced into areas w here they have not prev iou sly existed, without becom ing perm anently established, even though a tem porary beachhead m ay be m ade fo r one or m ore l i fe cyc les . A combination o f favourab le fa c to rs including c lim ate, topography, food plants, p resence o f g rav id fem a les o r both sexes, am ple population, etc. a re requ ired to assure a successfu l establishm ent in a new area. When introductions a re frequent enough, sooner o r la te r the righ t combinations o f conditions may resu lt in an establishm ent o f an infestation. L ik e a gam e of darts, the m ore you throw, the b e tte r chance there is to hit the bu llseye.

B io c lim a tic cham ber studies o ffe r con tro lled conditions to observe the response of insect pests in a r t if ic ia l c lim a tic situations s im ila r to any given loca lity . Such studies m ay indicate the need to maintain or in itia te quarantine res tr ic tion s against sp ec ific pests. How ever, cham ber studies cannot absolu tely p red ict whether or not an a lien organism w ill su rv ive in a new area.

PL-422/3 13

4. PR E D IC T IN G TH E PEST P O T E N T IA L IN A NEW A R E A

P red ic tin g the destructive potential of an introduced pest p r io r to establishm ent is d ifficu lt. It invo lves evaluating what we know about the l i fe h istory , host spectrum and c lim atic lim ita tion of the species. An alien organ ism 's response to eco log ica l conditions and host relationship in a new area can only be determ ined a fter the introduction takes place.

The Japanese beetle , a destructive pest in the New England states of the United States, does m inor damage in its native Japan.

The F lo r id a red sca le , a m a jo r citrus pest in Egypt, p reva len t in F lo r id a , is not considered an im portant pest in C a liforn ia .

O ryctes rh inoceros L . , the coconut rh inoceros beetle , is not considered a devastating pest in its native habitats of South A s ia and M alaya. It causes w idespread damage and destruction on coconut plantations in the Samoas, Tonga, Palau, F i j i and other P a c ific Islands.

5. Q U AR AN TIN E RESTR ICTIO NS

Plant quarantines and th e ir en forcem ent should s e rv e only the purpose of p rotectin g agricu ltu ra l crops and products (food and fib re ) against pests capable of causing sign ificant econom ic damage. The type of quarantine res tr ic tion s im posed by one nation against another depends la rg e ly on the pests involved , extent of involvem ent in international trade and the need to p ro tect th e ir agricu ltu ra l endeavour.

In this age of advanced e lectron ic devices, radar can tra ce the fligh t o f an insect 13 m iles away. L ik ew ise , rem ote sensing equipment orb iting the w orld on sa te llites can detect insect infestations at any point on the earth. W h ile detection devices have been used to loca te m eta l objects in baggage, no good means o f determ in ing plant m ateria l in baggage has been found other than in terrogation and inspection. It was suggested about 10 years ago that passen gers ' baggage m ight be irrad ia ted to s te r il iz e or k ill plant pests, but, this would be fraught with many p rac tica l d ifficu lties . Even com plete inspection of baggage does not o ffe r 100% protection against the m ovem ent of pests. The present in festation of the giant A fr ican snail in M iam i, F lo r id a began with snails ca rr ied from Hawaii in the pockets of a boy 's clothing.'

W ith the advent of the so -ca lled "jum bo je ts " the anticipated and long- talked-about workload in crease becam e a rea lity during 1970. The Honolulu fo re ign a rr iva ls inspection area with a capacity to handle 600 to 700 passengers per hour, regu la r ly had 800 to 1000 passengers per hour during peak periods and had surges up to 1700 passengers during an hour.

During F is c a l Y ea r 1970, o ver 231 m illion tra v e lle rs entered the United States o f A m er ica through a ll land, sea and a irports o f entry.O ver 600 000 lots o f plants, plant products and other regu lated a rtic les w e re refused entry. In addition, 43 000 pests w ere in tercepted during the year.

Today 's volum e of passengers, overburdened fa c ilit ie s , lim ited r e sources, and the p ressu re to expedite c learance procedures preclude 1 0 0 % inspection of a ll baggage entering from fo re ign orig ins o r p rec lea red fo r departure on dom estic fligh ts from Pu erto R ico and Hawaii to the United States mainland.

14 JA CK SO N

In response to the workload and pressu re , s e le c tiv e methods of inspection have evo lved and a re now used fo r c learance of fo re ign passengers and baggage and fo r agricu ltu ra l p rec lea ran ce of passengers departing from Hawaii to other parts of the United States. Th ese system s requ ire in te rrogation o f a ll passengers and inspection of a ll hand-carried baggage or item s. Our reco rd s show that 6 6 % of agricu ltu ra l se izu res com e from hand baggage. The system s take the calculated r isk of re lea s in g certa in kinds o f pit baggage without opening fo r examination.

A g r icu ltu ra lly speaking, the calculated r isk re fle c ts a p es t-r isk evaluation based on basic knowledge about ch aracteris tics o f passengers, c lim a tic conditions at orig ins and at destination, ava ilab le plant m ateria l in season, pest distribution and other factors . Obviously, a m ilita ry passenger on a fligh t from Vietnam o ffe rs less r isk than a c iv ilian passenger from the Ph ilipp ines v is it in g re la tives in Hawaii. M ost certa in ly the tra ve llin g business executive poses less risk than the school teacher loaded with the w orld 's educational cu rios ities .

The s e le c t iv e system of agricu ltu ra l p rec lea ran ce o f dom estic fligh ts w ill lik e ly continue in Hawaii in the fo reseeab le future. Suppression of the flow o f fru it - f ly host m ateria l at a reasonable cost is the goal.

Suppressing the flow of fru it - f ly host m a ter ia l to the mainland, coupled with ea r ly detection and prom pt eradication o f introduced fru it f l ie s , has precluded th e ir establishm ent in C a lifo rn ia and m ade poss ib le the e rad ication of the M ed fly in festations in F lo r id a and Texas.

F ru it - f ly introductions that lik e ly cam e from Hawaii have been detected in Southern C a lifo rn ia as fo llow s: one adult M elon fly , July 1956; and adult O rien ta l fru it f l ie s in 1960 (3), 1966 (4), 1967 (1), 1969 (18) and 1970 (7 ). Sex lu res a re responsib le fo r ea r ly detection. M ethyl eugenol used fo r O rien ta l fru it fl ie s is the m ost e ffe c tiv e of the lu res. A lso , applications o f a m ixtu re o f m ethyl eugenol and a poison dispensed system atica lly has erad icated fru it flie s in Southern C a lifo rn ia during 1969 and 1970.

During F is c a l Y ea r 1970 1 430 558 a ir passengers departing from Hawaii fo r the United States mainland w ere p rec lea red . In that p rocess , we picked up 11 125 lots of proh ibited plant m a ter ia l and in tercepted 4628 reportab le plant pests (including 325 M edfly , 42 7 O rien ta l fru it f ly and six M elon f ly in terceptions).

T h re e hundred and th ree of the M ed fly in terceptions w ere made at H ilo on the "B ig Island" of Hawaii w here one of th e ir h ighly p re fe r red hosts, the co ffee cherry , is grown com m erc ia lly . A s the tra ffic from that a rea in creases , the threat of M ed fly introductions w ill in crease accord ingly.

The O rien ta l fru it f ly dominating the low er elevations has fo rced the M ed fly into h igher elevations. Consequently, in fested fru it from low er elevations w il l lik e ly contain O rien ta l fru it - f ly la rvae . M elon f ly host m a ter ia l (cucum bers, tom atoes and peppers) a re not as a ttractive to tra v e lle rs as other hosts, thereby reducing the flow of M elon f ly hosts to a v e r y m in im al le ve l.

6 . O TH ER M ISCELLANEO U S IN SPE C TIO N A C T IV IT IE S

As w ide-bod ied jets becom e m ore numerous, the use o f in ter-m odal containers in the ava ilab le ca rgo space w ill b ring fru its and vegetab les

PL-422/3 15

to the w orld 's m arket from new areas in rem ote parts o f the globe. Know ledge about the pests attacking crops or pests lik e ly to be p resen t with im ported produce must be obtained in order to evaluate the pest r isk of each com m odity o ffe red fo r entry.

M ost countries requ ire phytosanitary ce r tifica tes fo r cargoes of fresh fru its , vegetab les and propagative m ateria l. They a re issued by the agricu ltu ra l o ffic ia ls o f the exporting country based on inspection at the tim e of export and, when requ ired , on nursery inspections during the grow ing season.

A l l v esse ls , a irc ra ft, cargo and p a ssen gers 'b a gga ge from fo re ign orig in s a re subject to P lant Quarantine inspection and clearance.

In the case o f V ietnam , the United States Pub lic Health S e rv ic e and the P lan t Quarantine D iv is ion a re co-opera ting with the A rm ed F o rces in the p rec lea ran ce of re tro g ra d e cargos and the inspection o f v esse ls and a irc ra ft. Such procedures have substantially reduced the r isk of introducing into the United States from S. E. A s ia pests of m ed ica l and agricu ltu ra l im portance. M ilita ry Quarantine Inspectors tra ined by the P lant Quarantine D iv is ion and the United States Pub lic Health S e rv ice p e r fo rm the inspection and en force the requ ired cleaning of a ll ca rgo and the application of any requ ired treatm ents to elim inate pest risk.

T h e inspection reco rd at Hickam A ir F o r c e B ase (Honolulu, Hawaii) shows insect and snail in terceptions as fo llow s:

L iv e DeadJanuary through O ctober 1969 3 74 834January through O ctober 1970 151 795

It is noteworthy that 9 7 o f the 151 liv e in terceptions w ere m ade during January and F eb ru a ry 1970. Since that tim e the average has held at about seven p e r month as a resu lt o f in creasing ly e ffe c t iv e p rec lea ran ce procedures.

7. E X A M PLE S OF Q U AR AN TIN E RESTRICTIO NS AG AIN ST SPE C IF ICPESTS AN D TH E IR E F F E C T

Exam ple 4 1. The P lant Quarantine D iv is ion 's Export C ertifica tion Manual b r ie f ly sum m arizes the plant im port regulations o f m ost of the countries in the w orld . The quarantine regulations of uninfested countries perta in ing to United States plant m ateria l gen era lly have a specia l section o f prohibitions and res tr ic tion s applicable to Hawaii because of the fru it f l ie s and the giant A fr ican snail.

Exam ple # 2 . The trapping of adult O rien ta l fru it f l ie s in the Los Angeles area caused concern in countries im porting fru its and vegetab les from C a lifo rn ia . Inqu iries im m ed iate ly surfaced try in g to v e r i fy whether o r not O rien ta l fru it f l ie s w e re actually established. A u stra lia has gone as fa r as to re s tr ic t the entry o f citrus grown within 50 m iles o f the reco rded trap locations.

Exam ple # 3. During June 1966, the M editerranean fru it f ly becam e established in B row n sv ille , Texas in the low er R io Grande V a lle y contiguous to M exico.

D om estic vegetab le and fru it shippers w ere im m ediate ly affected.V a lley fru its and vegetab les w ere either prohibited entry into M exico or subject to stringent inspections to m eet M exican requ irem ents.

16 JA C K SO N

A pp les, pears , peaches and other produce grown in uninfested parts of the United States w ere refused entry into M ex ico from the low er R io Grande V a lley . Consequently shipments to M ex ico had to avoid transiting the in fested areas in South Texas.

B ird lo v e rs and fish-pond owners protested and cla im ed losses caused by the m alathion bait spray applied by a irc ra ft to erad icate the flie s . Au tom obile owners in the in fested area w e re avoid ing the da ily spraying pattern to preclude spotting o f th e ir c a rs ' paint.

Exam ple 3 4. Appendix I to this paper lis ts M exican fru its and vegetab les enterable into the United States o f A m erica . Note that cucumbers, squash, w ater-m elons (cucurb its), banana, eggplant, litch i, papaya, pepper and tomato a re enterable from M exico without treatm ent. The sam e com m odities shipped from Hawaii to the United States mainland must be vapou r-heat-treated o r fum igated with either m ethyl brom ide or ethylene d ibrom ide because o f the M editerranean fru it fly , C era titis capitata (W ied. ), the O rien ta l fru it fly , Dacus dorsa lis Hendel and the M elon fly , Dacus cucurbitae Coq. , which occur in Hawaii but not in M exico . The M exican fru it fly , Anastrepha ludens (Lw . ), and other Anastrepha spp. re s tr ic ts its feed ing to citrus, mangoes, guavas and other pulpy fru it.

Exam ple 4 5. In Appendix II to this paper, com pare the l is t of item s enterable into the United States from New Zealand and A ustra lia . The Queensland fru it f ly (Dacus tryon i (F rogg . ), and the M editerranean fru it f ly occur in A u stra lia but not in New Zealand. T h ere fo re , many New Zealand fru its and cucurbits need only be inspected to con firm freedom from pests as a condition of entry.

S im ila r ly , certa in New Zealand products destined toH aw aii a re en terable only a fte r they a re fum igated because of the red -legged earth m ite, Halotydeus destructor Tucker. I f this pest did not occur in New Zealand, the products would be enterable without treatm ent i f inspection confirm ed they w ere f r e e of other pests.

8 . T R E A T M E N T S FO R P L A N T M A T E R IA L

8 . 1. Vapour heat

Th is treatm ent consists of ra is in g com m odity tem peratures to 110°F by means o f heated a ir which is saturated with w ater vapour. When the vapour condenses on the com m odity, it g ives up its latent heat thus ra is in g the tem perature of the com m odity. When the com m odity tem perature reaches 110°F, it is held at that le v e l fo r the p rescrib ed period.

8.2. F re e z in g

Th is treatm ent consists o f any com m erc ia lly acceptable method of in itia l fr e e z in g at su b -zero tem perature and subsequent s to rage at 0°F w ith a sto rage to leran ce of 20 degF.

8 . 3. Cold treatm ent

Cold treatm ent consists of p recoo lin g fru it to tem peratures ranging between 31°F and 36°F, with subsequent holding at the tem peratu re se lected

PL-422/3 17

fo r periods ranging from 10 to 22 days. Th is treatm ent m ay be a c com plished w hile en route to the United States aboard vesse ls approved by the P lant Quarantine D iv is ion , o r it m ay be conducted in approved co ld - treatm ent warehouses.

8.4. Fum igation

M ethyl b rom ide fum igations m ay be conducted in approved chambers in accordance with p rescrib ed dosages, exposures and pressu res as lis ted fo r each com m odity in the P lant Quarantine T reatm en t Manual. Additionally, m ethyl b rom ide fum igation m ay be conducted under tarpaulins or in s im ila r enclosures when therm al conductivity readings a re taken in o rd e r to m onitor the gas concentration and assure uniform gas distribution.

E thylene d ibrom ide fum igations a re conducted in approved chambers equipped with a heating d ev ice to v o la t iliz e the EDB and fans to c ircu la te the gas in the cham ber every 3 minutes throughout the exposure period.

8 . 5. Treatm ents fo r propagative m ateria l

Th ese m ay include: dipping in fungicides o r in sectic ides ; fum igation with m ethyl b rom ide; and hot-w ater bath of in fested plant parts.

A l l o f the fo rego in g treatm ents a re p rescrib ed in the P lant Quarantine T reatm en t Manual.

9. PRO B LEM S ASSOCIATED W ITH TR E A TM E N TS

The export papaya industry in Hawaii would not exist without the vapour heat and ethylene d ibrom ide treatm ents.

Except fo r the fru it from one treatm ent plant in H ilo, a ll Hawaiian papayas a re E D B -trea ted because it is fa s te r , eas ie r to handle and r e qu ires less equipment. The minimum e ffe c t iv e letha l dose fo r con tro lling fru it flie s in Hawaiian papayas is 8 ounces of EDB p e r 1000 ft3. Should the Food and Drug Adm in istration (FD A ) reduce the to lerance of 10-ppm inorgan ic b rom ide res idue in papayas treated with EDB, the industry would be fo rced to seek a lternate treatm ents.

Guam which has eradicated the O rien ta l fru it fly , has not been able to im port the m uch-savoured Ph ilipp ine mangoes because an e ffec tive treatm ent has not been developed. R esearch to develop a treatm ent using a combination hot-w ater dip, EDB fum igation and cold storage is in p ro gress in Hawaii and resu lts look v e ry encouraging.

Current and proposed treatm ents under consideration fo r possib le use on mangoes w ill not k ill the mango seed w eev il. Unless an acceptable treatm ent is developed (use o f m icrow ave equipment is being investigated ), Hawaiian mangoes w ill continue to be proh ibited to other parts of. the United States of A m erica .

Chem ical dips (except o il) fo r fresh produce or other products fo r human consumption a re not recom m ended because of residue prob lem s.

Fum igation invo lves many aspects including safety hazards, loading and unloading cham bers, use of penetrable containers with m in im al sorption qualities and aeration periods. Consideration must be given to each com m odity 's to lerance to the fumigant. Exam ples o f the e ffec t of

18 JACK SO N

m ethyl b rom ide on certa in com m odities include: certa in va r ie tie s of green tom atoes w ill not turn red ; internal d isco loration and decay les ions on certa in va r ie tie s of avocados; okra m ay be injured when m oistu re is presen t, and asparagus darkens and d eterio ra tes .

Surface treatm ent under norm al atm ospheric pressu re is not always e ffe c tiv e fo r in ternal feeders . By conducting the fum igation under vacuum, the treatm ent e ffe c t iv e ly k ills the in ternal fe ed e r. How ever, item s tolerant to surface treatm ent do not n ecessa r ily to le ra te the vacuum.

APPENDIX I

L IS T OF FR U ITS AND VE G E TAB LE S A P PR O V E D FO R E N T R Y 1

P re fa c e

1. The fru its and vegetab les lis ted a re approved fo r entry through the ports named from the various fo re ign countries as noted, subject to such spec ia l conditions as m ay be indicated. Unless o therw ise indicated, im port perm its a re requ ired fo r a ll com m odities listed . The perm it w ill outline the conditions o f entry, F o r this reason, inspectors should r e fe r to the port copy of the perm it to make sure that the entry is in com pliance with the stated conditions.2. P o rts of en try a re designated by groups, i. e. , " A l l P o r ts " , "N orth A tlan tic ", "South A tlan tic and G u lf", "M ex ican B o rd e r ", and "N orth P a c i f ic " , and a re abbreviated and p rescrib ed as fo llow s:

A l l — P o rts at which inspectors a re stationed or to which they m ove in the norm al d ischarge of th e ir duties.

N A — A tlan tic ports north of and including B a ltim ore ; ports on theG reat Lakes and St. Law rence Seaway; Canadian B o rd er ports east of and including North Dakota; Washington, D. C. , (in cluding D ulles) fo r a ir shipments.

SAG -A tla n tic ports south of B a ltim ore ; Gulf ports, Puerto R ico , and the V irg in Islands.

M B— M exican b order ports.N P — P a c ific ports north o f C a liforn ia , including A laska, Canadian

bo rd er ports w est of and including Montana, but not Hawaii.

3. D efin itions

No tops — L ea fy portions o f plant developed above the ground.Must be rem oved at orig in .

G reen corn — F resh edib le corn not rem oved from cob.

4. Paren thetic re fe ren ces

Item s m arked with parenthetic num erical re fe ren ces (1) through (21) a re requ ired to be trea ted as a condition of entry and, hence, the im p ortation of such com m odities m ay be made only at ports with the n ecessary treatm ent fa c ilit ie s within approved areas.

1 Excerpt only from inspectors' manual M319 56-2-A.

PL-422/3 19

M EXICO

A ll:

MB:NA:

A llium Culantro P a rs le yAmaranthus greens Dasheen Parsn ipA rrow head Dates (unrestricted ) PeaA rro w ro o t Durian P epp erA rtich oke (Gl. & Jer. ) Eggplant PineappleArtocarpus G inger root (except Haw;Asparagus Ginseng PurslaneA ya le Grape RadishBanana H orserad ish (10) RhubarbBean (3 ), pod Husk o r m il tomato R ose lle

or shelled* Jicam a RubusBean sprouts Lam bquarters RutabagaBeet Lem on SageB e llflo w e r Lettuce Sals ifyB rass ica spp. L im e (sour) SpinachBurdock L itch i S traw berryCacao bean pod Mint Swiss chardCactus Naran jilla Tom atoC arro t Okra ( l i ) w w TurnipCassava Oregano W a tercressC e le ry Pa lm heart W a te r lily rootCerim an Papache Yam beanChickpea Papaya (pod and rooC ichorium (except Hawaii)CucurbitIn addition: The fo llow ing item s enterable a fter treatm ent in

M ex ico under USDA. supervision:G rapefru it (5) Orange (5) Tangerin e (5)Mango (4) P lum (13)

A vocado** O live Plum (3) o r (1!A pp le (3) Mango (4) Tangerin e (5)G rapefru it (3) o r (5) O range (3) o r (5)

io: App le (3)

5,4 Importations infested with Maruca, Epinotia, or Laspeyresia are subject to treatment (MB-T105) or to bonded rail movement to destinations north of Baltimore and east of Great Falls, Montana, and Salt Lake City, Utah.

Not enterable at California ports; at other Mexican Border ports noncommercial lots with seeds removed are authorized.

Limes in commercial lots for California to be fumigated (or oil dip) if infested with surface pests (at L.A., rail or truck at Mexicán border points in Arizona and Texas.) Limes for destinations in Arizona require treatment as prescribed in Arizona Citrus Quarantine No. 5, except that noncommercial lots may be released without treatment if free from surface and other plant pests.

*!®Wofe Conditions of Entry:(a) Mandatory fumigation required for shipments destined to:

(1) California during the period 16 March - 21 December ; and(2) Ala., Ark., Fla., Ga., La., Miss., Nev., N. C., S,C., or Tenn., or any part of 111., Ky., Mo.,

or Va., south of the 38th parallel during the period 16 May - 30 November.(b) Approved entry without fumigation when destined to (1) above areas other than during treatment periods,

and (2) to all other areas.

20 JA C K SO N

APPENDIX II

NEW Z E A LA N D

AU: A lliu m(d ry - no tops)

App le A p rico t Chayóte C h erry C h erryChinese gooseberry F e ijo s

N P: Tom ato (T108(d))

Guam: C a rro t C e le ry Lettuce

H aw aii: Asparagus (16) Bean, s tr in g

and lim e ( 6 )

G inger root Grape M elon Nectarine Pa lm heart Pass ion fru it

(except Hawaii)

LoquatPers im m on

C arro t (no tops) Parsn ip ( 6 )P ea ( 6 )Pumpkin (15)

W est Coast P o rts : Asparagus (16)

AUSTRALIA .

1. F ro m a ll parts o f A ustra lia :

A ll: A lliu m(d ry - no tops)

A l l (except F lo r id a ):

Guam: C a rro t (no tops) C e le ry

2. F ro m Tasm an ia only:

G inger root

A pp le (3 )*

LettuceP ea

PeachP ea rPlumRubusS traw berryT r e e tomatoVaccin iumW aterm elon

Potato Stone fru it Tom ato

Rutabaga ( 6 ) Squash ( 6 ) Tom ato (T108(d))

Pa lm heart

P e a r (3 )*

PotatoRadish (no tops)

P rov id ed , that (a) each shipment be ce rtified as to o rig in by an authorized o ffic ia l o f Tasm ania; and (b) each container be m arked to indicate o rig in as State o f Tasm ania.

A ll: App le

NA & SAG : Grape

P ea r

Passion fru it

Special additional treatment required for entry into California.

B IB L IO G R A PH Y

MAEHLER, K. L., Tephritid fruit flies — containing them. Paper presented to the Pacific Branch ESA Meeting, 24 June 1970.

OMAN, P., Prevention, surveillance and management of invading pest insects. Bull. ent. Soc. Am. 14 2(1968) 98.

RYAN, H.J. (Chairman), Plant quarantines in California, a committee report, September 1969.

PL-422/4

USDA RESEARCH ON IRRADIATION TO SOLVE QUARANTINE PROBLEMS IN FRUIT

H.C. C O X

Entomology Research Division,

Agricultural Research Service,

United States Department of Agriculture,

Beltsville, Md.,


Abstract

USDA RESEARCH ON IRRADIATION TO SOLVE QUARANTINE PROBLEMS IN FRUIT.Research on the use of ionizing radiation as a possible broad-spectrum quarantine treatment for

subtropical fruits was first initiated at the USDA Fruit Fly Laboratory in Honolulu in 1949. Advances have been made with fruits infested by different insects. Alternative approaches to the problem will be discussed for certain areas.

One o f the m a jor ob jectives o f our Honolulu labora tory is to develop and im prove methods fo r treating fru it and vegetab les in fested with insect pests in o rd e r to perm it th e ir movem ent without the r isk o f pest in troduction to the mainland United States o r to other uninfested areas. The labora tory conducts research to determ ine fum igation dosages, exposure periods, and tem peratures that w ill k ill a ll live stages o f pest species in the product. E ffec tiven ess o f new chem icals as fumigants and new techniques, individually and in combination, are being evaluated. The labora tory also conducts research on chem ica l residues and th e ir rates o f d isappearance in fumigated com m odities, as w e ll as the determ ination o f the to lerance o f the com m odity to the treatm ent.

The labora tory f ir s t in itiated research on ion izing radiation as a possib le b road-spectrum quarantine treatm ent in 1949. W hile research on this method fo r d isin festation o f fru its and vegetab les has not been continuous in subsequent yea rs , we have maintained in terest in the method because of the obvious advantages that it has o ve r m ore conventional methods o f d is in festation, such as fum igation o r vapour heat s te r iliza tion . These methods have ra ther narrow m argins between the dosages that are requ ired to destroy insect in festations and the dosages that w ill cause in jury in the treated produce. In addition, some fumigants seem to be lim ited by the texture o r com position o f the fru it. A quarantine treatm ent that could be used on a wide range on subtropical fru its and vegetab les with e ffec tiven ess that would not be influenced appreciably by com position o r texture o f the produce, o r type o f packing, would be a sign ificant advance. Irrad ia tion as a com m odity treatm ent technique would requ ire a re la t iv e ly short treatm ent period . There would be no fumigant residues to necessitate post-treatm ent ven tila tion periods which would, in turn, prevent quick ch illing a fter picking. E lim ination o f the ventila tion period could subtract 1 day from the in terva l between picking and ava ilab ility to the consum er, a v e ry im portant consideration with highly perishable com m odities.

23

24 С О Х

D r. Burditt and others who have conducted much o f our research on irrad ia tion as a quarantine treatm ent w ill d iscuss the resu lts o f that r e search in g rea te r detail; however, as an introduction some o f the results o f th e ir work w ill be sum m arized at this tim e.

The f ir s t research on the e ffects o f irrad ia tion on fru it flie s involved the use o f a sm all cobalt unit with a flux o f 1 C i. La ter, the laboratory acquired a 416-C iunit that would accept quantities o f fru it and/or fl ie s up to 2. 5 l it r e s . Other work has been conducted with the 3000-Ci Hawaii R esearch Irrad ia to r, as w e ll as the 220 000-Ci Hawaii Developm ent Ir ra d iator.

R esearch to date indicates that dosages in excess o f 100 to 200 kR are requ ired to prevent pupation o f fru it f ly la rvae . However, low dosages of only 15 to 2 0 kR applied to eggs and la rvae o f fru it f l ie s caused death in the pupal stage, thereby preventing em ergence o f adult fl ie s . These results suggested the fea s ib ility o f using com parative ly low dosages o f irrad ia tion as a quarantine treatm ent fo r fresh fru its and vegetab les in fested with trop ica l fru it f l ie s . The laboratory found that mangoes in fested by the mango seed w eev il, which does not succumb to fum igation o r other known quarantine treatm ents, can be s te r iliz ed with about the same dosage as is e ffe c tiv e fo r fru it flie s .

I f the irrad ia tion technique is proven practica l, e ffec tive , and safe as a treatm ent fo r fresh fru its and vegetab les in Hawaii, the developm ent w ill have w orld -w ide sign ificance. We anticipate that there would be rapid extension o f the use o f such a treatm ent to many other p ractica l quarantine prob lem s throughout the United States and e lsew here.

A com m odity treatm ent involving the use o f ion izing radiation requ ires a dosage that insures com plete elim ination o f the reproductive potential o f trop ica l fru it f l ie s . Although desirab le , com plete k ill o f the fru it flie s in fru it and vegetab les is not absolutely n ecessary . H owever, there must be no poss ib ility that adult fl ie s , even i f s te r ile , w ill em erge from fru it that reaches the mainland. O therw ise, mainland authorities m ight have to institute an unnecessary, expensive erad ication program , inasmuch as d ifferen tia tion between the s te r ile and norm al f l ie s is often im possib le .

An e ffe c tiv e and w ide ly applicable quarantine treatm ent would go fa r in preventing the occurrence o r recu rrence o f pest infestations On the mainland from tim e to tim e. F o r exam ple, incipient infestations o f M ed iterranean fru it fly have been found in the continental United States five tim es during the past 37 years : 1929, 1956, 1962, 1963, and 1966. TheGovernm ent spent about $7 m illion in erad icating the fly in 1929 and approxim ately $10 m illion in erad icating the fly in 1956. In Septem ber 1969, eight O rien ta l fru it fl ie s w ere found in Los Angeles County, C a lifo rn ia and, in a ll p robab ility , cam e from Hawaii. This invasion was subsequently elim inated but as the speed and volum e o f in terstate com m erce, passengers as w e ll as fresh produce, in creases between Hawaii and C a lifo rn ia , the threat o f acciden ta l introduction o f harm ful insects into the mainland w ill continue to in tensify.

Some Hawaiian agricu ltu ra l products may always be subject to quarantine treatm ent, unless the pest insects are erad icated from Hawaii o r becom e firm ly established in a ll susceptible areas where the products might be m arketed. C erta in ly , permanent establishm ent o f any one o f the fru it flie s in the continental United States could cost A m erican agricu lture m illions o f do lla rs annually. Even incipient outbreaks could cost m illions o f do llars to delineate and erad ica te .

PL-422/4 25

W ith this in mind, our long-range ob jective is to dévelop methods that could be used to erad icate these pests from the State o f Hawaii. The spec ific and highly e ffe c tiv e m ale annihilation technique, fo r exam ple, was developed in Hawaii fo r the O rien ta l fru it f ly . Th is technique invo lves the use o f a highly se le c tiv e lure combined with a sm a ll amount o f a non-persistent in sectic id e . Th is research has reduced the cost o f erad ication o f this fly by about 90%. The m ale annihilation technique is also being developed fo r the m elon fly but la rg e -s ca le tests must be conducted in o rd e r to prove its fea s ib ility . The th ird species, the M editerranean fru it fly , cannot now be erad icated in this manner, but research cu rren tly underway holds p rom ise .

The s te r ile insect re lea se method appears to be v e ry prom is ing fo r a ll th ree species; how ever, current techniques fo r survey, rea rin g , ir r a d iation and distribution are not adequate fo r the sta te-w ide program which would requ ire a w eek ly distribution o f about 2 0 m illion f l ie s .

W e recogn ize that the erad ication o f pest species is not a solution to a ll insect prob lem s requ iring quarantine treatm ent; how ever, we be lieve that it must be considered fo r sp ec ia lized areas such as island environm ents and geograph ica lly iso la ted mainland areas.

PL-422/5

BASIS FOR DEVELOPING QUARANTINE TREATMENTS FOR FRUIT FLIES

A .K . BURDITT, Jr.Entomology Research Division,Agricultural Research Service,United States Department of Agriculture,Beltsville, Md.

S. T . SEOEntomology Research Division,Agricultural Research Service,United States Department of Agriculture,Honolulu, Hawaii

J. W. BALOCK 1508 Aalapapa Drive,Kailua, Hawaii,United States o f America

Abstract

BASIS FOR DEVELOPING QUARANTINE TREATMENTS FOR FRUIT FLIES.The Entomology Research Division, Agricultural Research Service, United States Department of

Agriculture at its Honolulu, Hawaii laboratory is investigating quarantine treatments for three species of subtropical fruit flies, Ceratitis capitata (Wiedemann). Dacus dorsalis Hendel, and Dacus cucurbitae Coquillett. Procedures used at the laboratory for selecting fruit to be tested and for supplementing the natural infestation of larvae in fruit are discussed. Factors considered in evaluating the results of these tests include maturity and firmness of fruit, uniformity of the infestation of larvae in the fruit, and the level of the natural infestation present in fruit. The results of these tests are used to develop dosage- mortality curves and estimate the dose required for quarantine security, 99. 9968̂ 0 mortality. These factors and judgements were used when gamma irradiation was tested as a possible quarantine treatment.

The developm ent o f new treatm ents fo r com m odities and the r e - evaluation o f treatm ents p resen tly in use are im portant parts o f the research done at the labora tory o f the Entom ology R esearch D ivision , A gricu ltu ra l R esearch S erv ice , United States Departm ent o f A gricu ltu re , in Honolulu, H awaii. Such treatm ents make it possib le to m ove fru its , vegetab les, and other com m odities from areas in fested with fru it flie s through quarantine b a rr ie rs into areas in the United States that are fr e e o f the pests. They have also been adapted fo r use by many fo re ign countries and are used between areas o f the mainland United States when incipient infestations of fru it fl ie s ex ist in one loca lity .

Subtropical species o f fru it fl ie s a re a constant threat to agricu lture in the continental United States. F o r exam ple, incipient infestations o f the M editerranean fru it fly , C era titis capitata (W iedemann), have had to be

27

28 BURDITT, Jt. e t a l.

erad icated from the continental United States in 1929, 1956, 1962, 1963, and 1966 at great cost to the governm ent and to the public. Thus, e ffec tive treatm ents are essen tia l.

T h ree species o f fru it flie s found in Hawaii, the o rien ta l fru it fly ,Dacus dorsa lis Hendel, the M editerranean fru it fly , and the m elon fly ,D. cucurbitae Coqu illett, are frequently in tercepted by our plant quarantine inspectors at ports o f en try from Hawaii and from other parts o f the world. Approved quarantine treatm ents cu rren tly in use in H aw aii fo r these pests include fum igation with ethylene d ibrom ide (EDB) and vapour heat. R esearch has been conducted on ethylene d ibrom ide-hot w ater dips [ 2 ], ethylene ch lorobrom ide fum igation [ 3 ] , and gamma irrad ia tion in a cobalt-60 source[4 ] as possib le future quarantine treatm ents fo r som e in fested fru its and vegetab les.

P re s en t ly papayas are the only fru its now being treated and shipped from Hawaii to the mainland in la rg e quantities, and shipments have in creased from 2. 7 X 106 lb in 1961 to 7. 2 X 106 lb in 1967 [ 1 ]. (Smooth cayenne pineapples are being shipped without treatm ent because they are not subject to fru it f ly attack .) H ow ever, with the expansion o f d iv e rs ified agricu ltu re in Hawaii, there w ill certa in ly be a substantial in crease in the amount o f fru it and vegetab les exported from Hawaii.

Our concept o f e ffe c tiv e quarantine treatm ents against fru it fl ie s is based on procedures developed by Baker [ 5 ] . The secu rity that he cited as a basis fo r recom m ended treatm ents, those that would perm it the entry o f com m odities from quarantine areas into areas fr e e o f fru it fl ie s , was a m orta lity o f 99.9968%. Such m orta lity would allow 32 su rv ivo rs from an in itia l population o f 10 0 0 000 fru it f ly eggs and la rvae , which could be expressed in dosage-m orta lity term s as prob it 9. Obviously, in developing such treatm ents, la rge populations o f f ly la rva e must be used. T h ere fo re , econom ics have dictated that m ost of this research must be done with fru it that are p lentifu l and w ill support la rg e la rv a l populations. As a resu lt we gen era lly use papayas to test quarantine methods against the th ree species of f l ie s found in H awaii. We m ay use se ve ra l hundred fru its which contain thousands o f la rva e fo r each experim ent, and we rep lica te such a test many tim es to Obtain adequate data.

F irm fresh produce o f uniform s ize and ripeness is used fo r the tests. A lso , the natural in festation o f fru it f ly eggs and la rvae is usually supplemented by p lacing the fru its in 7. 65-m 3 cages containing about 50 000 mature adults o f one o r m ore o f the species involved fo r 2. 5 to 3 days. H ow ever, fru its decay rap id ly when they a re exposed to these la rg e populations; the degree o f attraction to fru it f l ie s and the subsequent ra te o f in festation are influenced by the s ize and ripeness o f fru its , by the age and quality o f the adults, and by the location o f individual fru its in the cage. A lso , the behaviour and longev ity o f the adults are a ffected by weather. Thus, we must establish the e ffec t o f these fa c to rs . F o r exam ple, in tests re la ting to the e ffec tiven ess o f a quarantine treatm ent, the varia tion in infestation resu ltin g from d iffe ren ces in m aturity and firm ness o f papayas p r io r to and a fter exposure to a cage in festation o f orien ta l fru it f l ie s was determ ined as fo llow s : fru it w ere f ir s t rated fo r m aturity and firm n ess, p laced in in festation cages fo r 3days, and then rated again. Next, the in fested fru it w ere p laced in holding boxes until la rva e had m atured and pupated and could be counted. These data, given in Tab le I, show that the m ore m ature fru it had a h igher ra te o f infestation, whether the in festation was m easured by the percentage o f fru it in fested or

PL-422/5 29

T A B L E I. PE R C E N TA G E O F P A P A Y A S IN FESTED AND AVERAG E NU M BER O F M A TU R E L A R V A E AND P U P A E P E R F R U IT A F T E R 3 -D A Y EXPOSURE TO A D U LT O R IE N T A L FR U IT FLIES

Descriptionof

fruit

Before

°jo Infested fruits

exposure

No. pupae fruit

Infestation:

After exposure

per Infested No. pupae per fruits fruit

Maturity (determined by colour)

Green 24 11 3 1

One-fourth 54 25 13 4

One-half 78 59 24 6

Three-fourths 87 71 37 18

Ripe 94 104 78 61

Firmness (determined by finger pressure)

Firm 66 18 13 15

Slightly softa 77 24 65 36

Soft spots 71 3 76 43

Soft 7 82 87 70

Just beginning to yield to finger pressure.

by the average number o f m ature la rvae and pupae produced p er fru it. A s im ila r relationship ex isted when fru it softened a fter but not p r io r to in festation , indicating that fem ales could detect poten tia lly soft fru it.

Next we determ ined the e ffec t o f the density and age o f the orien ta l fru it fl ie s on the in festation o f papayas. Cages (0. 76 m 3) w ere provided with in itia l populations o f 9 56, 1800, 3600, o r 7500 adult f l ie s . Then, once a week fo r 5 weeks, 20 papayas w ere put in each cage fo r 3 days. Subsequently the in fested fru it w ere rem oved and p laced in holding boxes to p erm it la rva e to m ature and pupate. The data, sum m arized in Tab le II, show that 1 - to 2 -w eek -o ld flie s produced m ore flie s at a ll except the low est population le v e l. H ow ever, crowding o f the flie s did not produce a proportionate in crease in eggs deposited in fru it, and the number o f la rvae produced. Thus, the rate o f in crease was in ve rs e ly proportional to the in itia l number o f f l ie s .

As noted, in our investigation o f the proposed treatm ent, we placed fru it in la rg e cages fo r 2 1/2 to 3 days to in crease the le v e l o f in festation. Th is schedule perm itted us to make two experim ents a week, about the m aximum possib le with the fa c ilit ie s and personnel ava ilab le. R esearch indicated (see Tab le III) that m ost o f the eggs w ere la id the f ir s t day in the cage; how ever, the 2 - o r 3-day period o f in festation did reduce som e o f the va r ia b ility in the le v e l o f infestation.

30 BURDITT, Jr. e t a l.

T A B L E II. L E V E L O F IN FE STATIO N A F T E R 3 -D A Y EXPOSURES TO VARIOUS PO PU LA T IO N S O F O R IE N TA L FR U IT FL IE S O F D IFFE R E N T AGES

Time after emergence of

adults (weeks) 956

Infestation (no. flies/20 papayas) after exposure to adult populations of

1800 3600 7500

1 20 125 115 362

2 2056 3499 5823 5416

3 2150 1406 1738 1712

4 808 866 952 1454

5 182 56 0 83

Total 5216 5952 8628 9027

Rate ofIncrease 5.5 3.3 2.4 1.2

T A B L E III. L E V E L O F IN FE STA T IO N IN P A P A Y A S A F T E R EXPOSURET O P O P U L A T IO N S O F A D U L T O R IE N T A L F R U IT F L IE S

Test no.

