THE SHELF-LIFE OF MINIMALLY PROCESSED FRESH CUT MELONS

Z. AYHAN and G.W. CHISM

Department of Food Science and Technology The Ohio State University

Columbus, OH 43210

AND

E.R. RICHTER

Richter International 674 West Lane Avenue Columbus, OH 43210

Accepted for Publication January 23. 1997

ABSTRACT

Honeydew and can taloupe melons were sulface sterilized by scrubbing with a hypochlorite solution at low level (200 pprn total available chlorine) and high level (2000 pprn total available chlorine), peeled and cut into “chunks ”. Fruit pieces were dipped in a dilute hypochlorite solution @H 6) of 50 ppm total available chlorine prior to packaging under an atmosphere of 95 % N2 and 5 76 O2 and storage at 2.2C. Unwashed and water-washed samples were also prepared as controlr. Microbial counts and sensory analyses were monitored during a 20 day storage period. Microbial counts of unwashed and water-washed samples were found to be significantly @<0.05) different from the fruits which were chlorine washed initially, and during the storage time. However, increasing the free available chlorine concentration tenfold did not result in any further significaru increase in the shelj-life. Rapid decline was observed in all measured microbial and sensory qualify factors of unwashed samples during storage. Proper sanitation and production practices along with raw material selection can ensure a shelflife of 15 days for cantaloupe and honeydew pieces.

To whom correspondence should be addressed: Phone: (614)292.-7719, Fax: (614)292-0218. E- mail: chism.2@osu.edu

Journal of Food Quality 21 (1998) 29-40, All Rights Reserved. ‘Copyright 1998 by Food & Nutrition Press, Inc.. Trumbull, Connecticut. 29

30 Z. AYHAN. G.W. CHISM and E.R. RICHTER

INTRODUCTION

The demand for fresh-cut vegetables has increased in recent years because of their freshlike quality and convenience (Bolin and Huxsoll 1989). Future marketing of fresh-cut fruits in food service and retail establishments is con- sidered to be at least as large as that of vegetables (Marston 1995). However, production and distribution of safe, high quality, freshcut fruits is limited by our knowledge.

Minimally processed fresh (MPF) fruits and vegetables provide a good substrate for microbial growth (Nguyen and Carlin 1994; Marston 1995). Presence of cut surfaces and the high moisture content in packages increases potential spoilage by microorganisms. Contamination of MPF fruits and vegetables can occur at most steps of the food chain, from cultivation to processing. Contamination risk increases with a polluted environment during cultivation or poor hygienic conditions in processing (Nguyen and Carlin 1994).

Sanitation plays an important role in minimizing spoilage and maintaining quality of a product (Brackett 1992; Beuchat 1995). Washing with chlorinated water is recommended to remove soil from fresh produce (Madden 1992). If washing is done properly, microbial populations can be lowered. Effectiveness of chlorine is dependent upon the pH and amount of organic material in wash water (Dychdala 1991; Wei el al. 1985). If the pH is between 6 and 7, and the organic content is low, the antibacterial activity of chlorinated water will be adequate to destroy vegetative bacteria and fungi. Otherwise, the number of spoilage microorganisms and potential bacterial pathogens may increase due to contami- nated wash water (Marston 1995).

The objective of this study was to extend the shelf-life and maintain fresh-like quality of fresh cut melons by using a combination of two or more preservation methods, which is known as the “hurdle concept”. The “hurdles” suggested for minimally processed fruits and vegetables include low temperature storage, controlled/modified atmosphere packaging, pH control and preservatives (Wiley 1994). Multiple “hurdles” offer the best potential to extend the shelf-life of minimally processed fruits and vegetables (King and Bolin 1989). Changes in quality factors of cut melons that occurred during refrigerated storage were characterized by microbial quality analyses and sensory evaluations to determine how microbial growth contributes to spoilage of melon pieces stored at 2.2C.

MATERIALS AND METHODS

Materials

Cantaloupe and honeydew melons were obtained from commercial sources.

SHELF-LIFE 01' MINIMALLY PROCESSED FRESH CUTS 31

Whole fruits were kept at 2.2C until they were processed to be cut. Fruits were exposed to four different treatments; no washing, washing with water, and washing with two different concentrations of sodium hypochlorite (5.25% NaOCI) solutions. All utensils and equipment were sanitized with 200 ppm chlorinated water (100-200 ppm is used extensively in the food industry to sanitize food processing equipment and food containers (Foegeding 1983)).

