ANALYSIS OF VARIATION IN CONCENTRATION OF ESSENTIAL AND NON ESSENTIAL ELEMENTS IN CANNED AND FRESH...

ANALYSIS OF VARIATION IN CONCENTRATION OF ESSENTIALAND NON ESSENTIAL ELEMENTS IN CANNED

AND FRESH FOOD

UZAIRA RAFIQUE1, SUMREEN IQBAL, SAADIA FAIZ and AASIA HASHMI

Environmental Sciences ProgramFatima Jinnah Women University,

The Mall, Rawalpindi, 46000

Accepted for Publication March 27, 2008

ABSTRACT

Essential (copper, nickel and zinc) and nonessential (cadmium, lead andtin) elements were determined in canned and fresh food samples employing thetechnique of Flame Atomic Absorption Spectrophotometry. Food samples werepurchased from the shelves of local markets of Rawalpindi, Islamabad andWah Cantt, Pakistan. Canned food samples were analyzed to study the effect oftemperature, time and pH on concentration of elements. To determine themagnitude of variation in concentration of elements in canned food, elementalanalysis was performed on samples (food and medium) upon initial opening,and samples upon 4 weeks after opening. The physical observation of thecanned food samples was also made to determine the internal coating(lacquer), headspace level and pH of the medium upon opening the can. Theresult showed that concentration of elements in canned food samples wasgreater than fresh food, and it increases with increasing time and temperaturebut decreases with increasing pH. A low concentration of elements was foundrelated to fully lacquered cans, high pH of medium, low nitrate concentrationand small headspace. The concentration of elements in each sample wascompared statistically.

PRACTICAL APPLICATIONS

Food quality surveillance is a very important tool to develop a perspectiveof human health risks. The study is significant in evaluating the concentrationof different elements in the food and the effect of their toxicities. This researchhas a very significant application at the end user level as to give informationabout the benefits of the fresh food over the canned food. The food industry

1 Corresponding author. TEL: 92-51-9270050; FAX: 92-51-9271168; EMAIL: [email protected]

Journal of Food Processing and Preservation 33 (2009) 186–203.© 2009, The Author(s)Journal compilation © 2009 Wiley Periodicals, Inc.

186

mailto:[email protected]

can benefit from the study as it provides the details over the canned food aboutthe usage and storage. It also provides background knowledge about thedeadlines of storage with respect to different essential metal levels. Taking it asa precautionary measure, many of the digestive diseases and abdominal prob-lems can be avoided in masses. Industry can benefit by it to reduce theseelements to the minimum possible levels, and can search techniques todecrease the concentration of these elements. It will assist the industries todevelop procedures to conserve the food in good optimal manner for bestpossible, healthier levels. It will stress the desirability of the establishment oftolerances for metal in all foods as a public health measure. It will createawareness in Pakistan of food science and technology. It will also aid thehealth and food inspectors in improving food quality and developing strategiesto reduce the level of metal contamination in the food and to make it accordingto the WHO guidelines for food quality. This work has opened the doors toinvestigate the food quality in details with special reference to public health.

INTRODUCTION

Food consumed is a mixture of carbohydrates, fats, proteins, minerals andvitamins called nutrients that provide not only energy but also essential mol-ecules that cannot be synthesized by tissues for body maintenance and growth.Minerals (elements) occurring in the body constitute less than 0.01% of thebody mass and are termed as trace elements (Tanvir and Rakhshanda 2001).Certain trace elements (e.g., copper, zinc, nickel) are considered essential forlife, and their deficiency leads to related disorders in an otherwise well-fedindividual (Javaid et al. 1991). A micro nutrient deficiency is also termed ashidden hunger (Ayesha and Rakhshanda 2001). However, some trace metalsmay be toxic (e.g., lead, tin, cadmium) and eventually lethal. With increasingindustrialization and urbanization, more and more metals are entering into theenvironment. Metals are primarily distributed in the atmosphere, water, soiland sediments. Metals and other elements may enter the food chain at anypoint from growth and harvesting through storage and processing. However,certain food groups naturally contain and accumulate high concentrations ofthese elements (FSA 2004). The toxic effects of metals, particularly arsenic,mercury, cadmium and lead, have been broadly studied (Uchida et al. 1961;Schoerder 1965; Venugopal and Luckey 1975; Inskip and Piotrowsiki 1985;Nishihara et al. 1985; Kurieshy and D’siliva 1993; Narvaes 2002). Fresh foodsare preserved with different techniques such as canning, refrigeration, freez-ing, dehydration, freeze-drying, salting, pickling, pasteurization, fermenting,carbonating, chemical preservation, irradiation, etc., to avoid spoilage (Ahmad1993).