Replicate 1

No. pupae Coefficient per fruit of variation

Replicate 2

No. pupae Coefficient per fruit of variation

1 93 31.0 200 15.7

2 54 19.0 204 10.8

3 61 15.6 234 8.4

4 75 26.1 389 7.7

In developing data to support or rebut proposed quarantine treatm ents, a sam ple o f the in fested produce must be used to p rov ide an estim ate o f the o rig in a l population o f fru it flie s in the treated fru it. The s ize o f the untreated sam ple taken was usually about 25% o f the total amount tested. Then the rem ain ing fru its w ere divided random ly between treatm ents.A fte r treatm ent, both trea ted and untreated fru its w ere p laced in holding boxes to perm it the la rva e to m ature and pupate. Pupae w ere rem oved once a week and counted, and adults w ere perm itted to em erge . A lso , a fter 3 to 5 weeks, the fru it w ere opened, and any rem ain ing la rva e or pupae w ere rem oved . The pupae w ere held in sand to perm it adult em ergence.

PL-422/5 31

Treatm en ts must usually be repeated at d ifferen t doses to establish s e v e ra l points on the dosage-m orta lity curve. Then the p rov is ion a l dosage- m orta lity curve established in this manner can be calculated and the line extended to obtain an estim ate o f the dose requ ired fo r prob it 9 m orta lity . Subsequently, testing o f the proposed treatm ent was continued at this dose le v e l until the tota l number o f eggs and la rvae k illed in the sequence o f tests exceeded 100 000 without inclusion o f a su rv ivo r. Then the dose was assumed to g ive the expected m orta lity o f 99.997%.

The in festation o f fru it f ly la rvae in fru its and vegetab les va r ies with the com m odity and its m aturity, with the natural population o f flie s , and with the environm ental conditions. F ru it fo r shipment from Hawaii to the mainland United States by ship is usually harvested at a condition of m atu re-green to p a rtia lly r ip e to perm it treatm ent and shipment with a m inimum o f spoilage. H ow ever, the advent o f la rg e ca rgo -ca rry in g a irplanes means that r ip e r fru it w ill be harvested and shipped. Infestations are gen era lly low er in the less r ip e fru it shipped by boat than in the r ip er com m odities shipped by a ir.

In our resea rch to develop treatm ents that w ill k ill fru it f ly eggs and la rva e being conducted in Hawaii, we have established procedures to augment the natural in festation o f fru it fl ie s in fru it, to estim ate the population in the fru it to be treated, to trea t the fru it, and to determ ine the su rviv ing population. These data are used to estim ate the necessary le v e l o f m orta lity needed b e fo re a treatm ent can be recom m ended to treat in fested com m odities being shipped to f ly - fr e e areas.

R E F E R E N C E S

[1] ANONYMOUS, Hawaiian crop and livestock reporting service, Hawaii Dept, of Agriculture.[2] BURDITT, A. K., Jr., BALOCK, J.W., HINMAN, F.G., SEO, S. T ., Ethylene dibromide water dips

for destroying fruit fly infestations of quarantine significance in papayas, J. econ, Ent. 56 3 (1963)289.

[3] BENSCHOTER, C. A ., Evaluation of ethylene chlorobromide as a fumigant for citrus and mangoes infested by the Mexican fruit fly, J. econ. Ent. 5£3 (1963) 394.

[4] BALOCK, J.W., BURDITT, A. K ., Jr., SEO, S. T ., AKAMINE E.K., Gamma radiation as a quarantine treatment for Hawaiian fruit flies, J. econ. Ent. 5_9 1 (1966) 202.

[5] BAKER, A. C., The basis for treatment of products where fruit flies are involved as a condition for their entry into the United States, U.S.D. A. Cir. 551 (1939) 1-7.

PL-422/6

DOSE REQUIREMENTS FOR QUARANTINE TREATMENT OF FRUIT FLIES WITH GAMMA IRRADIATION

A .K . BURDITT, Jr.Entomology Research Division,Agricultural Research Service,United States Department o f Agriculture,B eltsville, Md.

S .T . SEOEntomology Research Division,Agricultural Research Service,United States Department o f Agriculture,Honolulu, Hawaii,United States o f Am erica

Abstract

DOSE REQUIREMENTS FOR Q U A R A N T IN E TR E A TM E N T OF FR U IT FLIES W IT H G A M M A IR R A D IA T IO N .

T h e E ntom ology Research D iv is ion , A gr icu ltu ra l Research S e rv ice , Un ited States D epartm ent o f

A gr icu ltu re at its Honolu lu, H aw a ii labora tory is in ves tiga tin g the use o f gam m a irrad ia tion as a possible

quarantine trea tm en t fo r three species o f trop ica l fru it flie s , the o r ien ta l fru it f ly , Dacus dorsalis H endel, the

M editerranean fru it f ly , C era titis cap ita ta (W ied em an n ), and the m elon f ly , D . cucu rb itae C o q u ille tt , and

fo r the m ango w e e v i l , Stem ochetus m an g ife rae ( F . ) . T h e em ergen ce o f adults from irrad iated naked eggs or

la rv a e o r from puparia con ta in ing fourth instar la rva e was p reven ted b y 15 kR o f gam m a irrad ia tion , but la rger

doses w ere required to p reven t em erg en ce o f irrad iated pupae. A lso , im m atu re fl ie s protected b y w ater o r by

fruits required h igher doses than s im ila r fl ie s that w ere unprotected . Th e loga rith m o f the m in im um doses w h ich

w ere needed to p reven t adu lt em ergen ce from in fested fru it packaged fo r export from H aw a ii was re la ted by

regression to thickness o f the pack age . M ango w e e v i l in festations in seeds w ere k ille d by m in im um doses o f

20 .8 to 3 2 .9 krad depend ing on thickness o f the package . A t low er doses adults d id not produce sperm or eggs

during th e ir l i fe t im e .

1. INTRODUCTION

The presence of three species of Hawaiian fruit flies , the oriental fruit fly, Dacus dorsalis Hendel, the Mediterranean fruit fly , Ceratitis capitata (Wiedemann), and the melon fly, D. cucurbitae Coquillett, and of the mango weevil, Sternochetus mangiferae (F. ), lim its the export of fruit and related commodities from Hawaii to areas where such pests do not occur. At present, the only fruit being treated fo r quarantine purposes in significant com m ercial quantities is papayas, over seven m illion pounds of which are treated annually either by ethylene dibromide fumigation or by vapour heat. Mangoes cannot be shipped because present quarantine treatments are not effective against the mango weevil, and avocados are not being shipped because the approved fumigation treatments are injurious to many com m ercial varieties of these fruit.

33

3 4 B URD ITT, Jr. and SEO

Gamma irradiation has shown great potential as a method of killing insects infesting commodities, and Hawaii has an ideal situation fo r the com m ercial application of such a treatment for quarantine purposes. For example, fruit for air shipment to the continental United States or to the Orient would all be handled at either the Honolulu or the Hilo airport. Sim ilarly, most fru it for boat shipment could be handled at one of these harbours. The present paper reviews the results of investigations made to determine whether such quarantine treatments would be effective.

2. EFFECTS OF GAMMA IRRADIATION ON IMMATURE FRUIT FLIES

Research into the effects of gamma irradiation on immature oriental fruit flies in Hawaii was initiated by Balock et al. [1 ] in 1949. They showed that young eggs less than 6 hours old did not hatch when they were treated with about 4 kR from a 1-Ci cobalt-60 source at the Hawaiian Sugar Planters Association Experiment Station. Eggs older than 24 hours were unaffected by 36 kR, but only 54% hatched when the dose was 120 kR; larvae developing from eggs treated at this dose did not form puparia. Third-instar larvae exposed to 15 kR formed puparia but did not develop to the adult stage.

A 416-Ci cobalt-60 source, the Fruit F ly Laboratory Irradiator, installed at our laboratory in 1957 was used to determine the effects of gamma irradiation on naked eggs, larvae, and pupae of a ll three species of fruit flies present in Hawaii [ 2]. The m aterial to be treated was placed in the centre of an aluminium canister which was inserted into the irradiator by remote control.

Eggs to be treated were placed on moist blotting paper in groups of 600 to 700. Then after treatment, they were counted and either placed on fresh moist blotting paper so we could determine hatch or on rearing medium so we could determine the effect on subsequent development. End points considered were pupation of larvae and emergence of adults from puparia.

Larvae to be treated were reared on medium fo r various intervals and treated in plastic dishes of rearing medium. Again the end points were pupation of larvae and emergence of adults. Puparia were treated in groups placed in plastic via ls. Since irradiated flies were frequently able to break the puparia at the eclosional suture but were then unable to em erge as fully developed flies , we counted both the number of partially emerged flies and the number of fully developed flies .

Although there is a minimum of variation in ambient temperature in Hawaii, the night temperatures in the winter were low enough to retard insect development. Therefore, the insects used in this research were held in a chamber at 25 to 28° C. At these temperatures, the egg stage of the melon fly persisted for 26 to 28 hours, that of the oriental fruit fly fo r 32to 35 hours, andthatoftheM editerraneanfru itflyfor48 to 50 hours. Melon fly larvae reached maturity in 7 days; larvae of the other species required 8 days. Upon reaching maturity, the third-instar larvae of these species leave the rearing medium. Therefore, at this time, we removed the larvae from the medium by washing with water and put them in sand to form puparia. Fru it fly larvae have three instars in the rearing medium and a fourth instar within the puparium [ 3]. Melon fly adults began to em erge from pupae after 9 days; adults of the other 2 species required 10 days.

PL-422/6 35

Our data [2 ] were prepared as dosage - mortality graphs drawn on logarithmic probability paper, and the curves were fitted by eye. Then LD-50 and LD-95 values were estimated from these curves. However, after these data were published, R. J. Daum, then of our B iom etrical Services Staff, developed a computer program for logit analysis maximum likelihood sim ilar to other such programs that he has developed [4 ]. We therefore asked Dr. Daum to analyse the data from these tests and to calculate the values for LD-50. Generally, the calculated values for the LD-50s required to prevent hatch of eggs were slightly lower than those we had determined visually. They are given in Table I and show that fruit fly eggs were very susceptible to irradiation during the firs t half of the development period, but that increasing doses were required during the last half of the development period. We did not determine the effects of irradiation on the em bryological development of the eggs.

TAB LE I. CALCULATED DOSE OF GAMMA IRRADIATION (kR) TO GIVE LD-50 FOR HATCH OF EGGS

A g e

(hours)

Species

M elon

f ly

O rien ta l

fru it f ly

M editerranean

fru it f ly

0 0 .5 0 .5 0 .5

5 2 .1 1 .5 a 0 .7

10 1 .8 0 .6 1 .4 a

15 10 .2 1 .0 0 .7

20 4 3 .2 14 .4 0 .6

25 305 .1 23 .5 3 .7

30 53 .2 1 8 .0a

35 23.0

40 37 .3

45 64.7

a Estim ated; data not adequate fo r sta tis tica l analysis.

Lim ited studies were also undertaken to determine whether irradiation of eggs or larvae could effectively prevent pupation. We found that the LD-50 fo r pupation of oriental fru it fly larvae treated as eggs was an estimated 5 kR; those fo r 1 -, 2-, or 3-day-old larvae were 14, 35, and 40 kR, respectively. The LD-50s required to prevent pupation of mature larvae of melon flies , oriental fruit flies , and Mediterranean fruit flies were 120, 115, and 95 kR, respectively.

The emphasis in our early studies [2 ] was the prevention of emergence of adult fruit flies . Therefore, eggs, larvae, and pupae were irradiated at each day of each stage and held until emergence was complete. Emergence of adults was judged on the basis of the breaking of the puparium at the eclosional suture and of the partial or fu ll emergence of flies . Data on

36 BU RD ITT, Jr. and SEO

TAB LE II. CALCULATED DOSE OF GAMMA IRRADIATION (kR) REQUIRED TO GIVE LD-50 FOR ADULT EMERGENCE

Species

A g e M elon O rien ta l M editerranean

(days ) f ly fru it f ly fru it f ly

Eggs

1 2 .6 a 1 .9 a 1 .0 a

2

Larvae

1 .6

1 3 .1 a 2 .0 b 1 .3

2 2 .9 1 .8 1 .5

3 3 .3 2 .1 1 .6

4 3 .7 b 2 .4 1 .7

5 3 .3 b 2 .7 1 .8

6

Pupae

2 .8 1 .9

1 2 .8 b 2 .2 1 .4

2 3 .1 b 2 .3 1 .2

3 3 .9 a 2 .7 1 .4

4 9 .8 8. l b 4 .2

5 3 0 .0a 2 4 .0b 1 7 .0b

6 4 4 .0b 3 0 .5 26 .7

7 56 .6 4 3 .0b 3 7 .0b

8 7 2 .2 55 .6 4 3 .0 a

9 88 .8 83 .7 5 7 .0b

10 1 0 5 .0b 77 .6

a Estim ated; data not adequate fo r s ta tis tica l analysis,

b Estim ated; error in com pu ter analysis.

the LD-50S fo r emergence calculated with Daum1 s logit analysis are given in Table II. Adult emergence could be reduced or prevented by treatment of eggs, larvae, or young puparia, but once the fourth-instar larva pupated within the puparium, many doses were required to prevent emergence of adult flies . The puparia were not examined critica lly to determine the effect of irradiation on pupal development. However, the exposure of immature stages to doses of gamma irradiation that were not high enough to prevent a ll emergence of flies did produce adverse effects on the flies that emerged. Less than 3% of untreated flies either failed to em erge completely or had vestigial-type wings; in contrast, when pupae were treated, as many as 40% of the flies failed to completely shed the puparium, and 49% had vestig ia l wings. Other studies [ 5] have shown that normal appearing adults emerging from pupae irradiated at 10 to 12 kR were sterile .

PL-422/6 37

Also, the wing venation of adult oriental fruit flies was disrupted when eggs or larvae were exposed to gamma irradiation, but abnormalities were most commonly in flies exposed to 5 kR as mature larvae. These abnormalities included splitting of the veins, extra cross-veins, and absence of parts of veins. One fly had eleven affected areas on the le ft wing but only two on the right.

The security basis for treatment of commodities infested with fruit flies is probit 9 [ 6 ], which is equivalent to 99.9968% mortality. We asked Dr. Daum to give us an estimate of the dose required for this mortality based on our early research; he found that in many instances, the data were not adequate to give a meaningful projection. Table III summarizes the doses that he was able to calculate fo r probit 9 security. Exposure to 15. 0 kR would apparently be adequate to prevent adult emergence from irradiated immature stages of fruit flies reared in the laboratory, but at the 5% leve l of probability, the upper and lower lim its o f the points for LD-99. 9968 are very wide, and statisticians do not consider these data to be very re liab le.

TAB LE Ш. CALCULATED PROBIT 9 DOSE OF GAMMA IRRADIATION (kR) REQUIRED TO GIVE LD-99. 9968 FOR ADULT EMERGENCE

A g e

(days )

Species

M e lon

fly

O rien ta l

fru it f ly

M editerranean

fru it f ly

Larvae

1 a b 4 .4

2 26 .8 6 .6 5 .0

3 14 .5 5 .9 6 .4

4 b 13 .4 5 .2

5 b 6 .9 6 .9

6 6 .3 5 .6

Pupae

1b

3 .9 6 .2

2 b 5 .1 5 .2

3 a 12.8 8 .7

4 956.3 b 966 .9

5a b b

6 b 117.7 119 .2

7 416 .3 b b

8 1114.6 133.3 a

9 410 .4 384 .1 b

10 b 312.0

a D ata not adequate fo r sta tis tica l analysis,

b Error in com pu ter analysis.

3 8 BU RD ITT, Jr. and SEO

Most of our research into the effects of gamma irradiation on immature stages of fruit flies was conducted by treating the insects in air or in partia lly consumed rearing medium. However, lim ited tests were made to determine the influence of other factors on the effects of gamma irradiation.

Higher doses of gamma irradiation were required to prevent hatch of eggs of the oriental fruit fly treated in water than in air: for eggs irradiated in water the LD-50 was 1. 7 kR; that for eggs treated in air was 1. 0 kR. The difference was not caused by the absorption coefficient of water because the LD-50 fo r eggs treated in a v ia l of air suspended in water was 1. 1 kR.

Sim ilar results were obtained when fruit fly larvae were irradiated in an aquatic medium. Larvae irradiated on the rearing medium where they have fed fo r 5 to 6 days are, essentially, being treated in air because the medium is fa ir ly dry and of a loose consistency. Thus, higher doses were required to prevent emergence of adult fruit flies from mature larvae irradiated in medium covered with water or in fresh medium, than from larvae treated in the original medium (see Table IV ). Since fru it fly larvae and eggs in nature are basically in an aquatic medium, we would expect that the dose required as an effective quarantine treatment would be 1. 6 to 2. 1 times that required for treatment of immature stages of fruit flies in air.

3 . I N F L U E N C E O F E N V I R O N M E N T A L C O N D I T I O N S O N E F F E C T I V E N E S S

O F I R R A D I A T I O N

TABLE IV. ESTIMATED DOSE OF GAMMA IRRADIATION (kR) REQUIRED TO GIVE LD-50 FOR ADULT EMERGENCE FROM IRRADIATED MATURE LARVAE

T rea tm en t

Species

M e lon

f ly

O rien ta l

fru it f ly

M ed iterranean

fru it f ly

O rig in a l m ed ium 3 .3 2 .7 1 .9

M ed iu m + w a te i 7 .0 5 .2 3 .1

Fresh m ed ium 4 .6 4 .0 2 .6

4. IRRADIATION OF FR U IT-FLY-IN FE STE D FRUITS

Three irradiators have been used since 1957 to determine the effectiveness of irradiation as a quarantine treatment fo r commodities infested with immature stages of fruit flies , the 416-C i Fru it F ly

'Laboratory Irradiator, the 30 000-Ci Hawaii Research Irradiator, and the 214 000-Ci Hawaii Development Irradiator. Each unit was loaded with cobalt-60 gamma-ray sources. The unit of the Fruit F ly Laboratory was one of a series that have been used by the USDA fo r about 15 years.. The

PL-422/6 39

TA B LE V. FRUIT F L Y INFESTATION PRESENT IN PRODUCE TREATED IN 416-Ci IRRADIATOR

T y p e o f

fru it

Num ber fru it

treated

Estimated fru it f ly

popu lation

Papayas 2600 201000

A vocados 1478 27000

M iscellaneous

Cucum bers ̂

Tom atoes

1575 26 000

Guava

K am an i

L itch i

Tangerines

O ther fru it .

- 22 000 55 000

Hawaii Research Irradiator is a pool-type Model Mark IV installed on the University of Hawaii campus in January 1965. The Hawaii Development Irradiator is a sem i-com m ercia l unit, completed in 1967, that is capable of treating 4000 lb/h of papayas or other products; the total dose applied can be varied from 10 to 500 kR.

As noted, studies of papayas, avocados, and other fruits infested with fruit flies were initiated in 1957 with the laboratory irrad iator [7 ].The canister of this unit was 5 inches in diameter and 19 inches deep.Two or three sm all papayas could be placed in the central 9-inch portion of the canister and treated at rates of 1. 6 to 0. 9 kR/min, depending on the decay of the cobalt-60 source. A lso, from 3 to 5 avocados could be treated at one time compared with as many as 75 sm aller fruits such as litchi. The total number of fruit and the estimated populations of fruit fly larvae treated are shown in Table V. In all, 44 000 of the total population were melon flies , 225 000 w ere oriental fru it flies , and 40 000 were Mediterranean fruit flies .Two adult oriental fruit flies of an estimated la rva l population in excess of 74 000 emerged when the larvae were irradiated at 10 kR; none of 18 000 melon fly larvae irradiated at 10 kR emerged. Only two Mediterranean fruit fly adults em erged from an estimated population of 1300 larvae treated with 10 kR, but none emerged from other tests in which sim ilar larvae were exposed to doses ranging from 2. 5 to 10 kR; therefore, we believe that the two adults resulted from contamination after the fruit had been treated. From these experiments, the quarantine dose (LD-99. 9968) was estimated to be 15. 6 kR fo r fruits infested with melon flies and from 21 to 28 kR for fruits infested with oriental fruit flies . The quarantine dose fo r Mediterranean fruit fly larvae could not be estimated because of the lack of survivors at the doses tested (2. 5 to 40 kR).

These studies were continued in 1965 using the Hawaii Research Irradiator and in 1967 using the Hawaii Development Irradiator to determine the dose requirements under various packaging conditions. In these tests, packaged papayas, bell peppers, and egg plants were irradiated in cartons measuring about 27 X 37 X 16 cm or 27 X 36 X 13 cm. The natural infestation

40 BU RD ITT, Jr. and SEO

of eggs and larvae present in these fruits was augmented by exposing papayas in large cages to adult flies , by injecting eggs into bell peppers [ 8], or by implanting nearly mature larvae into the fruits to be tested. Then the fruits were irradiated and held at ambient temperatures to determine pupation and emergence of adults.

The minimum exposure dose required to prevent metamorphosis of larvae into adults was found to vary d irectly with the thickness according to the equation

Y = 0. 189299 X + 2. 749076

where Y is the natural logarithm of the minimum exposure dose in krad and X is the thickness (one-half the dimension normal to the irradiated surface times the bulk of the irradiated volume) in g/cm2. We found that survivors were more likely to occur in fruit treated at conditions of higher bulk density (Table VI). Therefore, the minimum dose of irradiation required for a quarantine treatment would be about 21 to 25 krad. Upon extrapolation to X = 0, the minimum exposure dose required to prevent development of naked eggs and larvae to adults was about 15. 6 krad which is close to the 15. 0 kR found previously [ 2]. Therefore, doses reported in term s of kR could be converted to krad by multiplying the dose in kR by a factor of 1. 04.

TABLE VI. MINIMUM DOSE OF GAMMA RADIATION REQUIRED TO PREVENT FRUIT F L Y EMERGENCE

C om m od ityFruit f ly

p opu lationa

Bulk

(g / cm 9)

Dose

(krad )

B e ll pepper 122 968 0 .23 20 .0

Eggplant 139 763 0.27 2 1 .4

Papaya 141902 0.30 2 1 .4

356 857 0 .3 4 2 4 .6b

205 509 0 .35 25 .2

116 409 0 .40 29 .1

a Num ber o f adults estim ated to h ave em erged from an equ iva len t quantity o f untreated fru it,

b Fruit stored at 7 .2 °C for 1 to 3 days.

Papayas fo r shipment from Hawaii are dipped in hot water (118° C) to control disease and stored at 7. 2° С to extend shelf-life . Either of these treatments would reduce the infestation of fruit flies by küling eggs and some larvae. If irradiation were combined with such treatment, effectiveness would be enhanced to only a lim ited extent. Also, a combination treatment is much more difficult to regulate for quarantine purposes.

5. EFFECTS OF GAMMA RADIATION ON MANGO W EEVIL

Seeds of fresh mangoes in Hawaii are infested by larvae, pupae, and adult mango w eevils. We found that although weevils present in mango seeds were sterilized with about 20 to 33 krad of gamma radiation, they lived

PL-422/6 41

fo r over 5 months. However, they were usually unable to make an emergence exit and leave the seed. In another study, about 1000 mangoes were irradiated in the Hawaii Development Irradiator at minimum doses ranging from 23. 9 to 34. 5 kR. At the time of treatment, the control mango seeds contained 28 live pupae, 801 live larvae, and 3 dead larvae. Two months past treatment, sim ilar control seeds contained 713 live and 19 dead adults, 43 live and 39 dead pupae, 22 live and 35 dëad larvae, but seeds from the irradiated fruit contained 9 dead adults, 39 dead pupae,526 dead larvae, and a single live larva that died within 24 hours.

6. SUMMARY

Research at our Honolulu, Hawaii laboratory has demonstrated that emergence of adult fru it flies can be prevented by 15 kR (15. 6 krad) of gamma irradiation applied to naked eggs, larvae, or puparia containing fourth-instar larvae. However, once pupae have formed, increasing doses are required to prevent adult emergence, and a dose of 21 to 25 krad is necessary to prevent emergence of adults from pre-packaged fruit infested with eggs or larvae.

R E F E R E N C E S

[ 1 ] B ALO C K , J .W . , CHRISTENSON, L . D . , BURR, G .O . , E ffec t o f gam m a rays from cob a lt-6 0 on im m ature

stages o f the o r ien ta l fru it f ly ( Dacus dorsalis H en d e l) and possib le app lica tion to com m od ity treatm ent

problem s, P roc . 31st Ann . M tg . H aw a ii A ca d . S c i. (1956 ) 18.

[ 2 ] B ALO C K , J .W . , B U R D ITT , A . K . , J r ., C H R ISTENSO N , L .D . , E ffects o f gam m a rad iation on various

stages o f th ree fru it f l y species, J. econ . Ent. 56 (1963 ) 42 .

[ 3 ] CHRISTENSO N , L .D . , FOOTE, R .H . , "B io lo g y o f fru it f l i e s " , Annual R ev iew o f En tom ology 5

(S TE IN H A U S , E .A . , S M ITH , R .S . , Eds) Annual Review s, New Y ork (1960 ) 171.

[ 4 ] D A U M , R .J ., K ILLCREAS, W , , T w o com pu ter program s for probit analysis, B u ll. en t. Soc. A m .

12 (1966 ) 365. •

[ 5 ] STEINER, L .F . , M ITC H E LL, W . C . , BAUM HOVER, A . H . , Progress o f f ru it - f ly con tro l by irrad iation

s te r iliza tion in H aw a ii and the Marianas Islands, In t. J. app l. Radiat. Isotopes 13 (1962 ) 427.

[ 6 ] BAKER, A . C . , T h e basis for treatm ent o f products w here fru it fl ie s are in vo lv ed as a con d ition for

en try in to the Un ited States, U SD A, C ir c . 551 (1939 ).

[ 7 ] B A LO C K , J .W . , B U R D ITT , A . K . , J r., SEO, S. T . , A K A M INE , E .F . , G am m a rad iation as a

quarantine trea tm en t fo r H aw a iian fru it f l ie s , J. e c o n . Ent. 59 1 (1966 ) 202.

[ 8 ] FRIEND, A . H . , A r t i f ic ia l in festa tion o f oranges w ith the Queensland fru it f ly , J. Aust. Inst, a g r ie .

S c i. 23 1 (1957 ) 77.

PL-422/7

DOSIMETRY, TOLERANCE AND SHELF-LIFE EXTENSION RELATED TO DISINFESTATION OF TROPICAL FRUITS BY GAMMA IRRADIATION *

J .H . M OY, E .K . AKAMINE, J.L. BREWBAKER,I.W . BUDDENHAGEN, E. ROSS, H. SPIELMANN,M .D . UPADHYA, N. WENKAM, D. HELBER University o f Hawaii,Honolulu, Hawaii

A .M . DOLLAR, M . HANAOKA, G. A . M cCUSH Hawaiin Food Irradiation Program,Department o f Agriculture, State o f Hawaii,Honolulu, H awaii,United States o f Am erica

Abstract

D O SIM E TR Y , TOLERANCE A N D SHELF-LIFE EXTENSIO N RELATED T O D IS IN FE S TA T IO N OF T R O P IC A L

FRU ITS BY G A M M A IR R A D IA T IO N .

S ix aspects o f d is in festing tro p ica l fruits by gam m a irrad ia tion are sum m arized . (1 ) T h e p o o l- typ e

H aw aii Research Irrad iator w ith 30 000 C i (1965 ) o f c ob a lt-6 0 was used for various studies, w ith m axim um

dose rates o f c a .4 .7 krad/m in (p a p a y a - f i l le d ) and 5 .2 krad/m in (a ir ) in the cen tra l cham ber a fte r upgrading

in 1968. (2 ) T o le ra n ce doses o f e igh t d iffe ren t types o f trop ica l fruits w ere d e term ined ; papaya, m ango

and banana, to le ra b le to 100 krad, w ere most prom ising. (3 ) B io ch em ica l, p h ys io log ica l and ch em ica l

studies on the papaya* s (v a r . S o lo ) response to post-harvest ripen ing and to gam m a rad ia tion showed peroxidase

a c t iv ity in fruit pulp increased s ign ifican tly during post-harvest storage, but unaltered by low -dose irrad ia tion

to 100 krad. T h e ch em ica l com position o f papaya was not a ffe c ted by doses up to 125 krad. V aria tion in

som e analyses was due m a in ly to fru it ripeness at harvest. (4 ) E xtensive o rgan o lep tic eva luations o f irrad ia ted

papaya showed qu a lities unchanged at 100 to 150 krad. Q u a lities o f irrad ia ted m ango (v a r . H aden ) w ere

re ta in ed at 150 krad; ly ch ee (6 v a r . ) , 100 krad; banana, 100 krad, and p in eapp le , 150 to 200 krad. (5 )

M a rk e tab le l i f e o f in it ia l ly 1/4 -ripe papaya trea ted w ith hot w ater (1 2 0 °F , 20 m inutes for d ecay con tro l)

averaged 6 .5 days when stored at am bien t tem pera tu re (73 to 80eF ); com b ined hot w ater and irrad ia tion at

75 krad resulted in c a .9 .6 days. La rge -sca le shipping studies showed m arketab le l i f e o f irrad ia ted papaya

consisten tly equ a l to or better than those o f controls o r o ther quarantine treatm ents. (6 ) M arket analysis

and consum er a ccep tan ce study in d ica ted th ree out o f four persons w il l buy irrad ia ted papaya i f treatm ent

approved by regu la tory authorities.

1. INTRODUCTION

The irradiation program at the University of Hawaii, supported by the U.S. Atom ic Energy Commission on a contract basis, involves both applied and basic research aiming at disinfestation and shelf-life extension of tropical fruits and vegetables by gamma radiation. P rim ary emphasis has been on factors related to quality and shelf-life , FDA clearance, economics, packaging, and product handling, with major attention directed to

* Th is research program o f the sam e t it le was supported by the U .S . A to m ic Energy C om m ission under

Contract N o . A T (0 4 -3 )-2 3 5 , P ro ject A greem en t N o . 5.

4 3

4 4 M O Y e t a l .

ОТHH<P i

HотOQ

D

I—1

XC

S

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a«< !

SOu

wJfflcH

PL-422/7 45

Hawaii-grown papaya, mango, pineapple and several other tropical fruits. Close working relations and co-operation have been established between the University of Hawaii, the Hawaii Development Irradiator (HDI) and the Fruit F ly Investigation Laboratory of the USDA Entomology Research Division.

2. CHARACTERISTICS AND DOSIMETRY OFHAWAII RESEARCH IRRADIATOR (HRI)

The pool-type Hawaii Research Irradiator (HRI), Model Mark IV, was installed on the campus of the University of Hawaii in January 1965 with an initial strength of 30 000 C i of cobalt-60. The source was upgraded to 27 700 C i in July 1968. This unit has been used in research studies for dose tolerance, chemical analyses, and organoleptic evaluation o f a wide variety o f tropical fruits and fo r determinations o f fruit fly response to dose. Most of the studies have been carried out in the central chamber. Occasionally, the 3-in. wet tubes, the 6-in. wet tubes and the low-dose 6 -in. dry tube were used fo r other purposes.

Dose-rate data of the HRI are reported as measured on 1 March 1965 (in itia l installation) and 15 August 1968 (a fter upgrading) [13]. The standard Fricke method was used, with a Beckman DU spectrophotometer (w avelength 305 nm; slit width 0. 05 mm) standardized against solutions of known fe r r ic ion concentration prepared from a 0. 0996M fe r r ic sulphate solution obtained from the High Irradiation Development Laboratory, Brookhaven National Laboratory, Upton, New York, and from the Hawaii Development Irradiator respectively for the two periods of measurements.

Dose-rate distributions in the a ir-filled and papaya-filled central chamber were determined within the usable volume o f the plate coil which measures 5-3/4 in. wide, 17-1/4 in. long and 22 in. deep. These dose- rate measurements have served as the basis fo r irradiation research in the past severa l years as "minimum absorbed dose" at a given location within the chamber or as "approximate desired dose" within a defined region in the chamber, for example, 4 in. to 10 in. from the bottom of the chamber.

A comparison of the maximum and minimum dose rates between1 March 1965 and 15 August 1968 are given in Table I.

3. TOLERANCE OF TRO PICAL FRUITS TO GAMMA RADIATION

The feasib ility of applying ionizing radiation as a disinfestation technique depends on a fru it 's tolerance to a minimum disinfestation dose. In addition, if any benefit in shelf-life extension is to be gained, the fruit should probably tolerate a higher dose.

A number of tropical fruits were studied at the Hawaii Research Irradiator (HRI) to determine their tolerance dose to gamma irradiation [2,9-12, 17]. Fruits obtained from various islands in Hawaii were shipped to Honolulu and used on the day of a rriva l or held 1 to 3 days under r e frigeration (ca 55°F) or at ambient temperature (70 to 85°F) until used. A fter irradiation, fruits were stored mostly at ambient temperature to ripen. Observations were made on their external appearance, and in

48 M O Y et a l .

Chemical analyses include the following:

Total soluble solids (°B rix) : Abbe refractom eter;

Total dry matter: Vacuum drying (70°C) of 5-to 10-g sample to constant weight;

Total and reducing sugar: Am. Off. A gri. Chem. (AOAC) [4] Method 29. 035 Reducing sugar by the Lane-Eynon Volumetric Method;Total sugar by the AOAC Method 29. 032;

Total ascorbic acid: Assoc. Vit. Chem., 1966 [5 ];

Reduced ascorbic acid: AOAC Method 39. 041;

Carotenoids: AOAC Methods 39. 015 and 39. 017.

Two alternate methods for evaluating resilience were tested. The first, Durometer test, measures the resistance of the skin to puncture and the second, M agness-Taylor test, measures the yield force of the whole fruit. The form er has the advantage of allowing repeated tests on the same fruit while the M agness-Taylor method causes bruising. Though a shear press (shear compression) is available, our previous studies showed that it was difficult to obtain reproducible data on papaya texture with the shear press.

Results of analyses showed the following, based on fruit picked at three pre-harvest colour stages: colour-turning, l/4-coloured and 3/4-coloured.

Total soluble solids: There are significant differences (p = 0. 01) in total soluble solids within comparisons based on colour development at time o f harvest and date harvested. Values fo r rip er fruits are higher.

Dry m atter: There are no significant differences in dry-m atter contentwithin comparisons (harvest date, hot-water treatment, radiation dose and length of storage). More than two-thirds of the dry matter is reducing sugar.

Total sugar (as invert sugar): Quantitative analyses indicated 10 to 11% of the fresh weight of papaya pulp is sugar with no apparent changes in total sugars with post-harvest ripening.

Total reducing sugar: There are no significant differences in reducingsugar regardless of treatment or pre-harvest colour development.There were significant differences (p = 0. 01) when compared on the basis of harvest date.

Total ascorbic acid: Significantly increases with advancing pre-harvest colour development (p = 0. 01), irradiation at 125 krad (p = 0. 01), hot-water treatment (p = 0. 05) and different harvest dates (p = 0. 05).

PL-422/7 49

Reduced ascorbic acid: There are significant differences which parallelresults for total soluble solids within comparisons.

Carotenoids: Increasing caroteno id values para lle l advancing colour development.

Physical tests: Both the Durometer method and the M agness-Taylormethod show significantly (p= 0. 01) higher values when irradiated samples are compared to controls from the same harvest lot, indicating firm er fruit in the irradiated lo t .

O verall, the studies showed that there were no changes in papaya chemistry attributable to treatments. There are no indications that reduced ascorbic acid is affected significantly when papaya are treated by gamma radiation in the dose range of 25 to 250 krad. The ratio of reduced total ascorbic acid in papaya is constant at 67. 3 + 0. 7% of total ascorbic acid.

Table III shows the composition of papaya.

TABLE III. COMPOSITION OF PA PA Y A (var. Solo)

M eans ± standard error

T o ta l soluble solids (g/100 g pulp) 12 .2 ± 0 .9

Dry m atter (g/100-g pulp) 1 2 .9 ± 0 . 9

PH 5 .4 ± 0 .1

T itra ta b le a c id ity (g c itr ic/100 g dry m atte r) 1 .8 2 ± 0 .03

Reduced ascorb ic acid (m g/100 g dry m atter) 363 ± 15

T o ta l ascorb ic ac id (m g/100 g dry m atte r) 540 ± 10

Reducing sugar (g/100 g dry m atte r ) 7 7 .2 ± 1 .4

Carotenoids (m g 0-carotene/ lO O g dry m a t te r )a 17 .3 ± 2 .5

a 200 arbitrary units equ iva len t to 1 n g 6 -ca ro ten e .

5. ORGANOLEPTIC EVALUATIONS OF GAMMA-IRRADIATEDTRO PICAL FRUITS

Preserv ing the organoleptic qualities of fruits irradiated with ionizing radiation for disinfestation or shelf-life extension is one of the requirements of the radiation process. This aspect of the wholesomeness of the fruit must be determined and compared under various treatments, i. e. hot- water treatment (fo r decay control in papaya), varying dose levels, and other established quarantine procedures. Thus it w ill be assured that qualities of the irradiated fruit w ill be acceptable, and the fruit can be irradiated at an optimal dose range with the desirable preservation char a cte r ist ic s.

5 0 M O Y et a l .

Organoleptic qualities measured fo r various tropical fruits are: aroma, flavour, colour and texture. In the research phase o f the studies, the triangle test was the test method used. In the simulated and actual a ir- and marine-shipping studies, a multiple comparison test with a hedonic scale of 7 to 1 (like very much to dislike very much) was used.The taste panel consists of 10 to 15 trained personnel from the Department o f Food Science and Technology, University of Hawaii. Several trained persons from the HDI also participated in evaluation of papaya in the latter studies.

The tropical fruits that have been evaluated include papaya, mango, lychee, banana, and pineapple. A summary of the test results follows.

5.1. Papaya ( Carica papaya L . , var. Solo)

Three series o f tests were conducted at the HRI to compare the effects of hot-water treatment (120°F for 20 minutes), gamma irradiation and fumigation with ethylene dibromide [17].

Test Control sample Test sample

II

Not hot-water-treated; not fumigated

Not hot-water-treated; not fumigated

Not hot-water-treated; irradiated 75 to 800 krad

Hot-water-treated; irradiated at 75 to 100 krad

III Hot-water-treated; fumigated

Hot-water-treated; irradiated at 70 to 100 krad

Results of the first series of tests showed the effect o f high-dose gamma radiation on the quality of the fruits. While the flavour and texture of papaya flesh at the edible stage were found re lative ly insensitive to gamma radiation, the aroma was found significantly different (p = 0. 05 at 400 krad, p = 0. 001 at 800 krad) between the control and irradiated samples. M oreover, the shelf-life o f the fruit decreased with increasing dose at 400 krad and higher.

The second series of tests showed that papaya could tolerate hot-water treatment plus low-dose gamma radiation at 75 to 100 krad. Since irradiation has been found to have no effects on decay control, this combined treatment would bring the process closer to substituting the com m ercial practice of combining hot-water treatment and fumigation with ethylene dibromide while retaining the taste quality at the same time.

In the third series of tests, all samples were firs t treated in hot water. There were no significant differences in aroma and flavour between fumigated controls and test samples irradiated at 75 to 100 krad. Texture differences were observed in several runs in which the texture of the irradiated fruit was rated as firm er than that of the fumigated. Significant difference was also observed in flesh colour of the fruits. The panel members were not asked to indicate their preference. This difference is believed to be the result of delayed ripening in the irradiated samples.

To determine whether sensory data from taste panels in California would d iffer from those obtained in Hawaii, identical lots o f papaya, hot-

PL-422/7 5 1

water-treated and fumigated versus hot-water-treated and irradiated were a ir-freigh ted to the University o f California at Davis fo r evaluation. Varying degrees of fam iliarity and acceptance o f a given commodity by people at different localities could lead to different evaluation of an i r radiated product.

The test results showed no major differences in the papaya qualities detected by the two panels in spite of the difference in their degrees of fam iliarity to the fruits.

Quality U. of Hawaii

Arom a One series showed the irrad iated samples to have stronger aroma

U. of California

No difference

Flavour No difference One series showed the i r radiated sample to be slightly lacking in flavour

Quality U. of Hawaii U. o f California

Texture

Colour

Irradiated samples were rated as firm er

No difference

Odd samples were consistently picked out by both panels; no preference was indicated.

In the simulated shipping studies requiring the co-ordinated effort of HDI and HRI personnel, few significant differences were found in the organoleptic scores on absolute control, fumigated, vapour-heat-treated and irradiated (minimum absorbed dose o f 25, 50, 75, 100, 150 krad) fruit [7, 16]. The vapour-heat treatment resulted in a significantly lower aroma score in some lots while irradiation at 25 krad resulted in significantly higher aroma and flavour scores in half of the lots. In no instance were the irradiated papaya (25, 50, 75, 100, 150 krad) scored lower than the absolute controls, fumigated or vapour-heat-treated fruit.