Preparation of Cut Fruits

Five uncut melons were first dipped into water or chlorine (Dip 1) and were scrubbed with a brush. Scrubbed melons were soaked in the second (Dip 2) solution for 30 s. Melons were peeled by hand, and were cut in half, and the seeds were removed by hand. Cleaned melon halves were placed into a third solution (Dip 3) for 30 s. Melon halves were cut by hand into cubes. Fruit cubes were dipped into a fourth solution (Dip 4) for 30 s. Washed fruit cubes were placed into sterile strainers for drip drying. Cut fruits were weighed (9oog) into packs (polyethylene container sealed by a full barrier laminated nylon film), and were sealed with modified atmosphere (95% Nitrogen and 5% Oxygen). Packaged cut fruits were kept at 2.2C for 20 days in the dark.

I. Treatment: Fruits were prepared without washing treatment (control 1). 11. Treatment: Fruits were washed only with water (control 2).

The concentrations of four dip solutions of last two treatments were as follows respectively:

111. Treatment: 200 ppm, 200 ppm, 50 ppm, 50 ppm (low level chlorine

IV. Treatment: 2000 ppm, 2000 ppm, 50 ppm, 50 ppm (high level chlorine treatment).

treatment).

Preparation of Dip Solutions

Sodium hypochlorite (5.25% NaOCl) was added to tap water to provide desired concentrations (50, 200 and 2000 ppm) of chlorine in dip solutions. The pH was adjusted to 6 by adding citric acid. The temperature of the dipping solutions was approximately 10-15C. Dip solutions were changed every 5 or 6 melons.

32 2. AYHAN. G.W. CHISM and E.R. RICHTER

Methods

Free Available Chlorine (FAC) Determination. The free available chlorine concentration of the dip solution was determined by the n, n-diethyl-p- phenylene-diamine (DPD) colorimetric method (Greenbers et al. 1992). Determination of free available chlorine concentration was based on the reaction of free chlorine with DPD to form red color. Once the color was produced, the absorbance was read at 515 nm spectrophotornetically. A calibration curve (equation for the curve: y = 0.19209~ + 0.044, R2 = 0.986) was prepared from the standard potassium permanganate (KMnO,) solution (lOOg chlorine is equivalent to 89.1 g KMnO,).

Microbiological Quality Analyses. Microbial counts for aerobic plate count (APC), yeasts and molds, and total psychrotrophs were carried out, using standard methods (Speck 1984). Plate Count Agar (PCA: Difco, Detroit, MI) was used for each analysis. PCA was prepared with antibiotic solution (equal amount of chlortetracycline HCl and chloramphenicol with ethanol) for enumeration of yeasts and molds. Pour plating procedure was followed for APC and yeasts and molds, and incubation at 35C for 48 h and 20 to 22C for 5 to 7 days, respectively. Spread plating was used to enumerate psychrotrophs (incubation at 7C for 10 days). Duplicate platings were made at each dilution. Microbial counts were conducted on days 0, 10 and 20. All microbial counts were reported as CFU/g.

Sample Preparation. Samples (50 g) were weighed aseptically into a sterile stomacher bag, 450 mL of 0.1% peptone water was added to the bag and stomached (model 400 stomacher) for 2 min. Serial dilutions were prepared in 9 mL peptone water.

Sensory Analysis. Sensory analysis of color, texture and flavor was conducted immediately after the melon pieces were treated, and during refriger- ated storage (5, 10, 15 and 20 days). Evaluations were made by 3 expert panelists using a nine point hedonic scale (Brennan 1980).

Aerobic Plate Count on Melon Surfaces. Melons which were unwashed or washed only with water were considered as controls. Controls and melons, dipped in solutions containing various concentrates of chlorine, were individually placed in plastic bags and 100 mL sterile 0.1 % peptone was added. The bag was sealed and the surface of melon was rubbed by hand for 2 min to remove naturally present microorganisms. Mean populations of aerobic plate count detected on five melon surfaces for each treatment were represented as log CFU per square centimeter of external surface.

SHELF-LIFE OF MINMALLY PROCESSED FRESH CUTS 33

Surface area of melons were calculated, based on the following formula (Weast and Seleby 1967):

S = 2xa2 + nb2/e In (1 +e/l-e) e = (1 - (b/a)*)”’

a: long radius, b: small radius

Statistical Analyses. Results presented were means for three separate experiments (replications) conducted at different times with different lots of tests. Mean values were subjected to analysis of variance (3 way ANOVA), and the Tukey test (SAS) was used to determine significant differences (pi0.05) between treatments.