187ANALYSIS OF ELEMENTS IN CANNED AND FRESH FOOD

Canned foods are valuable commodities worldwide. Canning is a simpleand feasible technology for preservation of fruits and vegetables, and is asource of different metals into the food at the same time. The natural concen-tration of different elements in plant and animal tissues is low, and the maindietary source of these minerals are foods that have been in contact withmetallic cans (Greger and Baier 1981; Sherlock and Smart 1984; Rader 1991;Sumitani et al. 1993; Biego et al. 1999).

Food may be canned in glass jars or metal containers and require specialsealing equipments for canning; therefore, there is a need for regular moni-toring of toxic and essential trace elements in canned food products. Concen-tration of elements may exceed in canned foods due to the corrosion andleaching from un-lacquered or poorly lacquered cans (Fricke et al. 1979;Greger 1988). Different factors affecting the concentration of elements incanned foods are the lacquer of the can, the pH of the food, headspace,presence of nitrates, etc. In addition, it is essential to identify the interactionbetween the foodstuff and its package, particularly when it is being purchasedand consumed (Koçak et al. 2005).

The premium objective of the study is to ascertain the levels of differentelements in fresh and canned foodstuffs. For this purpose, the variation inconcentration was analyzed for essential (nickel, copper, zinc) and nonessen-tial elements (lead, cadmium, tin) in 10 canned foods and fresh food samples,each from local markets, and were determined by flame atomic absorptionspectrometry. The factors that are considered important, which enhance theleaching of elements into the canned medium, like presence or absence oflacquer, pH of food, storage conditions (time and temperature), storage ofopened cans, plant pigments and headspace level, were also studied.

EXPERIMENTAL

A food group of canned and fresh fruits, vegetables and cereals, includinglychee (L), pineapple, strawberry, corns, beans, peas, chickpeas, mushrooms,sweet potato and tomato, was purchased at random from the shelves of localmarkets of Rawalpindi, Islamabad and Wah Cantt. The canned food samplestaken were of different manufacturers (imported) except for corn and peas(local). Description of canned samples is presented in Table 1.

All glassware was soaked overnight in 10% (v/v) nitric acid, followed bywashing with 10% (v/v) hydrochloric acid, rinsed with double-distilled waterand dried before using. All reagents used were of analytical reagent grade(Merck, Germany). Standard stock solutions (1,000 mL) of nickel, copper,zinc, lead, cadmium and tin were prepared from nickel chloride (4.05 g),copper sulfate (3.93 g), zinc nitrate (4.54 g), lead nitrate (1.59 g), cadmium

188 U. RAFIQUE ET AL.

nitrate (2.74 g) and tin chloride (1.90 g), respectively. The working solutionswere freshly prepared by diluting an appropriate aliquot of the stock solutions.

To quantify the concentration of elements, each sample was preparedusing standard acid digestion procedure. Fresh and canned food samples weredried in an oven at 60–70C and were grounded to fine powder in pestle andmortar. A half gram each of dried samples was weighed into a 200-mL beakerand 10 mL of concentrated 65% nitric acid was added (Maas and Dressing1983). The beaker was covered with a watch glass and – after most of thesample had dissolved by standing overnight – heated on a hot plate to boil untilany vigorous reaction had subsided. The solution was allowed to cool, trans-ferred into a 50-mL volumetric flask and diluted to the mark with distilledwater. Five milliliters of medium of the canned samples were taken in a beakerand 10 mL concentrated 65% nitric acid was added to prepare the mediumsamples. Elements were determined by direct aspiration of the sample solutioninto the air/acetylene and NO2/acetylene flame. The blanks and calibrationstandard solutions were also analyzed in the same way as the sample solutions.

Headspace, thickness of can and pH of the medium was measured imme-diately after opening the cans. Nitrate concentration of the medium was alsodetermined by UV-Visible Spectrophotometer (UV-1601 Shimadzu, Japan) at220 nm. Each sample was analyzed separately for 4 weeks (80 samples) and attemperatures of 4, 30, 35, 40 and 45C (100 samples), to study the effect of timeand temperature. Can medium was also analyzed at pH of 3,4,5,6 and 7 (50samples) to observe the effect of pH. A Varian Model 220 atomic absorptionspectrophotometer (Varian, Australia) equipped with a deuterium backgroundcorrector was used for the quantification of essential (copper, zinc, nickel) andnonessential (lead, tin, cadmium) elements of 240 prepared samples includingfresh food, canned food and medium.