In the large-sca le shipping studies, also a joint effort between HRI and HDI [8 ] , where fumigated and vapour-heat-treated papaya were compared with those irradiated at 25 and 75 krad, the only significant difference was in the colour scores. The mean colour score fo r 75-krad-treated fruits was significantly (p = 0. 05) higher when compared with all other treatments. No other significant differences were found in aroma, flavour, or texture among these treatments.

5.2. Mango (Mangifera indica L . )

The organoleptic qualities of two varieties of Hawaii-grown mangoes (var. Haden and var. Golden Glow) were evaluated [10]. The latter variety actually is a hybrid o f the Haden and the Carabao. The objective was to

52 M O T et a l.

evaluate the colour, aroma, flavour, and texture qualities of these fruits irradiated at 33 to 150 krad, which is the disinfestation dose leve l and above for the mango seed weevil. A lso included were data on a tr ia l marine shipment to California and return.

Taste panel data and colour measurements showed that no significant d ifferences were detected between the fumigated control and the irradiated samples at these dose levels, with post-irradiation storage at 45°F up to2 weeks, or in the marine shipment, 55 to 65°F up to 3-1/2 weeks. For the purpose of seed weevil disinfestation, this study indicates that gamma irradiation could be used without any adverse effects on the organoleptic qualities of the fruit.

5. 3. Lychee (L itch i chine sis Sonn. )

The organoleptic qualities o f six varieties of Hawaii-grown lychee were studied: Brewster, Chong-Un-Hung, Groff, Kwai-m i, Pot-Po-Hung and Heung-Lai [12]. The objective is to evaluate the colour, aroma, flavour and texture qualities of these fruits when irradiated at 25 to 100 krad, which is the dose leve l for fruit fly disinfestation and above.

A ll six varieties of lychees were supplied by the Kona Agricultural Experiment Branch Station, University of Hawaii. Taste panel results showed that no significant differences were detected between the nonfumigated control and irradiated samples following post-irradiation storage at 45°F up to 3 weeks. Data on percentage decay also indicate that gamma irradiation might be effective in delaying the ripening of the fruit. For purpose of fruit fly disinfestation, this study indicates that gamma irradiation could be used without any adverse effects on the organoleptic qualities o f the fruit.

5.4. Banana (Musa acuminata L. )

The organoleptic qualities of Hawaii-grown bananas, "Apple" (Brazilian) variety, irradiated at three stages of ripening: mature-green, half-colour and fu ll-colour were evaluated [9 ]. The objective is to evaluate the colour, aroma, flavour and texture qualities of the fruit when irradiated in the region of a disinfestation dose level, 25 to 100 krad, and to determine if a lim iting dose leve l could be defined fo r the wholesomeness of the fruit.

Taste panel results showed that no significant differences were detected between the control and irradiated samples. In a few cases, some hands in the irradiated batch appeared to retain the bright-yellow colour longer than the control during post-irradiation storage at 55°F.

The tentative conclusion was that the Hawaii-grown banana o f Apple variety, v iz. Brazilian, could tolerate gamma radiation up to 100 krad with no changes in its organoleptic qualities. The stages of ripening prior to irradiation, namely, mature-green, half-colour, and full-colour, made little or no differences in the keeping and eating qualities of this variety.It appears that in Hawaii, the irradiation of Apple banana at low doses after harvesting at the normal grade has not resulted in delayed ripening.

PL-422/7 53

5.5. Pineapple ( Ananas cosmosus M. )

The organoleptic qualities of two varieties of Hawaii-grown pineapples were studied [11]. The Smooth Cayenne is an established com m ercial variety requiring no treatment for interstate shipment from Hawaii. The hybrid variety-A , prom ising but s till experimental, w ill require fumigation if com m ercialized. The objective of the study is to evaluate the colour, aroma, flavour and texture qualities of these fruits when irradiated in the region of a disinfestation dose leve l and above, 25 to 200 krad, and to determine if a lim iting dose leve l could be defined for the wholesomeness of the fruit.

Taste panel results showed that no significant differences were detected between the non-fumigated control and irradiated samples up to 200 krad fo r the Smooth Cayenne and 150 krad fo r the hybrid variety-A . Postirradiation storage at 45°F, 75 to 85% R. H. , from 5 to 12 days showed no chilling injury. For the purpose of fruit fly disinfestation o f potential new com m ercial varieties of pineapple, this study indicates that gamma irradiation could be the substitute for fumigation with no adverse effect on the quality.

6 . SHELF LIFE OF PA PA YA TREATED BY GAMMA RADIATIONALONE OR BY COMBINATION TREATMENTS

The shelf life of papaya is influenced by physiological and pathological factors. Physiological factors are rate o f ripening and onset of senescence, while pathological factor involves storage diseases. By delaying the physiologica l factors and controlling storage decay, a fru it 's marketable life can be extended.

In an early study on the use of gamma radiation to extend the shelf- life o f papaya at HRI, Akamine et al. [ l ] reported that irradiated papaya (in itia lly l/4-ripe) were firm er (M agness-Taylor test) than untreated contro ls when stored at room temperature to edib le-ripe. A lso, maximum firm ness was reached at 75 to 100 krad. By measuring the fru it 's firmness when edib le-ripe and 2 to 3 days later, the effect of gamma radiation on delayed senescence in term s of retaining the marketable life o f the fruit was observed. A fter becoming edib le-ripe, the untreated fruits were all over-ripe in 3 days, while fruit irradiated at 75 krad took 6 days to start becoming over-ripe.

Hot-water treatment (120°F fo r 20 minutes) of papaya effectively controls decay due to pathogenic fungi infection. In general, stem-end rot is more severe in winter fruit and anthracnose in summer fruit. Hot- water treatment appreciably reduces rot development by eliminating rhizopus spores and slowing incipient infections, but it does not eliminate rot development, nor the fungi in the fruit [6 ] . The drying effect of hot- water treatment is believed beneficial, if the stem-end of the fruit does not remain moist after treatment.

Further studies o f combination treatments of papaya at HRI confirm that hot-water treatment followed by gamma radiation at a minimum absorbed dose of 75 krad is the optimal combination of treatments fo r shelf-life extension [3 ]. Combination treatments with radiation at higher doses can

5 4 M O Y et a l .

TABLE IV. SH ELF-LIFE MEASURED AS DAYS M ARKETABLE(±1 STANDARD ERROR) OF l/ 8-to 1/4-YELLO W PA PA Y A TREATED BYCOMBINATION TREATM ENTS THEN STORED A T 73 to 80°F, R. H.60 to 78% (15 FRUITS PER TREATM ENT)

M in im u m

absorbed dose

(k rad )

Con tro lH ot water

on ly

Radiation

on ly

C om bination

treatm ents

Л (com b in a tion

— hot w ater)

25 4 .7 ± 0 .4 6 .4 ± 0 .4 5 .6 ± 0 . 4 6 .4 ± 0 .1 N i l

50 5 .8 ± 0 .3 6 .5 ± 0 .1 7 .1 ± 0 .5 8 .9 ± 0 .3 2 .4

75 5 .8 ± 0 .3 6. 5 ± 0 .1 6 .9 ± 0 .1 9 .6 ± 0 .2 3 .1

100 5 .8 ± 0 .3 6 .5 ± 0 .1 7 .5 ± 0 .1 9 .3 ± 0 .2 2 .8

increase sensitivity to injury and affect normal surface colour development during storage. Table IV shows the effects of single or combination treatments on the shelf-life o f papaya.

A shelf-life extension o f 3 to 3-1/2 days is achieved by the combination treatments at 75 krad when compared to the hot-water-treated controls.

In the simulated and large-sca le shipping studies, joint effort of HRI and HDI, the shelf-life o f irradiated papaya was consistently equal to or better than observed fo r controls, fumigated, or vapour-heat-treated [8 ,16]. In fumigated or vapour-heat-treated papaya, softening often occurs before decay develops while the reverse is true fo r irradiated fruit. Longer sh elf-life fo r irradiated fruit is apparently related to firmness, with decay the prim ary cause for discard.

7. M ARKET ANALYSIS AND CONSUMER ACCEPTANCE STUDY OF IRRADIATED PA PA Y A

A market survey concerned with the market behaviour of papaya at the reta il leve l was carried out in two California test cities during 1966-67 [18]. The survey revealed that papaya on the United States mainland markets are much less sensitive to price than to supply and display.

The survey also showed that income elasticities are re lative ly low implying that changes in income have a less than proportionate effect on papaya consumption [19]. In brief, neither price nor income changes have an important effect on papaya consumption unless these changes are quite drastic. Factors that w ill affect papaya consumption rate have been found to be: ( 1) product availability in the store; ( 2) product appearance;(3) degree of in -store promotion and store-identified newspaper advertising;(4) display attractiveness; and (5) effective quality control.

A telephone survey was designed to determine popular attitude toward consumption of irradiated foods, and the effect gamma irradiation o f a product would have on its market behaviour.

PL-422/7 5 5

Would you purchase or consume food that has been treated by X -ray provided that the U.S. Food and Drug Administration and the U. S. Department of Agriculture approved of this method?

T A B L E V . R E S P O N S E T O Q U E S T I O N 1

ResponseRedlands

(°Io)

C ity

Sacram ento

m

T o ta l sam ple

(°!o)

Y es 72 .6 76 .9 75 .0

N o 22 .4 2 0 .4 21 .3

Ind ifferen t 5 .0 2 .7 3 .7

TAB LE VI. RESPONSE TO QUESTION 2

Do you know what X -ray irradiation o f food means?

ResponseRedlands

№

C ity

Sacram ento

Cfr)

T o ta l sam ple

m

Yes 26 .0 30 .7 28 .6

No 64 .6 68 .9 67 .0

N o answer 9 .4 0 .4 4 .4

The responses to the three questions shown in Tables V, VI and VII were obtained through telephone interviews by random sampling from the telephone directory in the cities of Redlands and Sacramento of the State of California. In Redlands, 1005 individuals were contacted, with 807 completed responses; in Sacramento, 1552 individuals were contacted, with 997 completed responses. The incomplete responses were due to respondent1 s language problems, insufficient knowledge on the subject, plain refusal to telephone survey or sampling errors.

The results o f the survey showed that gamma irradiation of papaya would have very little effect upon the demand fo r the product. However, sanction by the Food and Drug Administration as w ell as the United States Department of Agriculture w ill be required. A lso, proper labelling of the irradiated product would be needed.

5 6 M O Y et a l .

You have indicated that you would not consume irradiated foods. Would you state some o f the reasons for your stand?

T A B L E V I I . R E S P O N S E T O Q U E S T I O N 3

ResponseRedlands

№

C ity

Sacram ento

№

T o ta l sam ple

(% )

1. Dangerous to hea lth 16 .6 1 5 .5 16.0

2. Relig ious reasons 0 .1 - 0 .1

3 . N e g a t iv e connotation

a. Bomb 0 .1 - 0 .1

b. N u c lea r fa llou t 0 .4 0 .1 0 .2

c . C ancer 1 .7 1 .3 1 .5

d. Burns - 0 .1 0 .1

e . Other 4 .0 3 .9 3 .7

f. N o answer 77 .1 7 9 .1 78 .3

R E F E R E N C E S

[ 1 ] A K A M IN E , E . K . , W O N G , R . , "S h e l f - l i fe extension o f papaya w ith gam m a irrad ia tion ” , D osim etry,

T o le ra n ce and S h e lf-L ife Extension Related to D is in festation o f Fruits and V ege tab les by G am m a Irrad ia tion ,

U H -235P5 -1 , 1964-65, U SAEC , Isotopes - Indus. T e c h . (1965 ) 55.

[ 2 ] A K A M IN E , E . K . , W O N G , R . , T o le ra n ce o f avocados to irrad ia tion , U H -235P5 -2 , 1965-66 , USAEC,

Isotopes - Indus. T e c h . , T ID -4500 (1966 ) 97.

[ 3 ] A K A M IN E , E. K . , GOO , T . , E ffec t o f gam m a irrad ia tion on s h e lf - l i fe extension o f fresh papaya,

H D I-N V O -3 7 4 - 1 7 -U H -2 3 5 P 5 -5, 1968-69, USAEC, Rad ioisotope and Rad. App . , T ID -4 5 0 0 (1969) 33.

[ 4 ] A S S O C IA T IO N OF O FF IC IA L AG R IC U LTU R AL CH EM ISTS , O f f ic ia l M ethods o f A na lysis , 10th Edn,

W ashington, D. C . (1965 ).

[ 5 ] A S S O C IA T IO N OF V IT A M IN C H EM ISTS , Inc. , M ethods o f V itam in Assay, 3rd Edn, In terscience

Publishers, I n c . , N ew York (1966 ).

[ 6 ] BUDDENHAGEN, I. W . , KO JIM A, E .S . , B io logy o f postharvest disease fungi o f papaya in re la tion

to gam m a irrad ia tion trea tm ents, U H -235P5-2 , 1965-66, USAEC. Isotopes-Indus. T e c h . , T ID -4500

(1966 ) 30.

[ 7 ] DOLLAR, A .M . , H A N A O K A , M . , M cC U S H , G .A . , ROSS, E. , M O Y , J .H . , "S im u la ted shipping

study p ro to c o l" , H aw a ii D eve lopm en t Irrad iator Program H D I-N V O -3 7 4 -1 7 -U H -2 3 5 P 5 -5 , 1968-69,

U SAEC , Rad ioisotope and Rad. App . , T ID -4 5 0 0 (1969 ) 130.

[ 8 ] DOLLAR, A . M . , H A N A O K A , M . , M cC U S H , G . A . , M O Y , J. H. , C H A N , K . C . , C O , H . Y . ,

C IN N A M O N , A .D . , H S IA , S .T . , Large sca le shipping studies - papaya, i b i d . , p age 195.

[ 9 ] M O Y , J . H . , ROSS, E . , GOOD, T . , H S IA , S . T . , "Sensory eva lu a tion o f irrad iated bananas",

D os im etry , T o le ra n c e , and S h e lf-L ife Extension Related to D isin festation o f Fruits and V egetab les

by G am m a Irrad ia tion , U H -235P5 -3 , 1966-67, USAEC, Isotopes-Indus. T e c h . , T ID -4 5 0 0 (1967 ) 129.

[1 0 ] M O Y , J . H . , H S IA , S . T . , S A W A T O , М . , O rgano lep tic eva lu a tion o f gam m a irrad ia ted m ango,

U H -235P5-4 , 1967-68, USAEC, Isotopes - Indus. T e c h . , T ID -4 5 0 0 (1968 ) 136.

[1 1 ] M O Y , J .H . , H S IA , S .T . , S A W A T O , М . , O rgan o lep tic eva lu a tion o f gam m a irrad iated p in eapp le ,

ib id . , page 152.

PL-422/7 5 7

[1 2 ] M O Y , J .H . , C H A N G , G . , H S IA , S .T . , O rgan o lep tic eva lu a tion o f gam m a irrad ia ted ly ch ee ,

i b id . , page 163.

[1 3 ] M O Y , J .H . , U P A D H Y A , M . D . , O H I N A T A . K . , H S IA , S . , D osim etry o f the H aw aii Research

Irrad ia tor, H D I-N V O -3 7 4 -1 7 -U H -2 3 5 P 5 -5 , 1968-69, USAEC, R adioisotope and Rad. A p p . , T ID -4 5 0 0 (1 9 6 9 )1 .

[1 4 ] M O Y , J .H . , DOLLAR, A . M . , H S IA , S , T . , Peroxidase a c t iv ity in papaya (C a r ic a papaya L . ,

var. S o lo ), ib id . page 18.

[1 5 ] M O Y , J .H . , C IN N A M O N , A . D . , H A M ILL , E. , HELBER, D. , H S IA , S .T . , W E N K A M , N . ,

DOLLAR, A . M . , H A N A O K A , M . , P h ys io lo g ica l, c h em ica l and physica l changes during r ipen ing

o f papaya, i b i d . , page 86.

[1 6 ] M O Y , J .H . , C H A N , K . C . , C IN N A M O N , A . D . , HELBER, D. , H S IA , S .T . , JAW , R .C . ,

D OLLAR, A .M . , H A N A O K A , M . , M cC U S H , G . A . , S im u lated shipping studies, ib id . , page 157.

[1 7 ] ROSS, E . , M O Y , J .H . , W O N G , R , , C A V A L E T T O , C . , "Sensory eva lu a tion o f irrad iated p a p a y a " ,

D osim etry , T o le ra n c e , and S h e lf-L ife Extension Related to D is in festation o f Fruits and V ege tab les by

G am m a Irrad ia tion , U H -235P5 -2 , 1965-66, USAEC, Isotopes - Indus. T e c h . , T ID -4 5 0 0 (1966 ) 7.

[1 8 ] SP IELM AN N , H . , M arket deve lopm en t o f irrad iated papaya, U H -235P5 -3 , 1966-67, USAEC,

Isotopes - Indus. T e c h . , T ID -4 5 0 0 (1967 ) 26.

[1 9 ] SP IE LM AN N , H . , Dem and characteristics for fresh and p o ten tia lly gam m a irrad ia ted papaya on

se lected U .S . m ain land m arkets, U H -235P5 -4 , 1967-68, USAEC, Isotopes - Indus. T e c h . , T ID -4500

(1968 ) 9.

PL-422/8

RADIATION TECHNIQUES AND THE EXPORT OF MANGOES FROM THE PHILIPPINES

I.D . CLARKE*Department of Biochemistry,University of Ibadan,Ibadan, Nigeria

Abstract

R A D IA T IO N TECHNIQUES A N D TH E EXPORT OF M ANGOES FROM TH E PHILIPPINES.

S eve ra l va r ie t ie s o f m ango are w id e ly grown in the Ph ilipp ines, but the m ost im portant c o m m erc ia l

va r ie ty is the carabao va r ie ty . T h e carabao m ango possesses e x c e lle n t fla vou r as w e l l as good textura l

properties and is a ccep ta b le to p eo p le o f d iffe ren t tastes and o r ig in . A p p rox im a te ly 134 090 tons o f m ango

w ere produced in 1967 from 46 000 hectares, w h ile on ly 2895 tons w ere exported to Hong K on g . A t the

present t im e this is the on ly ex te rn a l m arket a v a ila b le fo r the export o f m ango because o f the in festation

o f the fruits w ith the fru it f l y . T h e possib le use o f rad ia tion techniques in so lv in g quarantine problem s is

discussed, as w e l l as the possib le c o m m erc ia l benefits to be derived from d eve lop in g the ex is tin g industry

in the Ph ilipp ines on a la rger sca le .

1. INTRODUCTION

It is generally accepted that tropical countries need to increase their food production, not only for the home market but also to develop those agricultural products which can be sold for foreign exchange. The export markets of tropical fruits, such as bananas and pineapple, have been developed for many years, but little effort appears to have been made to develop the export potential of other tropical fruits. This may be due partly to the technical and financial difficulties of production and transport and partly due to the lack of interest of consumers in temperate climates. The continuing search for new food products and flavours in the industrialized countries of the temperate regions might result in the development of markets for the more exotic fruits grown in the tropical regions, such as mango.

Several varieties of mango are widely grown in the Philippines, but the variety carabao is regarded as the best from the point of view of eating quality. This particular mango has an excellent flavour, as w ell as good textural properties and is acceptable to consumers of many different tastes and origin.

Approximately 134 090 tons of mango were produced in the Philippines in 1967 from 46 000 hectares, which was the second most valued'fruit crop, banana being the largest. In the main, the industry is formed almost entirely of producers owning a small number of trees, but a number of plantations of a few hundred hectares have been developed in various places. This production of mango by small units tends to be inefficient, which is reflected in the low yield per tree in the national statistics of approximately 70 kg per tree. The number of small producers also creates problems in the harvesting, distribution and marketing of the mango.

* In ternationa l A to m ic Energy A g en cy e x p e r t .

59

62 CLARKE

T A B L E I . C O S T O F R A D I A T I O N T R E A T M E N T

D ose 75 000 rad

Throughput 12 000 tons/6000 hours

N o . C i requ ired 102 000 at 0 .4 0 $ /C i

C a p ita l cost (U S $ ):

P lant 210 000

C oba lt 40 000

250 000

Annual running costs: $

A m o rt iza t io n over 3 years 83 000

R ep lacem en t o f 60C o at 12 .5% per annum 5100

Insurance 50 000

Labour 20 000

U t il it ie s 20 000

M isce llaneou s 10 000

Interest at 8 % 20 000

208 700

12 000 tons cost $2 087 000. Cost per ton = $17 .3

acceptable, but as the method becomes proven and accepted, a reduction in the required dose could be anticipated. A dose of 25 000 rad would be much cheaper to apply than a dose of 75 000 rad.

The radiation treatment is a capital-intensive process and if it is to compete at a ll with the cheap chemical methods, the plant would have to be utilized throughout the year, which would necessitate continuous production of mango. If production is seasonal and no alternative products can be treated then the cost of the treatment is likely to be high. Whether it would be too high or not w ill depend upon the profitability of the mango export market and the possibility of alternative techniques. For example, i f the mango seed w eevil becomes a serious pest on mango, then it is likely that the radiation method would be the only suitable method. Table I indicates the cost of radiation treatment. A fter 3 years, when amortization is complete, the running costs become $105 000 and cost per ton becomes $8 . 7. The plant should operate for a minimum of 25 years.

If the required dose is reduced to 25 000 rad, the number of curies becomes 34 240, which represents a saving of almost 10% of the capital cost.

6 . PRODUCTION OF MANGO FOR EXPORT

To produce approximately 12 000 tons of mango throughout the year would require a well managed orchard of approximately 2000 hectares.The land should not be too expensive and close to a good port to minimize delays from harvesting to marketing. One possible site in the Philippines

PL-422/8 6 3

could be around Cebu, which offers suitable land, a climate which can produce mango all year round and is an excellent port.

If an area of 2000 hectares was planted at a density of 25 trees per hectare, then the orchard would contain 50 000 trees. One orchard [ 1] has already incurred development costs over a 10-year period of $2115/hectare. As this is probably sim ilar to the situation in the Cebu area, a capital investment of $4 250 000 would be needed for the firs t 10 years. This development cost includes the preparation of land, planting of trees, maintenance and labour costs. Assuming a yield o f 1000 fruits per tree per year fo r 10-year-o ld trees, which is a modest expectation, then 50 000 trees should yield 50 000 000 fruits per year or approximately 12 000 tons per year. If a value of $250 per ton is accepted, then the annual crop would have a value of $3 000 000 representing 66% of the total 10-year investment. The total cost per hectare becomes $1206. 25. With 25 trees per hectare yielding 16 Kaings per tree then the monetary yield per hectare becomes $1562. 5, assuming a price of $250 per ton. The estimated costs of marketing and production are shown in Table II.

TABLE II. ESTIMATED MARKETING AND PRODUCTION COSTS

M arketing costs: US $/hectare

H arvesting, c la ss ify in g and pack ing 170

Fre igh t and hand ling 255

D isin festation 100

525

Production costs:

U pkeep o f b locks, $1 per tree 25

C h em ica ls e tc . , $ 2 . 5 per tree 6 2 .5

Sm udging, 40% produce 600

687 .5

7. INTER-CROPPING

Mango trees do not produce fruits in com m ercial quantities until they achieve the 10th year of growth from planting. Most com m ercial organizations would not be interested in investing in such a long-term project without some earlie r return of their capital. For this reason, it would be necessary to make use of the land while the mango trees are maturing.A variety of vegetable crops have been suggested [1], but an alternative crop could be papaya, which produces fruit within the firs t 12 months after planting. The Philippine papaya tends to be a large, uneven shaped fruit with a skin colour, which is not particularly attractive. As in the case of mango, quarantine regulations forbid the importing of papaya because of infestation with fruit fly . Papaya would require sim ilar disinfestation procedures as mango and since sim ilar marketing procedures would be used, the experience gained with the marketing problems of papaya would be of considerable assistance in developing markets for mango.

6 4 CLARKE

A proposal has been outlined fo r developing a 2000-hectare estate of mango for export from the Philippines. Radiation techniques could play a critica l ro le in the development of this industry, by controlling fruit fly infesting the mangoes.

Total development costs fo r 2000 hectares are estimated at $4 250 000 for the firs t 10 years. No financial return w ill be possible for these 10years, unless some alternative crop is grown on the land while the mango trees are maturing. A fter 10 years, the annual value of the crop would be between $700 000 and $3 750 000 depending on the price structure of the mango market.

The cost o f disinfesting mango by the radiation method is estimated at $17. 3, falling to $8. 7 per ton after three years of operating for 6000 hours per year.

R E F E R E N C E S

[ 1 ] G E D N Z A N , J . , Survey on m ango p o ten tia l in the Ph ilipp ines. Prepared for D eve lop m en t Bank o f T h e

Ph ilipp in es (1968 ).

[ 2 ] CLARKE, I . D . , T e c h n ic a l Assistance Report 556, IA E A , V ienna (1970 ).

[ 3 ] Personal com m u n ica tion .

[ 4 ] M A N A L O , B . , personal com m u n ica tion (1969 ).

8 . S U M M A R Y

PL-422/9

PHYSIOLOGICAL EFFECTS OF GAMMA RADIATION ON SOME TROPICAL FRUITS

A . SREENIVASAN. P. THOMAS, S .D , DHARKAR Biochemistry and Food Technology Division,Bhabha Atom ic Research Centre,Trombay, Bombay,India

Abstract

PH YS IO LO G IC A L EFFECTS OF G A M M A R A D IA T IO N ON SOME TR O PIC A L FRUITS.

C onsiderab le quantities o f m angoes, bananas and o ther c o m m e rc ia lly im portant fruits grown in India

are spo ilt due to the adverse c l im a t ic cond itions and la ck o f adequate storage and transportation fa c il it ie s .

Low -dose rad ia tion treatm ent has b een found to extend the sh e lf l i f e o f this h igh ly perishab le produce

b y d e la y in g ripen ing and senescence. C erta in com b in a tion treatm ents in w h ich rad ia tion is used in con junction

w ith w ax c oa tin g , k in etin d ip , re fr ige ra tion or storage in m od ified atmospheres g iv e ben efits in term s o f a

further d e la y in r ipen ing . These processes cou ld b e o f advan tage in stretching the a v a ila b il ity o f the fruits as

w e l l as in their transportation both w ith in the country and abroad* Som e o f the b io c h e m ic a l and p h ys io lo g ica l

mechanism s underlying the rad ia tion -indu ced in h ib ition o f ripen ing and s en escen ceh aveb een e lu c id a ted . M aturity

at harvest and the p h ys io lo g ica l state o f the fru it at the t im e o f irrad ia tion h ave been shown to b e im portant

factors for consideration to ob ta in m axim um ben efits from the process. T h e respiratory pattern and onset

o f c lim a c te r ic are in flu en ced b y irrad ia tion and the a lterations induced are characteris tic o f the fru it. Th e

opera tion o f certa in a lternate pathways o f m etabo lism , notab ly a sw itch -o ver to the g ly o x y la te c y c le in m angoes

and to the pentose phosphate pathway in bananas, h ave b een observed to result from irrad ia tion . The

im portan ce o f p o lypheno l ox idase in browning due to rad iation in ju ry has been shown. T h e need fo r ( i ) a

rea lis t ic approach to the p rob lem o f wholesom eness eva lu a tion , and ( i i ) a com m on le g is la t iv e basis fo r the

p rom otion o f in ternationa l trade in fruits subjected to low -dose irrad ia tion are discussed.

1. INTRODUCTION

Fruits and vegetables consitute an important part of m an's food and are classified among the "protective foods" in view of their being rich sources of trace nutrients, including vitamins and m inerals. It is estimated that about a fourth o f the total food production in the world is comprised of fruits and vegetables.

India has its share of fruit production and, being a vast country with tropical and subtropical climates prevailing in different regions, a wide variety of fruits are cultivated; mangoes and bananas are by fa r the most economically important.

The annual production of mangoes in India is about 3 X 106 tons and one variety, the Alphonso, grown extensively on the West coast, south of Bombay, is particularly prized fo r its delicate flavour and taste. Even on ripening, when the fruit assumes a rich golden colour, the flesh remains firm .Because of its distinctive qualities, it is very popular with the canning trade as w ell as fo r consumption in the fresh state. The fruit is seasonal and is available during an extrem ely lim ited period (about 4 to 6 weeks) in the summer months. This results in a seasonal glut which the processing

65

66 SREENIVASAN e t a l .

factories find difficult to accommodate and a considerable proportion of the produce is wasted through spoilage.

The banana occupies an important place, second only to the mango, among the fruits cultivated in India. The annual production, most of which goes fo r internal consumption, is estimated to be w ell over 2 X 106 tons. The main producing areas lie in the states of Maharashtra and Gujarat in the West, besides, to a less extent, the Southern States. The fruit is transported by road or ra il to consuming centres some of which are far removed. India 's contribution to the international trade in this fruit has not been significant in the past though, of late, large amounts are being exported to countries of the Middle East as w ell as to the USSR and Japan with lim ited success.

2. ASPECTS OF FRUIT SPOILAGE

A large moisture content and the presence of readily utilizable nutrients such as sugars make fruits particularly prone to spoilage by microorganisms and insects, thus lim iting their shelf life . The post-harvest deterioration of fruits occurs as a result of: (i) biochemical and physiological changes of an endogenous nature; (ii) m icrobiological and insect spoilage; and (i i i ) dehydration and handling injury. While the problem of spoilage exists in all countries, it is often most severe in the developing countries lying in tropical and subtropical regions. The high ambient temperatures and re lative humidities obtaining during most parts of the year are conducive to spoilage arising from factors (i) and (ii), and the lack of adequate handling and storage facilities leads to physical damage to the fruit. An additional problem, imposed by the vastness of the country, is the need for haulage of the produce over long distances by non-refrigerated ra il and road transport both fo r internal consumption as w ell as fo r export.The use of such indifferent methods of storage and transportation inevitably results in significantly reducing the marketable shelf life of the produce.A considerable portion of the harvested fruits is lost through spoilage and, in addition to the economic loss to the country this represents, it also lim its the scope fo r increasing the cultivation of these fruits fo r internal as well as external markets.

3. EXTENSION IN SHELF L IFE BY GAMMA IRRADIATION

It has been conclusively shown that it is possible to extend the shelf life of fresh fruits at ambient as w ell as at re frigerated temperatures through the judicious application of gamma rays [ 1]. Ionizing radiations result in an extension of shelf life by: (i) disinfestation of fruit flies and weevils;(ii) inactivation or reduction of spoilage m icroorganisms; and (iii) delaying ripening and senescence by interfering with basic metabolic processes.

Complete sterilization of fresh fruits is not practicable, because the high doses required to achieve this would damage important quality attributes such as appearance, flavour, taste and texture. Greatest attention has, therefore, been centred around the use of sub-sterilization doses which inhibit physiological processes such as ripening and senescence and successful treatments have been developed for a number of fruits.

PL-422/9 67

A delay in ripening of Bartlett pears at doses of gamma rays higher than 300 krad has been reported [2 ]. Delay in ripening as assessed by retardation of red colour development in tomatoes was found to increase with increasing radiation doses [3 ]. S im ilar observations have been made with tomatoes, in the dose range of 100 to 400 krad [4 ]. It has been observed in our laboratories that it is possible to obtain a delay in the ripening of a variety of tomatoes by doses as low as 30 krad [ 5]. An extension in shelf life of cherries irradiated at 300 krad has also been reported [ 6 ]. Considerable amount of work has been done, on radiation-induced delayed ripening, with papayas [7 ], bananas [ 8 ], pineapples [7 ] and other fruits.

In addition to in terfering with physiological processes of ripening and senescence,, radiátion has been used fo r post-harvest control of fungal spoilage by,a number of workers. It has been reported [ 9] that strawberries could not be sterilized at non-injurious doses; however, the growth of Botrytis cinerea, the grey mould, could be controlled by a dose of 200 krad at 5°C. Sim ilarly, Monillinia fructicola and Rhizopus stolonifer in stone fruits (like peaches, plums, cherries, apricots, nectarines, etc. ) [ 10], Pénicillium italicum and _P_. digitatum in citrus fruits [11] and P^ expansum in apples [12], could be kept in check by irradiation. These observations point to the uniqueness of radiation treatment to reduce losses due to diseases which cannot be adequately controlled by other means.

An important aspect in the application of radiation to delay ripening is the ability of irradiated fruits to withstand transport. During transport, the fruit is subjected to a variety of damaging vibrations and impacts which may lead to rupture of the skin and, as a consequence, to dehydration, fungal and mould infestation, hastened ripening and senescence. Vibration injuries are known to be minimized when the fruits are re frigerated [ 13], possibly due to the turgidity of the fruit tissues at lower temperatures.Such observations point to the desirability of maintaining fruits in a hard condition during transit.

The influence of radiation on fruit texture is dose-dependent and could be either deleterious or beneficial. High doses of radiation tend to adversely affect texture as a result of degradation of pectin, cellulose, starch and other macromolecules. Low doses of radiation, which delay ripening, keep the fruit in the hard state fo r a longer tim e and could presumably be of advantage during transport.

4. STUDIES ON DELAYED RIPENING IN ALPHONSO MANGOES

Extensive studies have been carried out at Trombay on delayed ripening in Alphonso mangoes by low-dose irradiation. E arlie r work [ 14] has established that the optimum radiation dose fo r this fruit is 25 krad, giving an extension in shelf life of 6 to 8 days at ambient-temperature storage. It was further observed that doses higher than the optimum resulted in physiological damage and ea rlie r ripening. On the other hand, fruits irradiated under nitrogen atmosphere could withstand doses as high as 200 krad, without apparent radiation injury (see F ig . 1). Since fruits exposed to such high doses in a ir turned completely black, it appears likely that ozone may be responsible fo r this skin discoloration.

E arlie r investigations [ 15] had also shown that skin-coating of the fruits with a 6 per cent emulsion of an acetylated monoglyceride prior

68 SREENIVASAN e t a l.

FIG. 1. Alphonso mangoes, unirradiated and irradiated under nitrogen and air.The photographs were taken on the 10th day of storage. Fruits were given a dose of 200 krad under nitrogen (2) or air (3). Unirradiated mango (1) is ripe and orange yellow. Fruit (2), irradiated under nitrogen, is green in colour, unripe and does not show radiation injury. Fruit (3), irradiated in air, shows extensive blackening and is spoiled.

to irradiation at the optimum dose extended the ambient storage life further by 6 days. Such fruits had very good organoleptic attributes compared to the skin-coated unirradiated controls in which ripening did not progress satisfactorily.

While the studies on the extension of shelf life at ambient temperature would be of significance in the context of non-refrigerated transport practices within the country, transhipment to distant countries would require storage in the re frigerated holds of ships or aircraft. Studies have therefore been extended to assess the shelf life Of irradiated mangoes stored at sub-room temperatures.

The fruits (mature, unripe ones, uniformly olive green in colour and picked the previous day) were irradiated (25 krad) at room temperature and subsequently stored at 5, 10, 15 and 20° C. Storage life was determined by marketability which takes into reckoning a fresh-like glossy appearance and natural flavour; the percentage ripening was also determined. These studies (see Figs 2 and 3) revea l that, in general, ripening is faster with increasing storage temperature and that irradiation induces a delay in ripening at all temperatures. The delay in ripening due to irradiation is also dependent on storage temperature; at 5° C, the irradiated fruits ripen after a delay of 40 days over control and this decreases to 10 days at 20° C. The delayed ripening is also reflected in increased marketability of the treated fruits over longer periods.

PL-422/9 69

STORAGE TIME (DAYS)

F IG .2 . R ipen ing o f con tro l and irrad iated m angoes at d iffe ren t storage tem peratures.

M ature, unripe fru its, u n ifo rm ly o l iv e g reen in co lou r, w ere irrad iated (25 krad) at room tem perature, a day

fo llo w in g harvest, and subsequently stored at various sub-room tem peratures. T h e fruits w ere considered

fu lly rip e when th ey d eve lop ed a g o ld en y e llo w co lou r as w e l l as the characteris tic fla vou r.

STORAGE TIME (DAYS)

F IG .3 . M a rk e tab ility o f con tro l and irrad iated m angoes stored at d iffe ren t tem peratures.

E xperim enta l deta ils as in cap tion to F i g . l . M a rk e tab ility is determ ined b y reten tion o f fre sh -lik e glossy

appearance, natural fla vou r and firm textu re.

7 0 SREENIVASAN e t a l .

STORAGE TIME (DAYS)

О--------О CONTROL “ I NOT • -------в CONTROL 1 c o v - „ - DД ------- Л IRRADIATED-! COVERED Л -------& IRRADIATED- Г c o v e r e d

F IG . 4 . In flu en ce o f coverin gs on the ripen ing and m ark e ta b ility o f m angoes.

E xperim en ta l d e ta ils as under F i g . l e x cep t that the sam ples w ere a l l stored at 5”C . A part o f the con tro l and

irrad ia ted fruits w ere kept co ve red w ith e ith er paper cuttings or d ry paddy straw ( r ic e sta lk ). Ripeness and

m a rk e ta b ility w e re assessed as described in footnotes to Figs 1 and 2.

In the foregoing studies on the effects of re frigerated storage, the irradiated fruits were kept open to the atmosphere prevailing in the cold storage. Remarkable differences were observed when the fruits during storage at 5° С were kept covered under either paper cuttings or dry paddy straw, as normally adopted in com m ercial practice. The data obtained in such studies, presented in F ig . 4, indicate a slower ripening rate for the control as w ell as fo r the irradiated mangoes, resulting in shelf lives of 40 and 90 days, respectively. There are reports in the literature [ 16, 17] o f fruits stored in modified atmospheres, such as with lower oxygen or increased carbon dioxide contents, showing decreased respiration and an extension of storage life . In the light of these reports, it is conceivable that respired carbon dioxide, accumulating in the vicin ity of stored fruits kept tightly packed, slows respiration thereby delaying ripening.

Studies have also been carried out with other indigenous varieties of mangoes such as Totapuri, Langda and Duseri and all these show a comparable extension in shelf life on irradiation.

5. TRANSPORTATION STUDIES ON IRRADIATED MANGOES

In view of the known influence of irradiation on fruit texture and the importance of the latter as a factor determining damage during transit, it was desirable to compare the behaviour of irradiated and control mangoes during transit, especially under the hot and humid conditions prevalent in India.

PL-422/9 7 1

Mangoes, subjected to the various treatments (skin-coating, irradiated or both) were packed in baskets in dry paddy straw and shipped by ra il over a distance of about 1100 kilom etres. A fter storage there at room temperature (25 to 32° C) fo r a period of 8 days, the baskets were shipped back, the ra il journey each way taking about 36 hours. Temperatures during transit were quite high and reached up to 42° C. A fter receipt in the laboratory, the fruits were kept under observation fo r 5 more days and then scored fo r ripening and marketability as assessed by appearance, skin gloss and typical flavour.

The data, presented in F ig . 5, show that the combination treatment of skin-coating and irradiation is the best, 100 per cent of these fruits being marketable at the end of the experiment. None of the unirradiated control fruits were saleable by this time, while 66% of the irradiated fruits were in acceptable condition. Photographs of typical samples of fruits from the three groups at the end of the experimental period of 15 days are shown in F ig . 6. The picture shows that the unirradiated controls (1) are o verripe and blemished compared to the irradiated ones (2), while the skin-coated and irradiated mangoes (3) are s till in a fresh -like condition.

In lim ited tria ls , irradiated mangoes have also been successfully air-shipped to Hungary, the USSR and the United States of Am erica. Particu lar mention may be made of the studies carried out in collaboration with the Central Food Research Institute, Budapest, Hungary, the results of which are summarized here.

STORAGE TIME (DAYS)CONTROL Л ---------Û IRRADIATED- A SKIN COATED ft IRRADIATED

F IG .5 . Transportation studies w ith irrad ia ted m angoes (B om bay - B angalore - B om bay) - ripen ing and

m a rk e tab ility .

C on tro l as w e l l as sk in -coated (6 % "M y v a c e t " ) and/or irrad ia ted (25 krad ) fruits w ere packed in baskets in dry

paddy straw and shipped by ra il o v e r a d istance o f 1100 k ilom etres and b ack . T h e fruits w e re exam in ed a fter

a to ta l storage period o f 15 days, o f w h ich 3 days w ere taken up b y the ra il jou rney both ways. T h e fruits

w e re scored fo r ripen ing and m ark e ta b ility as described in footnotes to Figs 1 and 2.

72 SREENIVASAN e t a l .

2 3F IG .6 . Transportation studies w ith irrad ia ted m angoes (Bom bay - Bangalore - Bom bay) - photographs.