RESULTS AND DISCUSSIONS

A significant (pr0.05) reduction in the surface population was achieved by dipping cantaloupes in a solution containing 93 ppm free available chlorine (Table 1). Washing with water did not cause any reduction in microorganisms on the surfaces of the melons compared with the surface population of unwashed cantaloupes. Increased concentrations up to 328 ppm chlorine did not result in a microbial reduction compared with dipping cantaloupes in the 93 ppm solution. Dipping also in a solution containing 328 to 814 ppm free available chlorine did make a further decrease in the surface microbial population when compared with the unwashed and water-washed melons although there was not a difference between 328 to 814 ppm chlorine treated melons.

Total flora on unwashed whole honeydew melons were determined to be approximately log 3.26 CFU/cm2 which was less than that of cantaloupes (Table 1). Dipping whole honeydews into solutions containing different levels of free available chlorine led to further reduction in aerobic plate count as the concentra- tion of free available chlorine was increased compared with the surface population of unwashed and water-washed honeydew melons. No additional reduction occurred when the melons were dipped into chlorine solutions greater than 101 ppm. Dipping in 101 ppm chlorine solution caused approximately a 2 log microbial reduction on the surfaces of honeydew melons. The effects of increasing free available chlorine on shelf-life was similar to the effects on microbial counts. Total microbial counts were markedly reduced when concentra- tions of free chlorine were increased to 50 ppm on minimally processed green salads, but higher concentrations (up to 200 ppm) did not reduce the counts any further (Nguyen and Carlin 1994). Efficiency of decontamination depends on the product. Dipping in water containing 300 ppm free chlorine resulted in a 3 log

34 Z. AYHAN. G.W. CHISM and E.R. RICHTER

TABLE 1 . EFFECTIVENESS OF CHLORINE ON AEROBIC PLATE COUNT (APC)

ON THE SURFACES OF WHOLE CANTALOUPE AND HONEYDEW MELONS

- - Treatment F m available CI eonceotrrlloo’ Surface population’(logllCFU/cm’)

(PPm) Caotaloupe Honeydew

Unwashed 0

Dipped in water 0

Dipped in ZOO’ppm, pH 6

Dipped in SOO’ppm. pH 6

93-101

328-353

Dipped in 1000’ppm. pH 6

Dipped in 2000’ppm. pH 6

438-470

814-841

5.76a

5. I Sa

3.73b

3.09bc

2.48~

2.43~

3.26a

2.8%

2.02b

I .45b

1.40b

I .30b

.-

I Mean values in h e same column that arc not preceded by the m e lmcr indicate significant difference (pSO.05)

I Determination by DPD colonmemc method before addition of fruits. pH 6

Concentrations of total available chlorine (ppm)

reduction on lettuce but had no effect on carrots and red cabbage (Beuchat and Bracket 1990).

Populations of aerobic microorganisms (APC) on minimally processed fresh cut cantaloupes were increased in all samples as storage time increased, regardless of the treatment (Table 2). However, increases in population were much higher for unwashed samples than water and chlorine washed ones. Chlorine treatment significantly ( ~ ~ 0 . 0 5 ) reduced the initial population of the natural contaminants. Washing with water reduced the population of aerobic microorganisms initially but there was no difference between water-washed and unwashed controls after 10 days. By day 10 and 20, chlorine treated samples had lower microbial levels than nonchlorine treated samples. The microbial levels were the same for the low and the high level chlorine treatments during both initial time and the storage time. This result is consistent with the findings of Green and Stumpf (1946). and Nguyen and Carlin (1994) in that very low levels of chlorine are sufficient for bactericidal action.

Washing with water or chlorine had a significant effect on the initial

SHELF-LIFE OF MINIMALLY PROCESSED FRESH CUTS 35

population of psychrotrophs when compared with unwashed samples (Table 2 ) . During refrigerated storage, increase in total psychrotrophic count was higher for unwashed and water-washed samples than chlorine treated ones. Increasing the chlorine concentration did not show any further effect on reduction of total psychrotrophic count both at 0 day and during storage. Differences between chlorine treated samples and unwashed and water-washed samples became more apparent by days 10 and 20. Chlorine treatment was as effective in reducing initial psychrotrophic populations as it was in reducing aerobic populations. However, more increase occurred in psychrotrophic count as the storage time increased because lower refrigeration temperature would be expected to enhance the growth of psychrotrophs. Beuchat and Bracket (1990) stated that populations of psychrotrophs after 15 days at 5C generally exceeded those of mesophilic aerobic microorganisms capable of growing at 30C.