TABLE 1.ESTIMATION OF pH, HEADSPACE, INTERNAL COATING AND NITRATES

IN CANNED FOOD

Canned food Sample code Headspace (cm) Internal coating pH Nitrates (ppm)

Corns C 0.5 Lacquered 6.11 35.75Peas P 0.5 Lacquered 5.73 28.92Beans B 0.5 Partially lacquered 4.94 30.43Lychee L 0.4 Un-lacquered 3.94 22.91Chickpeas CP 0 Partially lacquered 6.24 38.24Strawberry S 0.3 Lacquered 3.5 35.10Pineapple PA 0.4 Un-lacquered 3.78 26.79Mushroom M 0.4 Un-lacquered 5.31 29.57Sweet potato SP 0.2 Lacquered 4.9 35.25Tomato T 0.3 Partially lacquered 4.52 29.05


RESULTS AND DISCUSSIONS

Results of pH, headspace, internal coating and nitrate concentration aretabulated in Table 1. It was noted that internal coating ranges from fullylacquered, partially lacquered to un-lacquered. No headspace was noted forchickpeas, whereas maximum headspace (0.5 cm) was found for corns, peasand beans. It was also observed that pH ranges from 3.5–6.24 (see Table 1). pHof the medium of all food samples was found in the acidic range with theobservation that strongly acidic pH (3.5–4.52) is of the fruits (strawberry,pineapple, lychee and tomato). The range of nitrate concentration in cannedfood samples was found between 22.19–38.24 ppm (see Table 1). A relationwas noted between concentration of nitrates, pH and internal coating. Theinternal coating is directly related to nitrate concentration but indirectly relatedto pH. The higher the nitrate contents and lower the pH, the higher theelemental concentration. This is also depicted by the presence of high amountsof elements (such as tin in sweet potato). Ability of acidic foods such astomatoes to leach elements from cans when they contain high concentration ofnitrate is well recognized (Vannoort et al. 2000).

Canned and fresh food samples were analyzed separately for thecomparative determination of elemental concentration. The result for themetal analysis in fresh food showed that the highest concentration of lead(0.2743 ppm) is present in tomato. The concentration of cadmium(0.0491 ppm), copper (0.4952 ppm) and zinc (0.9569 ppm) is found most inmushroom, whereas maximum tin (17.3895 ppm) and nickel (0.1859 ppm) isfound in strawberry (see Fig. 1). The result showed that the amounts ofcadmium, lead and tin are found to be exceeding the recommended tolerablelimits for food intake.

Canned food samples were analyzed immediately after opening the cans.The results are graphically presented in Fig. 1, showing that in the case of allthe food samples, the concentration of essential and nonessential elements isgreater in the case of canned samples than the fresh food samples.

The higher concentration of elements in the case of canned samples thanthe fresh food is perhaps due to the reason that canned food is subjected toheavy metal contamination during the canning process (Fong et al. 2006). Thehigher amount of elements in the canned samples are attributed to the canningor machining process (Nasir et al. 1990), and may be due to the corrosion ofcontainers caused by long storage of canned foods under improper conditions.

An exception was seen in the case of some food samples where theconcentration of elements (lead and cadmium) was insignificantly higher infresh samples than the canned ones (see Fig. 1b,d,f). The greater level of leadand cadmium may account from the natural levels of these elements in the soil;the accumulation of lead in the topsoil is of great ecological significance


because of its great effect on the biological activity of soil (Alloway 1995),whereas additional cadmium is added to the environment through differentprocesses. Further cadmium has been added to agricultural soils through theuse of phosphate fertilizers (WHO 1989) and certain organic fertilizers basedon manures.

a Nickel

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

C P B L CP S PA M SP T

Sample Code

Con

cent

rati

on (

ppm

)

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b Zinc

0

0.2

0.4

0.6

0.8

1

1.2

1.4

C P B L CP S PA M SP TSample Code

Con

cent

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on (

ppm

)

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c Copper

0

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Sample Code

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d Lead

0

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C P B L CP S P M SP TSample Code

Con

cent

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on (

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e Tin

0

5

10

15

20

25


Sample Code

Con

cent

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on (

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f Cadmium

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07


Sample Code

Con

cent

rati

on (

ppm

)

Fresh Canned

FIG. 1. VARIATION IN THE CONCENTRATION OF ESSENTIAL AND NONESSENTIALELEMENTS IN FRESH AND CANNED FOOD SAMPLES (a–f)

(C) corns. (P) peas. (B) beans. (L) lychee. (CP) chickpeas. (S) strawberry. (PA) pineapple.(M) mushrooms. (SP) sweet potato. (T) tomato.


The statistical analysis of the results of the canned food samples and itsmedium to study the effect of time, temperature and pH on the concentrationof essential and nonessential elements, are tabulated through Tables 2–4, andFig 2.