T y p ic a l sam ples o f fruits, at the end o f the studies (15 days), from the three groups, v i z . con tro l, irrad iated

or sk in -coated and irrad ia ted , are shown. Th e unirradiated controls (1 ) are o v e r -r ip e and b lem ished and none

o f them are m ark e tab le . T h e irrad ia ted fruits (2 ) are 66% m arketab le , w h ile the sk in -coated and irrad iated

sam ples (3 ) have a fre sh - lik e appearance and are 100% m arketab le .

The fruits were wrapped individually in tissue paper and packed tightly with paper cuttings in a plywood box provided with ventilation holes which were covered on the inside with 200-mesh w ire gauze to prevent insect infestation. The consignment was a ir-lifted to Budapest (a distance of about 5600 kilom etres) and the time interval between irradiation and their receipt in Hungary was 4 days. The mangoes were assessed for their storage characteristics by various parameters that included physiological loss in weight, puncture resistance of the skin, pulp texture, carotenoids, acidity and organoleptic attributes, at various periods during storage . 1

Stated in brie f, it was found that ripening and senescence are strikingly delayed in mangoes by skin-coating and radiation treatment (see F ig . 7).The treated mangoes retain their skin resistance while the disappearance of chlorophyll and formation of carotenoids are substantially delayed. Weight loss on storage is lower and reduction of acidity and formation of sugars in the fruit flesh take place la ter. Organoleptically, the fruits subjected to the combination treatment were very good followed by the irradiated fruits.These studies point to the feasib ility of the combination treatment in prolonging shelf life of fruits significantly to enable their transport to distant countries.

1 These studies w ere carried out in co llab o ra tion w ith Drs J. Farkas and K . Vas o f the C en tra l Food

Research Institu te, Budapest, Hungary, and the authors' g ra te fu l acknow ledgem en ts are due to th em .

PL-422/9 73

It t 1 9 6 9

9 < J 9 9I Я Я А О М Т C D

» «> » COATtb ‘ « i U O l A T C b

F IG .7 . Transportation studies w ith irrad ia ted m angoes (B om bay - Budapest)— photographs.

O ne dozen m angoes each from con tro l, irrad iated and sk in -coated and irrad ia ted groups w ere a ir - l i f te d to the

C en tra l Food Research Institu te, Budapest, Hungary, w here they w ere assessed for storage characteristics .

Photograph taken at end o f these tria ls (10 days) shows d e la y in ripen ing in the treated fruits, particu larly the

sk in -coated and irrad iated sam ples.

6. STUDIES ON DELAYED RIPENING IN BANANAS

The banana has also been studied critica lly to determine the optimum conditions fo r delayed ripening. Researches have been carried out using severa l banana varieties such as Giant Cavendish, Red (Red skin).F il l Basket or Poovan, French Plantain and the Dwarf Cavendish.Fruits of the firs t four varieties were harvested at known maturity from a plantation 40 m iles from the laboratory and utilized the same day for experiments. Dwarf Cavendish bananas were obtained through a local dealer, after being transported over a distance of 200 m iles by truck and were 1-day old. Only fruits free from abrasions and mechanical bruises were chosen fo r the studies.

7 4 SREENTVASAN e t a l .

Maturity of the fruit at harvest was determined on the basis of pulp- to-skin ratio and fullness of the fingers as judged by angularities [ 18].That the bananas were in the preclim acteric stage was ascertained by odour of the pulp and respiration rate. Prelim inary experiments for assessing the optimum dose were carried out with 20 fingers for each dose of radiation.

It was observed that, in general, the irradiated fruits showed delayed ripening, irrespective of the dosage employed or the variety. A linear relationship seemed to exist between delay in ripening and dose up to 35 krad (see F ig . 8). Doses above 35 krad did not show any corresponding decrease in rate of ripening. Data on the optimum dose leve ls, the maximum tolerable dose and extension in storage life obtained when 75% mature bananas are irradiated in the preclim acteric stage and stored at 24 to 29° С are summarized in Table I.

Among the five varieties screened, the Red one could withstand doses up to 50 krad without much skin damage, whereas F il l Basket and French Plantain were highly susceptible to radiation doses exceeding 30 krad. The Cavendish group could tolerate up to 40 krad of gamma rays. Irrespective of varieta l differences, doses higher than 50 krad caused severe deleterious effects on bananas irradiated in the preclim acteric stage. A dose of 100 krad and above caused extensive splitting of the skin and the pulp along the length of the fruit and complete blackening of the skin during subsequent storage (see F ig . 9). Such fruits had soft and mealy pulp with a somewhat cooked flavour and broke into lumps on slight application of pressure.

The physiological state of the fruit at the tim e of irradiation is an important factor determining radiation sensitivity. Thus, Giant Cavendish fruits irradiated after onset of clim acteric at colour stage 3 (yellowish green; see footnote to Table IX for a description of the colour stages) could withstand up to 200 krad without any pronounced radiation damage except that the fruit tips remain brownish green at the fu lly ripe stage. However, irradiation does not induce any delay in the ripening as judged by skin colour and total soluble solids.

Results of studies in which bananas harvested at different stages of maturity were irradiated at the optimum dose are given in Table П. It can be concluded from these studies that (i) the maturity of the fruit at the tim e of irradiation considerably influences the post-irradiation storage behaviour, the maximum responses to irradiation in terms of delayed ripening being observed with the lower maturity, and (ii) the temperature of post-irradiation storage influences the rate of ripening, the lower temperature of 21° С giving a greater delay in ripening. Fruits of maturity lower than those studied failed to ripen uniformly without the application of external ripening stimulants [ 18].

A combination treatment involving irradiation along with either waxing or dipping in kinetin solution, is found to give added benefits in terms of increased shelf-life . From the data, presented in Table Ш, it may be seen that waxing as w ell as kinetin dip given alone can extend the shelf-life by 2 to 3 days at ambient temperature. In combination with irradiation, either of these treatments delays ripening by 2 to 3 days over that obtained due to radiation treatment alone. The delayed ripening in the combination- treated bananas was also reflected in a decreased rate of respiration and a delay in onset of clim acteric. Kinetin is known to inhibit or delay

PL-422/9 75

senescence in many horticultural products, especially lea fy vegetables, and this has been attributed to a decrease in overa ll resp iratory rates [ 19].An added advantage of using radiation along with waxing is a reduction in weight loss and discoloration usually observed in irradiated bananas during storage under low-humidity conditions.

Though transport studies s im ilar to those with mangoes have not so fa r been conducted withbananas, the effect of radiation treatment on texture has been assessed. The immediate effects of gamma irradiation on the texture o f whole fruit and pulp are summarized in Table IV and F ig . 10. The extent of radiation-induced softening was found to vary among the varieties. There was little e ffect on texture up to a dose of 50 krad which is higher than the optimum fo r a ll the varieties. In the range o f 50 to 100 krad, there was marked loss in texture of whole fruit as w ell as pulp. F i l l Basket shows the least damage in the dose range of 100 to 200 krad.

Examination of Dwarf Cavendish bananas, immediately after irradiation at doses up to 200 krad, failed to revea l any increase in reducing sugars, suggesting that starch degradation may not be contributing to loss of texture.

Results of organoleptic evaluation of ripe fruits from irradiated and control groups are summarized in Table V. The average scores, based on taste, flavour, texture and appearance indicate that bananas irradiated up to a dose o f 40 krad compared favourably with unirradiated fruits. According to some of the panel members, the irradiated fruits were slightly unripe and starchy even though fruits of the same colour stage were chosen fo r evaluation. This may be attributable to some of the biochemical changes during ripening proceeding at a slower rate than others such as skin coloration in the irradiated fruits.

7. STUDIES ON DELAYED RIPENING WITH OTHER FRUITS

Sapodillas and guavas are other major fru it crops that are extensively grown in several parts of the country and these have also been investigated [ 20 ] fo r the development of suitable radiation treatments to obtain an extension in their shelf life .

Sapodillas, when exposed to a radiation dose of 10 krad, show an extension in storage life of 3 to 5 days at ambient temperature (25 to 32° C) storage which can be increased to 15 days at re frigerated temperature (10° C). The irradiated fruits did not show any greater loss of ascorbic acid while decrease in weight on storage was less compared to controls (see Table V I).

Guavas, likew ise, showed a maximum delay in ripening of 3 to 5 days at room temperature storage (25 to 32° C), when treated with 30 krad. The ascorbic acid content of irradiated fruits was not significantly different from that of controls, while the physiological loss in weight was less in the form er (see Table V II).

8. BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF DELAYEDRIPENING

Relatively little attention has been paid to the physiology and biochemistry of the developing fruit and its relation to post-harvest storage and ripening characteristics. Such knowledge and, more specifically, the biochemical

76 SREENIVASAN et a l.

F IG .8 . E ffec t o f d iffe ren t doses o f gam m a irrad ia tion on bananas.

Fruits o f F i l l Basket v a r ie ty (75% m atu rity ) w ere exposed to various doses o f rad iation as in d ica ted b e low and

the photographs taken on the 14th day o f storage at 24 to 29°C .

1. - con tro l 5 . - 3 0 krad

2 . - 15 krad 6. - 35 krad

3 . - 2 0 krad 7 . - 4 0 krad

4 . - 25 krad 8 . - 5 0 krad

Fruits irrad iated up to 30 krad show progressive d e la y in r ipen ing . Doses o f 35 krad and above cause skin

d isco lo ra tion .

TABLE I. RADIATION-INDUCED EXTENSION IN SHELF L IFE OF BANANAS

V a r ie ty

O ptim um

dose

(k rad )

M axim um

to leran ce

dose

(k rad )

Extension in storage l i f e o ver

controls (days )

In p rec lim a c te r ic

stageT o ta l

D w arf Cavendish 30 40 4 8

G iant Cavendish 35 40 3 -4 7-8

F ill Basket 25 35 4-5 8 -9

Red 40 50 4 -5 7-8

French P lantain 20 30 8 14

Fruits harvested a t 75% m atu rity (as assessed b y pu lp -to -sk in ratio , w h ich was 1 .4 to 1 .5 ) w ere irrad iated

in the p re c lim a c te r ic con d ition . Th e fruits w ere stored at room tem perature (24 to 29“C ) w ith a re la t iv e

h u m id ity o f 75 to 80%.

PL-422/9 77

FIG . 9 . Radiation in ju ry in bananas exposed to h igh doses.

Red bananas o f 75% m aturity w ere exposed to d iffe ren t doses o f rad ia tion as ind ica ted b e low :

1. - con tro l 4 . - 35 krad

2 . - 20 krad 5. - 40 krad

3 . - 2 5 krad 6 . - 100 krad

Photographs taken on the 13th day o f storage show that con tro l fruits w ere e ith er rip e o r o v e r -r ip e . Fruits

irrad ia ted up to 40 krad w ere s till unripe. H igh er doses result in b lacken in g and fru it sp littin g .

TABLE П. INFLUENCE OF FRUIT M ATU RITY AND STORAGE TEM PERATURE ON DELAYED RIPENING IN IRRADIATED BANANAS

M aturity

at harvest

Extension in storage l i f e o ve r controls

(days)

V a r ie ty Dose29 to 32°C 21°C

(p e r c en t) (k rad ) In p rec lim a c te r ic

con d itionT o ta l

In p rec lim a c te r ic

con d itionT o ta l

G iant Cavendish 75 35 2 4-5 5-6 9-10

85 35 1 3 4 7-8

Red 70 40 4-5 7-8 6 -7 9-10

85 40 2-3 4 -5 4 -5 7-8

F il l Basket 75 25 - - 7-8 11-12

90 25 - - 3 -4 7-8

Fruits o f d iffe ren t m aturities, as assessed by pu lp -to -sk in ratio (70% m ature, 1 .3 0 ; 75% m ature, 1 .45 ;

85% m ature, 1 .7 0 ; 90% m ature, 1 .8 0 ), w ere irrad iated in the p rec lim a c te r ic stage . For each m aturity

s tage, 25 fruits w ere studied in du p lica te .


TAB LE III. SHELF-L IF E EXTENSION IN BANANAS BY COMBINATION TREATM ENTS

T rea tm en t

Storage l i f e

(days)

Extension in sh e lf l i f e

o ve r controls

(days )

24 to 29°C 21°C 24 to 29°C 21°C

Giant C avend isha

C on tro l 16 23 - -

6% w ax d ip 18 28 2 5

35 krad 21 31 5 8

6% w ax d ip + 35 krad 23 33 7 10

D w arf Cavendish*3

' C on tro l 17 - - -

K in e tin d ip 20 - 3 -

30 krad 22 - 5 -

K in e tin d ip + 30 krad 24 - 7 -

30 krad + k in e tin d ip 22 - 5 -

â Fruits o f 80% m atu rity w ere d ipped in a 6% w ax em ulsion (Carnauba and para ffin w axes ) fo r 1 m inute and

dried under a fan at am b ien t tem perature,

k Fruits o f 75% m atu rity w e re im m ersed fo r 10 m inutes in a solu tion (50 ppm ) o f k in etin

(N 6 -b en zy lam in op u rin e ) con ta in ing 1% Tw een -80 as an adjuvant.

Results are from one ty p ic a l exper im en t out o f three conducted w ith 20 fruits fo r each trea tm en t.

TAB LE IV. TE X TU R AL CHANGES IN IRRADIATED BANANAS

V a r ie ty C om ponent

Fru it firmness

(as % decrease from con tro l)

50 krad 100 krad 200 krad

D w arf C avend ish W h o le fru it 4 .4 37 .0 48 .0

Pulp 9 .4 4 2 .0 52 .0

Red W h o le fru it 4 .0 2 4 .0 4 4 .0

Pulp 3 .0 25 .0 50 .0

F i l l Basket W h o le fru it 3 .4 24 .0 3 4 .5

Pulp 0 .0 16 .6 2 1 .0

T h e results are averages o f 10 independent determ inations. T ex tu re measurem ents w ere m ade im m ed ia te ly

fo llo w in g irrad ia tion w ith a M agn ess -Tay lo r pressure tester [ 1 8 ] . Essentially s im ila r results w ere also

obta ined using "Instron " f itted w ith a 5 / 6 -in . tip .

PL-422/9 79

4 -

______ I______ I I-----------1-----------О 50 IOO 150 200

DOSE (krod)

FIG . 10. Im m ed ia te e f fe c t o f irrad ia tion on texture in bananas.

T ex tu re o f the w h o le fru it or o f the pulp was m easured w ith a M agn ess -T ay lo r pressure tester im m ed ia te ly

fo llo w in g irrad ia tion at the various doses. Results are averages o f 8 to 10 readings.

TA B LE V. ORGANOLEPTIC EVALUATION OF IRRADIATED BANANAS

Dose

(k rad )

G iant

C avend ish

D w arf

C avend ishRed F il l Basket

0 6 .0 6 .0 7 .0 6 .5

20 6 .8 7 .0 7 .0 6 .7

25 6 .5 6 .8 6 .8 6 .2

30 7 .0 6 .8 6 .3 5 .6

35 6 .8 6 .2 7 .0 6 .0

40 6 .5 6 .0 6 .9 6 .3

Fruits w ere assessed, on reach ing co lou r stage 5 ( fu l l y e llo w / fu ll red ; see foo tn o te to T a b le IX for

descrip tion o f co lou r stages), fo r taste, textu re, fla vou r and o v e ra ll appearance b y a 1 0 -m em ber pane l.

T h e organ o lep tic scores are based on a 9 -p o in t h edon ic sca le and are averages o f tw o independent eva luations.

A score o f 5 .5 or above ind ica tes that the sam p le is a ccep ta b le .

TAB LE VI. DELAYED RIPENING IN IRRADIATED SAPODILLAS

80 SREENIVASAN e t a l.

Storage

tem pera tu re3

Fruit

texture*3

(lb )

T o ta l

soluble

solids0

6 ° )

A scorb ic

ac id0

(m g/100 g )

P h ys io lo g ica l

loss

(°Io)

Extension o f

she lf l i f e

(days )

A m b ien t (25 to 32 °C )

C ontrol 1 .0 22 .0 8 .5 32 .0 -

Irradiated 9 .5 15.0 9 .5 19 .5 3 -5

10°C

Contro l . 1 .5 27 .5 16.0 36 .0 -

Irrad iated 6 .5 19.0 24.0 25 .0 15

T h e irrad ia ted sam ples re c e iv ed a dose o f 10 krad.

a T h e sam ples stored at am b ien t tem perature w ere analysed on the 8th day o f storage, w h ile those stored

at 10°C w ere analysed on the 35th day o f storage,

b A v e ra g e o f 8 to 10 determ inations.

c A v e ra g e o f 3 to 4 determ inations.

Fruit texture was assessed b y a M agn ess -Tay lo r pressure tester.

T o ta l solub le solids w ere determ ined w ith a B e llin gh am and Stanly pocket re fra c tom eter and expressed

as °jo sucrose.

A scorb ic acid was estim ated b y the 2, 4 -d ich lo rop h en o l indophenol m ethod.

TA B LE VII. DELAYED RIPENING IN GUAVAS

Sam ple

Fruit

tex tu rea

( lb )

T o ta l

soluble

solids*5

Ascorb ic

acidb

(m g/100 g )

P h ys io lo g ica l

loss

(1o)

Extension o f

sh e lf l i f e

(days)

C on tro l 3 .5 9 .5 140 35 -

Irrad iated 9 .0 7 .0 132 26 3 -5

T h e fruits w ere g iv e n a rad ia tion dose o f 30 krad. T h e various determ inations w ere m ade on the 8th day

o f storage a t 25 to 32°C .

a A v e ra g e o f 8 to 10 determ inations,

k A v e ra g e o f 3 to 4 determ inations.

O ther d e ta ils as in foo tn o te to T a b le V I .

PL-422/9 81

mechanisms underlying radiation-induced delay in ripening as well as damage, would be of practical value in developing suitable radiation preservation processes.

Accordingly, attempts have been made to elucidate metabolic processes associated with ripening and the effect of radiation thereon. Studies have also been undertaken on the biochemistry of radiation induced browning in bananas.

9. STUDIES ON RESPIRATION

In view of the important role of respiration in the overa ll physiology of fruit, including the ripening process, studies have been carried out on the resp iratory activity of irradiated fruits. Irradiation brings about marked alterations in the respiration of the fruits at various periods up to and during the onset of clim acteric, in both mangoes and bananas. Significant differences in the responses of the two fruits, both of which belong to the clim acteric type, are also observed.

In mangoes, skin-coated or otherwise, irradiation results in an immediate and severa l-fo ld spurt of resp iratory activity which reaches a maximum by the 1st day and drops gradually thereafter t i l l it becomes comparable to that of control between the 3rd and 6th days (see F ig . 11). C lim acteric onset is seen in both control and irradiated mangoes by about the 6th day, reaching a peak by about the 10th day. At clim acteric peak, the irradiated fruits show a lower rate of respiration than the control. The skin-coated unirradiated mangoes show a considerable reduction in resp iratory activity throughout compared to controls and exhibit a broad clim acteric peak. The skin-coated and irradiated mangoes show at all times up to the clim acteric peak, higher respiratory activity than the

о-------- о UNIRRADIATED

a--------a IRRADIATED

— ■ ■ « SKIN COATED UNIRRADIATED*--------л SKIN COATED & IRRADIATED

FIG. 11 . Respiratory patterns of control and irradiated mangoes.The fruits were skin coated (6°]o "Myvacet") or irradiated (25 krad) or both and respiration of individual fruits were determined daily at constant temperature (25 ± l eC) by the continuous-current method [18].


skin-coated unirradiated controls. The very low resp iratory activity in the latter may be responsible fo r its poor ripening characteristics as well as acceptability.

Studies have also been carried out on the ability of mango tissues to oxidize various Krebs' cycle intermediates and the data are depicted in F ig . 12. The increase in respiration, due to addition of citrate and malate, is observable in both control and irradiated (25 krad) mango tissue homogen- ates. However, with succinate, this marked effect is observable only with control homogenate and is considerably less in the irradiated mangoes suggesting an impairment in the utilization of this substrate. This has also been substantiated by studies using 14C-labelled succinate. It is interesting to note in this connection that an inactivation of the enzyme, succinic dehydrogenase, in irradiated plant tissues has been reported [ 21 ].

F IG . 12. O xida tion o f K rebs ' c y c le in term ed ia tes b y m ango hom ogenates.

Endogenous ox ida tion as w e l l as that o f added substrates w ere fo llo w in g in a Warburg resp irom eter. H om ogenates

w e re m ade in 0 .5 M sucrose in phosphate bu ffer, pH 7 .4 , con ta in in g 0 .0 1 M ED TA and incubated w ith substrates

at 25°C . E xperim enta l d e ta ils are described elsew here [ 2 2 ] .

Data on the label in respired carbon dioxide when mango tissue was incubated with 14C-acetate are shown in Table VIH. Suprisingly, in these studies, perform ed 24 hours post-irradiation, the radioactivity in C02 respired by the irradiated mangoes was less than that of control tissue.The irradiated fruits show an increased respiration at this time, as observed earlie r, and this anomaly has been traced to a diminished uptake of exogenous acetate by the irradiated fruit cells . A decrease in uptake of both acetate and succinate by carrot tissues, as a result of irradiation, has also been reported [21]. The mechanism of this decreased uptake is not clear at the present time. It could conceivably result from a derangement of cellu lar energy-generating processes and consequent impairment of active transport of solutes into the irradiated cell.

The incorporation of 14C-acetate into cellu lar constituents such as lipids, amino acids, sugars and tricarboxylic acid cycle intermediates by slices from irradiated mangoes is also significantly decreased [ 22 ].While this may be a consequence of reduced uptake of acetate by the cell, an inhibition of some metabolic pathways cannot be ruled out.

The labelling pattern of some of the Krebs' cycle intermediates shows that the irradiated tissues incorporate only 20% as much label into these as control tissue. A notable exception is succinate, the labelling

PL-422/9 83

TAB LE VIII. RESPIRATORY STUDIES WITH MANGO SLICES USING 14C- ACETATE

S am ple

R ad ioa c tiv ity

in C 0 2

(counts/m in )

Ratio o f la b e l in

control/ irrad ia ted

Experim ent I

C on tro l 5280

1 .50Irrad iated 3560

Experim ent I I

C on tro l 6520

1 .35Irrad iated 4850

T h e irrad iated fruits r e c e iv ed a dose o f 25 krad. Tissue s lices w ere used 24 hours a fte r irrad ia tion .

Respiration was fo llo w ed e ith er in a Warburg resp irom eter using 1 g tissue for 150 m inutes (E xperim en t I ) or

b y the C onw ay m ethod using 2 g tissue and fo llo w in g the C 0 2 output for 60 m inutes (E xperim en t I I ) .

Respired C 0 2 was trapped in sodium h yd rox id e and the ra d io a c tiv ity in the p rec ip ita ted B a C 0 3 was

determ ined using a g a s - flo w counter.

of which is only slightly affected due to irradiation [22]. This difference in the labelling behaviour of succinate as compared to the other Krebs' intermediates studied,, may result from an accumulation of this metabolite. E a rlie r studies on oxidation of succinate have shown an impairment of this function in the irradiated mangoes and this could lead to its accumulation.

Autoradiographic studies of the various amino acids separated by paper chromatography from mango slices incubated with 14C-acetate show the absence of label in glutamic acid in the irradiated tissue [ 22]. Since this amino acid arises from a -keto-glutarate, this observation may point to the operation o f the glyoxylate bypass in irradiated mangoes.

The resp iratory pattern of Giant Cavendish bananas harvested at 75% maturity and irradiated at 35 and 100 krad is depicted in F ig . 13.The bananas, unlike the mangoes and other fruits of the clim acteric type, do not show an increase in respiration immediately following irradiation. Another significant difference is that the clim acteric peak was reached 5 days later in the 35-krad samples compared to control fruits.A sm aller delay of 2 days in reaching clim acteric peak was observed in bananas irradiated at 100 krad. Even though the clim acteric peak was delayed due to irradiation, the time required to reach this peak after the clim acteric onset was about the same for both irradiated and control fruits.The resp iratory C02at the clim acteric peak was found to be comparatively low in irradiated bananas.

The resp iratory patterns of F il l Basket and Red bananas irradiated at two different stages of maturity are shown in Figs 14 and 15, respectively.In F il l Basket, the onset of clim acteric was delayed by 1 day arid 3 days in fully mature preclim acteric fruits irradiated at 50 and 25 krad respectively. In 80% maturity fruits, irradiation at 25 krad delayed clim acteric onset by4 days. Sim ilarly, in Red , 35 krad delayed the clim acteric onset by5 days in 70% mature bananas as against only 3 days in 85% mature bananas.


FIG . 13. Respiratory patterns o f con tro l and irrad ia ted bananas (G ian t C avend ish ).

G iant Cavendish fruits o f 75% m aturity w ere irrad ia ted at 35 or 100 krad and respiration studied as d e ta iled

under F i g . 11.

F IG .1 4 . Respiratory patterns o f con tro l and irrad iated bananas (F i l l Basket).

T h e fruits, e ith er fu lly m ature or 80% m ature w e re irrad ia ted at 25 and 50 krad and resp iration fo llo w ed as

described under F ig . 11.

PL-422/9 85

F IG . 15. Respiratory patterns o f con tro l and irrad iated bananas (R ed ).

T h e fruits, harvested at tw o stages o f m atu rity , v i z . IV jo and 85%, w ere irrad iated at 35 and 50 krad and

resp iration fo llo w ed as described under F ig . 11.

Fruits at 85% maturity, when irradiated at 50 krad, delayed onset of clim acteric by only 1 day. These data indicate that the extent of delay in the onset of clim acteric varied with fruit maturity at time of irradiation.

10. M ETABOLIC SHIFTS IN IRRADIATED BANANA

Evidence has been obtained for a shift in metabolic pathways in irradiated banana fruits [23]. The ratio of label in CO2 produced from glucose-6-14C to that from glucose- 1-14C was approximately 0. 8 in control bananas and 0. 37 in the case of irradiated bananas, indicating a shift from the glycolytic pathway to the pentose phosphate pathway in irradiated bananas. Increased glucose-6-phosphate dehydrogenase, phosphorylase, phosphoglucomutase and fructose-1, 6-diphosphatase and a decreased hexokinase activity have been observed in irradiated fruits.

A gradual shift in the metabolic pathways during ageing of plants [24] and in particular a shift from the pentose phosphate pathway to glycolytic pathway in the ripening banana fruit [25] have been reported. The shift from the glycolytic pathway to the pentose phosphate pathway and an increased glucose-6-phosphate dehydrogenase, a key enzyme in the pentose phosphate pathway, in irradiated banana fruits, might explain partly the radiation-induced inhibition of ripening in banana fruits.

11. INFLUENCE OF RIPENING STIMULANTS ON IRRADIATED BANANAS

In view of the interference by irradiation on the ripening process, theeffect of stimulants like ethylene and 2, 4-dichlorophenoxyacetic acid(2, 4-D) on irradiated bananas has been studied. From the results presented


TAB LE IX. REVERSAL OF RADIATION-INDUCED DELAY IN RIPENING BY EXOGENOUS STIMULANTS

T rea tm en t

2 4 6

M ean co lou r index

days a fte r treatm ent

8 11 13 14 16 18 20

C on tro l 1 .0 1 .0 1.0 3 .0 5 .5 7 .0

2, 4 -D (1000 ppm ) 1 .0 3 .5 4 .7 5 .6 7 .0

" + 36 krad 1 .0 1 .0 2 .0 3 .5 4 .7 6 .6 7 .0

35 krad +

2, 4 -D (1000 ppm ) 1 .0 1 .0 1 .5 3 .0 4 .2 6 .5 7 .0

Ethylene (200 ppm ) 2 .0 4 .0 5 .0 7 .0

+ 35 krad 1 .0 3 .0 5 .0 7 .0

35 krad +

Ethylene (200 ppm ) 1 .0 3 .0 4 .0 6 .0

35 krad 1 .0 1 .0 1 .0 1 .0 1 .0 2 .5 3 .5 4 .8 5 .5 6 .0

G iant Cavendish bananas o f 75% m aturity w ere used. Fruits w e re a llow ed to ripen at 2 Г С and a t a

r e la t iv e h u m id ity o f 85 to 90%. T h e fruits w ere in d iv id u a lly scored fo r co lou r at regu lar in terva ls and

the m ean co lou r index represents the average va lu e fo r 20 fruits from each sam ple.

N u m erica l values o f colour* 1 - g reen ; 2 - greenish y e llo w ; 3 - y e llow ish green ; 4 - y e llo w w ith

green tip ; 5 - fu ll y e llo w ; 6 — y e llo w w ith brown flecks ; 7 — y e llo w w ith brown or b la ck patches

(o v e r - r ip e ) .

in Table IX, it may be observed that ethylene or 2, 4-D treatment, either before or after irradiation, offsets the delay in ripening. However, the response of the irradiated fruit to the stimulant is reduced compared to that of control; this is particularly seen with 2, 4-D. The observed difference in the ripening rates between 2, 4-D- and ethylene-treated fruits is not surprising. Ethylene is far more potent and is effective even at0. 1 to 10 ppm if applied to the fruits in the preclim acteric state [26].2, 4-D application is known to stimulate ethylene production [27, 28] and this endogenously induced ethylene may be responsible fo r the enhanced ripening.

The rate of ripening was comparatively slower in bananas when irradiation preceded ethylene treatment as against irradiation following the application of the stimulant. This suggests that the decreased response of irradiated fruits to the ripening action of ethylene may underlie the radiation- induced inhibition of ripening in bananas. The fact that irradiation of bananas in which ripening has already been initiated, as in the case of ethylene treatment prior to irradiation, does not result in inhibition of ripening changes suggests that irradiation, like other treatments (gas storage, refrigeration , etc. ) should be given when the fruits are s till in the preclim acteric stage.

PL-422/9 8 7

Irradiation above a threshold dose resulted in skin browning in preclim acteric bananas and this has been attributed to ozone formed during irradiation in a ir rather than direct radiation damage [29, 30]. However, we have observed browning in bananas even when fruits are irradiated in absence of oxygen (N2 or C02). This suggests that factors other than ozone are also responsible fo r the radiation-induced browning in bananas.

It is known that phenol oxidases are of wide occurrence in fruits and vegetables and that they catalyse the aerobic oxidation of phenolic substrates to quinones which by further auto-oxidative polym erization are converted to dark-brown pigments, generally known as melanins. It was of interest, therefore, to examine whether the radiation-induced browning in bananas was associated with alterations in the activity of polyphenol oxidase.

It is observed that irradiation results in increased polyphenol oxidase activity in the skin as w ell as pulp of banana. Polyphenol oxidase activity can be resolved into two components, one due to phenol-o-hydroxylase (cresolase) and the other due to o-diphenol dehydrogenase (catecholase).The effects of gamma irradiation at various doses up to 500 krad on the polyphenol oxidase activity in three varieties of bananas have been studied and the data are presented in Table X. Gamma irradiation is observed to exhibit a differential effect on cresolase and catecholase activities. While catecholase activity increases with dose up to 500 krad, cresolase activity shows an initial increase with dose up to 100 krad and a decrease at higher doses. The trends in the radiation-induced increase in enzyme activity are s im ilar in all the three varieties.

Other studies have further shown that the increased enzyme activity in the irradiated bananas is due to an activation rather than de-novo synthesis [31].

1 2 . R A D I A T I O N - I N D U C E D B R O W N I N G O F B A N A N A S

TABLE X. PO LYPH ENO L OXIDASE IN IRRADIATED BANANAS

G iant Cavendish Red F il l Basket

(k rad ) C reso lase C a techo lase Creso lase C a tech o lase Cresolase C a techo lase

0 14 1260 35 938 6 2188

30 27 1575 108; 1260 8 2938

100 30 1380 124 1276 10 3855

200 20 1422 90 1169 - -

500 11 1807 29 1318 - -

T h e en zym e was extracted from fro zen pulp tissues, 24 hours a fte r irrad ia tion using 0 .0 2 M potassium

phosphate bu ffer, pH 7 .0 , con ta in in g 1% T w een 80 . Th e 20 000 x g supernatant was treated in the co ld

w ith 1 .5 vo lum es c h ille d a ce ton e and the p re c ip ita te red issolved in 0 .0 2 M potassium phosphate bu ffer,

pH 7 .0 , and was assayed fo r en zym e a c t iv it y . E nzym e a c t iv ity is expressed in tim ó les oxygen consumed

m g "1 prote in m in "1. T h e creso lase and ca tech o la se a c t iv it ie s w ere estim ated using p -c re s o l and dopam ine

h ydroch loride as substrates re sp ec tiv e ly [ 3 1 ] .

8 8 SREENIVASAN et a l .

TABLE XI. PO LYPH ENO L OXIDASE A C T IV ITY IN PU LP AND SKIN TISSUES OF IRRADIATED BANANA

Substrate

E nzym e a c t iv ity

Skin Pulp

C on tro l 100 krad 500 krad C on tro l 100 krad 500 krad

p -C reso l * 1 .8 13 .2 12 .3 35 .0 124.0 29 .0

Pyroca tech o l 8 1 .4 193.6 122 .5 56 .0 94 .0 69 .0

D L -n orad ren a lin e -H C l 1406.0 2858.0 1862.0 475 .0 542 .0 685 .0

D op am in e-H C l 1493.0 4395.0 3529.0 938.0 1276.0 1318.0

T h e en zym e was ex tracted and assayed as described in the foo tn o te to T a b le X . Enzym e a c t iv ity is

expressed as ¿m oles o x ygen consum ed m g "1 protein m in -1 .

W h ile p -c reso l was used to estim a te cresolase a c t iv ity , o x ygen consum ption w ith the other th ree substrates

re fle c ts ca tech o la se a c t iv ity .

A comparative study of the enzyme activity in pulp and skin of bananas (see Table XI) reveals that while the form er contains considerably higher amounts of cresolase, the latter shows greater catecholase activity. Irrad iation at doses of 100 and 500 krad significantly increases both these activities (in case of cresolase, 100 krad shows a greater effect than 500 krad) in skin and pulp. However, the skin shows a greater increase of both activities than the pulp. Thus, at 100 krad, cresolase and catecholase activities show respective ly 6- and 3-fold increases in skin and 3|- and l i- fo ld increases in pulp.

Irradiation particularly at high doses is known to result in damage to ce ll membranes [ 32, 33] thus bringing into contact enzymes and substrate which are normally contained in separate compartments. It is conceivable that the increased polyphenol oxidase activity and the availability of substrates such as dopamine [34 ] and arterenol [35] might contribute to the radiation-induced skin browning in bananas at higher doses.

13. SCOPE FOR INCREASING FRUIT PRODUCTION VIS-A-VISEXTENSION IN SHELF L IFE

Agro-clim atic conditions in India, as in many other tropical and subtropical zones, are ideally suited for the cultivation of a large variety of fruits. Unfortunately, however, the scope fo r stepping up the output is severe ly lim ited by factors such as: (i) short seasonal availability of many of the fruits which results in flooding of the market and consequent high spoilage losses; (ii ) vastness of the country and localized centres of production, making widespread distribution difficult; and (iii) highly perishable nature of the produce posing obstacles in the exploitation of the export potential.

An increased utilization of the produce fo r both internal and export markets is im perative fo r stimulating agricultural production with attendant economic benefits. In this regard, one could cite the example of onions.

PL-422/9 89

The growing of this crop in India is very much confined to a few regions only with as much as one fourth of the total produce being grown in one area in Maharashtra. This has inevitably resulted in spoilage of large quantities during transportation and storage and, in the absence of exports, the agriculturist has been reluctant to increase its cultivation. The setting up of a few processing units (dehydration) and a rapid increase in exports during the recent past have, however, given a great impetus to increased production of this commodity bringing with it economic prosperity to the farm ers.

In the case of highly perishable foods such as fruits, attempts at increasing utilization both within the country and for exports should basically aim at developing suitable methods of extending the shelf life of the produce. Fruits are valued as a delicacy mainly in the fresh state; other methods of preservation such as heat processing greatly alter the desirable quality characteristics such as taste, texture, flavour and colour. In this context, the use of low-dose irradiation fo r lim ited extension of shelf life could o ffer prom ise.

14. PO TENTIALS OF RADIATION-INDUCED DELAY IN RIPENING OFFRUITS

The present studies have established the usefulness of radiation treatment in delaying the ripening of mangoes, bananas and other tropical fruits. Combination treatments, in which radiation is used in conjunction with skin-coating, re frigeration or modified atmosphere during storage, confer additional extension in shelf life and could be of significance in transporting over long distances. These expectations have been borne out by the lim ited studies carried out so far.

Some of the biochemical and physiological mechanisms underlying radiation-induced delay in ripening as w ell as radiation damage to the fruit have been elucidated. Studies on possible relationships between resp iratory activity and rate of ripening and the effect of radiation thereon have been useful in determining processing parameters to obtain the optimum extension in shelf life of mangoes and bananas, commensurate with maximum retention of organoleptic attribute. Varieta l differences in radiation sensitivity of bananas emphasize the hazards of extrapolating and the need fo r detailed studies with individual varieties to establish radiation dose. The influence of maturity at harvest as w ell as the physiological state of the fruit on radiation-induced delay in ripening point to the need fo r a proper choice of fruit with respect to these variables.

15. HINDRANCES TO PR A C TIC AL IM PLEM ENTATIO N

In spite of the prom ising nature of low-dose irradiation for obtaining an extension in shelf life of fruits and the obvious export potential as w ell as the added advantages of the process from a quarantine point of view, such as disinfestation of insects and elimination of pathological and ro t- producing m icroorganisms, it has not been com m ercially exploited as yet.

90 SREENIVASAN et a l .

The m ajor reason is that governmental clearances, which necessarily have to precede la rge-sca le application of the process and wholesale distribution of the treated fruit through regular trade channels, are, for the most part, lacking at the present time. The general prejudice regarding the safety, fo r human consumption, of irradiated foods and an attitude of extrem e caution on the part of governments have resulted in the snail- slow progress in this direction.

The wholesomeness of a wide variety of irradiated foods, including those subjected to steriliz ing doses, has been established [36]. Notwithstanding this evidence, there have been needless roadblocks resulting from a hypersensitive approach to the problem and the insistence on methods of toxicity evaluation that are unrealistic and inappropriate.There is considerable experimental evidence collected over the past two decades to show conclusively that: (i) the effects of ionizing energy on nutrients in foods, especially vitamins, are no more than those observed with thermally processed foods; (ii) there is no potential hazard of induced radioactivity; (i ii) there are no m icrobiological problems of practical significance.

It is in establishing freedom from toxicity and the absence of carcinogenic and mutagenic compounds that totally unrealistic requirements have been laid down. The stipulation that irradiated foods be fed as a large proportion of diet, simply for toxicity challenge is im practical as w ell as irrational. Excessive intake of any nutrient could lead to metabolic disturbances and toxic manifestations [37]. Adverse effects, including nutritional imbalance, may be inadvertently introduced by feeding such products as oranges or strawberries at the totally unrealistic leve l of 35% of solids in diet; additionally, some of the foods tested, not being normal constituents of the diet of the animals, could lead to low acceptability and low food intake and thereby vitiate the long-term experiments. A rational approach is called for, bearing in mind that fruits and vegetables are supplementary foods which normally do not exceed 5% of total dietary intake.

The reported toxic effects of irradiated sucrose solution to ce ll cultures in v itro has also been interpreted in some quarters to ra ise doubts regarding the safety of irradiated foods, particularly those of a saccharine nature such as fruits [38]. It is well known that a variety of commonly and widely used food adjuncts could cause chromosomal breaks and cytological abnormalities in v itro [39]. However, the results of such studies are not extrapolatable to the higher organisms endowed with such elaborate mechanisms as digestion, absorption, detoxification, excretion and so forth, besides various regulatory metabolic pathways [40].

There is also the lack of an internationally agreed legislation that is necessary fo r a free world-w ide trade in irradiated foods. A common approach by countries to the formulation of relevant national legislation w ill not only safeguard both consumer and producer but can also promote m ore equitable distribution of world food supplies. The joint efforts of the WHO/FAO/IAEA Committee [41,42] to draw the attention of member states to the need for establishing legislation according to internationally agreed procedures and its recommendations are a step in the right direction and need to be followed up.

PL-422/9 91

R E F E R E N C E S

[ 1 ] Preservation o f Fruit and V ege tab le s b y Radiation (P ro c . P an e l, V ien n a , 1966), IA E A , V ien n a (1968 ).

[ 2 ] M A X IE , E .C . , SOMMER, N .F . , MULLER, C . , RAU, H .L . , P lant Phys io l. 41 (1 9 6 6 )4 3 7 .