TABLE 2. THE EFFECT OF DIFFERENT TREATMENTS ON APC AND TOTAL PHYSCROTROPHIC

COUNT (TPC) OF MINIMALLY PROCESSED FRESH CUT CANTALOUPE

Treatment Mean log,^ CFU/g population during storage time'

0 dav 10 dav 20 day Odav IOdsv ZOday

Unwashed 4.8a 5.2a 6.7a 4.3a 6.Oa 7.4a

Dipped in water 2.7b 3.9ab 5.8a 1.8b 4.4a 7 . la

Dipped in low level chlorine 1.0b 2.2b 2.9b I.Ob 1.8b 3.3b

Dipped in high level chlorine 1.0b 2.0b 3.lb I.Ob 2.3b 3.8b

'Mean values (n=3) in the same column that are not followed by the same letter show significant difference (~10.05) among treatments for a given day

No differences were noted on cut cantaloupes in terms of mold count at 0 days, regardless of treatment (Table 3). By day 10, washing with water and chlorine affected mold count in contrast to unwashed samples. Effects of chlorine were most apparent after 20 days because the mold counts for the chlorine treated samples remained at the initial levels while the other samples increased in mold levels. Chlorine treatment appeared to be more effective in reducing the mold population than aerobic and total psychrotrophic organisms.

36 Z. AYHAN. G.W. CHISM and E.R. RICHTER

TABLE 3. THE EFFECT OF DIFFERENT TREATMENTS ON MOLD AND YEAST COUNTS

OF MINIMALLY PROCESSED FRESH CUT CANTALOUPES

Tre8tmenI Meno log lo CFUlg popularion during storage fime'

Mold Yeas1

Od8v 10d.v 20 dav Odav lOdrv 2Odiy

Unwashed 1.2a 2.0a 3.4a 1.8a 2.ba 3.6a

Dipped in wnier 1.01 1.2b 2.8a I .Oa I . l b 2.7ac

Dipped in low level chlorine 1.01 I.Ob I.Ob 1 .oa 1.0b 1.5bc

Dipped in high level chlorine I .Oa I .Ob I . l b I .oa I .Ob 1.0b

'Mean values (n=3) in the same column that are not followed by the same letter show significant difference (ps0.05) among treatmen6 for a given day

Initially there was no difference between the treatments in terms of reduction of yeast on cut cantaloupes (Table 3). However, chlorine treatment and washing with water caused a reduction of yeast count after 10 days when compared with unwashed samples. There waq no difference between the low and the high levels of chlorine treatments in terms of reduction of the yeast population during both initial time and the prolonged storage time.

Sensory characteristics of fresh cut cantaloupes (odor, taste, overall flavor, texture, appearance and overall acceptance) were evaluated during a 20 day storage period (Table 4). Differences between the treatments were not different throughout 15 days in terms of odor of cantaloupes, but chlorine treated samples received higher scores than the unwashed samples for odor. There were no adverse effects of chlorine on judges' preferences for all sensory characteristics. Unwashed samples were not tasted at day 20 because of off flavor formation. Chlorine treated samples maintained their quality in terms of taste better than unwashed samples, and received higher scores on days 15 and 20. For overall flavor, no difference was observed between the treatments throughout 10 days, but chlorine treated samples received higher scores than unwashed and water- washed samples for days 15 and 20. Off-flavor formation was observed for nonchlorine treated samples after 10 days. For texture, the most significant difference occurred between chlorine treated samples and nonchlorine treated samples after 10 days. After 10 days, chlorine treated samples were different

SHELF-LIFE OF MINIMALLY PROCESSED FRESH CUTS 37

TABLE 4. SENSORY CHARACTERISTICS FOR FRESH CUT CANTALOUPE EXPOSED TO

DIFFERENT TREATMENTS AND STORED UP TO 20 DAYS AT 2.2C

Mean values' from sensory scale' during storage time Treatment) Od 5d I Od 15d 20d