For essential elements, the highest mean concentration of nickel(0.340 � 0.021) and copper (1.570 � 0.338) is found in tomato, whereas zinc(1.465 � 0.310) is found in mushroom canned food samples. The same case isobserved in medium samples with concentrations of nickel (0.750 � 0.050)and copper (2.275 � 0.310) in tomato, whereas zinc has the concentrationof 1.643 � 0.088 but the amounts are a little higher than the food samples.For nonessential elements in food samples, lead (0.400 � 0.079 and0.525 � 0.079) is found to be maximum in tomato, both in medium and foodsamples, respectively. The maximum concentration of tin, 26.258 � 4.383 and33.575 � 4.216, is found in food and medium samples of lychee, respectively.The cadmium concentration is present in tomato (0.059 � 0.000) and mush-room (0.098 � 0.001) in food and medium samples, respectively. The resultsrevealed that tomato has the maximum levels of most of the elements analyzed.

It was noted that with increase in time there is an increase in the concen-tration of elements, with a highest concentration in week four or the final weekof sampling. This is perhaps because when foods are stored in cans afteropening, even when refrigerated (Greger and Baier 1981), with each removalof a portion of food from the can, a new tin-food–air interface is formed,which results in the dissolution of greater quantities of elements in the food(Capar and Boyer 1980). Medium showed relatively higher concentration ofelements as compared with food samples. The results demonstrated a betterindication on the relationship of storage time with the metal contents alsoobserved by Arwanitoyannis (1990). Among all the elements studied, tin was

TABLE 2.CONCENTRATION (IN ppm) OF ESSENTIAL AND NON ESSENTIAL ELEMENTS

IN FRESH FOOD SAMPLES

Fresh food Cadmium Lead Tin Nickel Copper Zinc

Corns 0.0193 0.1119 10.4192 0.0478 0.3257 0.4729Peas 0.0247 0.0872 11.6062 0.0567 0.366 0.2049Beans 0.0348 0.1538 9.2999 0.0414 0.4511 0.3701Lychee 0.0132 0.1631 18.0416 0.0951 0.4536 0.7809Chickpeas 0.0142 0.1165 13.8713 0.0567 0.2483 0.4172Strawberry 0.0137 0.2353 17.3895 0.1859 0.2576 0.2095Pineapple 0.0171 0.1449 16.9837 0.0933 0.276 0.4647Mushroom 0.0491 0.2219 14.6951 0.0844 0.4952 0.9569Sweet potato 0.0358 0.2504 14.9342 0.0862 0.1394 0.6992Tomato 0.0414 0.2743 13.3464 0.0966 0.4025 0.6056


TAB

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4.73

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370

9.98

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002

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573

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000

PA21

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�2.

295

1.14

818

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0.00

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165

2.08

214

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17.9

95�

1.28

70.

643

27.9

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000

26.4

70�

4.94

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474

10.6

990.

002

SP20

.195

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989

0.99

420

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720

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93�

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719

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001

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mC

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000

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000

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214

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003

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193

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417.

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000

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002

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0.00

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097

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002

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0.00

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0.05

9�

0.00

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000

293.

590

0.00

00.

187

�0.

007

0.00

356

.262

0.00

0

C,c

orns

;P,p

eas;

B,b

eans

;L,l

yche

e;C

P,ch

ickp

eas;

S,st

raw

berr

y;PA

,pin

eapp

le;M

,mus

hroo

ms;

SP,s

wee

tpot

ato;

T,to

mat

o;SD

,sta

ndar

dde

viat

ion;

SE,s

tand

ard

erro

r;df

,deg

rees

offr

eedo

m.


TAB

LE

4.(a

)E

FFE

CT

OF

TE

MPE

RA

TU

RE

VA

RIA

TIO

NO

NC

ON

CE

NT

RA

TIO

N.(

INpp

m)

OF

ESS

EN

TIA

LE

LE

ME

NT

SIN

CA

NN

ED

FOO

DA

ND

ITS

ME

DIU

M(b

)E

FFE

CT

OF

TE

MPE

RA

TU

RE

VA

RIA

TIO

NO

NC

ON

CE

NT

RA

TIO

N(I

Npp

m)

OF

NO

NE

SSE

NT

IAL

EL

EM

EN

TS

INC

AN

NE

DFO

OD

AN

DIT

SM

ED

IUM

(a)

Nic

kel

Food

Med

ium

Sam

ple

Mea

n�

SESD

Var

ianc

eSk

ewne

ssK

urto

sis

Mea

n�

SESD

Var

ianc

eSk

ewne

ssK

urto

sis

C0.

266

�0.

010

0.02

00.

009

0.84

61.

745

0.61

60�

0.01

810.

036

0.04

9-0

.579

-1.2

21P

0.30

6�

0.00

90.