[ 3 ] ABDEL-KADER, A . , MORRIS, L . L . , M A X IE , E .C . , USABC Research D eve lop m en t Rep. N o .U C D 3 4

P80 -2 (1964 ) p . 7 .

[ 4 ] van K O O Y , J .G . , "R esp iration patterns o f irrad iated tom a toes ", Preservation o f Fruits and V ege ta b le s

b y Rad iation (P ro c . Pan e l, V ien n a , 1966) IA E A , V ien n a (1968 ) 129.

[ 5 ] SRIRANGARAJAN, A . N . , D H ARKAR, S .D . , unpublished observation .

[ 6 ] COOPER, G . M . , SALUNKHE, D .K . , Fd T e ch n o l. 17 (1963 ) 123.

[ 7 ] M A X IE , E .C . , S T A L L M A N , R . , Annual Rep. C on tract N o . A T ( l l - l ) - 3 4 . P ro je c t A g re em en t N o .80,

USA EC, Section I "Papayas and P in eapp les" (1963 ) p .89.

[ 8 ] K A H A N , R .S . , N A D E L-S H IFM A N , М . , TA M K IN -G O R O D E IS K I. N . , EISENBERG, E . , ZAU BERM AN , G . ,

A H A R O N I, Y . , "E ffe c t o f rad ia tion on the ripen ing o f bananas and avocado p ears". Preservation o f

Fruits and V eg e ta b le s b y Radiation (P ro c . Pan e l, V ien n a , 1966) IA E A , V ien n a (1968 ) 3 .

[ 9 ] NELSON, K .E . , M A X IE , E .C . , ENKEL, W . , Phytopatho logy 49 (1959 ) 475.

[1 0 ] SOMMER, N .F . , FORTLAGE, R .J . , A d v . Fd Res. 15 (1966 ) 147.

[1 1 ] K L O T Z , L .J . , C o lo r Handbook o f C itrus D iseases, U n iv . o f C a lifo rn ia , B erk e ley , C a l i f . (1961 ) 75.

[1 2 ] BERAHA, L . . RAM SEY, G .N . , SM ITH , M . A . , W R IG H T . W .R . , Ph ytopatho logy 47 (1957 ) 4 .

[1 3 ] SOMMER, N .F . , M ITC H E LL. F .G . , G U ILLO N , R . , LU IV IS I, D . A . , P ro c . A m . Soc. hort. Sci.

76 (1960 ) 156.

[1 4 ] D H ARKAR, S .D . , S A V A G A O N , K . A . , SRIRANGARAJAN, A . N . , SREENIVASAN, A . , J. Fd Sc i.

31 (1966 ) 863.

[1 5 ] D H ARKAR S .D . , S A V A G A O N , K . A . , SRIRANGARAJAN, A . N . , SREENIVASAN, A . , ib id . , p . 870.

[1 6 ] W O R K M A N , М . , P roc . A m . Soc. hort. S c i. 83 (1963 ) 126.

[1 7 ] EDNEY, K . L . , Ann . app l. B io l. 54 (1964 ) 327.

[1 8 ] TH O M A S , P . , Ph . D . Thesis, Madras U n ivers ity (1969 ).

[1 9 ] T U L I, V . , D ILLEY, D .R . , W ITTW E R , S .H . , S c ien ce 146 (1964 ) 1477.

[2 0 ] D H ARKAR, S .D . , SREENIVASAN, A . , " Irrad ia tion o f trop ica l fruits and v e g e ta b le s " , Food Irrad iation

(P ro c . Sym p. Karlsruhe, 1966), IA E A , V ien n a (1966 ) 635.

[2 1 ] M ASSEY, L . M . , J r . , "T issu e texture and in te rm ed ia ry m etabo lism o f irrad ia ted fresh fruits and

v e g e ta b le s " , Preservation o f Fru it and V ege tab le s b y Rad iation (P ro c . P an e l, V ien n a , 1966), IA E A ,

V ien n a (1968 ) 105.

[2 2 ] D H ARKAR, S .D . , P h .D . Thesis, U n ivers ity o f Bom bay (1969 ).

[2 3 ] N A IR , P .M . , SU REND RANATH AN , K . K . , unpublished observation .

[2 4 ] M acD O N A LD , J .R ., D e K O C K , P . C . , Ph ys io log ia P I. 11 (1 9 5 8 )4 6 4 .

[2 5 ] TAG ER, J .M . , BIALE, J .B ., Ph ys io log ia P I. 10 (1957 ) 79.

[2 6 ] B IALE, J .B ., A d v . Fd Res. 10 (1960 ) 293.

[2 7 ] M O RG AN , P .W . , H ALL , W .C . , Ph ys io log ia P I. 15 (1962 ) 420.

[2 8 ] H O LM , R .E ., ABELES, F .В ., P I . P h y s io l., Lancaster 42 (1967 ) 5.

[2 9 ] FERGUSON, W .E . , Y A T E S , A .R . , M ac QUEEN, K .F . , ROBB, J .A . , Fd T e ch n o l. 20 (1966 ) 105.

[3 0 ] M A X IE , E .C . , A M E Z Q U IT A , R . , H A SSA N , В .М . , JOHNSON, C .F . , P roc . A m . Soc. hort. S c i.

92 (1968 ) 235.

[3 1 ] TH O M A S , P . , N A IR , P . M . , Phytochem istry 10 (1971 ) 771.

[3 2 ] SKOU, J .P . , Ph ys io log ia P l . 16 (1962 ) 423.

[3 3 ] FORS SB ERG, A . , in A d v . in R ad iob io logy , (A U G E N STE IN , C .G . , M ASO N , R . , QUASTLER, H . , Eds),

A c a d e m ic Press, New York (1964 ) p . 117.

[3 4 ] B U C K LE Y , E .H . , in P lan t Ph en o lic Group o f North A m e r ic a , P roceed ings o f a Sym posium , Un ited

Fruit C o . , M ass ., USA (1964 ).

[3 5 ] W AALKERS, T . P . , SJOERDSMA, A . , CREVELING, C .R . , UNDENFRIEND, S ., S c ien ce 127 (1958 ) 648.

[3 6 ] REBER, E .F . , RAHEJA, K . , D A V IS , D . , Fedn P ro c . Fedn A m . Socs e x p . B io l . 25 (1966 ) 1530.

[3 7 ] GRASSO, P . , C hem istry in B rita in 6 (1970 ) 17.

[3 8 ] H O LSTEN , R .D . , SUG II, М . , STEW ARD, F .C . , Nature, Lond. 208 (1965 ) 850.

[3 9 ] S A X , K . , SAX , H .J . , P roc . natn. A c a d . S c i. U .S .A . 55 (1966 ) 1431.

[4 0 ] DE, A . К . , A IY A R , A . S . , SREENIVASAN, A . , Radiat. Res. 37 (1969 ) 202.

[4 1 ] T h e T e ch n ica l Basis fo r L eg is la t ion on Irrad iated Food, W H O T ech n ica l Reports Series N o . 316,

W H O , G eneva (1966 ).

[4 2 ] IN T E R N A T IO N A L A T O M IC ENERGY A G E N C Y , Study on the present status o f le g is la t io n on irrad iated

food in m em ber states, Rep. PL -313/R ev. 1, IA E A , V ien n a (1969 ); IA E A unpublished docum ent

N o .69-7192 .

PL-422/10

CHEMICAL, ECONOMIC, PHYSICAL AND PHYSIOLOGICAL LIMITATIONS TO IRRADIATION OF FRUITS

E .C . MAXIE, N .F . SOMMER, F .G . MITCHELL

University of California,Davis, C a lif .,United States of Am erica

Abstract

C H E M IC A L . E CO NO M IC , PH YS IC A L A N D PH YSIO LO G IC AL L IM IT A T IO N S T O IR R A D IA T IO N OF FRU ITS.

Ion iz in g rad ia tion holds tech n ica l prom ise fo r con tro llin g ripen ing and rot in but few com m od ities

in the Un ited States o f A m e r ic a . Since re fr ig e ra tion is requ ired for irrad ia ted com m od ities , d eve lop in g

nations can exp ec t a g rea ter return ort investm ents in re fr igera ted fa c il it ie s than in irrad iators. Loss in

texture is the m ajor c h em ica l p rob lem lim it in g the use o f irrad ia tion w ith fruits and veg e ta b le s . Increased

sens itiv ity to m ech an ica l in jury and to p h ys io lo g ica l disorders by irrad ia ted com m od ities are m a jor lim it in g

factors . For most com m od it ies the doses requ ired for d isin festation o f insects are not injurious. Thus, the

ou tlook fo r insect d isin festation by irrad ia tion is considerab ly m ore op tim is tic than is con tro l o f ripen ing

and rot.

1. INTRODUCTION

Since World War II the news media have carried occasional stories claiming unusually long shelf-lives for irradiated fruits and vegetables, often at room temperature. The biochemistry and physiology of senescence make these claims biologically absurd. P r io r to 1964, a non-critical review of the "sc ien tific " literature might have led one to believe that irradiation had a com m ercial potential for a wide variety of commodities. Many studies were of questionable validity, however. Products were sealed in airtight containers, physiological state (maturity) was ignored, quality evaluation was ignored, or at best, subjective; sample size was inadequate for statistical treatment, dosimetry was not reliab ly determined, geometry of radiation distribution into the product seemed highly variable, pathological studies were not quantitative and often not even qualitative, and experiments were stationary precluding exposure of the commodity to transit injury or any of the environmental fluctuations associated with transport and marketing. Our studies, in contrast„.covering 15 years and designed to avoid these critic ism s, have led us to conclude that in the United States of Am erica irradiation has technical promise for contro lling ripening and rot in but few commodities. Economic feasib ility reduces possible application even further. There are currently no major insect disinfestation problems in the fruit industry within the continental United States of Am erica. If such a problem should arise, irradiation might be an efficient and economical process to use.

Several reviews of the h istorical and technical aspects of fruit and vegetable irradiation have appeared [ 1-9] . The information in the reviews published since 1964 is s till relevant and w ill not be repeated here. The

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objectives of this paper are to: ( 1) assess the com m ercial feasib ilityof irradiating fresh fruits, and (2) evaluate the chemical, economic, physical and physiological limitations to comm ercialization of the process.

2. FE AS IB IL ITY OF IRRADIATING FRESH FRUITS

Table I lists the species we have studied, the desired technical effects under American conditions, estimated maximum dose tolerable to the commodity, estimated minimum dose required for a technical effect, and the phenomena we judge to be lim iting com m ercial application. Textural damage to flesh and skin by irradiation is so severe that processing or shipping quality is unacceptable in apricots, avocados, cucumbers, lemons, lim es, nectarines, o lives, peaches, peppers, plums, raspberries, table grapes and tomatoes. Further, irradiation increases decay in lemons and grapes in storage. Ripening in pears is irrevers ib ly inhibited. Apples, cantaloupes, mushrooms and oranges are moderately tolerant to radiation but show no benefit over cold storage. Ripening of bananas, sprouting of carrots, onions and potatoes, and the elongation of asparagus is controlled by irradiation without severe loss in quality, but more economical methods that are equally e ffective are available fo r all but asparagus.The California asparagus season is so short, and the industry so small, that irradiation is not economically feasible for that crop.

Of the species we have studied, only strawberries and papayas show technical promise fo r com m ercial application of irradiation. Irradiated strawberries show less decay and a slightly greater amount of transit injury during shipment (see Table II). In only two of seven tests (No. 4 to Atlanta; No. 6 to Honolulu) was the amount of unmarketable fruit reduced sufficiently to justify the treatment and only No. 6 would qualify on arrival. Under present conditions and marketing procedures employed by the California strawberry industry, irradiation would not be economical though it might become so in the .future. I f quality control reverts to the 1960 situation, or i f the marketing area is expanded overseas, irradiation might become an economic and technical asset. Currently, it is beneficial only in rare instances when rot levels are abnormally high. In California, this probably w ill occur too infrequently to justify the costs of the treatment.

As w ill be described by other participants in this meeting, irradiation of papayas seems to hold considerable technical promise for the disinfestation of the Hawaiian fruit fly. We have played a minor co-operative role in studies conducted by the Hawaii Department of Agriculture and the University of Hawaii and defer to these agencies for details of this work.Our impression is that irradiated papayas are of higher quality than those subjected to ethylene dibromide fumigation.

3. PHYSIOLOGICAL STATE AND D IFFERENTIAL SENSITIVITY TO RADIATION INJURY

F or irradiation of a perishable commodity to be practical, the commodity must have a substantially greater tolerance to radiation injury than the deteriorative organisms or endogenous metabolic systems needing control. As shown in Table I, few of the commodities we have studied

98 M AXIE e t a l .

have the required tolerance. Determining the maximum tolerable dose fo r a commodity is difficult under the best of circumstances. To achieve even a close approximation, it is necessary to consider the effect of physiological state (degree of ripeness or senescence) of the commodity on the maximum tolerable dose. A good example of this necessity is seen with the banana where preclim acteric fruit can tolerate no more than 50 krad. Once ripening is initiated, the tolerable dose may be as high as 200 krad. Sim ilar effects of physiological state can be seen with nectarines and peaches where irradiation of preclim acteric fruits stimulates ripening but has no measurable effect on partially ripened fruits.There are a number of practical indexes to physiological state that can be used; rates of changes of green and yellow colour, firmness of the flesh, percentage of soluble solids, titratable activity, rate of respiration, rate of ethylene (C2H4) production, etc. One or more of these may be adapted fo r a given fruit. However, the critica l matter is the stage in the respiratory clim acteric fo r those commodities exhibiting this phenomenon. Thus, the indexes noted must be experimentally related to the clim acteric before they can be reliab ly used. In determining the stages in the clim acteric sequence, the rate of C2H4 produced and the respiratory rate (oxygen consumed or carbon dioxide produced) should be measured. Samples fo r determining the other indexes should be taken at several points along the clim acteric curve and the data related to the changes in respiratory rate.

The minimum effective dose for inhibiting rot development is difficult, i f not impossible, to define precisely for it'depends upon the extent of the fungus invasion at the time of irradiation and the degree of control required. W ell developed lesions may require a much higher dose than new, tiny lesions. With the grey mould disease (Botrytis cinerea) for example,200 krad delays disease development for 3 to 5 days at 5°C. With strawberries, such a delay may be highly beneficial. With grapes destined for long-term storage, however, 200 krad would do little to control the disease. Instead, nearly complete inactivation would be required involving doses many hundred-fold higher than the tolerable dose of the commodity.

4. CHEMICAL EFFECTS OF IRRADIATION

The effect of irradiation on the chemicalj constituents in fresh fruits has been reviewed by Maxie and Abdel-Kader [5], and Maxie and Sommer [ 7] . Any radiation-induced chemical change in fruits is of academic interest but in practical term s the most significant chemical change is the ir re - versable cleavage of cellulose, hemicellulose and pectin in cell walls.The resulting softening of the flesh and skin of the fruit increases the susceptibility to mechanical injury to such a degree as to preclude the com m ercial application of irradiation for many commodities. As shown in Table I, excessive softening occurs in many instances at doses well below the minimum needed for a technical effect. To date, no practical means of preventing, or partially alleviating, this softening of the fruit tissues has been developed. Considering the nature of the cleavage of the macromolecules it is doubtful that such a means w ill be developed.

Radiation-induced changes in pigments, vitamins, volatile compounds, etc. are not lim iting because major alterations occur only at doses w ell above those required to cause excessive softening of the commodity.

PL-422/10 9 9

The two major physical effects of irradiation on fruits and vegetables are: (1) increased susceptibility to mechanical injury, and (2) increasedtendency to lose water.

Textural effects noted above account for the increased susceptibility to mechanical injury. The nature of the increased tendency of irradiated commodities to lose water has not been studied in detail. However, it is known that irradiation increases the permeability of membranes, increases metabolic activity, and ruptures chemical bonds. Thus, it is likely that the cellular membranes and the cuticle of fresh fruits are rendered more permeable to water vapour, and the movement of water from the cell into the intercellular spaces and thence through the cuticle are increased by irradiation. One of the principle reasons underlying the need for refrigeration in the storage and shipment of irradiated commodities is the suppression of water loss.

5 . P H Y S I C A L E F F E C T S O F I R R A D I A T I O N

6. PHYSIOLOGICAL EFFECTS OF IRRADIATION

Irradiation characteristically increases the respiratory rate of fruits and vegetables. The response may be small and short-lived at low doses or high and prolonged at high doses. With fruits of the climacteric class, the same dose may give very different results depending on the pre- or post- climacteric stage of the fruit as noted earlier. When the increased respiratory heat resulting from irradiation is calculated, it is not enough to materially affect the refrigeration requirements of the fruit.

The effect of irradiation on ripening varies with species. In bananas, ripening is reversably inhibited apparently by a reduction in the sensitivity of the fruit to the ripening hormone, ethylene. Ripening in pears is irre- versably inhibited by some unknown mechanism. Degreening of lemons and ripening of nectarines and peaches are stimulated by radiation-induced ethylene production.

Ethylene is produced by irradiated fruits through two mechanisms:(1) direct radiological degradation of fruit constituents such as lipids and organic acids, and (2) as yet unexplained metabolic mechanisms. The first of these occurs during irradiation; the second begins during irradiation and persists for several days, often reaching a maximum rate several days after treatment as in lemons, nectarines and peaches.

Most of the above physiological effects of irradiation could be tolerated in commercial practice. There is an additional physiological effect that is more serious with some fruits; increased sensitivity to other stresses. The most critical of these stresses is chilling injury. In every chilling- sensitive fruit we have studied, irradiation significantly increases the sensitivity of the fruit to low temperature. The effect is seen dramatically with bananas, lemons, oranges and tomatoes at doses well below those required for a desirable technical effect. In all the chilling-sensitive fruits we have studied, the order of exposure to chilling and irradiation is immaterial.

100 M AXIE e t a l .

Irradiation is occasionally suggested as a promising technology for the developing nations. This should be generally dispelled with respect to fruits and vegetables for the purposes of controlling ripening or decay.At best, irradiation could only be supplemental to cool storage, and in most cases cannot be employed without it. While irradiation has potential application with only a very few commodities, refrigeration is applicable to all. Therefore, a nation with limited resources can achieve a much greater return on its investment by developing conventional refrigerated facilities than by building irradiation facilities. The latter should be considered only where the process has been shown to be economically and technologically feasible and where the product has been cleared for human consumption by the government involved.

REFERENCES

[ 1 ] Radiation Preservation o f Food, U . S. A rm y Quarterm aster Corps, W ashington, D .C . (1 9 5 7 ) .

[ 2] Rad iation Preservation o f S e le c ted Fruits and V ege tab les , Stanford Research Institu tion. M en lo Park,

C a li f . (1 9 6 1 ).

[ 3 ] A p p lic a t io n o f Food Irrad iation in D eve lop in g Countries, T e ch n ica l Reports Series N o 64, IA E A , V ienna

(1 9 6 6 ).

[ 4 ] BROWNELL, L .E . , Rad iation Uses in Industry, U n ivers ity o f M ich igan and the U .S . A to m ic Energy

Com m ission (1 9 6 1 ).

[5 ] M AX IE , E .C . , ABDEL-KADER, A . , Food irrad ia tion -ph ys io logy o f fruits as re la ted to fe a s ib ility o f

the tech n o logy , A d v . Fd. Res. 1 5 (1 9 6 6 ) 105.

[ 6 ] M AX IE , E .C . , SOMMER, N .F . , "Irrad ia tion o f fruits and v e g e ta b le s " , Radiation Preservation o f Foods,

pu b lica tion 1273, N a tion a l A ca d em y o f S c ien ces -N a tion a l Research C ou n c il. Washington, D .C . (1965 ).

[ 7 ] M AX IE , E .C . , SOMMER, N .F . , "Changes in som e ch em ica l constituents in irrad ia ted fruits and

v e g e ta b le s " , P reserva tion o f Fruit and V eg e ta b le s by Rad iation (P ro c . Panel, V ienna , 1966), IA E A , V ienna

(1968 ) 39.

[ 8 ] R O M AN I, R .J ., R ad iob io lo g ica l param eters in the irrad ia tion o f fruits and vege tab les . A d v . Fd. Res.

J_5 (1966 ) 57.

[ 9 ] SOMMER, N . F . , FORTLAGE, R .J ., Ion iz in g rad ia tion for con tro l o f postharvest diseases o f fruits and

vege ta b le s , A d v . Fd. Res. J j> (1966 ) 147.

7 . I R R A D I A T I O N A S A T E C H N O L O G Y F O R D E V E L O P I N G N A T I O N S

PL-422/11

SENSORY, CHEMICAL, AND NUTRITIONAL EVALUATION ON THE EFFECT OF IONIZING RADIATION ON MANGOES (Mangifera indica, Linn),CARABAO VARIETY *

I.S . PABLO, Juanita A. MANALO, V ictoria A. CARDENO Philippine Institute of Nutrition,Food Science and Technology,The Philippine W omen's University,Manila, Philippines

Abstract

SENSORY, C H E M IC A L ,A N D N U T R IT IO N A L E V A LU A T IO N ON TH E EFFECT OF IO N IZ IN G R A D IA T IO N ON

M ANGOES ( M an g ife ra ind ica . L inn), CARABAO V A R IE T Y .

Th e op tim um irrad ia tion dose was determ ined in order to extend the s h e lf - l i fe o f m a tu re-green m angoes

when stored at 30eC . It has been found that 6 0 -k rad -irrad ia ted m angoes exh ib ited the low est p ercen tage o f

d ecay a fter 3 w eeks o f storage at 30°C . S ix ty -seven per cen t o f the unirradiated sam ples spo iled a fte r 10 days,

w h ile on ly 5Sffo o f the irrad ia ted sam ples spo iled . Sensory e va lu a tion re v ea led that the irrad iated sam ples w ere

just as accep tab le as the unirradiated sam ples. H ow ever, there was a s ign ifican t d iffe ren ce in co lou r. S in ce

co lou r was the m a in d iffe ren c e be tw een the tw o sam ples, co lu m n chrom atography was used to frac tion a te the

carotenoids. T h e concen tra tion o f the caro teno id e lu a te , measured as fl-ca ro ten e was determ ined using a

Spectron ic 20. A fte r 8 days o f storage, the 6 -ca ro ten e con ten t o f the irrad iated sam ple was s ign ifican tly

h igher than the 8 -ca ro ten e o f the unirradiated sam ple. T o substantiate further the above findings, the e lu a te

was subjected to th in -la yer ch rom atography. T h e chrom atogram s c le a r ly in d ica te that 6 -ca ro ten e was not

destroyed by io n iz in g rad ia tion at a dose w h ich preduced s h e lf - l i fe extension on m atu re-green m angoes.

In add ition to 6 -ca ro ten e analysis, ascorb ic ac id was determ in ed . It was found that the irrad iated sam ples

had h igher ascorb ic a c id contents during storage as com pared to un irrad iated sam ples.

1. INTRODUCTION

The mango, one of the most popular fruits in the Philippines is a potential export product. However, due to limited shelf-life and quarantine problems, its exportation in the fresh form has not yet been realized on a large scale.

The two common commercial mango varieties in the Philippines are named Piko and Carabao. The Carabao variety is preferred to the Piko variety due to its size and texture advantage. The Carabao variety, therefore, has the higher potential for export.

Several studies have been conducted on the use of ionizing radiation for shelf-life extension and its effect on the organoleptic characteristics of mangoes. Graham and Luse [ 7] investigated the use of ionizing radiation in order to produce a maximal delay of ripening and extension of shelf- life. They showed that ionizing radiation was effective in producing a shelf- life extension on mangoes. Their work also indicated that variety is an

* Research supported by the In ternational A to m ic Energy A g en cy .

101

102 PABLO e t a l.

important factor in influencing the optimum dose in the irradiation of mangoes. Dharkar and Sreenivasan [4] showed that an extension in storage life of Alphonso mangoes was achieved when 25 krad was used.Solanas and Darder [16] showed that when Venezuelan mangoes (Bocodo variety) were irradiated at 100 krad, 75% of the mangoes remained in good condition after 15 days of storage at 18°C and 80% humidity. However, the unirradiated samples exhibited 75% spoilage.

Mangoes are a good source of vitamin A (or its precursor) and vitamin С [5]. It would be undesirable, if a significant amount of vitamin A or С were destroyed due to ionizing radiation. Very limited studies have been done on the effect of y-radiation on the destruction of vitamin A or С in fruits and vegetables. Lukton and MacKinney [11] reported that carotene loss in irradiated whole tomatoes was negligible. Franceschini et al. [6] showed that the carotenoids of the sweet potato exhibited relatively little destruction on irradiation at 1.86 Mrad. Carrots irradiated in vacuum and nitrogen at 1. 86 Mrad showed a moderate loss of carotenoids.

Washington Navel oranges irradiated at 200 krad showed no loss in ascorbic acid even after 95 days at 0°C, according to Maxie and Sommer [ 12]. However,Krummel peaches irradiated at 150 and 300 krad had 23 and 35% ascorbic acid loss, respectively, when stored for 10 days at 5°C, according to Maxie et al. [ 13]. Abdel-Kader et al. [1] showed that pink and fully ripe tomatoes when irradiated at 400 krad contained more ascorbic acid during storage at 20°C compared to the ascorbic acid content of ripened unirradiated fruits harvested in the mature-green stage.

Since mangoes are generally harvested in the mature-green stage and this is also the desirable stage of ripeness for export purposes, this study concentrated on defining the effects of ionizing radiation on the shelf-life extension, organoleptic, chemical, and nutritional characteristics of mature-green mangoes (Carabao variety) when stored at 30°C. Both the (3-carotene and the ascorbic acid content of irradiated mangoes were determined during storage at 30°C.

2. MATERIALS AND METHODS

2. 1. Sample preparation

Mature-green mangoes of the Carabao variety, were obtained from Cavite. The fruits were randomly distributed into three lots containing 25 mangoes each. A day after arrival, the samples were irradiated at0, 60, and 80 krad using a 60Co source. The samples were then stored at 30°C.

2.2. Shelf-life study

Regular visual evaluation of fruit quality was made until all samples decayed. Shelf-life was determined from the percentage decay of the fruits using the following formula

Number of decayed fruits ,— -—=--- ;—1———— X 100 = % decayOriginal number of fruits

PL-422/11 103

2.3. Sensory evaluation

Flavour and texture were evaluated using the duo-trio method by a panel of 8 to 10 trained judges. After washing and peeling, one-third of the fruit was sliced for the texture evaluation. The remainder of the fruit was diced for evaluation of aroma and flavour. Approximately 500 g of the diced mangoes was puréed and placed in Petri dishes. These samples were visually evaluated under white fluorescent light for colour determination.

2.4. Carotene content

Carotene was determined using the standard AOAC method [2]. Three replicates for each dose were used for the analysis. For each replication, a 10-g sample, obtained from the mesocarp tissue of three fruits, was used. The sample in alcohol was saponified with 5% KOH and extracted several times with other, washed with water, dried, evaporated, and diluted with petroleum ether. The petroleum ether solution was then passed through a chromatographic column of aluminium trioxide using a1. 2 X 9-cm glass tube. Elution of the carotene portion using 16% diethyl ether in petroleum ether eluent was analysed using a Spectronic 20 (Bausch and Lomb, Standard Model) at 450 nm in a 1-cm cell. The amount of carotene (iug) as units of vitamin A per 100 g of sample was calculated.

2.5. Thin-layer chromatography (TLC)

Carotene extracts from the chromatographic column were analysed using thin-layer chromatography. The TLC technique as outlined by Stahl[17] was used in this study. Rf values were determined using /3-carotene as standard.

2.6. Spectroscopic analysis

Fractions or spots that gave the same Rf values as the 0-carotene standard were eluted from the TLC adsorbent with diethyl ether, concentrated and dissolved in an appropriate volume with carbon disulphide.Using a Shimadzu Recording Spectrophotometer (Model Seisakusho), the maximum absorption of the samples was determined between 400 and 700 nm. A standard solution of 0-carotene was used as a control.

2.7. Ascorbic acid determination

The ascorbic acid content of the samples was determined using the method of Loeffer and Ponting [10]. Approximately 12. 5 g of the tissue from three fruits per replicate was blended with 1% meta-phosphoric acid for 3 minutes using a Waring Blender at high speed. Three replicates were used for each analysis. A 1-ml aliquot portion from the filtrate was taken for colorimetric reading using standardized dichlorophenol-indophenol solution as dye. Total ascorbic acid is expressed as mg of ascorbic acid per 100 g of tissue.

1 0 4 PABLO e t a l.

A previous investigation conducted in our laboratory showed that variety and stage of ripeness are two important factors that influence the response of mangoes to ionizing radiation. Piko and Carabao varieties at two different stages of ripeness were irradiated at 0, 30, 60, 100, 200, and 300 krad. For the Carabao variety, a higher optimum dose was required for the "yellow-ripe" than the "mature-green" mangoes for maximum shelf-life extension. However, for both stages of ripeness, mangoes exposed to doses higher than 100 krad exhibited a higher percentage of decay than those exposed at doses lower than 100 krad.

Table I shows the percentage decay of mangoes irradiated at 0, 60, and 80 krad during storage at 30°C. After 10 days of storage, 45% of the irradiated fruits at 60 krad were edible compared to only 33% of the unirradiated control. Dharkar and Sreenivasan [4], Upadhya and Brewbaker[18], and Solanas and Darder [16] also showed that ionizing radiation produced an extension of storage life in mangoes as compared to the unirradiated control. In these three studies, the dose range for shelf-life extension of irradiated mangoes of different varieties was from 1 to 120 krad. For the Carabao variety, a dose of 60 krad gave the lowest percentage of decay even after 20 days of storage, as shown in Table I.This is in agreement with the work of Upadhya and Brewbaker [18] which showed that only 60-krad treatment retarded the ripening of mature-green Chinese mangoes.

3 . R E S U L T S A N D D I S C U S S I O N

TABLE I. DECAY OF IRRADIATED MATURE-GREEN MANGOES STORED AT 30°C

Storage

tim e

(days)

D eca y (% )

0 krad 60 krad 80 krad

1 0 0 0

5 13 4 9

10 67 55 69

15 93 87 97

20 100 95 98

Table II shows the results of sensory evaluation between 0- and 60-krad-irradiated fruits. Irradiated fruits were generally preferred to the controls during the first few weeks of storage. The panel claimed that the irradiated fruits were relatively sweeter than the control. This apparent sweetness may probably be attributed to the higher total-solid content of irradiated mangoes, which was shown in our previous study; or possibly a modified acid metabolism of the fruit exists due to ionizing radiation. No significant differences were found in flavour, texture and aroma scores between irradiated and unirradiated fruits when stored at 30°C, even up to 15 days. However, the panel detected significant differences in the colour of the mango flesh.

PL-422/11 1 0 5

TABLE II. SENSORY EVALUATION OF MATURE-GREEN MANGO IRRADIATED AT 60 krad AND STORED AT 30°C

Days o f

storage

F lavour a Tex tu re b C o lo u rc A rom a ^

0 krad 60 krad 0 krad 60 krad 0 krad 60 krad 0 krad 60 krad

5 5 .1 4 .6 4 .7 3 .9 0 .34 1 .30 3 .9 3 .5

10 4 .5 4 .3 4 .1 3 .8 0.68 1 .90 2 .8 3 .2

15 4 .1 3 .8 3 .3 3 .3 0 .63 1 .40 2 .9 3 .2

3 F lavour: 7 = l ik e ex trem e ly ; 1 = d is lik e e x trem e ly

** Tex tu re : 7 = e x trem e ly f irm ; 1 = ex trem e ly soft

° C o lou r : 0 = sam e as the re fe ren ce ; 4 = e x trem e ly d iffe ren t from the re fe ren ce

** A rom a : 5 = e x trem e ly ty p ic a l m ango arom a; 0 = e x trem e ly o ff-a ro m a

TABLE III. CAROTENE CONTENT OF MATURED GREEN MANGO IRRADIATED AT 60 krad AND STORED AT 30°C

Days o f

storage

Carotene/100 g

0 krad 60 krad

1 913 924

4 2191 2121

6 5634 4103

8 6716 6546

10 6763 7127

13 6834 7522

In a previous study, we have showed that the weight losses of both irradiated and unirradiated mature-green mangoes during storage at 30°C are essentially the same. This seems to indicate that the levels of 0 to 300 krad had no significant effect on the rate of dehydration of the samples during storage.

Since carotene is a major contributory pigment to the formation of yellow colour and secondly, because of its nutritional importance, the carotene content of the samples was determined. John et al. [9] determined the carotenoid content of three stages of mango by using chromatographic, spectroscopic and chemical methods. They showed that unripe mangoes contained 57.47% of /З-carotene while fully ripe mangoes contained 50.64%. Their study showed that (3-carotene was the major carotenoid in both the unripe and fully ripe mangoes.

Table III shows the carotene content of both irradiated and unirradiated mangoes during storage at 30°C. During the first 4 days of storage, the irradiated and unirradiated samples contain essentially the same amount of


£ *2

PL-422/11 1 0 7

carotene. However, on the 6th day of storage, the carotene content of the irradiated sample was significantly lower than the control. This probably is due to the radiation-induced delay in ripening of irradiated mangoes. Surprisingly enough, on the 10th and 13th days of storage, the carotene content of the irradiated fruits was significantly higher than the unirradiated controls.

The above results are in agreement with the study of Maxie et al. [ 14] on the effect of ionizing radiation on the red pigment of peaches and nectarines. They showed that the red pigment of irradiated peaches and nectarines markedly increased as a function of storage time. They presume that the apparent increase in red pigment may be the result of stimulated synthesis of pigments due to radiation. However, for tomatoes treated with 4. 5-MeV cathode rays at doses of 0. 5 Mrep, the synthesis of phytofluene, 7 -carotene, and lycopene was inhibited, according to Burns and Desrosier [ 3 ]. On the otherhand, the 0-carotene of irradiated tomatoes increased as the fruit ripened.

Studies on the sensitivity of carotene in fruits to ionizing radiation are very limited. Figures 1 to 5 show the TLC chromatograms of the j3-carotene of both irradiated and unirradiated mangoes.

It is clear from the chromatograms that a dose of 60 krad had no destructive effect on ,8-carotene even up to 13 days of storage at 30°C.

F IG .3 . C om para tive th in -la yer

ch rom atogram s o f б -ca ro ten e extracts

a fter 8 days o f storage at 30eC .

Legend

1: 0-krad sam ple

2: 60 “ krad sam ple

3: standard S -caro tene

S OLVENT FRONT

00

0 00

8 80 0

t «

1 2 3


-о "22 « J2 'о

O. CQ• B.Ÿ

<D 2 & DO ТЗ Л I

J Н 05 «

PL-422/11 109

LI>%

(°/„)30NV8U0SaV

n o PABLO e t a l.

TABLE IV. TOTAL ASCORBIC ACID CONTENT OF MATURE-GREEN MANGOES IRRADIATED AT 60 krad AND STORED AT 30°C

Days o f

storage

T o ta l ascorbic acid (m g ) per 100-g

sam ple

0 krad 60 krad

1 64 78

6 68 76

11 60 74

13 76 92

Lukton and MacKinney [11] showed that carotene in solution was quite sensitive to ionizing radiation. They concluded that destruction is caused by secondary reactions and depends on the amount of free radicals formed in the solution. However, carotene present in plant tissues was more resistant to destruction by radiation. They claimed that this was probably due to the protection offered by other compounds present in the tissue, against radiation-induced free radicals. This may be the reason for the resistance of /З-carotene of mangoes when irradiated at 60 krad. The same authors also studied the effect of 7 -radiation on tomato purees, whole tomatoes, and carrot purees. Their results showed that the carotenoids were very stable to doses up to 12 Mrep.

For a confirmatory test, the /З-carotene extracts obtained from the irradiated mangoes after 10 days of storage was spectrophotometrically analysed. Interestingly enough, the results of the carotene analysis using Spectronic 20 is in agreement with the absorption spectra, as shown in Fig. 6. Thus it can be claimed that the /З-carotene of mangoes is not destroyed by y-radiation at doses which produced shelf-life extension, and an increase in /З-carotene is obtained during the storage of irradiated mangoes as compared to the unirradiated controls.

Mangoes are an excellent source of vitamin C; one mango can sufficiently satisfy the recommended daily intake of 20 mg. Table IV shows the results obtained from the ascorbic acid determination of both irradiated and unirradiated mangoes. It can be seen from Table IV that the ascorbic acid content of irradiated mangoes was higher than the unirradiated controls during the whole storage study. The ascorbic acid content of the irradiated fruits was essentially constant for the first 11 days of storage. However, on the 13th day of storage, the ascorbic acid increased. This increase in ascorbic acid, due to ionizing radiation may be attributed to any of these three factors as postulated by Maxie et al. [ 15] : (1) greater or ease of extraction; (2) synthesis of the vitamin; and (3) presence of interfering substances which react like the vitamin chemically but not physiologically. It seems that the increase in ascorbic acid in mangoes irradiated at 60 krad is probably due either to a radiation-induced compound which had stimulated the synthesis of vitamin С during storage, or to the presence of a third substance that behaves chemically like the vitamin. Maxie et al. [ 13] showed an insignificant loss of vitamin С in Bing cherries irradiated at 0, 200, and 400 krad after 10 days of storage at 5°C. Hilker

PL-422/11 111

and Young [8] showed that no appreciable changes in the ascorbic acid content of papayas took place at different stages of ripeness after being irradiated at 0, 25, 75, 100 and 150 krad.

The tolerance of mangoes (Carabao variety) to 60 krad dose is of importance to disinfestation problems, particularly seed weevil. Upadhya and Brewbaker [18] showed that adult weevils in mangoes were not able to survive a dose of 120 krad after 3 weeks of storage at 9°C, while 60 krad was sufficient for complete lethality after 5 weeks of storage. However, the fruit fly is more of a problem than seed weevil for Philippine mangoes. It is our plan to conduct studies on the irradiation of mangoes for the control of fruit fly.

In summary, this study indicates clearly the tolerance of the mango (Carabao variety) to a 60-krad dose. Vitamin С and 3-carotene tolerate an irradiation dose that successfully extends the shelf-life of mangoes without any significant alteration in flavour, texture and aroma.

REFERENCES

[ 1 ] ABDEL-KADER, A . , MORRIS, L . L . , M A X IE , E .C . , T h e e f fe c t o f gam m a irrad ia tion on the postharvest

b ehav io r o f tom ato fruits, USAEC Research and D eve lopm en t Rep. U C D -34 P80-3 (1965).

[ 2 ] A S S O C IA T IO N OF O FF IC IAL AG R IC U LTU R AL CHEM ISTS, T h e D eterm in a tion o f C arotene, 10th

Edn (1965 ).

[ 3 ] BURNS, E .E ., DESROSIER, N. W . , M aturation changes in tom ato fruits induced by io n iz in g rad ia tion ,

Fd T e ch n o l. U (1957) 313.

[ 4 ] D HARKAR, S .O . , SREENIVASAN, A . , Irrad iation o f m angoes. I. R ad ia tion -induced d e la y in ripen ing

o f Alphonso m angoes, J. Fd. S c i. 31 (1966) 863.

[ 5 ] Food C om position T a b le , Food and N utrition Research C en ter, N a tion a l S c ien ce D eve lop m en t Board,

11 (1964).

[ 6 ] FRANCESCH IN I, R . , FRANCIS, F .J ., L IV IN G S TO N , G .E . , FAGERSON, I. S., E ffe c t o f gam m a ray

irrad ia tion on caro ten o id reten tion and c o lo r o f carrots, sweet potatoes, green beans and b ro c co li, Fd

T ech n o l. 31 7 (1959) 358.

[ 7 ] G R AH AM , H . D . , LUSE, R .A . , "R ad ia tion preservation o f trop ica l foodstu ffs", Radiation Pasteurization

o f Foods, 5th Annual Contractors M ee tin g (1965) 56.

[ 8 ] HILKER, D .M . , YO U N G , R .L., T h e e f fe c t o f io n iz in g ra d ia tion on some nutritional and b io ch em ica l

properties o f papaya, H aw a ii Fm Sc. 15 1 (1966) 9.

[ 9 ] JOHN, J ., SU B LARAYAN , С . , C A M A , H.R., Carotenoids in 3 stages o f ripen ing o f m ango, J. Fd Sci.

35 (1970) 262.

[1 0 ] LOEFFER, A . D . , PO N T IN G , S .D ., T h e d eterm ination o f ascorb ic ac id , Ind. Engng C hem . A na l. Edn

14 (1942) 846.

[1 1 ] LU K TO N , A . , M acK IN N E Y , G ., E ffec t o f io n iz in g rad ia tion on caro teno id s tab ility , Fd T e ch n o l. 10̂

(1956) 630.