Sensory characteristic

Odor

- .... . -

Taste

Overall flavor

Texture

Appearance

Overall acceptability

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

7.50a 7.50a 5.83a 5.66a

6.00a 6.16a 5.33a 5.16a

5.83a 6.66a 5.50a 5.33a

6.66ab 7.00b 6.66bc 5.50ac

7.33a 7.50a 7.00a 6.83a

6.83a 7.00a 5.83a

6.50a 7.00a 7.50a 5.66a

4.16a 4.33a 4.83a 5.66a

4.66a 5.33a 5.33a 5.50a

4.83a 6.16b 6.66b 7.00b

5.33a 6.50ab 6.66b 6.66b

4.66a 6.23a 5.50a

5.83a 6.66a 6.83a 5.16a

4.50a 6.16a 5.50a 5.00a

4.66a 6.16a 5.50a 5.16a

4.83a 6.50b 6.00ab 6.00ab

5.66a 6.33ab 7.33b 7.16b

5.50a 5.16a 6.00a

3.00a 2. OOa 3.83a 2.66ab 5.17a 5.16cb 5.33a 5 .66~

2.33a 4.33a 5.83b 5.16a 5.66b 6.33a

4

2.50a 2.OOa 3.33a 2.83a 5.50b 5.50b 5.66b 5.66b

4.50a 4.00a 5.33a 5.33b 6.83b 6 . 8 3 ~ 6.83b 7 . m

5.16a 5.50a 5.66a 5.66a 7.33b 7.00b 7.16b 6.83b

3.50a 2.16a 4.50ab 3.33a 6.00b 6.16b

5.50a 5.66a 5.50a 6.00b 6.00b

' Mean values in the same column and within the same sensory characteristic which are not preceded by the same letter are significantly different (~10.05)

9 point hedonic scale: I = extremely dislike, and 9= extremely like

' The number under treatment represents I=conaol 1 (unwashed), 2= control 2 (water washed), 3= low level chlorine treatment. and 4= high level chlorine treatment

%ot tasted

38 Z. AYHAN. G.W. CHISM and E.R. RICHTER

than nonchlorine treated samples in terms of appearance. Appearance of the fruit became translucent for unwashed cut cantaloupe chunks during the prolonged storage time. The overall acceptability scores were higher for chlorine treated samples after 10 days. Unwashed or water-washed samples received lower scores ( ~ ~ 0 . 0 5 ) than the chlorine treated samples. No difference occurred between the low and the high levels of chlorine treatments for all sensory characteristics.

Microbial analyses and sensory evaluations were also done for minimally processed fresh-cut honeydcw melons. Results were similar to those for cantaloupes except that honeydew had lower counts and slightly better physical quality. Correlation existed between microbial growth and sensory parameters for unwashed and water-washed samples. Correlation between sensory quality and microbial growth varied for chlorine treated samples.

TABLE 5 . DRIP LOSS OF MINIMALLY PROCESSED FRESH CUT CANTALOUPE IN PACK (mL)

DURING REFRIGERATED STORAGE

Accumulated juice '(ml) in the packages during storage time

. 5 day 10 day ISday 20 day Treatment

-

Unwashed 32.5a 33.5a 45a 67.5a

Dipped in water 14.5b 29b 3 1.5b 37.5b

Dipped in low level chlorine 14.2b 25.3b 26b 37b

Dipped in high level chlorine 18.3b 23.3b 25.7b 34.2b

~ ~ _ _ _ ~~ ~ ~ ~ _ _ _ ~

' Mean values in the same column which are not followed by the same letter indicates

significant difference (pSO.05)

The amount of juice accumulated in the package of minimally processed fresh cut cantaloupes during the 20 day storage time is shown in Table 5. As presented, juice loss from the flesh was increased by prolonged storage time. Juice loss especially was determined to be higher in the pack containing unwashed cut melons than the other samples. Increase in loss of juice appeared to be proportional to increases in microbial count. Samples with higher microbial count also had more juice loss in packages.

SHELF-LIFE OF MINIMALLY PROCESSED FRESH CUTS 39

Unwashed and water-washed samples underwent rapid quality changes in terms of the physiological and microbial qualities when compared with chlorine treated samples even if the packaging and storage conditions were the same. Since high chlorine treated samples did not show any further changes in any quality parameter, washing with low level chlorine can be recommended for cantaloupe and honeydew melons.

Rapid changes in the quality parameters such as texture, flavor and appearance occurred when the microbial growth increased on minimally processed fresh cut cantaloupe and honeydew melons. This study revealed that effective sanitation and washing procedure by the use of proper disinfectant had a complementary effect on minimizing the microbial spoilage and maintaining the quality prior to the modified atmosphere packaging and the refrigerated storage. Safety and quality retention of fresh cuts can be maximized when temperature management is used in conjunction with proper modified atmosphere packaging (Marston 1995; Nguyen and Carlin 1994). Fresh cut cantaloupe and honeydew were not exposed to chill injury when they were stored at temperatures as low as (2.2C) 36F which can cause chill injury for some whole fruits (O’connor-Shaw ef al. 1994).