017

0.01

2-0

.081

-0.8

170.

5480

�0.

0185

0.03

70.

038

0.23

6-1

.963

B0.

270

�0.

015

0.03

00.

009

0.57

70.

488

0.65

00�

0.01

640.

033

0.05

5-0

.353

-1.2

92L

0.33

0�

0.01

20.

025

0.01

40.

609

-0.1

330.

7440

�0.

0181

0.03

60.

073

0.12

30.

676

CP

0.30

4�

0.01

40.

027

0.01

2-0

.543

-0.0

030.

4780

�0.

0166

0.03

30.

029

0.60

7-1

.174

S0.

372

�0.

022

0.04

40.

017

1.16

31.

922

0.84

40�

0.01

440.

029

0.09

60.

608

-0.6

81PA

0.29

4�

0.01

50.

030

0.01

10.

147

0.15

40.

5940

�0.

0191

0.03

80.

045

0.11

6-0

.861

M0.

362

�0.

024

0.04

90.

016

-0.5

36-1

.973

0.59

40�

0.02

180.

044

0.04

5-0

.770

0.89

7SP

0.37

2�

0.01

70.

034

0.01

70.

863

1.09

20.

7600

�0.

0110

0.02

20.

078

1.36

12.

000

T0.

426

�0.

021

0.04

30.

023

-0.4

14-0

.961

0.77

80�

0.01

930.

0387

0.07

93-1

.258

0.51

4Z

inc

C1.

236

�0.

140

0.28

050.

1960

-0.2

06-2

.314

1.52

20�

0.14

160.

2832

0.28

610.

065

-1.4

50P

0.74

8�

0.02

30.

0453

0.07

220.

098

-2.6

950.

9280

�0.

1229

0.24

580.

1168

1.26

31.

644

B0.

622

�0.

022

0.04

400.

0493

1.27

00.

861

0.78

20�

0.06

300.

1261

0.07

470.

106

-1.9

47L

1.49

8�

0.05

80.

1151

0.28

42-0

.918

-1.0

351.

8560

�0.

1204

0.24

090.

4210

1.00

5-0

.449

CP

0.75

2�

0.04

30.

0866

0.06

950.

947

0.52

11.

1460

�0.

0596

0.11

930.

1625

-0.2

82-1

.457

S0.

494

�0.

051

0.10

210.

0306

1.04

20.

492

0.53

40�

0.01

860.

0372

0.03

640.

397

-1.5

78PA

0.64

6�

0.04

30.

0850

0.05

100.

600

-1.1

130.

8540

�0.

0273

0.05

460.

0938

0.21

3-2

.329

M1.

658

�0.

069

0.13

820.

3459

-0.4

86-0

.935

1.77

40�

0.05

180.

1037

0.40

75-0

.162

1.13

9SP

1.43

6�

0.11

50.

2291

0.25

18-0

.248

-2.2

841.

5380

�0.

1490

0.29

810.

2937

-0.2

91-2

.078

T1.

226

�0.

129

0.25

830.

1894

0.13

2-2

.871

1.26

60�

0.07

850.

1570

0.19

62-1

.205

0.66

8C

oppe

rC

0.85

8�

0.08

50.

1693

0.09

160.

762

0.03

81.

320

�0.

120

0.24

020.

2146

-0.7

210.

186

P0.

978

�0.

143

0.28

560.

1365

0.59

8-0

.858

1.28

2�

0.11

60.

2325

0.20

240.

374

-0.6

64B

1.00

8�

0.09

20.

1845

0.12

520.

173

-2.3

301.

408

�0.

126

0.25

280.

2439

-0.6

08-0

.492

L1.

020

�0.

108

0.21

580.

1312

0.61

9-1

.650

1.34

6�

0.08

990.

1797

0.22

120.

604

0.01

3C

P1.

218

�0.

170

0.33

980.

2064

0.11

2-2

.015

1.35

8�

0.15

00.

3002

0.23

500.

263

-0.5

10S

1.39

2�

0.16

80.

3371

0.25

37-0

.077

-1.6

311.

446

�0.

121

0.24

200.

2559

0.27

90.

500

PA1.

376

�0.

092

0.18

340.

2312

0.74

9-0

.059

1.56

0�

0.08

80.

1758

0.29

950.

567

0.75

1M

0.97

2�

0.09

50.

1898

0.11

74-0

.139

-1.4

171.

226

�0.

087

0.17

420.

1833

0.02

7-1

.301

SP0.

342

�0.

020

0.03

970.

0144

0.20

8-1

.464

0.74

0�

0.05

70.

1137

0.06

680.

267

-1.8

26T

1.66

0�

0.15

50.

3093

0.34

040.

298

-0.9

081.