[1 2 ] M A X IE , E. C . , SOMMER, N .F . Rad iation techno logy in con junction w ith post-harvest procedures

as a m eans o f extend ing the s h e lf - l i fe o f fruits and vege tab les . Annual Report (Feb . 1, 1962-Jan. 30,

1963), USAEC (1963).

[1 3 ] M A X IE , E .C . , SOMMER, N . F . , BROWN, D .S ., Radiation tech n o logy in con jucn tion w ith post

harvest procedures as a m eans o f ex ten d in g the s h e lf- l i fe o f fruits and vege tab les , USAEC Research

and D eve lop m en t Rep. N o . U C D -34 P80-2 (1964).

[1 4 ] M A X IE , E .C . , JOHNSON, C .F . , BOYD, D . , RAE, H. С . , SOMMER, N .F ., E ffe c t o f gam m a-rad ia tion

on ripen ing and qu a lity o f nectarines and peaches, Proc. A m . Soc. hort. S c i. (1966).

[1 5 ] M A X IE , E. C . , RAE, R. L . , BOYD, C ., E ffe c t o f gam m a -irrad ia tion on the ascorb ic acid , th iam ine

and n iacin con ten t o f Gros M ic h e l bananas, USAEC Rep. U C D -P80-437 (1966).

[1 6 ] SO LANAS , J ., DARDER, A . "F ood irrad ia tion program m e in V en e zu e la ” , P reservation o f Fruit and

V ege tab le s by Rad ia tion (P roc . Panel, V ienna , 1966) IAEA , V ienna (1968) 13.

[1 7 ] STAH L, E ., T h in -L a ye r C hrom atography, A ca d em ic Press, N ew York (1965) 215.

[1 8 ] U P A D H Y A , M . D . , BREWBAKER, J.L., Irrad iation o f m angoes for con tro l o f the m ango seed w e e v il,

H aw a ii Fm Sc. 15 1 (1966) 6.

PL-422/12

RECENT RESEARCH ON THE INFLUENCE OF IRRADIATION OF CERTAIN TROPICAL FRUITS IN THAILAND

P. LOAHARANU Biological Science Division,O ffice o f Atomic Energy for Peace,Bangkok, Thailand

Abstract

RECENT RESEARCH O N TH E INFLUENCE OF IR R A D IA T IO N OF C E R TA IN TR O PIC A L FRU ITS IN T H A IL A N D .

P re lim in a ry studies on the e f fe c t o f gam m a irrad iation on trop ica l fruits such as m angoes, papayas,

rambutans, and longans have been carried out. Irrad iation o f trop ica l fruits at optim um doses caused an

extension in storage l i f e . No s ign ifican t d iffe ren ces w ere detec ted in terms o f nu tritive values and organo

lep t ic properties betw een fruits irrad iated a t optim um doses and unirradiated fru its. In add ition , the com bined

e ffe c ts o f irrad iation and low -tem pera tu re storage fo r the d isin festation o f O rien ta l fru it f l y , Dacus dorsalis,

H en de l in m angoes are described .

1. INTRODUCTION

Food preservation by irradiation in Thailand was initiated at the Office of Atomic Energy for Peace (OAEP) in 1964. Earlier work was accomplished by the use of the gamma radiation from the Thai Research Reactor. Favourable results were obtained in the demonstration of the extension of storage life of certain fresh foods. However, pure gamma rays could not be obtained from the reactor.

In March 1966 a small gamma irradiator was supplied to the OAEP by the International Atomic Energy Agency. This irradiator contained 8000 Ci 60Co, with an irradiating capacity of approximately 1. 5 litres. Consequently, it was possible to initiate programs in food irradiation of certain tropical fruits, seafoods, and grains.

At the OAEP, mangoes, papayas, bananas, rambutans, and longans were selected for irradiation, since they might have good export potentials. These fruits, with the exception of the longan which grows in the northern part of Thailand, are generally grown within 300 kilometres from Bangkok. However, the methods of handling and transporting these fruits to markets in Bangkok are not efficient. In addition, their transportation under tropical heat contributes to high losses owing to the rapid onset of ripening and spoilage. The refrigerated shipment of fresh commodities has not yet been practised in Thailand.

For export purposes, steps are taken to minimize the rough handling of fruits. Fruits of good quality are selected and repacked for shipment overseas. They are then taken for inspection at the Department of Agriculture where phytosanitary certificates are issued. Most of the fruit is transported by non-refrigerated freighters. Hence, high losses due to ripening and rottening of fruits usually occur.

A means of extending the storage life of fresh fruit would contribute significantly to the economy of the country.

113

2. MANGO (Magnifera indica, Linn)

2.1. Effect of irradiation on storage life

114 LOAHARANU

Mangoes of the Okrong variety were investigated. This variety of mango is by far the most popular in Thailand. They are usually picked from trees at the mature-green stage, and would normally ripen within 2 to 3 days at room temperature. This variety of mango is mainly consumed when ripe.

The application of gamma rays for mango preservation was investigated in 1966 by Teng-Umnuay [1]. Preliminary studies on the Okrong mango at different stages of maturity when subjected to irradiation at doses ranging from 10 to 80 krad were carried out. Mangoes were irradiated in air at room temperature and were stored at 21°C after irradiation. It was found that the Okrong mango harvested when 104 days old yielded the best results in storage life extension. A dose of 40 krad was found to be the optimum which extended the storage life of the mangoes for about 16 days.The 100% ripening index for the control mango was 20 days and was 36 days for 40-krad samples.

Extensive investigations on the effect of irradiation on the Okrong mango were later carried out by Kovacs et al. [2]. Only 104-day-old mangoes were used in the study.

2.1.1. Material and methods

Green Okrong mangoes, about 104 days old at harvest time, were sorted into groups of 100 mangoes each. They were then subjected to irradiation in air at room temperature with 20, 30, 40, 50 and 60 krad one day after harvesting. The dose rate was approximately 8800 rad/min.

After irradiation, all samples were stored at 18°C and at 80 to 90% relative humidity. Weight loss, ripening, and rottening changes were recorded daily. Vitamin С content and reducing-sugar determinations, and organoleptic testing of samples were carried out at certain intervals during storage. The vitamin С content was determined by Tillmann1 s titration method, and reducing sugars were determined by Steinhoff1 s iodometric method according to Ref.[3], A nine-point hedonic scale was used for organoleptic testing.

2.1.2. Results and discussion

Results of the storage testing of Okrong mangoes irradiated at different doses are shown in Table I.

It was evident that all of the control samples showed 100% ripening within 24 days. Those irradiated at 20 krad were ripe within 29 days. Samples irradiated at 40 krad were ripe (100%) within 32 days. Samples irradiated at 50 krad showed results similar to those at 40 krad.Samples irradiated at 60 krad showed a favourable delay in ripening. They were 100% ripe after 36 days of storage, but a relatively high rottening effect was observed.

It was also observed that the texture of irradiated mangoes showed signs of softening during storage, although the fruits were still green. These results agreed with those of Dharkar and Sreenivasan [4] who indicated that irradiation of Alphonso mangoes tended to inhibit chlorophyll disappearance and carotenoid formation of the skin of the Alphonso mango.

PL-422/12 1 1 5

The changes in vitamin С content in irradiated and unirradiated mangoes during storage are shown in Table II.

The data summarized in Table II showed that no significant losses in vitamin С content in irradiated mangoes were found.

Percentage weight losses of irradiated and unirradiated mangoes showed no difference during storage, as shown in Table III.

The preliminary test on reducing sugar contents during storage showed that no significant difference was found between irradiated and unirradiated samples.

TABLE I. RIPENING INDEX (%) OF OKRONG MANGOES STORED AT 18°C

Storage tim e

(days)

Dose (krad)

0 20 40 50 60

8 22 10 5 10 0

12 63 23 30 22 15

16 74 50 52 54 35

20 94 70 70 68 55

24 100 88 90 92 75

28 - 95 95 95 90

32 - 100 100 100 90

36 - - - - 100

TABLE II. VITAMIN С CONTENT (mg %) OF OKRONG MANGOES STORED AT 18°C

Storage tim e

(days)

Dose (krad)

0 20 30 40 50

7 15 .3 15 .5 16 .2 14 .6 16 .6

14 42 .5 33 .0 3 2 .2 37 .0 3 3 .0

22 34 .3 28 .8 24.1 25 .3 2 7 .9

TABLE III. WEIGHT LOSSES (%) OF MANGOES DURING STORAGE AT 18°C

Storage tim e

(days)

Dose (krad)

0 20 30 40 50

10 8 .3 7 .4

COCO 8 .9 7 .3

11 7 .2 8 .7 8 .3 8.1 8.1

16 10 .0 10 .2 9 .0 11 .3 11 .5

18 12 .5 14 .4 14 .6 14 .8 12 .9

116 LOAHARANU

TABLE IV. ORGANOLEPTIC SCORES OF OKRONG MANGOES STORED AT 18°C

Storage tim eDose (krad)

(days)0 20 30 40 50

20 6 .6 5 .3 4 .9 2 4 .3 0 5 .23

22 7 .35 6 .04 4 .9 5 4 .3 5 5 .40

Taste tests were carried out after the samples had begun to ripen. The results are shown in Table IV.

High scores in the control samples were attributed to the full ripeness of the samples, which would be more attractive to the taste of the panel members. On the other hand, samples irradiated at 40 krad at the time of taste testing were still green. Hence, lower scores were given by the panel.

2.1.3. Conclusions

From the results of our preliminary investigations of irradiated Okrong mangoes, it appeared that a dose of 40 krad would be the optimum for this variety with approximately 8 days storage life extension over the unirradiated samples.

2.2. Combined effects of irradiation and low temperature for the disinfestation of oriental fruit fly, Dacus dorsalis, Hendel

It is known that the fruit fly can deposit eggs in the green as well as in ripened mangoes. Young larvae are occasionally found in green mangoes, whereas mature larvae are commonly found in ripened ones. A preliminary study on the combined effects of gamma irradiation and low-temperature storage for inactivating the Oriental fruit fly, Dacus dorsalis, Hendel in mangoes of the Namdocmai variety was carried out by Loaharanu [5].

2.2.1. Material and methods

For the inactivation of the Oriental fruit fly, 30 larvae were implanted into each mango of the Namdocmai variety. The mangoes were then irradiated in air at room temperature. Approximately 2- to 4-day-old larvae, implanted in mature-green-stage mangoes were exposed to 6, 12, 25, 50 and 80 krad. The 6-day-old larvae implanted in quarter-ripened mangoes were exposed to 25, 50, 100, and 150 krad. After irradiation, the mangoes containing larvae were stored at 20°C and at 80 to 90% relative humidity.

2.2.2. Results

Results of the inactivation of the Oriental fruit fly showed that a dose of 50 krad prevented the 2-day-old larvae from pupation. The control larvae showed 63.3% pupation in 21 days as shown in Table V.

PL-422/12 11 7

TABLE V. IRRADIATION OF APPROXIMATELY 2-DAY-OLD LARVAE OF D. dorsalis, Hendel, IN NAMDOCMAI MANGOES STORED AT 20°C

Dose

(krad)

Percen tage pupation a fte r irrad iation

14 days 21 days

0 (con tro l) 46 .6 63.3

6 36 .6 56 .6

12 29 .9 50 .0

25 26 .6 3 6 .6

50 0 0

80 0 0

TABLE VI. IRRADIATION OF APPROXIMATELY 6-DAY-OLD LARVAE OF D. dorsalis, Hendel, IN NAMDOCMAI MANGOES STORED AT 20°C

Dose

(krad )

Percen tage pupation a fte r irrad iation

8 days 14 days

0 (con tro l) 83 .3 89 .9

25 39 .9 53 .3 '

50 13 .3 39 .9

100 0 3 .3

150 0 0

The percentage of pupation from 6-day-old larvae in the control, irradiated at 100 krad, and at 150 krad was 89. 9, 3. 3, and 0 in 14 days respectively, as shown in Table VI. All irradiated larvae failed to develop into adults.

3. PAPAYA (Carica papaya, L. )

Papayas of the Hawaiian variety were investigated owing to the fact that they were small enough to fit into the container of our gamma-cell irradiator. The local varieties are larger in size and are not able to be irradiated as whole fruit.

3.1. Material and methods

Papayas of the Hawaiian variety were selected from orchards in Pak Chong, 150 kilometres from Bangkok, in the mature-green stage. They were sorted at the laboratory into groups of 15 fruits each of about the

1 18 LOAHARANU

same maturity. Before irradiation, the fruits were washed in 0.01% KMnCU solution for 15 to 20 minutes. Irradiation took place in air at room temperature. The samples were irradiated at 30, 50 and 70 krad one day after harvesting. Three storage temperatures at 15, 18 and 22°C were used.The relative humidity in storage rooms was 80 to 90%.

The respiratory rates of samples were studied by measuring the rate of carbon dioxide evolution [6]. The vitamin С content of samples was determined by Tillmann1 s titration method [3]. The weight loss and degree of ripening were recorded daily. Organoleptic tests of samples were carried out at certain intervals.

3.2. Results and discussion

Only a few experiments were carried out on papayas irradiated at different doses. Results from our investigation showed wide variation in delayed ripening of irradiated papayas. The results may be summarized as follows:

(1) The respiratory rate measurements showed that irradiation caused an increase in respiration rate in each treated sample. Delay in ripening was not significant according to respiration rates in both control and irradiated samples.

(2) It was found that irradiation stimulated ripening of papayas in the "climacteric rise" period. In another lot it was found that irradiation delayed ripening of unripe papayas irradiated at the preclimacteric period.

(3) The most favourable data were observed at 18°C storage and 30 to 50 krad irradiation. Extension of storage life of approximately 10 days was found, as shown in Table VII.

Samples irradiated at 70 krad showed a favourable delay in ripening, but a high loss due to infection was observed on the fruits.

TABLE VII. RIPENING INDICTS (%) OF PAPAYAS STORED AT 18°C

Storage tim e

(days)

Dose (krad)

0 30 50 70

5 0 6 6 2

10 9 26 23 8

14 26 33 24 15

. 20 64 51 56 28

25 79 68 78 49

27 100 68 84 50

32 91 95 76

38 100 100 95

42 -■ - - 100

PL-422/12 119

4. RAMBUTAN (Nephelium lappaceum, L. )

The rambutan is a tropical fruit which grows mainly in Southeast Asian countries. The fruit has a soft hairy skin; the flesh is firm, juicy and sweet. The fruits are picked when fully mature and ready to be consumed. The rambutan usually has a storage life of a few days at room temperature. Rottening and dessication are the main causes of spoilage.

The season for rambutans in Thailand is from May to August. There are several varieties grown in Thailand, but the best known are the Pink, Bangyeekhan, and Rong Rean varieties.


Rambutans of the Pink and Bangyeekhan varieties were used in our investigations on the ground that they are more popular and readily available. They were bought from orchards in the Chantaburi province 300 kilometres from Bangkok and transported by car to the laboratory. On the following day they were sorted for uniform maturity and irradiated in air at room temperature.

From the first few lots, samples were subjected to irradiation at 10,20, 30, 40, 50, and 60 krad. After preliminary results were obtained, it was decided to use higher doses of 40, 60, 80, 100, and 120 krad. After irradiation, all samples were stored at 17 to 18°C.


Results of the preliminary investigations on the influence of irradiation of the Pink and Bangyeekhan varieties have been summarized in Table VIII.

TABLE Vni. ROTTENING INDICES OF PINK AND BANGYEEKHAN RAMBUTANS STORED AT 18°C

Storage t im e

(days)

Dose

(krad)

Rottening ind ices (% )

Pink Bangyeekhan

8 0 1 2

40 0 2

60 0 2

12 0 3 6

40 1 8

60 2 10

14 0 37 68

40 11 52

60 3 36

16 0 100 100

40 65 100

60 31 100

19 0 100 -

40 100 -

60 100 -

120 LOAHARANU

It is clearly indicated in Table VIII that better results were obtained from the storage test on the Pink variety. It was also indicated that higher doses might be able to extend the storage life of rambutans. Results on the influence of irradiation at doses higher than 60 krad were obtained later as is shown in Table IX.

The results showed that the control samples rot within 12 days at 17°C storage. Samples irradiated at 80 to 100 krad showed a storage life extension of 4 days. Samples irradiated at 120 krad exhibited skin darkening during storage. It was concluded that doses between 80 to 100 krad would be optimum for the irradiation of Pink rambutans.

No significant difference in weight losses during storage was found between irradiated and unirradiated Pink rambutans, as shown in Table X.

Results on determinations of vitamin C, total acidity, and reducing sugars of Pink rambutans are shown in Table XI.

No significant difference was found between the vitamin С content of irradiated and unirradiated samples. The total acidity content was slightly less with increasing storage time in all samples. No noticeable change was found between the reducing sugar content of irradiated and control samples.

Results on organoleptic tests of Pink rambutans showed no difference between irradiated and control samples after 7 days storage at 17°C, as shown in Table XII.

TABLE IX. ROTTENING INDICES (%) OF PINK RAMBUTANS STORED AT 17°C

Storage tim e

(days)

Dose (k rad )

0 40 60 80 10 120

6 8 .8 5 .6 5 .8 3 .7 2 .5 4 .6

8 14 .3 6 .9 11 .2 12 .0 4 .2 7 .2

10 52 .0 3 2 .9 3 3 .5 4 2 .5 16 .7 28.1

12 100 58 .9 63 .2 60 .0 4 0 .8 4 6 .6

14 100 100 96 94 93

16 100 100 100

TABLE X. WEIGHT LOSSES (%) OF PINK RAMBUTANS STORED AT 17°C

Storage tim e

(days)

Dose (k rad )

0 40 60 80 100 120

6 2 .8 2 .6 3 .7 3 .3 3 .2 2 .2

8 3 .7 - 6 . 9 5 .4 6 .0 6 .5 5 .3

10 8 .9 9 .9 9 .9 10 .2 9 .6 10 .0

12 1 1 .4 11 .8 12 .6 13 .7 14 .8 14 .6

PL-422/12 121

TABLE XI. VITAMIN C, TOTAL ACIDITY, AND REDUCING SUGAR CONTENTS OF PINK RAMBUTANTS STORED AT 17°C

Storage tim e Dose V itam in С T o ta l a c id ity Reducing sugar

(days) (krad) (m g % (m l/100 g) (m g dextrose/g)

0 51 .5 0.41 33 .72

40 50 .8 0 .43 33 .36

60 4 8 .5 0 .32 35 .15

0 80 54 .4 0 .37 33 .06

100 51 .8 0 .32 31 .55

120 52.8 0.37 30 .72

0 50.9 0 .36 33 .02

40 53 .4 0.37 34 .44

60 47 .0 0 .34 36 .89

7 80 47 .2 0 .34 35 .34

100 4 8 .4 0 .30 33 .44

120 52 .4 0.31 30.38

0 - - -

40 4 9 .8 0 .34 34 .68

60 4 7 .4 0.31 35 .36

14 80 4 7 .5 0 .29 33 .40

100 4 8 .4 0 .27 30 .40

120 52 .8 0 .40 30 .16

TABLE ХП. ORGANOLEPTIC SCORES OF PINK RAMBUTANS STORED FOR 7 DAYS AT 17°C

Dose (krad) 0 40 60 80 100 120

Mean score 7.5 5.9 5.2 5.9 6.8 6.1

Source o f varia tion d f SS MS F

Sam ple 5 3 5 .2 5 .8 1.13

Panelist 9 64 .2 4 .7 0 .93

Error 45 228.1 5.05

T o ta l 59 327 .5

122 LOAHARANU

5. LONGAN (Euphoria longana, Lank)

The longan is a tasty tropical fruit. It is very similar to the lychee and the rambutan. At present there are about seven or eight varieties. The northern part of Thailand is the largest producer of longans.

The season of the longan is from July to August. It takes about 5 months for flowers to develop to mature fruits. A longan tree about 10 years old can bear about 1000 kilograms of fruit each year. The life of a longan tree is very long and it can produce fruit even after 100 years.


Longans grown in Chiengmai were selected as it is the area that produces the largest quantity and best quality. The Beaw Keaw variety was obtained since they are more plentiful than other varieties. After harvesting, they were packed in bamboo baskets and transported to Bangkok by train on the following day. From harvesting to irradiation the time lapse was approximately 24 to 36 hours.

At the laboratory the longan clusters were separated, leaving approximately 2 cm of stalk to minimize infection by microorganisms. The fruits were irradiated in air at room temperature in a gamma cell at doses of 50, 100, 150, 200, and 250 krad. After irradiation the fruits were packed in partially perforated plastic bags and stored at 17°C and 80 to 90% relative humidity. About 300 fruits were used for each treatment. They were observed until decay over a period of 4 to 6 weeks. Weight losses, appearance, and degree of rottening were recorded daily. At certain intervals, 30 fruits were taken at random from each treatment for analyses of vitamin C, reducing sugar, and organoleptic testing.


Results of degree of rottening and weight losses of each treatment of longans are shown in Table XIII and Table XIV, respectively.

The results showed that the rottening index of the control samples was 100% after 13 days of storage time. All of the irradiated samples at 200 and 250 krad were in relatively good condition after 10 days of storage time.

TABLE XIII. ROTTENING INDICES (%) OF LONGANS STORED AT 17°C

Storage tim e

(days)

Dose (k rad )

0 100 150 200 250

3 0 0 0 0 0

6 31 9 3 2 3

8 57 15 13 8 9

10 73 37 20 26 23

13 100 80 65 59 63

15 100 100 69 65

17 100 100

PL-422/12 123

TABLE XIV. WEIGHT LOSSES (%) OF LONGANS STORED AT 17°C

Storage tim e

(days)

Dose (k rad )

0 100 150 200 250

3 1 .2 2 .4 3 .1 3 .1 2 .4

6 2 .8 3 .6 4 .3 4 .3 4 .0

8 5 .0 4 .6 5 .2 5 .2 4 .0

10 7 .7 5 .6 6 .3 6 .3 4. 0

13 7 .7 5 .6 6 .3 6 .3 4 .0

15 7 .7 5 .6 6 .3 6 .3 4 .0

17 7 .7 5 .6 6 .3 6 .3 4 .0

TABLE XV. VITAMIN С CONTENT (in mg %) OF BEAW KEAW LONGANS STORED AT 17°C

Storage tim e

(days)

Dose (k rad )

0 100 150 200 250

0 92 .4 9 1 .9 88 .0 95 .9 90 .2

7 95. 7 91.7 89 .0 88.9 89 .5

14 a 88 .5 86.7 89 .4 86 .5

21 a 7 9 .3 88 .4 68 .9 65. 0

28 a 64 .0 68 .8 60 .8 56 .0

a Sam ple was too spo iled to analyse.

Samples irradiated at 200 to 250 krad showed 4 to 5 days of storage life extension. Weight losses of unirradiated longans appeared to be slightly higher than irradiated ones. There seemed to be a significant tendency toward a decrease in weight loss with increased doses.

Results on weight loss and rottening index were comparable with those investigated by Kovacs et al. [2] who studied the effects of irradiation on the Doh Yod Khao variety of longans. They reported that Doh Yod Khao longans stored at 18°C showed a 100% rottening index after 15 days of storage time. However, in samples irradiated at 150 and 200 krad, the rottening indices were only 60 to 80% after 30 days of storage time. They also reported that the weight loss of irradiated samples was slightly, less compared with the control longan after 20 days of storage time.

Results on vitamin С and reducing sugar determinations in Beaw Keaw longans are shown in Table XV and Table XVI, respectively.

Results from vitamin С determinations in both irradiated and unirradiated longans showed that there was no initial effect of irradiation. However, with increasing storage time, there appeared to be a slight reduction of vitamin С content in each treatment. Results from reducing sugar determinations indicated the same trend, i.e. slight reduction of reducing sugar content with increasing time of storage.

124 LOAH ARANU

TABLE XVI. REDUCING SUGAR CHANGES (g dextrose/100 g) OF LONGANS DURING STORAGE AT 17°C

Storage tim e

(days)

Dose (k rad )

0 100 ' 150 200 250

0 5 .99 6 .50 6 .39 6 .84 6.34

7 5 .65 5.77 5 .64 5 .43 6.42

14 a 6.71 5 .97 6 .15 6.66

21 a 5 .79 5 .96 6.09 5.92

28 a 3. 09 2 .77 4 .3 2 3 .57

a Sam ple was too spoiled to analyse.

TABLE XVII. ORGANOLEPTIC SCORES OF BEAW KEAW LONGANS STORED FOR 7 DAYS AT 17°C

No

rep lica te

Colou r Taste

Dose (k rad ) Dose (krad)

0 100 150 200 250 0 100 150 200 250

1 5 .5 6 .8 7 .2 7 .5 7 .0 6 .5 6 .8 7 .5 7 .5 6 .0

2 7 .3 7 .4 7 .1 7 .7 6 .7 7 .4 7 .1 7 .9 8 .0 6 .2

3 7 .5 7 .4 7 .7 7 .4 6 .9 6 .3 5 .6 7 .8 5 .2 4 .4

Results from organoleptic tests of Beaw Keaw longans have been summarized in Table XVII.

Results from the organoleptic tests indicated that there was no significant difference in colour between irradiated and unirradiated samples.In addition, no difference in taste was found between longans irradiated up to 200 krad and the unirradiated sample. However, the panel could detect some differences in taste between longans irradiated at 250 krad and other treatments. The taste scores of longans irradiated at 250 krad were significantly lower than those of other treatments. It appears that the maximum acceptable dose for Beaw Keaw longans would be 200 krad.

REFERENCES

[ 1 ] T E N G -U M N U A Y , C . , "T h e rad iation preservation o f lim es and m an goes ", Papers on C erta in Aspects

o f Food P reserva tion , T h a i A E C -9 , O ff ic e o f A tom ic Energy for P ea ce , Bangkok (1966 ).

[ 2 ] K O V A C S e t a l . , Fruit irrad ia tion , T h a i AE C -33 , O ff ic e o f A tom ic Energy for P ea ce , Bangkok (1970 ).

[ 3 ] JACOBS, M .B . , T h e C h em ica l Analysis o f Foods and Food Products, D . Van Nostrand C o . , In c . ,

P rin ceton , N ew Jersey (1959 ).

[4 ] DH ARKAR , S .D . , SREENIVASAN, A . , "Irrad ia tion o f trop ica l fruits and v e g e ta b le s " , Food Irrad iation

(P ro c . S ym p ., Karlsruhe, 1966), IA E A , V ien n a (1966) 635.

[ 5 ] LO A H A R A N U , S . , A p re lim in ary study on the com b ined e f fe c t o f gam m a rad iation and low tem perature

fo r the in a c tiva tion o f the O rien ta l fru it f ly , Dacus dorsa lis , H endel in m ango, T h a i A E C -37 , O ff ic e

o f A to m ic Energy for P ea c e , Bangkok (1 9 7 0 ).

[ 6 ] VOGEL, J .A . , A T ex tb ook o f Q uantita tive Inorgan ic Analysis In c lu d ing E lem entary Instrum ental Analysis,

Longm ans, G reen , London (1964 ).

PL-422/13

EXTENSION OF STORAGE LIFE OF BANANAS BY GAMMA IRRADIATION

Hung-yen KAOUnion Industrial Research Institute,Ministry of Economic Affairs,Republic o f China

Abstract

EXTENSION OF STORAGE LIFE OF B A N A N A S BY G A M M A IR R A D IA T IO N .

G am m a irrad ia tion o f green bananas has been in vestiga ted through the use o f 6t o in an a ttem pt to

d e la y ripen ing and increase the storage l i f e o f this fru it. V en tila t io n was necessary in the rad iation cham ber

and the rad ia tion tem perature was kept at 12eC in order to decrease rad iation dam age when the bananas w ere

exposed to gam m a rays in a ir . Experim enta l results showed that the app lied dose o f 20 to 30 krad was optim um

and e f fe c t iv e in d e la y in g so lu b le -so lid form ation , starch d isappearance and respiratory a c t iv ity . Results

showed that the irrad iated bananas stored a t 12 to 20eC and a t 25 to 30eC resulted in a d e la y in ripen ing o f

about 7 and 5 days, re sp e c tiv e ly . Banana sam ples w ere supplied throughout d iffe ren t seasons from the cen tra l

and southern parts o f T a iw a n . Th e ch e m ic a l analysis o f green bananas a fter p ick in g was carried out for research

re fe ren ce .

1. INTRODUCTION

-Tropical fruits and vegetables are produced abundantly in Taiwan, Republic of China. In recent years, owing to growing demands on the international markets, the production of bananas has increased to enormous proportions. Unfortunately, the export of bananas is limited by their relatively short storage life. Spoilage of bananas has become a serious problem during transportation. In Taiwan, bananas are produced all the year round in regions located mostly in the central and southern parts of the island.

The majority of bananas cultivated in Taiwan belong to the variety of Musa sapientum, Linn. Because of differences in climate, soil and cultivation practice, the composition of the fruit varies somewhat even in the same variety [2]. For trade purposes, banana growers in Taiwan classify this variety into eight "sub-varieties" and name them according to their quality characteristics. For research information, chemical analysis of the green bananas from different growing regions was carried out in this laboratory.

The Agricultural Chemistry Research Laboratory of the Union Industrial Research Institute has conducted research on the effect of gamma irradiation upon the extension of storage life of bananas. This research project was sponsored by the Joint Commission on Rural Reconstruction of the Republic of China.

2. MATERIALS AND METHODS

Bananas (Musa sapientum, Linn) were received on the day after picking to a program carried out by the Taiwan Provincial Federation of Fruit Marketing Co-operatives. Samples were supplied in November and December

125

126 KAO

from three growing regions, namely the Central Highland (CHL), Central Plain (CP), and Southern Plain (SP) for irradiation studies. The person in charge of picking was a well-trained and experienced worker capable of recognizing the degrees of maturity by touch and inspection. The picked bananas were immediately packed and sent by train to this laboratory within24 hours. The packaging was very carefully done in order to reduce physical injury to the bananas to a minimum.

Bananas were irradiated with 60Co y-rays at the rate of 8X104 R/h in the 10- to 80-krad range (10, 20, 30, 40, 50, 60, 70, 80 krad). The irradiation temperature was either 30°C or 12°C in an air-conditioned chamber.

After irradiation, the respiration rates of the different samples of bananas were measured. Post-irradiation storage tests were conducted in an air-conditioned room at 12 to 20°C and in another storage room at25 to 30°C. After the samples had been stored for different times, chemical analyses were carried out on the decrease of starch and the increase of soluble solids.

Green bananas received all the year round from the three growing regions were also subjected to analysis for research reference.

3. RESULTS AND DISCUSSION

3.1. Radiation damage

Skin damage was observed in all experiments for all the samples supplied from different growing regions. Bananas irradiated by gamma rays above 50 krad usually incurred skin darkening and sometimes splitting during storage. The skin-splitting phenomenon may be associated with degradative changes in the middle lamella of plant cells [3]. Bananas which were irradiated at 20 or 30 krad at 12°C in air incurred no skin damage during storage.

3.2. Respiration

Respiration curves were made for irradiated bananas at doses of 20,30 and 50 krad, as shown in Figs 1, 2, and 3. Respiration rates were measured at 21 to 22°C for 5 to 7 days, and at 15 to 16°C for 10 or more days, as shown respectively in Figs 1, 2 and 3.

The experimental results showed that C02 evolution of the samples irradiated at 20 or 30 krad was much less than that of unirradiated controls. Samples treated with 50 krad did not show much change in respiratory behaviour.

3.3. Delay of ripening

It has been observed that bananas irradiated in a stuffy chamber at a temperature of 25 to 30°C did not show any positive increase in storage life regardless of the dose rates being applied, a result which is in agreement with that obtained by W. E. Ferguson and co-workers in 1966 [1].The present author believes that the irradiation temperature is closely related to the shelf-life extension of individual fruit. Bananas irradiated

•mg

CO

2 kg

PL-422/13 127

T I M E ( d a y s )

F IG . l . E ffec t o f gam m a irrad iation on the respiratory rate o f Ta iw an CH L bananas.

F IG . 2. E ffec t o f gam m a irrad ia tion on the respiratory rate o f T a iw an C P bananas.

1 2 8 KAO

F IG .3 . E ffec t o f gam m a irrad iation on the respiratory rate o f T a iw an SP bananas.

at various doses were stored at 25 to 30°C for 2 weeks and at 12 to 20°C for 1 month respectively. Analytical data indicated that bananas treated at 20 to 30 krad showed a retardation in starch degradation, as shown in Tables I to VI, and in the formation of soluble solids as shown in Tables VII to XII. The mean values of data in the tables1 were significantly different at the 5% level of probability as calculated by Duncan1 s multiple-range test. It could be concluded at this stage of the experiments that: (1) the applied dose of 20 to 30 krad was optimum for the purpose of shelf-life extension;(2) the irradiated bananas in the optimum dose range and stored at 12 to 20°C or 25 to 30°C resulted in an added delay in ripening of about 7 to 5 days, respectively.

3.4. Chemical analysis of bananas after picking

Bananas used in all the experiments belonged to the variety Musa sapientum, Linn, which is cultivated mostly in central and southern regions through the year. For the study of quality characteristics of bananas in relation to the climate and to cultivation practices, samples were collected and analysed the whole year round. The results are shown in Table XIII and Figs 4 and 5. The analytical data indicate that the starch content is relatively lower and the moisture content higher in the samples picked from July to September than those picked in other months of the year.

1 An asterisk in each tab le ind icates the s ta tis tica l s ign ifican ce at the 0 .05 le v e l .

PL-422/13 1 2 9

T A B L E I . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N S T A R C H

C O N T E N T ( % ) O F T A I W A N C H L B A N A N A S S T O R E D A T 2 5 T O 3 0 ° C

F O R 2 W E E K S

R ep lica te 0 50 krad 20 krad 30 krad

1 2 .2 7 .5 1 2 .0 13.52 a.8 6 .2 9 .2 8.83 2 .0 5 .3 13.5 12 .2

T o ta l 6 .0 19.0 34 .7 34 .9

M ean 2 .0 6 .3 11 .6 11 .6

S ta tis tica l

s ign ifican ce

at 0 .0 5 le v e l

Analysis o f v a rian ce

Source D .F . M .S . F . ra tio

T rea tm en t 3 64.647 2 0 .2 4 6 *

Error 8T o ta l 11 3.193

TABLE II. INFLUENCE OF GAMMA IRRADIATION ON STARCH CONTENT (%) OF TAIWAN CP BANANAS STORED AT 25 TO 30°C FOR 2 WEEKS


1 1 .4 4 .8 11 .2 1 2 .5

2 1 .4 6 .6 8 .0 1 1 .4

3 1 .5 4 .6 13 .5 9 .5

T o ta l 4 .3 16 .0 32 .7 3 3 .4

M ean 1 .4 5 .3 10 .9 11.1

S tatistica l

s ign ifican ce

at 0 .05 le v e l

Analysis o f variance


T rea tm en t 3 65.900 2 3 .6 3 7 *

Error 8 2 .788

T o ta l 11

1 3 0 KAO

T A B L E I I I . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N S T A R C H

C O N T E N T ( % ) O F T A I W A N S P B A N A N A S S T O R E D A T 2 5 T O 3 0 ° C

F O R 2 W E E K S


1 0 .9 4 .8 9 .5 10 .42 1 .6 5 .6 8 .4 9 .23 0 .8 5 .3 9 .4 9 .9

T o ta l 3 .3 15 .7 27 .3 2 9 .5M ean 1.1 5 .2 9 .1 9 .8

S ta tistica l

s ign ifican ce

a t 0 .0 5 le v e l


Source D . F. M .S . F .r a t io

T rea tm en t i 48.503 1 7 8 .9 7 8 *Error 13 0.271T o ta l 11

TABLE IV. INFLUENCE OF GAMMA IRRADIATION ON STARCH CONTENT (%) OF TAIWAN CHL BANANAS STORED AT 12 TO 20°C FOR 1 MONTH


1 0 .7 5 .0 10 .4 10 .5

2 0 .8 6 .8

(oCO 10.0

3 0 .6 7 .2 1 0 .9 9 .4

T o ta l 2 .1 19 .0 29 .9 29 .0

M ean 0.7 6 .3 10 .0 10 .0

S tatistica l

s ign ifican ce

at 0 .0 5 le v e l


Source D .F . M .S . F . ratio

T rea tm en t 3 57.470 7 2 .9 3 1 *

Error 8 0 .788

T o ta l 11

PL-422/13 1 3 1

T A B L E V . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N S T A R C H

C O N T E N T ( % ) O F T A I W A N C P B A N A N A S S T O R E D A T 1 2 T O 2 0 ° C

F O R 1 M O N T H


1 2 .0 8 .0 11 .4 12 .02 2 .3 4 .6 9 .2 9 .63 0 .9 8 .9 1 3 .4 13 .7

T o ta l 5 .2 21 .5 34 .0 35 .3M ean 1 .7 7 .2 11 .3 11 .8

S ta tistica l

s ign ifican ce

at 0. 05 le v e l



T rea tm en t 3 65.263 18.199*Error 8 3 .586

T o ta l 11

TABLE VI. INFLUENCE OF GAMMA IRRADIATION ON STARCH CONTENT (%) OF TAIWAN SP BANANAS STORED AT 12 TO 20°C FOR 1 MONTH


1 0 .8 5 .2 10 .8 11 .2

2 0 .6 7 .1 8 .8 8 .4

3 0 .6 4 .5 9 .0 9 .4

T o ta l 2 .0 16 .8 2 8 .6 2 9 .0

M ean 0.7 5 .6 9 .6 9 .7

S tatistica l

s ign ifican ce

at 0 .0 5 le v e l



T rea tm en t 3 53.997 4 2 .7 5 3 *

Error 8 1 .263

T o ta l 11

1 3 2 KAO

T A B L E V I I . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N ° B R I X

O F T A I W A N C H L B A N A N A S S T O R E D A T 2 5 T O 3 0 ° C F O R 2 W E E K S

R ep lica te 20 krad 30 krad 50 krad 0 krad

1 12 .8 17 .0 17 .4 2 3 .42 1 7 .0 11 .2 1 8 .2 2 2 .43 1 1 .8 13 .9 18.7 2 0 .4

T o ta l 4 1 .6 4 2 .1 54 .3 66 .2M ean 13 .9 14 .0 18.1 22.1

S ta tis tica l

s ign ifican ce

at 0 .0 5 le v e l



T rea tm en t 3 45 .500 9 .6 8 1 *Error 8

T o ta l 11 4 .700

TABLE VIII. INFLUENCE OF GAMMA IRRADIATION ON °BRIX OF TAIWAN CP BANANAS STORED AT 25 TO 30°C FOR 2 WEEKS


1 11 .8 10 .7 20 .2 2 2 .6

2 15 .8 16 .5 20 .6 2 3 .6

3 13 .0 14 .0 18.7 2 3 .4

T o ta l 4 0 .6 4 1 .2 59 .5 69 .2

M ean 13 .5 13.7 19 .8 23 .1

S ta tis tica l

s ign ifican ce

at 0. 05 le v e l



T rea tm en t 3 66.347 1 9 .1 5 3 *

Error 8 3 .464

T o ta l 11

PL-422/13 1 3 3

T A B L E I X . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N ° B R I X

O F T A I W A N S P B A N A N A S S T O R E D A T 2 5 T O 3 0 ° C F O R 2 W E E K S


1 15 .8 16 .5 20 .2 21 .82 16 .0 16 .2 2 1 .6 22 .83 1 6 .4 16 .8 19 .8 2 2 .4

T o ta l 4 8 .2 49 .5 61 .6 67 .0M ean 16.1 16 .5 20 .5 22 .3

Sta tistica l

s ign ifican ce

at 0 .05 le v e l

Analysis o f va rian ce


T rea tm en t 3 28.237 84 .7 9 6 *

Error 8 0.333

T o ta l 11

TABLE X. INFLUENCE OF GAMMA IRRADIATION ON °BRIX OF TAIWAN CHL BANANAS STORED AT 12 TO 20°C FOR ONE MONTH


1 15 .4 15 .8 1 7 .8 23 .0

2 15 .5 16 .9 18 .9 2 2 .6

3 17 .2 15 .5 1 9 .4 23 .8

T o ta l 48 .1 4 8 .2 56.1 6 9 .4

M ean 16 .0 16.1 18 .7 23 .1

S ta tis tica l

s ign ifican ce

at 0 .0 5 le v e l



T rea tm en t 3 33 .513 51. 322*

Error 8 0 .653

T o ta l 11

1 3 4 K AO

T A B L E X I . I N F L U E N C E O F G A M M A I R R A D I A T I O N O N ° B R I X

O F T A I W A N C P B A N A N A S S T O R E D A T 1 2 T O 2 0 ° C F O R 1 M O N T H


1

2

3

10 .2

1 6 .2

12 .6

11 .4

1 6 .0

12 .9

18 .8

20 .8

18 .5

23 .9

2 1 .6

21 .8

T o ta l

M ean

39 .0

13 .0

4 0 .3

1 3 .4

58.1

1 9 .4

67 .3

2 2 .4

S ta tis tica l

s ign ifican ce

at 0 .05 le v e l



T rea tm en t 3 64.830 15 .8 9 7 *

Error 8 4 .0 7 8

T o ta l 11

TABLE XII. INFLUENCE OF GAMMA IRRADIATION ON °BRIX OF TAIWAN SP BANANAS STORED AT 12 TO 20°C FOR 1 MONTH


1 1 2 .3 . 15 .2 17 .8 22 .2

2 16 .6 16 .4 1 9 .8 22 .2

3 16 .0 16 .2 2 0 .9 22 .7

T o ta l 4 4 .9 4 7 .8 58 .5 6 7 .4

M ean 1 5 .0 15 .9 1 9 .5 22 .5

S ta tis tica l

s ign ifican ce

at 0*05 le v e l



T rea tm en t 3 35.487 1 6 .9 5 3 *

Error 8 2 .093

T o ta l 11

PL-422/13 135

TABLE XIII. CHEMICAL ANALYSIS OF TAIWAN BANANAS AFTER PICKING (wt%)