In conclusion, proper sanitation and production practices along with raw material selection can ensure a shelf life of 15 days for cantaloupe and honeydew pieces. Quality of whole fruits from the physiological point of view as well as the microbial point of view also plays a vital role in achieving this shelf-life.

ACKNOWLEDGMENTS

Some salary and research support were provided by the Ohio Agricultural Research Development Center. Fruits were provided by Freshway Fruit Company (Sidney, Ohio).

REFERENCES

BEUCHAT, L.R. 1995. Pathogenic microorganisms associated with fresh produce. J . Food Protect. 59(2), 204-216.

BEUCHAT, L.R. and BRACKETT, R.E. 1990. Survival and growth of Listeria monocytogenes on lettuce as influenced by shredding, chlorine treatment, modified atmosphere packaging and temperature. J. Food Sci. 55, 755-758.

BOLIN, H.R. and HUXSOLL, C.C. 1989. Storage stability of minimally processed fruit. J . Food Processing and Preservation 13, 281-292.

40 Z. AYHAN, G.W. CHISM and E.R. RICHTER

BRACKET, R.E. 1992. Shelf stability and safety of fresh produce as influenced by sanitation and disinfection. J. Food Protect. 55( lo), 808-814.

BRENNAN, J.G. Food Texture Measurement. 1980. In Development in Food Analysis Techniques-2, (R.D. King, ed.) pp. 1-78, Applied Science Publishers Ltd, London.

DYCHDALA, G.R. 1991. Chlorine and chlorine compounds. In Disinfection, Sterilization and Preservation, 4th Ed., ( S . S . Block, ed.) pp. 131-151, Lea & Febiger, Philadelphia.

FOEGEDING, P.M. 1983. Bacterial spore resistance to chlorine compounds. Food Technol. 37( 1 l), 100-104.

GREEN, D.E. and STUMPF, P.K. 1946. The mode of action of chlorine. J. Am. Water. Works Assoc. 38, 1301-1305.

GREENBERS, A.E., CLESCERL, L.S. and EATON, A.D., ed. 1992. Standard Methodr for the Examination of Water and Wastewater. 18th Ed. part 4000, pp. 445-447. Am. Publ. Health Assoc. Inc., Washington, D.C.

HADFIELD, W.A. 1954. Chlorine and chlorine compounds. In Antiseptics, Disinfectants, Fungicides and Chemical and Physical Sterilization, 2nd Ed. , (G.F. Reddish, ed.) pp. 558-580, Lea & Febiger, Philadelphia.

KING, A.D. and BOLIN, H.R. 1989. Physiological and microbiological storage stability of minimally processed fruits and vegetables. Food Technol. 43(2),

MADDEN, J .M. 1992. Microbial pathogens in fresh produce-the regulatory perspective. J. Food Protect. 55( lo), 821-823.

MARSTON, E.V. 1995. Freshcut fruit: maximizing quality. Cutting Edge. 9(3), 3-5.

NGUYEN-the, C. and CARLIN, F. 1994. The microbiology of minimally processed fresh fruits and vegetables. Crit. Rev. Food Sci. Nutr. 34(4),

O’CONNOR-SHAW, R.E., ROBERTS, R., FORD, A.L. and NOTTIGHAM, S.M. 1994. Shelflife of minimally processed honeydew, kiwifruit, papaya, pineapple and cantaloupe. J . Food Sci. 59, 1202-1206.

SPECK, M.L. 1984. Compendium of methods for the microbiological examina- tion of foods. 2nd Ed., pp.135-140, 636-641, Am. Publ HealthAssoc, Inc., Washington, D.C.

WEAST, R.C. and SELEBY, S.M. 1967. Handbook of Chemistry and Physics. 48th Ed., pp. A258-259. The Chemical Rubber Co., Cleveland, OH.

WEI, C.1, COOK, D.L. and KIRK, J.R. 1985. Use of chlorine compounds in the food industry. Food Technol. 39(1), 107-115.

WILEY, R.C. 1994. Preservation methods for minimally processed refrigerated fruits and vegetables. In Minimally Processed Refngerated Fruits & Vegetables, (R.C. Wiley. ed.) pp. 66-127, Chapman & Hall, New York.

132- 135.

371-401.