738

�0.

085

0.16

920.

3755

0.03

6-0

.205


TAB

LE

4.C

ON

TIN

UE

D

(b)

Lea

d

Food

Med

ium

Sam

ple

Mea

n�

SESD

Var

ianc

eSk

ewne

ssK

urto

sis

Mea

n�

SESD

Var

ianc

eSk

ewne

ssK

urto

sis

C0.

270

�0.

034

0.06

80.

010

1.08

71.

334

0.33

0�

0.02

70.

053

0.01

30.

390

-1.2

06P

0.26

6�

0.05

90.

117

0.01

50.

473

-2.5

310.

348

�0.

033

0.06

70.

015

0.34

4-0

.883

B0.

272

�0.

031

0.06

10.

010

0.05

9-1

.433

0.30

2�

0.02

50.

050

0.01

10.

792

-1.5

66L

0.37

8�

0.03

00.

060

0.01

7-0

.058

-2.0

850.

384

�0.

026

0.05

10.

018

0.30

7-1

.544

CP

0.20

2�

0.02

80.

055

0.00

61.

111

1.43

40.

302

�0.

015

0.02

90.

011

0.84

9-0

.666

S0.

354

�0.

025

0.05

00.

015

-0.2

69-1

.151

0.38

2�

0.02

40.

048

0.01

80.

150

-1.9

37PA

0.35

4�

0.02

30.

047

0.01

50.

095

-1.4

980.

382

�0.

031

0.06

20.

018

1.09

40.

379

M0.

384

�0.

047

0.09

40.

019

-0.0

47-1

.864

0.36

2�

0.02

50.

049

0.01

60.

242

0.80

3SP

0.35

6�

0.02

40.

048

0.01

6-0

.407

-0.4

380.

410

�0.

025

0.05

10.

021

0.00

0-1

.711

T0.

422

�0.

024

0.04

90.

022

0.57

6-0

.422

0.46

4�

0.02

60.

052

0.02

7-0

.330

-1.8

62T

inC

15.8

78�

0.82

21.

6437

31.1

970.

970

-0.0

4222

.130

�1.

506

3.01

259

.785

0.29

4-2

.560

P15

.028

�0.

444

0.88

8429

.219

0.20

1-2

.764

19.7

30�

0.91

91.

838

48.5

470.

672

0.15

0B

15.4

50�

0.36

80.

7356

31.3

81-0

.407

-0.8

4321

.234

�1.

123

2.24

655

.710

0.69

8-1

.607

L25

.188

�1.

569

3.13

6977

.665

0.33

2-0

.977

34.5

28�

2.18

84.

376

145.

836

0.74

60.

245

CP

19.0

28�

1.07

12.

1427

44.5

570.

450

-0.6

4126

.018

�1.

537

3.07

583

.077

-0.0

85-2

.040

S24

.092

�1.

564

3.12

7070

.939

0.30

5-1

.278

26.8

96�

1.20

02.

401

90.5

20-0

.315

-0.9

39PA

24.3

80�

1.25

32.

5069

73.5

85-0

.226

-1.8

0629

.488

�1.

744

3.48

910

6.70

90.

079

-2.2

28M

18.9

98�

0.81

71.

6346

45.2

960.

459

-0.7

8126

.752

�1.

590

3.18

087

.804

0.41

8-0

.553

SP21

.846

�1.

215

2.43

0058

.775

0.43

4-0

.995

26.8

08�

1.67

53.

351

87.9

620.

622

-0.3

40T

25.4

54�

2.23

34.

4662

79.5

490.

291

-1.3

0030

.450

�1.

535

3.07

011

4.95

00.

445

-0.8

94C

adm

ium

C0.

0289

�0.

0002

0.00

040.

0001

-1.7

933.

447

0.02

94�

0.00

030.

0006

0.00

010.

600

-1.2

72P

0.03

67�

0.00

160.

0031

0.00

02-1

.534

2.67

10.

0382

�0.

0008

0.00

170.

0002

-0.4

94-3

.126

B0.

0671

�0.

0008

0.00

160.

0006

-0.9

270.

968

0.06

73�

0.00

070.

0014

0.00

060.

653

-0.2

35L

0.02

67�

0.00

040.

0008

0.00

01-0

.861

-1.7

060.

0271

�0.

0009

0.00

180.

0001

0.05

7-1

.194

CP

0.02

82�

0.00

060.

0012

0.00

01-0

.538

-3.1

670.

0284

�0.

0007

0.00

140.

0001

-1.6

733.

417

S0.

0275

�0.

0013

0.00

250.

0001

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14-2

.363

0.02

63�

0.00

140.

0028

0.00

01-1

.414

2.11

5PA

0.02

59�

0.00

080.