D ate a Starch Pectin SucroseInvert

sugar

O rgan ic

acidM oisture Others pH

0425 2 6 .8 0.13 0.10 0 .04 0.07 66.31 6 .35 6 .0

0513 25 .1 0 .14 0.19 0.09 0.21 66 .90 7 .37 5 .9

0606 2 5 .5 0 .13 0.30 0 .10 0.23 68. 01 5 .73 5 .9

0618 1 9 .6 0.17 0.11 0 .04 ■ 0 .22 71 .24 8 .62 5 .80712 1 8 .9 0.17 0 .26 0.13 0 .19 72.23 8 .12 5 .7

0724 1 4 .0 0 .26 0 .32 0 .16 0.19 72.92 12 .15 5 .7

0806 1 6 .2 0 .22 0 .25 0 .10 0.24 72 .15 10 .84 5 .7

CH L 0917 2 1 .4 0 .19 0.21 0 .12 0.28 71.67 6 .13 5 .8

1005 2 5 .6 0 .18 0.23 0 .08 0.22 70.34 3 .3 5 5.7

1101 2 6 .5 0 .16 0 .20 0.09 0.20 69.82 3 .03 5 .8

1207 2 7 .2 0 .18 0.32 0 .12 0 .18 68.94 3 .1 6 5 .8

0316 2 6 .9 0.11 0 .24 0 .08 0.38 68.33 3 .9 6 5 .8

0325 26 .7 0 .12 0 .15 0 .05 0.30 67.85 4 .83 5 .8

0403 2 7 .8 0 .13 0.15 0 .05 0.27 66 .99 4 .61 5 .9

0412 2 6 .0 0 .13 0.21 0 .06 0.28 66.98 6 .34 5 .9

0427 28 .3 0.11 0.17 0 .10 0.29 63.62 7 .41 5 .9

0519 2 6 .2 0 .15 0 .19 0 .09 0.26 67.13 5 .98 5 .9

0612 25 .2 0 .23 0 .12 0.12 0.29 68.91 5 .13 6 .0

0624 22 .2 0 .19 0 .25 0 .08 0.29 70 .92 6. 07 6 .0

0706 1 6 .4 0 .12 0 .29 0.11 0 .22 70.47 12.39 5 .8

0731 17 .3 0 .18 0 .27 0 .03 0.30 71.63 10.29 5 .7

0824CP

0929

18.1 0.21 0 .16 0 .08 0.30 72 .38 8.77 5 .8

2 1 .4 0 .23 0 .25 0.11 0.26 72 .12 5 .63 5 .8

1017 2 3 .6 0 .23 0.25 0 .12 0 .25 71 .56 3 .99 5 .81122 2 5 .4 0.21 0 .24 0.13 0 .28 70 .52 3 .2 2 5 .81210 26 .8 0 .19 0 .30 0 .16 0.34 70 .90 1.31 5 .7

0318 22 .2 0 .22 0.21 0 .11 0.43 71 .40 5 .43 5 .7

0327 23.1 0 .19 0.25 0 .16 0.40 69.41 6 .49 5 .7

0406 2 5 .4 0 .26 0 .15 0.09 0 .35 68.52 5.23 5 .8

0430 25 .1 0 .16 0.21 0 .08 0.22 69.21 50 .20 5 .90510 24 .6 0 .13 0.18 0 .06 0.18 69.84 5. 01 5 .9

0528 22 .5 0 .12 0.18 0.12 0 .23 71 .46 5 .39 5 .90621 18 .4 0 .14 0.13 0 .08 0 .29 72.38 8 .58 5 .9

0709 16.7 0 .20 0 .23 0 .09 0 .22 71 .12 11 .44 5 .80721 14 .8 0 .26 0 .23 0 .08 0 .19 70.73 13.71 5 .70822 15.1 0 .19 0 .15 0 .09 0 .23 70 .94 13.30 5 .8

SP 0924 19 .9 0 .22 0 .20 0 .12 0.22 70.67 8 .67 . 5 .81011 21 .7 0 .18 0 .24 0 .15 0.25 70 .56 6 .92 5 .81117 24 .3 0.21 0 ,20 0.08 0.23 69 .84 5 .14 5 .9

1213 2 6 .4 0.19 0 .22 0 .06 0.25 70.10 2 .7 8 5 .90313 28 .8 0.17 0 .19 0 .04 0.35 69.54 0.91 6 .0

0322 24 .9 0 .22 0 .24 0 .05 0.32 69.93 4 .3 4 5 .90331 2 3 .6 0 .16 0 .22 0 .03 0.32 69.12 6 .55 5 .70409 22 .3 0 .29 0.21 0 .09 0.36 68.89 7 .86 5 .9

First two d ig its in d ica te m onth; third and fourth d ig its in d ica te the day in that m onth.

1 3 6 KAO

F IG .4 . Starch contents o f Ta iw an bananas a fte r p ick in g through d iffe ren t seasons.

M O N TH

•FIG. 5 . M oisture contents o f Ta iw an bananas a fter p ick in g through d iffe ren t seasons.

REFERENCES

E l ] FERGUSON. W .E . , Y A T E S , A .R . , M cOUEEN, K . F . , ROBB. J .A . , T h e e f fe c t o f gam m a rad iation on

bananas, Fd T e ch n o l. _20 (1966) 203.

[ 2 ] K A H A N , R .S . , N ADEL- SHIFM A N , М . , TE M K IN -G O R O D E ISK I, N . . EISENBERG, E ., 2AU B ERM AN , G . ,

A H ARON I , Y . , "E ffe c t o f rad iation on the ripen ing o f bananas and avocado p ears". P reservation o f Fruit

and V ege ta b le s by Rad iation (P ro c . P an e l, V ien n a , 1966), IA E A , V ienna (1968 ) 3.

[ 3 ] M A X IE , E .C . , ABDEL-KADER, A . , Food irrad iation — physio logy o f fruits as re la ted to fe a s ib ility o f

the tech n o lo gy , A d v . Fd Res. 15 (1966) 105.

PL-422/14

SEMI-COMMERCIAL-SCALE STUDIES ON IRRADIATED PAPAYA *

A .M . DOLLAR, M. HANAOKA Hawaiian Food Irradiation Program,Department o f Agriculture,State o f Hawaii,Honolulu, Hawaii

G. A . M cCUSH 6 111 Summer Street,Honolulu, Hawaii

J.H . MOYDepartment o f Food Science and Technology,C ollege o f Tropical Agriculture,University o f Hawaii,Honolulu, Hawaii,United States o f Am erica

Abstract

S E M I-C O M M E R C IAL-SC ALE STUDIES O N IRRAD IATED P A P A Y A .

Th ree sim u lated shipping studies and tw o la rge sh ipping studies o f papaya h ave com pared the e ffec t?

o f rad ia tion trea tm en t w ith ex is tin g c o m m erc ia l d isin festation m ethods, w h ich now m eet quarantine

restrictions. T h e she lf l i f e o f papayas trea ted by io n iz in g rad ia tion was consistently equ a l t o , or better

than that observed for controls, fum iga ted or vapou r-h ea t-trea ted fruits. Irrad iation o f papayas assures

im proved sh e lf l i f e through d e la yed so ften ing. T h e re is no s ign ifican t im provem en t by trea tin g at the

h igher or 75-krad m in im um absorbed dose.

1. INTRODUCTION

The two basic requirements for U.S. Food and Drug Administration clearance of any new food additive are proof of: (1) technical benefit, and (2) biological safety. The biological safety evaluations require supplies of product treated at the optimum recommended minimum absorbed dose,75 krad, and twice that dose. The Hawaii Development Irradiator (HDI) has supplied these materials in addition to carrying out the technical effect or shelf-life studies. These studies have as their objective comparison of the effectiveness of radiation treatments with other treatments presently accepted for disinfestation.

Comprehensive shipping studies have compared the effects of radiation treatment with existing commercial methods which now meet quarantine restrictions. Current commercial quarantine control measures which are accepted by the United States Department of Agriculture USDA) Plant Quarantine Service are ethylene dibromide treatment or vapour-heat treatment.

* Supported by the D iv is ion o f Isotopes D eve lop m en t, U .S . A to m ic Energy Com m ission ,

Contract N o . A T (2 6 - l ) - 4 7 3 .

1 3 7

1 3 8 DOLLAR e t a l .

The USDA Agricultural Research Service Fruit Fly Investigations Laboratories have found that treatment with ionizing radiation at a minimum absorbed dose of 21 krad will meet quarantine requirements for papaya, however, for practical commercial-scale treatment an absorbed dose of 25 krad is recommended. University of Hawaii (UH) studies support the conclusion that shelf-life improvement can be an added benefit of radiation treatment up to a maximum absorbed dose of 150 krad wherein shelf life is considered to be the summation of shipping, storage and market display life. The optimal treatment for disinfestation and shelf-life improvement is a minimum absorbed dose of 75 krad.

Shipping studies required randomization of approximately 907 kg (2000 lb) of fruit at time of harvest into six lots: first, the absolute control which receives no further treatment; second, the vapour-heat-treated control; third, the hot-water-treated, fumigated control; and fourth, fifth, and sixth lots which are hot-water-treated and then irradiated.

For the complete simulated shipping study series, irradiated lots were treated at minimum absorbed doses of 25, 50, 75, 100, and 150 krad. Repetition of the control, fumigated and 25-krad-treated lots were included in each series to aid in statistical comparisons. For the large-scale shipping studies irradiated fruits were treated at minimum absorbed doses of 25 and 75 krad.

Three simulated shipping studies, one surface and two large-scale air shipping studies were conducted according to standardized procedures except for slight modifications which were required in shipping, processing and packaging practices in order to stay within limits imposed by transportation, harvesting and processing schedules.

2. HOT-WATER TREATMENT

Hot-water treatment is used whenever fruits are treated by fumigation as an added precaution to reduce the occurrence of storage mould and decay. This same step is recommended for use in combination with treatment by ionizing radiation. Treatment is accomplished by immersing the papaya for 20 minutes in 48 + 1°C (118 + 2°F) hot water and then in a 23 ± 2°C (74 ± 4°F) cool-water shower, for an equal time. A special study of

TABLE I. FRUIT PULP TEMPERATURE CHANGES DURING HOT-WATER TREATMENT

Before treatm ent A fte r treatm ent A fte r co o lin g

°C °F °C °F °C °F

M ean 24 76 .0 34 93 .2 29 84 .7

Standard d ev ia tion 1 .14 2 .0 5 0 .46 0 .82 0.60 1 .08

Standard error 0 .6 3 1 .73 0 .2 6 0 .33 0 .33 0 .44

PL-422/14 139

commercial practices determined that the temperature of the treatment water leaving the heat exchanger was 47 + 1°C (116 ± 2°F) throughout the treatment cycle. Fruit pulp temperatures were recorded for fruit located at random throughout the load before treatment, before cooling and upon removal from the cooling-water cycle (see Table I).

3. EXPERIMENTAL - SHIPPING STUDIES

Papayas were harvested at Hana, and Kahului, Maui; or the Puna District, Hawaii. The normal commercial practice is to begin harvesting as early as practicable in the morning, 6. 30 to 7. 00 a. m ., and continue harvesting until early afternoon. Except where noted the fruit were selected on the basis of apparent colour and were further sorted by condition, colour and size before packing for transport to assembly and treatment plants.Maui fruit were transported to Hilo by air for treatment in commercial packing plants. These air-freight operations required 2-hours handling from harvest area, to the Hilo packing plant. This contrasts with Puna fruit which require 1 -hour truck transport from field operations to the processing plant in Hilo. All transhipment and handling was through commercial channels except where noted.

Absolute control, fumigated and vapour-heat-treated fruit were processed in commercial plants under the same conditions as fruit destined for mainland markets. The only special handling required was re stacking field crates prior to any treatment to assure randomization between treatments. The handling of papayas from Maui deviated slightly from normal practice in that fibreboard cartons were used for shipment from field packing operations to assembly plant. In Hilo the fruit were transferred to wooden field boxes prior to any subsequent treatments. All lots were held at ambient temperatures of 80 to 85°F for the entire cycle of harvest to air-freight delivery in Honolulu.

4. MATERIALS - SIMULATED SHIPPING STUDIES

Fruit were harvested in the normal manner for the harvesting area.In the Hana, Maui area fruit is collected in knapsacks which hold about 66 to 110 lb (30 to 50 kg). This method differs from Puna where fruit is placed in 7. 5-litre (2 US gallons) buckets which hold about 33 lb (15 kg).The weight of fruit in the shoulder knapsacks is sufficient to cause bruising which appears within 2 to 5 days, thus more careful packing inspection of these fruit is mandatory. All fruit were harvested at mature-green to 1/8-colour-development stages.

All lots except absolute control and vapour-heat-treated fruits received hot-water treatment on arrival in Hilo. Vapour-heat-treated fruit were processed the evening of arrival in Hilo. Fruit were repacked after treatment, the day following harvest, in "12-fruit" fibreboard cartons. This 18- to 20-hour delay is normal commercial practice because vapour-heat treatment requires an overnight process cycle and the fumigation treatment normally takes place the day following hot-water treatment. The fruit must be at room temperature or above at the time of fumigation treatment.

1 4 0 DOLLAR et a l.

The control fruit and the fruit for irradiation treatment were repacked in the morning immediately prior to packing the other two lots. All lots were intermixed randomly when stacked on pallets for air shipment to Honolulu on the normal afternoon freight flights. Conventionally interisland shipment of papayas is by barge.

It should be noted that normally fruit for export are assembled and stored under refrigeration at 7 + 1°C (45 ± 2°P) until ready for shipment.Fruit are usually air-freighted to mainland destinations direct from Hilo within 24 hours of packaging.

All fruit were delivered to Honolulu on the day of packing but were not received at the Hawaii Development Irradiator (HDI) facility until the following morning (2 days after harvest). During this second delay period the fruit were held at ambient temperatures of 24 to 29°C (75 to 85°F). All lots were randomized on receipt and those requiring treatment by ionizing radiation were treated before all lots were transported by pick-up truck to the University of Hawaii. All fruit were placed in storage at 10 + 1°C (50 ± 2°F) for a period representative of normal transport and storage cycles. It should be noted that normal commercial storage temperatures are 7 ± 1°C (45 ± 2°F). Storage schedules simulated wholesale distribution and retail display. Thermal histories for each lot were derived from thermograph records by accumulating the number of °F hours. This method of expressing temperature effect was chosen because each treatment introduces slight variations in thermal history. For example vapour-heat treatment is in itself a thermal process. Fruit ripen in response to variations in temperature hence the thermal exposure is cumulative for each treatment in terms of °F hours.

In the first series a portion of each lot was stored for 5 days at shipping temperatures of 10 ± 1°C (50 ± 2°F). This schedule was considered to be equivalent to air shipment. The normal surface-equivalent schedule required 7 days storage at shipping temperatures ofl0±l°C(50± 2°F). When the fruit were removed from storage for simulated display shelf-life evaluations, the cartons were opened, fruit examined according to the plan and placed in an air-conditioned room at 21 + 1°C (70 + 2°F).

The first series was placed in chilled storage at a relative humidity of 85 to 95% which exceeds that prevailing in commercial practice. In all subsequent series, the relative humidity was maintained at less than 70% by adding a supplemental heat load to achieve humidities more closely resembling normal commercial storage and handling conditions.

5. MATERIALS - SURFACE SHIPPING STUDY

Papayas were harvested from a commercial field near Kahului, Maui.The normal commercial practice for all papaya operations is to begin harvesting as early as practicable in the morning, 6. 30 to 7. 00 a. m. , and continue harvesting until 3. 00 p. m. Fruit are selected and field- sorted on the basis of apparent colour (ranging from tinge (# 2) to quarter- colour (ft 3) at the blossom end) condition, and size.

For these studies the Maui fruit were harvested into plastic field crates and transported by truck 11. 2 km (7 miles) to the air-freight terminal for air-freighting to Hilo. This is the normal practice for this grower. The fruit arrived in Hilo in the early evening of the same day.

PL-422/14 141

The field crates were randomized to treatment lots. Vapour-heat treatment was completed the next night. All remaining lots, except the absolute control were hot-water-treated at noon the next day and the fumigated lot was treated late the same afternoon.

In the morning the vapour-heat-treated fruit was packed in HDI "12-pack" trial container (a two-layer pack in an 20. 4 cmX 20. 4 cmX 30. 5 cm (8 in. X 8 in. X 12 in. ) fibreboard carton with only a fibreboard divider between the layers and no other filling material). All cartons were sealed by tape in the customary manner and marked to identify treatment. Similarly the other lots were packed in the afternoon and early evening of the same day. All cartons were assembled on pallets for air shipment.

All cartons were shipped to Honolulu to arrive late (5. 00 p. m. ) in the afternoon at the HDI facility where they were placed in a Matson refrigerated container at 9 + 1°C (48 + 2°F) for overnight storage.

The irradiated lots were treated the following morning, the 4th day after harvest. Processing schedules and dosimetry procedures complied with pre-established procedures. Dosimetry was monitored by standard procedures using the cross-calibrated, modified Fricke system.

All lots were reloaded in the Matson container randomizing a carton from each treatment into each stack. The cartons were stacked three high in a pinwheel pattern with a patch of glue between layers. This glue system provides for stack integrity and the glue is brittle giving a clean separation when a carton is removed. The lots designated for University of Hawaii storage were transported by pick-up truck and placed in storage in a room at 9 ± 1°C (48 ± 2°F).

The humidity in the Matson container was less than 80% r. h. The relative humidity at the University of Hawaii was maintained at about 70%.The 48°F temperature was necessary because the container refrigeration automatic defrost system does not operate reliably at higher temperatures. Should the defrost fail to function there would be excessive temperature variation in the container.

6. MATERIALS - LARGE-SCALE AIR SHIPMENTS

Papayas for both air shipments were harvested from the Pohoiki fields in the Puna District of Hawaii using normal commercial harvesting procedures. The fruit were field-sorted into wooden field crates and transported to the Hilo plant for treatment, inspection and packing. All subsequent operations for the first air shipment conformed to those described previously for the surface shipment.

TABLE II. MARKETABLE FRUIT 7 DAYS AFTER HARVEST (%)

Location C ontrol Fum igated V apour-heat 25 krad 75 krad

U n ivers ity

o f H aw a ii 14 .5 22 .7 2 5 .2 4 5 .7 34 .5

Davis a 1 2 .5 2 .0 18.1 30 .8

a T rea tm en t not included .

TABLE

III.

DOSI

METRY

POR

SHIP

PIN

G

STU

DIE

S

142 DOLLAR e t a l .

c o c o m o í

CO 00 CO CO 00

QОHСЛОZ

<О

S =

Su

rfac

e sh

ippi

ng

stu

dy.

Al

= A

ir

ship

pin

g st

udy

1.

A2

= A

ir

ship

pin

g st

udy

2.

PL-422/14 143

Temperatures during this shipment rose to 31°C (87°F) and remained at this high level for extended periods of time. These high temperatures accelerated the ripening process and favoured the breakdown of fruit. Consequently over 70% of the fruit shipped to Davis was non-marketable. UH-inspected lots were less than 50% marketable.

The study was terminated after the first inspection at Davis because of the excessive damage. It is worthwhile to note that a significant number (p = 0. 01) of the irradiated fruit were in better condition than were the control or fumigated lots. Evidently treatment at the fully-ripe stage had a beneficial effect which was most noticeable when fruit were chilled immediately after irradiation.

The fruit air-shipped to California were exposed to high temperatures during transfer and loading operations at the Honolulu and Los Angeles Terminals. Recorded temperatures in the range 32 + 2°C (90 + 3°F) were sustained over a 12-hour period and resulted in a mean temperature3 degC (5 degF) higher than those retained at the University of Hawaii. Arrival conditions at Davis varied from a low of 2% marketable for the vapour-heat-treated fruit to a high of 30.8% for fruit irradiated at 75 krad. All irradiated lots contained significantly higher proportions of marketable fruits than either vapour-heat or fumigated lots, as shown in Table II.

6. 2. Second air shipment

Approximately 952 kg (2100 lb) of papayas were obtained from a commercial orchard in the Puna district of the Island of Hawaii. Papayas for the second air shipment were picked in the morning and processed through normal commercial channels in their original wooden crates. All fruits except the absolute controls were hot-water-treated and shipped by barge from Hilo the day after harvest. The barge arrived in Honolulu about5. 00 p. m. the second day after harvest. These fruits of the size and quality normally found on the Honolulu market are larger and more irregularly shaped than fruits typically shipped to West Coast markets.

Fruit inspected in Hilo at 5. 00 p. m. on the day of harvest were found to be firm and generally mature. Colour development at that time was 2% for colour grade jf 1, 34% for colour jf 2, 45% for colour grade jf 3,16% for colour grade jf 4, and 3% for colour grade jf 5. No decay was observed but on average 24% of the fruit showed signs of grade defects consisting of punctures, bruises, scars, creasing and catface or immature and misshapen. These fruits could not meet the grade standards for Hawaii jf 1 papayas because of this incidence of defects. 113 kg (250 lb) of fruit were culled during packing in Honolulu because of grade defects and colour development beyond grade jf 4.

Upon arrival in Honolulu the fruits were randomized into four lots before treatment; absolute controls, fumigated, and irradiated at 25 and 75 krad. No vapour-heat treatment was included since no such facility is present on Oahu.

The control lot which did not require further treatment was packed into the HDI fibreboard trial container on the morning of the 3rd day after harvest. The fumigated lots were treated under normal commercial conditions in the State of Hawaii Plant Quarantine Station fumigation chamber.

6 . 1 . F i r s t a i r s h i p m e n t

1 4 4 DOLLAR e t a l .

The irradiated lots packed in the HDI fibreboard trial containers were treated in the HDI facility in accordance with standard procedure. Except for the absolute controls, each lot was randomly divided into three groups, one for shipment to Davis, a second for storage at the University of Hawaii and the third for the turn-around air shipment to the University of Hawaii via San Francisco.

7. RADIATION PROCESSING

The lots for irradiation were segregated onto separate pallets. All fruits were stored and handled under ambient conditions, i. e. 29 to 32°C (85 to 90°F), relative humidity 50 to 60%. No special atmosphere control measures were required.

Dosimetry was by the standard Fricke method or a modified Fricke method cross-calibrated to the standard Fricke method. Dosimeters, flame-sealed 5-ml ampoules, are fastened in positions representing previously determined maximum and minimum absorbed doses in two papaya cartons of each lot processed. Five dosimeters are positioned in each carton, two in the maximum- and three in the minimum-dose areas.

The package has the dimensions 31.8 cmX 21.0 cmX 21.6 cm (12| in. X 85 in. X 8-j in. ) and a volume of 0. 14 m3 (0. 51 ft3). The bulk density and gross weight vary from run to run because of variations in fruit sizes, hence these values must be determined for cartons sampled from each lot. Two packages are placed in each carrier entering the process cycle. The process conveyor is adjusted to assure that the top or bottom on respective passes is at a 19. 1-cm (7f-in. ) distance when passing the source. The number of source modules and step-dwell times are given for each run. Dosimetry is monitored and the individual values are recorded, but only the maximum and minimum absorbed dose values are given in Table III.

8. EFFECT OF TEMPERATURE ON COLOUR DEVELOPMENT

Supplemental studies have established the relationship of temperature to rates of colour development for papayas at different initial colour stages and different storage cycles. Colour is scored wherein the colour grade conforms to the following scale:

1. Mature-green to "blush" of colour.2. "Blush" to definite colour on approximately 1/8 of the blossom

end surface.3. From 1/8-colour to definite colour on 1/4 of the total surface.4. From 1/4-colour to definite colour on 1/2 of the total surface.5. From 1/2-colour to definite colour over 3/4 of the total surface.6. Full or nearly full colour development.

Colour development advances 0. 97 + 0. 2 colour unit increments per day when stored at 23 ± 0. 5°C (74 + 1°F) and 0. 54 + 0. 2 colour unit increments per day when stored at 19 ± 0. 5°C (66 ± 1°F). Fruit stored at

PL-422/14 145

12 ± 0. 5°C (54 + 1°F) advances 0. 8 ± 0. 2 colour unit increments during the 6 days of low-temperature storage and subsequent colour development is normal when transferred to 23 + 0. 5°C (74 + 1°F).

9. EFFECT OF VAPOUR-HEAT TREATMENT

The thermal profile for vapour-heat treatment is significantly higher than all other treatments because prolonged exposure to elevated pulp temperature reaches 47°C (117°F). There is a significant weight loss during treatment which is attributable to evaporation during the vapour- heat-treatment cycle. There is a significant (p = 0. 05) 8% loss in weight when fruit is treated by the vapour-heat process while there is no weight loss attributable to other treatments. This loss in moisture by vapour- heat-treated fruit is a factor to consider in relation to shelf-life effects and to costs of processing.

10. RESULTS AND DISCUSSION

The simulated shipping protocol was followed for large-scale shipping studies. Field sorting eliminated defective fruits or fruits not complying with the colour development grades. The results for chemical analyses confirmed earlier ripening parameter studies which found that radiation treatments did not effect pH, ascorbic acid and titratable acidity values.

Pulp colour and carotenoid values reflected ripening and consequently delays in ripening which resulted from radiation treatment.

11. SHELF LIFE AND COLOUR DEVELOPMENT - SIMULATED SHIPPING STUDIES

Mean colour development grades were derived by the same procedures used for shelf-life data. Colour grades were judged on a subjective scale of 1 to 6 where mature-green equals Grade 1 and full colour development equals Grade 6. While there were significant differences within each series of the simulated shipping studies, there was no consistent trend specifically related to irradiation or other treatments but only to thermal history.

In the first series vapour-heat-treated fruit had a significantly better shelf life (p = 0. 05) by about 1 day than any other treatment (see Table IV). This shelf-life difference of the vapour-heat-treated lot could be attributed to surface drying during treatment which would reduce free moisture thus inhibiting or limiting mould development. The overall shelf life for this series was poor possibly due to high humidity during chilled storage.This humidity was reduced in subsequent studies.

No shelf-life comparison with absolute controls was possible for the first series because the number of samples was inadequate. In the subsequent two series the shelf life for controls was significantly poorer (p = 0. 05) than all other treatments except for the fumigated lot in the second series. The shelf-life data are summarized below.

146 DOLLAR et a l.

TABLE IV. SIMULATED SHIPPING STUDIES (mean days ± 1 SE)

T rea tm en tDays to

co lou r Grade 6 a

D

Series 1

ays m arketab le

Series 2 Series 3

SE ± 0 .1 SE ± 0 .5

Control 12 .2 11 .5

(N o treatm ents) 5 .3

Fum igated (hot w ater) 5 .6 10 .7 12.7 17 .8

Vapour-heat 5 .6 11 .9 14 .6 12.6

Irrad iated krad

(h o t w a ter )

25 5 .6 11 .1 15 .8 19 .5

50 5 .5 10 .7

75 4 .6

100 5 .6 16 .3 1 9 .8

150 5 .6 16 .0 19.1

a A l l series poo led .

Differences in half-life between lots and treatments apparently related to some unidentified factor in processing, handling or storage. Data indicate that irradiation at minimum absorbed doses in the range of 25 to 150 krad consistently equalled or improved the shelf life when compared to the absolute control or to lots treated by fumigation. When all irradiated and vapour- heat-treated lots were compared, the shelf life of all irradiated lots were equal to or significantly better than the vapour-heat-treated lots. The longer shelf life of vapour-heat-treated papayas when compared to controls or fumigated fruit could reflect the physical effects of the treatment to reduce surface moisture and firm the fruit.

Colour development was independent of series or treatment except for those irradiated at 75 krad (series 3). The mean days for full colour development was 5. 6. The effects of improved handling or other factors is quite evident for series-2 and -3 data. Here the shelf-life extension effect of radiation is 2 to 3 days (series 2) and 1 to 2 days (series 3) when compared to the fumigated fruit. There are no significant differences of radiation doses on shelf life in the range of 25 to 150 krad.

Shelf life can be related to moisture balance which is influenced by the constant dew-point of 17 to 18°C (63 to 65°F) prevailing at lower elevations in the State of Hawaii.

While no special effort was taken to modify or specifically monitor humidity during commercial treatment operations, analysis of data suggests that more careful monitoring and control of each process step would be necessary before results can be fully interpreted. Furthermore, commercial storage handling conditions will vary from plant to plant and from day to day, depending on shipping and marketing pressures.

PL-422/14 147

TABLE V. RELATIONSHIP OF TREATMENT TO INCIDENCE OF DECAY

Series C ontrol Fum igatedVapour-heat-

-trea ted25

Irra

50

d ia ted (k r

75

ad)

100 150

First NS 67 .9 69 .1 78 .0 8 1 .5 N T N T N T

Second 4 4 .7 29 .3 62 .2 77 .7 N T N T 83 .2 76 .5

Th ird 9 8 .1 19 .2 27 .8 60 .2 72 .0 66 .7 N T N T

NS = In su ffic ien t numbers rem a in in g .

N T = N on e trea ted .

TABLE VI. RELATIONSHIPS OF TREATMENT TO SHELF LIFE

Fum igated Pooled data Irrad iated 25 krad

M ean days sh e lf l i f e

by trea tm en t a ll series 15 .3 ± 0 .23 (N = 357) 1 5 .8 ± 0 .2 5 (N = 405)

M ean days to d iscard-

softness 1 6 .2 ± 0 .2 5 (N = 348)

M ean days to d iscard-

decay 14 .0 ± 0 .2 2 (N = 4 1 4 )


by trea tm en t, first

series om itted 16 .1 ± 0 .2 7 (N = 235) 1 7 .7 ± 0 .30 (N = 264)

M ean days to discard

Pooled-softness 17. 5 ± 0 .2 8 (N = 264)

Poo le d -d e ca y 16 .3 ± 0 .3 1 (N = 235)


each series harvest

dates

First a ir equ iv . 12 .1 ± 0 .16 (N = 157)

First surface equ iv . 10 .5 ± 0 .1 7 (N = 106)

Second 15 .1 ± 0 ,3 1 (N = 246)

Th ird 1 8 .8 ± 0 .23 (N = 253)

A l l com parisons betw een treatm ents and harvest da te series are s ign ifican tly d iffe ren t (p = 0 .0 1 ).

148 DOLLAR et a l .

Laboratory-scale storage facilities necessary for detailed shelf-life evaluations introduced a new variable of high humidity which affected the results of the first series. In subsequent series this variable was controlled, hence separate consideration of these data is necessary. Fruit treated by fumigation and by 25 krad of irradiation were included in each series allowing for improved interpretation of data pooled for the series of studies.

Nearly two-thirds of the fruit were discarded because of decay in all instances except the control in the second series, the vapour-heat-treated lot in the third series and the fumigated fruit in the second and third series. The percentages of fruit discarded as the result of decay are summarized in Table V.

In the two instances where softness and not decay was the predominant cause for discard, the lots were packed last. Both these lots, absolute control and the fumigated lot which were packed last were free of sensible moisture when packed.

It is important to note that in all series irradiated lots were packed first and free moisture was noticeable at the time of packaging. This effect could account for some of the variation between treatments (see Table VI).

12. CAUSES FOR DISCARD - SHIPPING STUDIES

Normally hot-water treatment which coagulates latex and washes the fruit reduces the incidence of decay and increases shelf life. Fruit that does not decay ultimately is discarded because of softness. Other variables introduced by the sequence of treatment and packaging can affect the incidence of decay but for these studies no special effort was taken to identify, control or measure these variable factors. For example, free surface moisture develops during the fumigation cycle under certain high-humidity conditions prevailing at the time of treatment. Short periods of ventilation which are required for the removal of the fumigant will cause free moisture to form on the surface of the fruit while prolonged ventilation periods will tend to remove this condensed moisture. In normal practice this post-fumigation ventilation cycle can vary widely which is probably the major cause of variation.

13. FIRMNESS - SIMULATED AND LARGE-SCALE SHIPPINGSTUDIES

Two measures of firmness were evaluated in earlier studies. The Magness-Taylor method provided a good measure of firmness, however, this injures the fruit causing it to be discarded. The Durometer method which measures the force required to penetrate the skin however, allows continuing examinations of the fruit even though it does not give a completely representative measure of pulp firmness. The Durometer method was chosen because the fruit is not seriously injured thus allowing for repeated measurements of firmness and shelf life on the same fruit. In all three simulated shipping studies those fruit treated by radiation were firmer with the firmness directly related to dose (see Tables VII, VIII,IX, X and XI).

PL-422/14 149

Comparisons of durometer measurements for both surface and air shipments confirm that fruit irradiated at both dose levels remain significantly (p = 0. 01) firmer throughout the storage and display cycle. The means for 21 or 22 sets of data with at least 6 0 observations for each treatment were significantly firmer (p = 0. 01). During the first 4 days after arrival the irradiated fruit were at least 10% firmer as measured by the durometer than fumigated fruits. After the 4th day comparative interpretation of results is questionable since by that time significant numbers of the fumigated fruit had been discarded.

TABLE VII. SIMULATED SHIPPING STUDY - PAPAYA (FIRST SERIES)

POOLED DUROMETER READINGS FOR FIRST 5 D A Y S OF D IS PLA Y UFE

Fum igated Vapour heat 25 krad 50 krad

Sum o f observations 8 536 23 904 25 758 23 776

Sum o f squares 309 896 1 343 448 1 577 436 1.460 304

Num ber 327 540 489 474

M ean 26 .10 44 .2 7 52.67 50 .16

Standard d ev ia tion 16 .34 23.01 21 .26 23 .79

Standard error 0 .90 0 .99 0 .96 1 .09

A N A L Y S IS OF V AR IAN C E

Sum o f squaresD egrees o f

freedomM ean square F

B etween groups 158 398 3 52 799 .19 112.02

W ith in groups 860 699 1826 471 .36

T o ta l 1 019 097 1829

Required F 5% = 2 .6 1 1% = 3 .80

D U N C A N M U LT IPLE -R A N G E TE ST OF S IG N IF IC AN C E

Fum igated Vapour heat 50 krad 25 krad

26 .10 4 4 .2 7 50 .16 52.67

N o s ign ifican t d iffe ren ce

p = 0 .0 1 --------------------------

p = 0 .05 -------------------

150 DOLLAR et al.

TABLE VIII. SIMULATED SHIPPING STUDY - PAPAYA (SECOND SERIES)

POOLED DUROMETER READINGS FOR FIRST 5 D A YS OF D ISPLA Y UFE

C ontrol Vapour heat Fum igated 25 krad 100 krad 150 krad

Sum o f observations 34 827 41 337 27 807 45 272 46 545 56 149

Sum o f squares 2 506 409 2 841 611 1 514 743 3 483 408 3 657 887 4 759 543

Num ber 552 660 691 645 648 710

M ean 63.09 62 .63 47 .0 5 70 .19 71 .83 79 .08

Standard d ev ia tion 23 .68 19.58 18.70 21 .79 22 .05 21.22

Standard error 1 .01 0 .7 6 0 .77 0 .86 0 .87 0 .80

A N A LY S IS OF V AR IAN C E

Sum o f

squares

Degrees o f


Between groups 379 085 5 75 817.08 168.72

W ith in groups 1 707 623 3800 449 .37

T o ta l 2 086 708 3805

Required F 5°jo = 2 . 2 1 1 °Jo = 3 . 02

D U N C A N M U LTIPLE -R AN G E TEST OF S IG N IF IC AN C E

Fum igated Vapour heat C ontrol 25 krad 100 krad 150 krad

47 .0 5 62.63 63.09 70 .19 71.83 79 .08


p s 0 .0 1 ------------------------

p = 0.05 ........................

PL-422/14 15 1

TABLE IX. SIMULATED SHIPPING STUDY - PAPAYA (THIRD SERIES)

POOLED DUROMETER READING FOR FIRST 5 D A YS OF D IS PLA Y UFE

C ontro l Fum igated Vapour heat 25 krad 50 krad 75 krad

Sum o f observations 27 009 30 038 24 690 30 527 31 825 33 642

Sum o f squares 2 476 253 2 641 514 1 885 202 2 752 737 2 910 219 2 887 540

Numbers 304 354 357 351 361 360

M ean 88 .85 84 .85 69.16 86.97 88 .16 93 .45

Standard d ev ia tion 15.90 16.20 22.34 16.71 17.05 26 .72

Standard error 0 .91 0 .86 1.18 0 .89 0 .90 1 .41

A N A L Y S IS OF V AR IAN C E

Sum o f

squares

D egrees o f


Between groups 182 643.30 6 30 440 .55 249.77

W ith in groups 296 270 .99 2431 121.87

T o ta l 478 914 .29 2437

Required F ЬЦо = 2 .61 1% = 3. 80

D U N C A N M U LT IPLE -R AN G E TEST OF S IG N IF IC AN C E

Vapour heat Fum igated 25 krad 50 krad C ontrol 75 krad

69 .16 84 .85 86.97 88.16 88.85 93 .45


p = 0 .0 1 ------------------------

p = 0 .0 5 -------------------

1 5 2 DOLLAR et al.

T A B L E X . L A R G E - S C A L E S H I P P I N G S T U D Y - P A P A Y A

SURFACE SH IPM E N T , SU M M A R Y OF DUROMETER READINGS

LocationDate

exam inedFum igated Vapour heat 25 krad 75 krad

UH 4 93 ± 2 a 97 ± 1 94 ± 1 99 ± 0 . 4 b

UH 13 86 ± 2 85 ± 3 86 ± 2 94 ± 2 b

UH 14 75 ± 3 a 81 ± 2 92 ± 1 b 91 i 1 b

A ir return at UH 14 81 ± 2 69 ± 2 a 86 ± 2 b 88 ± 2 b

UH 15 74 ± 2 a 80 à 2 85 ± 1 91 ± l b

A ir return at UH 15 73 ± 3 66 ± 2 3 72 ± 2 72 ± 3

UH 16 64 ± 2 a 76 à 2 81 ± 2 90 ± 1 b

UCD 16 59 ± 3 a 68 ± З а 86 ± 2 b 75 i 3

A ir return at UH 16 66 ± 3 64 ± 2 62 ± 2 63 ± 2

3 S ign ifican tly so fter, p = 0 .0 5 .

b S ign ifica n tly firm er, p = 0 .05 .

14. CHEMICAL ANALYSES

There were few significant differences in the results of chemical analyses which could reflect treatments (result summarized in Table XII). Radiation had little to no effect on reduced ascorbic acid and carotenoid values. Carotenoid values, which reflect ripening, increased significantly to a maximum value within 8 to 10 days after harvest for the simulated shipping studies.

No significant differences between treatments were observed for total soluble solids, dry matter, or reduced ascorbic acid in either large- scale shipping study.

There were no significant differences in reduced ascorbic acid values for the large-scale shipping studies. This further reconfirms that in papayas this sensitive reducing agent is protected from loss regardless of treatment, storage or handling conditions.

15. ORGANOLEPTIC EVALUATIONS

There were few significant differences in the organoleptic scores for any shipping study. The results for fumigated, vapour-heat-treated and irradiated 25 krad included in all simulated shipping study series are pooled and summarized ( see Table XIII). There were no significant

PL-422/14 153

TABLE XI. LARGE-SCALE SHIPPING STUDY - PAPAYA

A IR SH IPM E N T , S U M M A R Y OF DUROMETER READINGS

LocationDays

post-harvest

Absolu te

con tro lFum igated 25 krad 75 krad

UH 4 90 i 1 85 ± I a 88 ± 1 89 ± 1

UCD 4 92 ± 2 a 97 ± 1 98 ± 1

UH 5 81 1 I a 84 ± I a 87 ± 1 89 ± 1

U C D 5 87 ± 2 3 98 ± 1 96 ± 1

UH 6 82 i 1 78 ± I a 84 ± 1 85 i 1

UCD 6 80 è 2 a 94 ± 1 91 ± 1

UH 7 88 ± 1 76 ± 1 78 ± 2 84 ± 1 b

UCD 7 72 ± 2 90 à l b 84 i 2

UH 8 72 ± 1 74 ± 1 74 ± 1 72 ± 1

UCD ’ 8 75 ± 2 83 ± 2 b 72 ± 2

UH 9 64 ± 1 60 i 1 63 i 1 56 ± 1

UCD 9 66 t 2 76 ± 2 b 59 ± 2 a

3 S ign ifica n tly so fter, p = 0 .0 5 .

b S ign ific a n tly firm er, p = 0 .0 5 .

differences in colour or texture values. The fruit that was subjected to the vapour-heat treatment had a significantly lower aroma score for two of six comparisons while those subjected to 25 krad of irradiation had significantly higher aroma scores in two of six comparisons.

In three of six comparisons, the 25-krad irradiated samples had significantly better flavour scores. In no instance were the organoleptic scores for irradiated (25-, 50-, 75-, 100-, 150-krad) papayas lower than the scores for absolute controls, fumigated or vapour-heat-treated fruit.

16. SUMMARY

Three simulated shipping studies and two large-scale shipping studies compared the effects of different treatments on papayas. Papayas were harvested and handled in a normal commercial manner and randomly assigned to the treatments. Irradiation treatment was carried out in a commercial manner in the facilities of the Hawaii Development Irradiator.

1 5 4 DOLLAR et a l .

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PL-422/14 155

TABLE XIII. SIMULATED SHIPPING STUDY - PAPAYA

CO M PARISO N OF O RG ANO LEPTIC SCORES FOR TR E A TM E N TS

INCLU D ED IN A L L PANELS

(M eans ± 1 standard e rro r )

D ate o f

h a rves ta

D ate o f

paneI aFum igated Vapour heat 25 krad

Colour 4/30 5/5t 5/6 6 .2 5 ± 0 .18 5 .96 ± 0 .22 5 .63 ± 0 .33

5/12-5/13 5 .88 ± 0 .27 6 .00 ± 0 .26 6 .33 ± 0 .18

6/17 6/27 6 .0 8 ± 0 .34 5 .67 ± 0 .26 6 .00 ± 0 .28

7/2 6 .0 8 ± 0 .29 5.67 ± 0 .28 6 .1 5 ± 0 .22

8/4 8/19-8/20 5.30 ± 0 .30 6 .0 0 ± 0 .2 0 d 5 .57 ± 0 .25

N o s ign ifican t d iffe ren ces - not poo led

A rom a 4/30 5/5-5/6 5.21 ± 0 .30 4 .2 9 ± 0 .39 6 .2 9 ± 0 .1 4 c

5/12-5/13 4 .6 3 ± 0 .31 3 .5 8 ± 0 . 35c 5 .17 ± 0 .32

6/17 6/27 5.00 ± 0 .4 2 3 .4 5 ± 0 .4 3 b 5 .62 ± 0 .35

7/2 5.42 ± 0 .43 4 .8 3 ± 0 .32 5. 58 ± 0 .42

8/4 8/19-8/20 4 .6 3 ± 0 .26 5 .33 ± 0 .32d 4 .7 0 ± 0 .30

Pooled 4 .9 0 ± 0 .1 5 4 .5 0 ± 0 .15 5 .39 ± 0 .1 5 b

Flavour 4/30 5/5-5/6 5 .46 ± 0 .30 5.50 ± 0 .28 6 .17 ± 0 .2 1 b

5/12-5/13 5 .00 ± 0 .39 5 .29 ± 0 .34 6 .13 ± 0 .2 3 b

6/17 6/27 4 .8 3 ± 0 .5 2 5 .08 ± 0 .51 5 .92 ± 0 .45

7/2 5 .08 ± 0. 50 4 .6 7 ± 0 .33 5 .83 ± 0 .39

8/4 8/19-8/20 5 .43 ± 0 .21 5 .47 ± 0 .23 d 5 .40 ± 0 .24

P ooled 5 .18 ± 0 .16 5 .31 ± 0 .14 5 .86 ± 0 .13 c

T ex tu re 4/30 5/5-5/6 5 .42 ± 0 .32 5 .2 9 ± 0 .31 5 .25 ± 0 .36

5/12-5/13 5 .92 ± 0 .31 5 .6 7 ± 0 .30 5 .67 ± 0 .30

6/7 6/27 5 .50 ± 0 .3 8 5 .50 ± 0 .40 6 .3 3 ± 0 .19

7/2 4 .7 5 ± 0 .4 9 5 .7 5 ± 0 .3 5 5 .5 8 ± 0 .40

8/4 8/19-8/20 4 .8 7 ± 0 .27 5 .47 ± 0 .22d 5 .43 ± 0 .23

Pooled 5 .33 ± 0 .1 5 5 .51 ± 0 .13 5 .57 ± 0 .14

aDates expressed as m onth/day in m onth ; a l l in 1969.

S ign ifican t d ifferen ces :

ь p = 0.05. c p = 0 .0 1 .

^ D iffe ren t source o f fru it.

156 DOLLAR et a l.

TABLE XIV. SHELF LIFE (Mean number of days marketable)

Vapou r-h ea t-

-trea ted

Irrad iated

Control Fum igated

25 krad 75 krad

Surface - 16 .6 16 .6 16 .4 16.0

A ir 8 .9 8 .8 - 9 .5 9 .8

Storage, inspection, chemical and organoleptic evaluations were conducted at the University of Hawaii or at the University of California at Davis facilities. The shelf life of papaya treated by ionizing radiation was consistently equal to or better than that observed for controls, fumigated or vapour- heat-treated fruit. There were significant delays in softening for fruit treated by ionizing radiation. There were no other consistent differences in chemical composition or in organoleptic changes which could be attributed to treatment except the aroma changes seen when fruit were subjected to the vapour-heat treatment.

The two large-scale shipping studies generally conformed to the range of results found in'the simulated shipping studies (see Table XIV).

The prolonged refrigeration period combined with pre-treatment and other handling delays depressed the effects of radiation for the surface shipment. Irradiation increased shelf life by approximately 1 day for the air shipment.

In summary, irradiation of papayas assures improved shelf life through delayed softening. The onset of decay occurs late in the display cycle by which time the fruit treated by either vapour-heat or fumigation are discarded due to a loss of firmness. There is no significant improvement by treating at the higher or 75 krad minimum absorbed dose. More carefully controlled studies will be required before the variable effects of treatment, storage, shipping and display conditions can be fully interpreted.

17. CONCLUSIONS AND RECOMMENDATIONS

Present processes impose significant delays from field harvest to delivery due to exposure-time requirements for processing steps or the batch nature of disinfestation processes. Radiation disinfestation can reduce these delays by as much as 1 day which when added to the specific beneficial effects of radiation on shelf life can extend marketing times by 2 to 5 days.

Variability in results and progressive improvements achieved by small changes in handling and storage in combination with low-dose radiation can further extend shelf life. The critical features to improve shelf life are control of environmental humidities and temperatures and reduction of surface moisture, all steps compatible with the adoption of radiation disinfestation.

Furthermore, radiation allows pre-packaging inspection reducing post-treatment losses intrinsic to pre-packaging disinfestation. Treatment of the finished package reduces chances of re-infection providing a further assurance of reliability of the quarantine treatment.

PL-422/15

BENEFIT-COST ANALYSIS FOR EXPORT PA PAYA DISINFESTED BY IONI ZING R AD I AT ION *

A . M . DOLLAR, M. HANAOKA Hawaiian Food Irradiation Program,Department of Agriculture,State of Hawaii,Honolulu, Hawaii

G . A . McCLISHState Department of Education,Honolulu, Hawaii,United States of Am erica

Abstract

B E N E FIT -C O ST A N A L Y S IS FOR EXPORT P A P A Y A DISINFESTED BY IO N IZ IN G R A D IA T IO N .

Papaya m arketing o ffers a unique opportunity fo r ea r ly c o m m erc ia liz a t io n o f an irrad ia tion trea tm en t,

s ince a d isin festation o f this product is requ ired fo r export. T h e production and m arketing o f H aw a iian papayas

is described in d e ta il. A t present rad ia tion d isin festation appears the most lo g ic a l a lte rn a tive to the present

d isin festation processes, and the b en e fit-co s t analysis shows net ben efits fo r this process.

1. INTRODUCTION

The export market for papaya (Carica papaya, L. Var. solo) has an annual growth of more than 10 per cent with a volume of nearly 8 X 106 lb in 1968 (See Tables I and II). The local fresh market for papaya remains fairly steady at nearly 11 X 106 lb.

Papaya marketing offers a unique opportunity for early commercialization of radiation since a disinfestation treatment is required for entry into mainland United States or Japan markets. The U.S. Department of Agriculture - Pest Quarantine Service provisionally accepts radiation treatment at a minimum absorbed dose of 21 krad as a satisfactory treatment for the control of three species of fruit flies. The U.S. Food and Drug Administration approval of the process remains as a barrier.

There are two acceptable batch treatments which presently meet quarantine requirements, fumigation with ethylene dibromide or vapour-heat treatment. The fumigation process leaves a residue of bromine and its effectiveness is open to some question when the fruit are harvested riper than the l/4-colour stage. Vapour-heat treatment affects the flavour and texture of the papaya and is used for a limited proportion (less than 20 per cent) of the fruit currently exported.

* Supported by the D iv is ion o f Isotopes D eve lop m en t, U .S . A to m ic Energy Com m ission,

C on tract N o . A T (2 6 - 1 ) -4 7 3 .

1 5 7

TABLE

I.

PAPAYA

PRODUCTIO

N

AND

MA

RK

ET

ING


Per

-ca

plt

a

con

sum

pti

on

Wes

t C

oa

std

(l

b)

0.3

0.3

0.5

1.3

Per

-ca

pit

a

con

sum

pti

on

,

loc

alk

(lb

)

18

.5

16

.1

13

.1

19

.6

14

.0

13

.9

16

.4

15

.4

15

.0

16 16

Pe

rcen

tag

e

pro

du

ctio

n

exp

ort

ed

17

.3

22

.5

22

.6

17

.8

25

.4

28

.4

31

.6

33

.4

31

.3

56 79

Yie

ld

per

bear

ing

acr

e

(100

0 lb

)

27

.7

26

.3

30

.7

33

.2

24

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57

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54

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75

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79

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60

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76

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83

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85

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28

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use

s

(100

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11

21

8

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15

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85

29

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97

59

99

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12

16

9

12

20

9

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5

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(100

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96

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36

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39

53

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72

24

78

76

60

32

16

57

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(100

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76

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80

22

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19

61

19

62

19

63

19

64

19

65

19

66

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67

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68

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69

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75

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1985

c

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PL-422/15 1 5 9

TABLE П. ANALYSES OF GROWTH OF THE PAPAYA INDUSTRY, 1961 TO 1969

Least-squares fit of the growth equations

Param eter (Q ) EquationA

Q -in te rc ep t

В

S lope

r

Corr. c o e f f .

SE o f

es tim a te

T o ta l production

(1000 lb )

Q = A B X

14840 1.049 0 .6 3 3 * 1 .188

A cres bearing Q = A B X 403 .1 1 .063 0 .7 6 4 * 1 .163

Outshipments

(1000 lb ) О ii > CO X 2513 1 .134 0 .9 3 3 * " 1 .134

Production

(1000 lb )/ a c re Q = A + Bx 4235 22 .00 0 .794 s** 2549 .0

Q = quantity x = t im e in years

S ign ifican t d iffe ren c e : * p 0 .05 = 0 .632 ; * * p 0 .01 = 0 .765

Y ie ld per bearing acre: m ean 28 .29 _+ 1 .13 (1000 lb)

L o ca l consum ption: 15 .9 + 0 .08 lb/year/person

L o ca l and other uses: 10 827 000 + 491000 lb

TABLE III. MONTHLY PAPAYA PRODUCTION AS PERCENTAGE OF ANNUAL PRODUCTION a

Month OutshipmentsT o ta l

production

January 7 .2 7 .2

February 6 .8 7 .3

M arch 7 .1 8 .0

A p r il 9 .1 8 .6

M ay 9 .0 10 .0

June 10 .5 10 .0

July 1 1 .0 8 .2

August 7 .6 8 .0

Septem ber 6 .7 7 .7

October 8 .4 8 .9

N ovem ber 8 .0 8 .1

D ecem b er 8 .6 8 .0

100 .0 100 .0

a Based on a ve rage from 1964 to 1967»

1 6 0 DOLLAR e t a l.

Papaya production is concentrated in the Puna District of the Island County of Hawaii. Nearly 80 per cent of the exported fruit is assembled and treated at one plant in Hilo. The production cycle is not seasonal but continues throughout the year favouring full utilization of a radiation processing plant (see Table III).

Annual per-capita consumption in the local market is 15 to 16 lb and consumption in the West Coast market area (18 million persons) is about 1/3 lb. New market areas such as the Midwest, East Coast and Japan afford outstanding opportunities for expansion into population target areas of more than 70-million persons.

Most of the papayas now exported are moved by air freight out of Hilo. Future expansion of markets will require improvements in surface freight services. Controlled-atmosphere (Oxytrol and Techtrol) refrigerated containers show promise and afford opportunities for improved in-transit protection. Increased use of surface transport is required for the economical movement of perishables to more distant markets such as Japan and the East Coast. These container systems when combined with the shelf-life improvement achieved by disinfestation with ionizing radiation show promise for expanded marketing of papayas.

2. PRODUCT VALUE

The product value to growers in 1968 to 1970 for export markets alone is in the range $ 0.11 to 0.14/lb., or nearly $ 1 X 106 farm income. The average wholesale price in Los Angeles for fresh market is in the range $2.50 to $4. 50 for a 10-lb carton. The retail price is in the range $0. 33/lb for promotional sales to $ 0.69/lb during periods of short supply. At present the product is marketed as a gourmet item, but improved flow of supplies could expand the market potential at an average annual retail market price of $0.35/lb in West Coast markets.

3. ELASTICITY OF DEMAND COEFFICIENT

The farm price elasticity demand coefficient was estimated on the basis of monthly intervals during 1968 to 1969. This period represents the introduction and expansion of the direct Hilo-mainland air-freight service. For â 1 per cent change in quantity of papayas available for fresh local and export market (1200 to 2500 X 103 lb per month) there is an associated 0.49 ± 0.08 (N = 18) per cent change in price in the opposite direction.

The regression relating farm price (P) in cents per lb to quantity (Q) in 1000 lb for monthly data during the 24 months from January 1968 to December 1969 shows

P = 18.80 - 0.0039 Q r = 0.688 (significant p 0 .01)

Spielxnann1 in his analyses of the West Coast markets found retail papaya price sensitivity is likely to be low as long as the product is a novelty.

1 SP IELM AN N , H . , D em and analysis and m arket deve lopm en t for fresh and p o ten tia lly g a m m a-irrad ia ted

papaya on U .S . m ain land markets, A g r ie . Econom ics Bull. 28, H aw a ii A g r ie . E x p .S ta ., U n iv . o f H aw a ii,

Honolu lu (1968 ).

P L -4 22 /15 161

Furthermore, papaya demand is more sensitive to quantity on display, location of display in relation to pineapple, bananas and white grapefruit and product condition than to price.

4. SHELF LIFE AND SPOILAGE LOSSES

The present shelf life (combined distribution and display life) of fresh papayas harvested at colour turning to 1/4-colour is 14 to 16 days without refrigeration. A major cause of loss of market quality is decay at the stem- end and on side surfaces. Treatment by first immersion in hot water (118°F) for 20 minutes and second cooling with running tap water for 20 minutes provides some control of decay.

All present disinfestation processes are of a batch type requiring an overnight holding step. The ethylene dibromide (1/2 lb per 1000ft3) fumigation step requires 2 j hours and immediately precedes packing operations. The fruit are inspected following treatment and before packing and the rejects range from 10 to 20 per cent of the treated fruit. Vapour heat used as a disinfestation treatment introduces an additional 8 per cent loss in weight due to moisture removal. Increased costs due to post-treatment quantity losses would be savings gained by adoption of radiation processing.

Direct savings at wholesale and retail level due to shelf-life improvement while less well identified are probably in the 5 per cent range. Some real quality advantages and savings would accrue to the consumer because of the greater firmness and extension of shelf life after ripening.

5. ALTERNATIVE PRESERVATION TECHNIQUES

Irradiated papayas would be shipped and handled under the same conditions as those disinfested by either of the two presently approved processes. At the present time virtually all papayas are moved by air to mainland destinations.

Growing production and the new market development in Japan and elsewhere create a need for improved shelf life for surface shipment in controlled- atmosphere refrigerated containers.

Marketing requirements are encouraging harvesting fruit at a more advanced tree-ripe stage. Presently approved quarantine treatments are acceptable for fruit harvested at colour turning to 1/4-colour stages, but these treatments have a questionable effectiveness for fruit harvested at more advanced stages of colour development. Disinfestation by radiation treatment is equally effective for fruit harvested at all stages of ripeness. Furthermore, fruit treated at more advanced colour stages respond favourably by remaining firm longer. Riper fruit can retain their desirable qualities when held at temperatures below 50°F, which presently is the recommended minimum holding temperature. This change in harvest standard would create new opportunities for surface shipment at lower temperatures.

At present, radiation disinfestation appears the most logical alternative to the present disinfestation processes. Furthermore, radiation significantly reduces the time sequence for harvest to chilling thus achieving a significant improvement in shelf life.


TABLE IV. OPERATIONAL DATA USED FOR CALCULATION OF INVESTMENT COSTS

A. THROUGHPUT

Assumptions;

Downtime = 10 per cent

1985 volume 60 per cent of total or 30 000 000 Ib/yr

6 hours/day, 6 days/week = 144 hours/month

Operating level (90 per cent of capacity, downtime 10 per cent or 0.9 * 0.9) = 0.81

30 000 0001985 Й ^ Г ш Ь о и а Д Г ° 1̂ ° ° lb/h

18 000 = 22 000 lb/h0.81

B. SOURCE COST

Assumptions:

Minimum dose 25 krad at a ratio max./min. of 1.4

(0.000085)* U W h r )* tjos?-r*d) efficiency

Source size = (0.085) ^ 0 0 )J 2 5 k r a d ) . = ш ^

Source cost at $500/kCi = $93 500

C. PLANT COST

Assumptions:

1985 source size requirements 187 kCi

Plant cost = (70 000) (187) °-43 = $654 000

(Building cost) 60 per cent = $ 3 9 4 000(Conveyor) 10 per cent = $ 65 000(Other equipment) 30 per cent = $ 1 9 5 000

6. COMMERCIAL FEASIBILITY

Benefit-cost analysis was developed on the basis of methods used by Claflin2. The analyses, as shown in Tables IV, V and VI, indicated irradiation of papaya is feasible as an investment for industry at the 15 per cent criterion rate.

2 CLAFLIN, A .B ., Benefit-cost analysis of low-dose radiation processed foods, U .S. Atomic Energy Commission, Wash. 1131 (UC 23) (1969).

PL-4 2 2 /15 163

TABLE V. DETAILS OF OPERATING COSTS OF RADIATION FACILITY

EXPENSES

Direct labour

Overhead/interest, 50 per cent of direct labour

Maintenance

Building $394 000 at \ per cent

Equipment $260 000 at 5 per cent

Operating supplies at 2 per cent of equipment

Utilities at \ per cent of equipment

Insurance

Public liability and property damage

Workmens' compensations at 3.6 per cent of payroll

Temporary disability at $41/employee-year

Fire and allied perils - building and equipment

A ll masonry - Building

Radiation equipment

Plant equipment

Total........................................

DEPRECIATION

Building and source Basis of 10 years - no salvage value

Equipment Basis of 5 years - no salvage value

7. PUBLIC BENEFIT ANALYSIS

Reduction of post-harvest costs or losses in quality are identified as savings to the consumer. Some of the real benefits are reduced posttreatment, transport and distribution losses, the costs of which directly affect the fruit available to the consumer. Additional assumptions relate to the distribution of riper fruit with improved organoleptic values which would be apparent to the consumer. Since there is very little expectation of significant commercial profitability above the 15 per cent criterion return after taxes, the primary savings to the consumer would be in the combination of reduced distribution losses and improved quantity and quality of supplies.

The public benefit-cost analysis is discounted to present value with rates of 10 per cent and 7. 5 per cent. The analysis represents the years 1970 to 1985 with research and development costs accrued from 1970 to 1975 or 1967 to 1975 with public benefits accruing for the same years (1975 to 1985) represented by the commercial feasibility analysis.

$ 42 500

21250

1970

13 000

5200

1300

300

1550

123

645

241

121

$ 88200

TABLE

VI.

COM

MERCIA

L

BENEFIT

-COST

ANALYSIS

(tho

usan

ds

of dollars

)

164 DOLLAR e t a l.

TABLE

VII.

DIS

COUNTED

CASH

FL

OW

- PUBLI

C

BENEFIT

-COST

ANALYSIS

(tho

usan

ds

of dollars

)P L -4 2 2 /15 165

Î .§

<N OJ N CO

Д О с© o)

8“-■3 S. a a« § a > g 2 ^ , S á

t - СО 05

S ОТ 05


Research and Development (R and D) Investments are the estimated dollar costs for the U.S. Atomic Energy Commission and State of Hawaii to develop radiation processing of the product through the U.S. Food and Drug Administration clearance. Investments prior to 1970 are adjusted to the 1970 dollar value for the comparisons of benefits.

Reduced loss and lower price estimates are the saving in dollars accruing to the consumer as a result of lower prices resulting from improved availability and lowered distribution costs. Assumption is that delivery to destinations other than the West Coast will employ refrigerated containers and surface transport.

Derived benefit is the portion of the taxable income as quantified in the commercial feasibility analysis which could be passed along as reduced consumer costs. The basis for these calculations is that 25 per cent of the taxable income will reduce costs especially during the months when high prices prevail.

Total public benefit is the estimated government expenditure of $508000 for 1970 to 1975 to develop radiation disinfestation for papaya, which is increased to $ 1 574 000 when 1966 to 1970 investment is included.

The benefit-cost analyses at both 7. 5 (see Table VII) and 10 per cent show net benefits. Two approaches were considered separately; in one, only investments from 1970 were included and in the other, all prior expenditures for the Hawaii Development Irradiator were included. There is a significant net public benefit from state and public expenditures for papaya, as shown in Table VIII.

TABLE VIII. PUBLIC BENEFIT/COST ANALYSIS

PeriodDiscount rate

(per cent)Net benefit ($ x 103)

Benefit-costratio

1970 to 1985 7.5 3143 6.19

10.0 2075 4.15

1966 to 1985 7.5 2077 1.32

10.0 1049 0.69

SUMMARIES, CONCLUSIONS, CONSIDERATIONS AND RECOMMENDATIONS OF THE PANEL

1. INTRODUCTION

Fruits and vegetables account for approximately one fourth of the total food production in the world. Plant pests cause considerable damage to both growing and stored produce. It is generally agreed that the economic value of these losses amounts to at least 30% of the value of the total production. Most countries spend considerable amounts of money to control insect pests, which would severely limit agricultural production if allowed to increase without restriction. The exchange of produce in international trade increases the risk of transferring a pest from one country to another and, therefore, most governments have introduced plant quarantine laws defining the conditions under which produce may be imported. Plant quarantine laws and regulations provide the authority and machinery for effective enforcement of the ban against entry of foreign pests and plant material which may harbour pests. These regulations automatically restrict international trade and are particularly important when considering developing export markets for tropical fruits.

It is generally agreed that alternative methods to the present conventional techniques for disinfestation should be developed. Conventional methods have limitations imposed by the difficulty of ensuring uniform application, damage caused during treatment and the health hazards arising from chemical residues.

The method of disinfestation of food commodities by radiation offers some unique advantages, such as the uniformity of treatment in sealed containers. For some fruits, additional benefits may be obtained by delaying the ripening processes, which improves the quality of the product for the consumer.

For this reason, a Panel was convened in Hawaii, United States of America, from 7 to 11 December 1970 to collate existing knowledge of radiation technique and to define future activities for overcoming existing quarantine barriers in the international fruit trade by this method.

After having studied and discussed the technical papers presented by the panel members as well as the specific questions raised by the Secretariat, the Panel came to the following conclusions.

2. ENTOMOLOGICAL ASPECTS OF IRRADIATION AS A QUARANTINE TREATMENT

The Panel heard reports that quarantine regulations restricted the movement of fruits subject to infestation of insects, such as fruit flies and mango weevil. In the instance of tropical and subtropical fruit flies, only eggs and larvae are of quarantine importance. Generally, pupae and adults would not be present on or in the fruit at the time of treatment. Adequacy of various types of quarantine treatments would be dependent on the response of both pests and host to treatment.

The magnitude and complexity of insect quarantine problems associated with the international fruit trade make the promulgation of simple rules

167

168 SUMMARIES, CON CLU SIO N S, CON SIDERATION S A N D RECOM M ENDATIONS

a practical impossibility. The great variety of pests in addition to fruit flies, their uneven distribution around the world, the many forms in which they appear and the many different plants attacked by the different pests make it necessary to conduct extensive research on a wide variety of specific problems to meet specific situations.

Present quarantine regulations require that all living stages of pest species in fruits must be killed. Chemical fumigation, using ethylene dibromide or methyl bromide and/or physical treatments using vapour heat or low-temperature storage have rather narrow margins of safety between the doses required to destroy insect pests and those that will cause injury to the treated produce. Furthermore, use of some fumigants is limited by the composition of the fruit, as well as the packing material, and residues that might remain in the fruit.

The Panel heard evidence that gamma irradiation from 60Co sources would be a suitable method for disinfestation of fruit infested with three species of fruit flies found in Hawaii. There is evidence in the literature that gamma irradiation shows similar promise for fruit flies found in Australia and Mexico. Research from Hawaii has demonstrated that an absorbed dose of 25 krad applied to eggs or larvae will prevent emergence of adult insects. Exposure of immature insects to gamma irradiation does not result in immediate death. Quarantine officials should be aware that living insect larvae that may be found in irradiated fruit will not mature. In the event that living, immature, insects are found in such treated commodities, inspectors may want to keep them alive in order to observe at first hand that they are unable to complete their development. Current practice would be for the inspectors to preserve the specimens for identification. However, at present, there is no method whereby irradiated immature specimens may be distinguished from immature stages not exposed to irradiation.

Data were presented to show that in evaluating the potential effectiveness of irradiation as a quarantine treatment for insects, consideration must be given to the conditions under which the host material will be irradiated. Preliminary research in Hawaii, using a laboratory-scale irradiator demonstrated the feasibility of gamma irradiation as a quarantine treatment. However, use of a quasi-commercial-size irradiator that could handle fruit packaged for commercial shipment was necessary to determine the variation of the absorbed dose within the package and determine the minimum dose necessary for a quarantine treatment. The effectiveness of the dose absorbed by the insect could be influenced by a number of factors such as the presence of oxygen, carbon dioxide or water, the chemical content of the host fruit and the density of the container in which irradiation took place. The effect of these factors on the treatment must be considered by researchers and quarantine authorities.

The minimum dose level considered adequate for quarantine treatment of fruit subject to infestation by fruit flies would be between 21 and 25 krad or less using current treatment procedures. A lower dose would permit some adults to emerge; however, there is evidence that such adults would not be capable of reproducing.

Extensive research is necessary to develop entomological data required for the approval of a quarantine treatment. For fruit flies, where large- scale tests can be conducted, a security of 99. 9968% mortality can be used as a basis for developing a quarantine treatment. However, with other species, research to develop such data may not be feasible.

SUMMARIES, CON CLU SO IN S. CON SID ERATION S AN D RECOM M ENDATIONS 169

The Panel concludes that gamma irradiation is an effective quarantine treatment for papayas infested with the three species of fruit flies found in Hawaii. There is considerable evidence that such a treatment will prove effective for other species of fruit flies infesting tropical and subtropical fruit, as well as mango weevil.

2.1. Considerations

1. Research workers involved in irradiation studies should report experimental results in detail, providing information on the number of replications of treatments, number of specimens per replicate, stage of development (instar per stadium), maturity of fruit, etc.2. Research should be conducted on samples of sufficient size to allow statistical analysis of the data and to permit an estimate of the probability of insect survival. Sequential sampling techniques should be developed for estimating the dose required in developing and evaluating effectiveness of quarantine treatments.3. The effectiveness of irradiation as a quarantine treatment for immature insect stages should first be determined by exposing naked eggs and larvae in air, water or other media, to different doses in order to obtain a preliminary dose versus mortality curve. End points to be considered would include pupation of larvae and emergence of adults.4. The above studies should be followed by replicated treatments of fruits using sequential sampling procedures in order to determine minimum lethal doses. The fruits would normally have to be artificially infested in order to obtain populations of sufficient size. The criterion of effectiveness would beto prevent introduction and establishment of insect pests. However, research should be conducted to determine if sub-lethal doses would induce sterility or otherwise prevent reproduction of any adults that might emerge.5. Since immature insects present in irradiated fruits may survive until the next metamorphosis, consumer acceptance of an occasional fruit containing a fruit fly larvae should be determined. The outcome may necessitate initiation of an information campaign in order to secure consumer acceptance.

3. BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF IRRADIATION DISINFESTATION

The Panel heard impressive evidence that banana, guava, longan, lychee, mango, papaya, pineapple, rambutan, tomato and sapodilla fruits generally tolerate doses of gamma radiation in excess of the minimum required to meet quarantine disinfestation requirements for most tropical and subtropical fruit flies. Additionally, several of these fruits show a slightly longer shelf life at recommended disinfestation doses. Thus, it appears that full development and legal approval of irradiation for disinfestation holds promises for increasing the export sale of these species and expanding their domestic availability. Implementation of irradiation disinfestation could contribute significantly to the economic and nutritional well-being of the nations involved.

The evidence currently available indicates that few fruits can tolerate radiation doses high enough to effectively control decay. However, with some of the tropical species, disinfestation doses delay rot development

170 SUMMARIES, CON CLU SIO N S, CON SIDERATION S A N D RECOM M ENDATIONS

significantly, apparently, by retarding the onset of ripening. While the mechanism of inhibition of ripening is not understood, it seems probable that irradiation reduces the sensitivity of the fruit to the ripening action of ethylene.

There is emerging evidence that tropical fruits may be considerably more responsive to the inhibitory action of irradiation on ripening than are temperate-zone fruits. It should be noted that these species are also more susceptible to chilling stress than are fruits indigenous to cooler, more variable climates, indicating fundamental biochemical differences in the fruits from the two regions. This phenomenon should be explored and exploited with respect to irradiation and its application for insect disinfestation.

Current evidence indicates that inhibition of ripening by irradiation depends upon treatment prior to the onset of the first biochemical and physiological steps in the ripening process. Thus, for uniform results in experimental work, and more critically, in later commercial practice, precise indices of physiological state - degree of ripening - should be developed for each fruit wherever practicable. For practical application the indices should be inexpensive, rapid and reliable. Some processes involved in the ripening process that might prove valuable are: ratio ofgreen to yellow colour, flesh firmness, percentage soluble (or total) solids and titratable acids in the juice of the fruit. Since environmental and cultural conditions may have opposite effects on these indices, high-temperature effects on flesh firmness and percentage soluble solids for example, dual indices should be considered. In climacteric fruits greater reliability can be achieved by relating the suggested indices to the preclimacteric stage.

At disinfestation doses irradiation has little direct effect on the chemical constituents of the fruits reviewed before the Panel. However, some published data are confusing because of the lack of uniformity in the way results are calculated. For example, ascorbic acid analyses were most often expressed on a fresh-weight basis, but the investigators did not consider the impact of harvest quality or dehydration of the fruit. While the errors involved are not great enough to invalidate the conclusion that disinfestation doses do not significantly reduce the amount of the vitamin, they could be objectionable to health authorities asked to approve irradiated fruits for human consumption.

3.1. Considerations

1. Results of chemical analysis should be expressed on both a fresh- and dry-weight basis. Doses should be expressed in rad and each treatment should show maximum and minimum absorbed doses within the product or package.2. Data on all experiments should show the number of replicates, number of fruits (or samples) per replicate, and the statistical procedures used for analysing the results.3. Intensive efforts to develop practical indices of physiological state for tropical fruits should be made in order to assure reproducible results.These indices should be related to the preclimacteric stage where feasible.4. Actual test shipments should be conducted before recommendations are presented for approval of the commercialization of radiation.

SUMMARIES, CON CLU SIO N S, CON SID ERATION S A N D RECOM M ENDATIONS 171

4. APPLIED ASPECTS OF RADIATION DISINFESTATION

The Panel heard reports on pilot-plant-scale costs and efficiencies of pilot-plant-scale processing. Radiation disinfestation of papayas and mangoes would be economically feasible once the treatment is cleared by health authorities. Processing costs at disinfestation doses are less than US$20 per ton when sufficient quantities of the product are available. Papayas, which are harvested the whole year round, offer a significant opportunity for early commercialization in Hawaii. Post-treatment losses increase the costs of presently accepted physical and chemical quarantine treatments favouring the economic opportunities for radiation disinfestation.

Radiation disinfestation has a significant and specific place since the biological effectiveness of the treatment is dependent solely on the dose absorbed by the pest and independent of product, package composition or configuration. Biological effectiveness, once the required dose is established, is relatively independent of environmental factors, while other treatment methods are subject to a variety of constraints and generally must be applied at the point of final assembly before packaging.

Disinfestation by radiation affords a significant advance over chemical or other physical methods for control of insect pests because;

1. The product can be pre-packaged at any desirable time or place before assembly and treatment. No special containers or pre-treatment holding conditions are necessary.2. The physical effects of package composition, shape and density arenot obstacles to successful disinfestation treatment. Barrier films frequently used in export packaging limit penetration and/or dissipation of volatile chemicals preventing packaging before treatment.3. No special post-treatment handling delays are necessary as in the case of chemical fumigants.4. A treatment dose may be chosen which controls most pests that may be present without adversely affecting the product.

Chemical disinfestation results in significant concentrations of residues requiring extensive specific studies to determine the tolerance limits of biological safety, often complicated by difficulties in applying suitable monitoring methods. There are a limited number of fumigants available which have been approved by health authorities and all leave chemical residues whose tolerance limits vary.

Although the primary concern is disinfestation of tropical fruits by radiation, the Panel expressed considerable concern at the great risk associated with the transportation of personal effects. While application of radiation to this form of international commerce may be desirable, it is not deemed feasible at this time. With the advent of new pressures on the movement of personal effects, especially the use of X-rays for examining objects in transported packages, the use of other forms of ionizing radiation can become more acceptable. Continuing vigilance by the International Atomic Energy Agency to this application of radiation in controlling the movement of pests is essential.

The Panel discussion emphasized certain steps which are required before any quarantine action is taken:

172 SUMMARIES, CON CLU SIO N S. CON SIDERATION S AN D RECOM M ENDATIONS

1. Identify the origins of products in relation to known pests.2. Biological determinations of pest risk. These evaluations include estimates or extent of damage by the pest or related species in the country of origin and anticipated economic impact of introduction in the countryof destination.3. Evaluate effectiveness of alternative measures for control, should a hazard be deemed to exist, by means of:

(a) cultivation and harvest practices;(b) inspection and culling;(c) physical treatments as for thermal methods;(d) chemical treatments;(e) pest eradication.

4. Determination of the biological effectiveness of treatment. The efficiency of treatment relates to the elimination of the possible introductions of pests either in the reproductive stage or prevention of development toa reproductive life stage.

The Panel has listed certain essential steps establishing economic feasibility:

1. Identification of principal insect pests in relation to present and newly developing production areas and to probable markets.2. Determining minimum absorbed doses required to assure maximum effective protection at a minimum cost and interference to ready movement of products to marketing areas.3. Identifying and assessing biological hazards of pest movement from point of origin, in transit and at point of destination.4. Identifying combinations of radiation and other treatment methods, packaging systems and environmental control measures which optimize shelf life, especially systems which minimize costs and need for refrigeration.5. Advancing from research to developmental studies, once pest risks are assessed, product tolerances are known, and economic studies of both production and marketing destinations are favourable.6. Emphasize methods and absorbed dose ranges of radiation which maximize efficiency of plant operations while minimizing risks of pest survival and product injury.

5. RECOMMENDATIONS

1. The Panel urges FAO and IAEA to encourage international co-operation in the development of uniform pest quarantine requirements wherever possible. Moreover, the acceptance by pest quarantine officials of the concept of the accumulative reduction of risk of pest introductions through the combination of cultivation, processing, and treatment practices, and realistic evaluation of the total risk of introduction can reduce the rigorousness of required disinfestation treatments.2. A manual of dosimetry procedures should be prepared and distributed to researchers involved in disinfestation research.3. The Panel urges FAO and IAEA to promote wholesomeness tests for fruits, such as mangoes and citrus, which show economic promise for dis-

SUMMARIES, CON CLU SIO N S, CON SID ERATION S A N D RECOM M EN DATIONS 173

infestation by ionizing radiation, where no information on wholesomeness is available.4. The FAO and IAEA should continue urging health or other regulatory authorities to accept radiation as a treatment rather than classifying it as a food additive.5. The Panel urges FAO and IAEA to foster pilot-plant studies to determine the feasibility of disinfestation treatment by ionizing radiation wheneverand wherever appropriate.6. FAO and other international Agencies should co-operate to produce a manual describing the methods used to evaluate the effectiveness of disinfestation techniques.

LIST OF PANEL MEMBERS

A.K. BURDITT, Jr. U.S. Department of Agriculture,Agricultural Research Service, Entomology Research Division, Belts ville, Maryland 20705, United States of America

D. L. CHAMBERS U.S. Department of Agriculture,Agricultural Research Service, Entomology Research Division, Hawaiian Fruit Flies Investigations, P.O. Box 2280,Honolulu, Hawaii 96 804,United States of America

I.D. CLARKE* Department of Biochemistry,University of Ibadan,Ibadan,Nigeria

H.C. COX U.S. Department of Agriculture,Agricultural Research Service, Entomology Research Division, Beltsville, Maryland 20705, United 'States of America

A.M. DOLLAR Department of Agriculture,14 28 So. King Street,P.O. Box 5425,Honolulu, Hawaii 96814, United States of America

E.E. FOWLER Division of Isotopes Development,U.S. Atomic Energy Commission, Washington, D.C. 20545,United States of America

E. W. JACKSON U.S. Department of Agriculture,Agricultural Research Service, Plant Quarantine Division,P.O. Box 340,Honolulu, Hawaii 96809,United States of America

* International Atomic Energy Agency expert.

175

176 LIST OF PANEL MEMBERS

Hung-yen KAO Agricultural Chemistry Research Laboratory,

Union Industrial Research Institute, Ministry of Economic Affairs,P.O. Box 100,Hsinchu, Taiwan,Republic of China

P. LOAHARANU Biological Science Division,Office of Atomic Energy for Peace, Srirubsook Road,Bangkhen, Bangkok-9,Thailand

E.C. MAXIE (Vice-Chairman)

University of California,College of Agriculture, Agricultural Experiment Station, Department of Pomology,Davis, California 95616,United States of America

J.H. MOY University of Hawaii,College of Tropical Agriculture, Department of Food Science and

Technology,1920 Edmondson Road,Honolulu, Hawaii 96822,United States of America

K. OHINATA United States Department of Agriculture, Agricultural Research Service, Entomology Research Division,Hawaiian Fruit Flies Investigations,P.O. Box 2280,Honolulu, Hawaii 96 804,United States of America

K.K. OTAGAKI (Chairman)

Board of Agriculture, Department of Agriculture, 1428 So. King Street,P.O. Box 5425,Honolulu, Hawaii 96 814, United States of America

I. S. PABLO Philippines Women's University, Taft Avenue,Manila,The Philippines

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A. SREENIVASAN

Observer

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Editor

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Biochemistry and Food Technology Division,

Bhabha Atomic Research Centre, Trombay, Bombay 85,India

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Joint FAO/IAEA Division of Atomic Energy in Food and Agriculture,

IAEA, Vienna

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EMBE i/IAEA D RICULTURE

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