0016

0.00

010.

584

1.24

30.

0265

�0.

0006

0.00

110.

0001

0.41

0-2

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M0.

0654

�0.

0012

0.00

240.

0006

0.26

9-1

.818

0.06

66�

0.00

100.

0019

0.00

06-0

.475

-0.7

50SP

0.05

52�

0.00

130.

0026

0.00

040.

499

-1.1

200.

0570

�0.

0008

0.00

160.

0004

0.06

60.

077

T0.

0666

�0.

0013

0.00

260.

0006

-0.0

21-2

.542

0.06

77�

0.00

080.

0016

0.00

060.

109

-2.3

61

C,c

orns

;P,

peas

;B

,bea

ns;

L,l

yche

e;C

P,ch

ickp

eas;

S,st

raw

berr

y;PA

,pin

eapp

le;

M,m

ushr

oom

s;SP

,sw

eet

pota

to;

T,to

mat

o;SD

,sta

ndar

dde

viat

ion;

SE,s

tand

ard

erro

r.


found majorily in all food and medium samples. Higher levels of tin may befound in canned foods as a result of the tin coating breaking down. Theconcentration of tin in foods from lacquered cans is generally lower than theconcentration of tin in foods from un-lacquered cans (WHO 1989; WHO2001). The tin contents of foods stored in opened cans was reported to increaseover a period of time (Dickinson and Raven 1962), and two to five times more

e Tin

0

10

20

30

40

50


Sample Code

Con

cent

rati

on (

ppm

)

pH 3 pH 4 pH 5 pH 6 pH 7

a Nickel

00.20.40.60.8

11.21.41.61.8

2


Sample Code

Con

cent

rati

on (

ppm

)


b Zinc

0

0.5

1

1.5

2

2.5

3

3.5


Sample Code

Con

cent

rati

on (

ppm

)


c Copper

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


Sample Code

Con

cent

rati

on (

ppm

)


d Lead

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

C P B L CP S PA M SP TSample Code

Con

cent

rati

on (

ppm

)


f Cadmium

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09


Sample Code

Con

cent

rati

on (

ppm

)


FIG. 2. STUDY OF EFFECT OF pH VARIATION ON CONCENTRATION (ppm) OFESSENTIAL AND NONESSENTIAL ELEMENTS IN CANNED MEDIUM (a–f)

(C) corns. (P) peas. (B) beans. (L) lychee. (CP) chickpeas. (S) strawberry. (PA) pineapple.(M) mushrooms. (SP) sweet potato. (T) tomato.


tin was found in canned food that had been open for 48 h (Iwamoto et al.1970). Thus, the elemental content of canned foods was affected by the lengthof storage. The tin in canned food is likely to be in the form of inorganic tinsalts (Sherlock and Smart 1984; Marro 1996; Vannoort et al. 2000). Bigelow,and Adam and Horner showed that tin concentration in canned food increasedover periods of a few months to 2 years (Bigelow 1916; Adam and Horner1937). This was subsequently supported by other investigators that cannedfood accumulated more tin and other metals when stored for longer periods(Arwanitoyannis 1990; Cichon 1995). Capar and Boyer (1980) also found thatthe tin content of foods in opened un-lacquered cans increased by an averageof about fourfold when stored for 5 days.

A maximum of fivefold increase was noted for tin in week three and fourin lychee, strawberry food samples, respectively, whereas in medium, fourthweek showed a fivefold increase in sweet potato and mushroom. The resultshowed that there is a considerable effect of storage time after opening of canon the concentration of tin in canned food samples. There is a consensus thatthe natural concentration of tin in plant and animal tissues is low and that themain dietary source of this mineral are foods that have been in contact withmetallic tin from the tinplate of cans used to preserve them (Monier-Williams1949; Schroeder et al. 1964; Greger and Baier 1981; Sherlock and Smart1984; Rader 1991; Sumitani et al. 1993; Biego et al. 1996).

An increase in concentration is related to a number of physicochemicalcharacteristics investigated in the present study. The observed increased con-centration of tin in lychee (food and medium) may be attributed to theun-lacquered coating, which is observed during the physical examination ofthe can of the lychee showing a good agreement with the earlier studies whichsuggests that most high concentrations of tin are found in canned foods due tothe corrosion and leaching of tin from un-lacquered or poorly lacquered cans(Monier-Williams 1949; Schroeder et al. 1964; Fricke et al. 1979; Greger1988) and acidic medium.

A relation is observed between low pH and high nitrate concentration onmetals amount. Low pH speeds up the dissolution of elements through oxida-tion of uncoated sides and seals of cans (Vannoort et al. 2000). High concen-tration of tin in strawberry is perhaps related not only to high acidity ofmedium, but also to high nitrates (Sherlock and Smart 1984) and high pig-mentation (Smart and Sherlock 1989).

Other factors that may increase the concentration of tin in canned foodsare the presence of oxygen in the can, headspace and of nitrate. The presenceof oxygen and other compounds can increase the rate of dissolution of tin intocanned foods to result in unacceptably high tin concentrations within a fewmonths (Sherlock and Smart 1984), and nitrates (Davis et al. 1979, 1980)favor corrosion of the internal surface of tin cans. These factors can also


increase the rate of pitting and increase the migration of tin from un-lacqueredcans into foods (Davis et al. 1980; Sherlock and Smart 1984). The ability ofacidic foods such as tomatoes, apricots and peaches to leach tin from canswhen they contain high concentrations of nitrate is well recognized (Vannoortet al. 2000). Tomatoes sometimes have high concentrations of nitrate (Sher-lock and Smart 1984; Meah et al. 1991), thus, are susceptible to leaching ofelements into the food from the can. Presence of other elements such as nickeland lead may also come from the canning process. Contamination of lead incanned food may be attributed to two sources: the solder used in fabrication ofcan seams and the lead contained in the tin coating on tinplate (Cichon 1995).Food processing and storage methods apparently add to the nickel levelsalready present in foodstuffs through leaching from nickel-containing alloys infood-processing equipment (NAS 1975).

In order to study the effect of temperature, variation in concentration ofelements was measured at below room (4C), room (30C) and above room(45C) temperatures. The range of concentration of elements in food samplesfrom minimum to maximum increases 21, 22 and 32-fold at 4C, 30C and 45C,respectively. Maximum variation was found in the case of tin. The highestincrease is found in tomato. Medium samples also showed similar behavior ascanned food samples. The variation in the concentration of elements on heattreatment can be a result of the migration of elements from can into medium,which is accelerated when the ambient temperature exceeds 40C (Nagy et al.1980). Calloway and McMullen (1966) and Biego et al. (1999), also found asignificant effect of temperature on the amount of tin in canned food.

The effect of pH on chemical extraction of elements into the medium arestudied at variable pH, from strongly acidic to neutral (pH 3–pH 7) areselected. The concentration range of pH 3, pH 5 and pH 7 is found to be0.0354–45.6982 ppm, 0.0274–41.2694 ppm and 0.0142–38.2514 ppm, re-spectively, showing an evident effect of increase of elemental concentrationwhile moving from basic to acidic pH, evident from Fig. 2a–f. The highestelemental concentration found is of tin at acidic pH. It is found with theresearch that foods with a low pH are more aggressive to tin coating thanneutral or less acid foods. Acidic foods oxidize the uncoated sides or seals ofcans (Fricke et al. 1979), and the dissolution of tin can be rapid in an acidenvironment (Davis et al. 1979). In a study, the highest concentrations ofelements were found in canned acidic foods (Vannoort et al. 2000).

The tolerable limit for cadmium, tin, lead, copper are 0.007 mg/kg,14 mg/kg, 0.025 mg/kg, 0.2 mg/kg of body weight (bw)/week and zinc as45 mg/day, respectively, which was set at the different meetings of the FAO/WHO Joint Expert Committee on Food Additives (WHO 1989; WHO 1996;WHO 2000; WHO 2001). The study showed that the canned food in many ofthe cases exceeded the tolerable limits.


The concentration of each sample was compared statistically to othersamples taken at different stages of the process. Analysis of the data wasperformed on the results using Student’s t-test with a significance level set at0.05. Statistical analysis revealed a significant (P value is less than 0.05)difference at 95% confidence level for metal contents in cans with respect totime. Most of the sample analyzed to study the effect of temperature showeda positive skewness, which is an indication of a distribution with a symmetrictail extending towards more positive values characterizing the degree of sym-metry of the distribution towards right tail which is also verified by the resultsof kurtosis.

CONCLUSION

The study of the variation in concentration of essential (nickel, copperand zinc) and nonessential (lead, tin and cadmium) elements along with theinfluencing factors in canned and fresh food samples comes to the followingconclusions: that the concentration of elements increases with increasingstorage time of opened cans and increasing temperature but decreases withincreasing pH. It was noticed in almost all food samples that the concentrationof elements was higher in the case of canned food samples as compared withthe fresh one. The result showed that the elemental contents of productspacked in completely un-lacquered and end-lacquered cans were not signifi-cantly different from each other, but were higher than the content of productspacked in fully lacquered cans.

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ANALYSIS OF VARIATION IN CONCENTRATION OF ESSENTIAL AND NON ESSENTIAL ELEMENTS IN CANNED AND FRESH...

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