7/29/2019 1-s2.0-S0969806X05002112-main

1/4

Radiation Physics and Chemistry 75 (2006) 297300

Effect of irradiation and storage on the antioxidative activity

of cashew nuts

M.G. Sajilata, R.S. Singhal

Food and Fermentation Technology Department, Institute of Chemical Technology, University of Mumbai, Matunga,

Mumbai 400019, India

Received 7 February 2005; accepted 24 July 2005

Abstract

Food irradiation, a cold process employed for preservation of food has been studied extensively for its beneficial and

undesirable effects on food constituents. Since nuts have been shown to contain several antioxidants, and ionizing

irradiation is known to result in the formation of free radicals, investigation on the antioxidative potential of cashew

nuts after irradiation and subsequent storage was undertaken by assessing their ability to inhibit lipid peroxidation

using the 1,3-diethyl-2-thiobarbituric acid (DETBA) assay. Irradiation at 0.251.00 kGy and subsequent storage was

found to considerably reduce antioxidative activity in the cashew nuts.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Irradiation; Cashew nuts; Antioxidative activity; Storage

1. Introduction

Food irradiation is a physical process involving

treatment of food with ionizing radiation that can

effectively delay a number of problems such as ripening

of fruits, bacterial growth, insect infestation and reduced

shelf life. The forms of ionizing energy, which may be

used in food processing, include g-rays (from 60Co or137Cs), X-rays and accelerated electrons (electron

beams) (Kader, 1986).

An undesirable effect of irradiation is the formation

of lipid oxides by the reaction of membrane lipids and

other lipids in foods with oxygen radicals produced by

g-rays (Ahn et al., 1998). Reducing oxygen and

temperature levels can decrease formation of these

oxides during irradiation. g-rays interact directly with

lipid molecules to form cation radicals or excited lipid

molecules. These products may generate lipid oxides and

small amounts of fatty acids, aldehydes, esters, ketones

and other compounds. If the radiolytic compounds from

saturated and unsaturated compounds are compared, it

can be seen that the major hydrocarbons, fatty acids and

symmetric ketones are produced in lesser quantities

from the unsaturated compounds (Vajdi and Nawar,

1978).

More recently, interest in the adverse biological effects

of free radicals has encouraged research on antioxidant

vitamins and other constituents of plants that act

as antioxidants in the body. There is overwhelming

evidence to indicate that free radicals cause oxidative

damage to lipids, proteins and nucleic acids. Nuts

contain many different antioxidative components. Be-

sides vitamin A, vitamin C and b-carotene, nuts are also

known to contain antioxidant phytochemicals such as

flavonoids, phenolic compounds, luteolin, tocotrienols,

isoflavones, ellagic acid as well as other components

like plant sterols (Rainey and Nyquist, 1997). Some

ARTICLE IN PRESS

www.elsevier.com/locate/radphyschem

0969-806X/$ - see front matterr 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.radphyschem.2005.07.004

Corresponding author. Fax: +91 22 24145614.

E-mail address: rekha@udct.org (R.S. Singhal).

http://www.elsevier.com/locate/radphyschem

7/29/2019 1-s2.0-S0969806X05002112-main

2/4

flavonoids such as catechin are reported to demonstrate

strong antioxidative activities (Bors et al., 1990).

Previous work from our institute has shown irradia-

tion at 0.251.00kGy to arrest insect infestation in

cashew nuts (Bhattacharjee et al., 2003a, b). Sinceionizing radiation is known to produce free radicals

and antioxidants have been reported to protect foods

from oxidative damage, it was of interest to study the

effect of irradiation and subsequent storage on the

antioxidative potential of cashew nuts. Any decrease in

antioxidative activity could be correlated with the

scavenging of free radicals, produced on irradiation,

by the naturally occurring antioxidants in cashew nuts.

A simple fluorometric method, which could quickly

estimate the antioxidative activity of ethanol extracts of

samples, was used to evaluate the antioxidative activity

of nuts (Furuta et al., 1997).

2. Materials and methods

2.1. Raw materials

Cashew nuts were procured from the local market of

Mumbai city.

2.2. Chemicals and reagents

1,3-diethyl-2-thiobarbituric acid (DETBA) was ob-

tained from Aldrich Chemical Company Inc, Milwau-

kee, WI, USA. Linoleic acid was obtained from Sisco

Research Laboratories, Mumbai. SDS and vitamin C

were procured from S.D. Fine Chemicals Ltd., Mumbai.

All other chemicals were of analytical grade.

2.3. Irradiation of cashew nuts

Twenty-five gram cashew nuts packed in heat-sealed

polyethylene pouches were placed in Al containers and

passed by a 60Co source for irradiation at dosages of

0.25, 0.5, 0.75 and 1 kGy using the Food Package

Irradiator at BARC, Mumbai. The dose was controlled

by the exposure time of each container to the source.

The temperature and dose rate for all samples were

30 1C and 28Gy/min, respectively. The dose rangewithin the samples was 720% of the actual dose. The

control and irradiated samples were stored in plastic

containers at room temperature (2830 1C) under

identical conditions.

2.4. Assessment of antioxidative activity

A fluorometric assay for evaluating antioxidative

activities was principally based on inhibition of lipid

peroxidation accompanied by autoxidation of linoleic

acid (Furuta et al., 1997). The standard procedure used

with few modifications was as follows:

An extract of the powdered sample was prepared in

80% ethanol using a cyclomixer, followed by centrifuga-

tion at low temperature (8 1C) and re-extraction andcentrifugation, and then diluting the supernatant to

25 ml with 80% ethanol.

To 50200mL of the extract in a test tube, 200 mL of

linoleic acid (20 mg/100mL absolute alcohol) and

required quantity of diluent was added so as to make

the final volume to 400mL. This was incubated at 80 1C

for 1 h. To stop the autoxidation of linoleic acid,

incubated samples were cooled in an ice bath and to

them were sequentially added 200mL BHA (36mg/10mL

absolute ethanol), 400mL ascorbic acid (80 mg/25 mL

water) and 200mL 8% SDS. BHA and ascorbic acid were

used to minimize oxidation during the DETBA test. SDS

was used to increase the affinity between linoleic acid and

other reagents. The degree of autoxidation was measured

by the DETBA test (Suda et al., 1994). Briefly, 3.2 mL of

12.5 mM DETBA in a sodium phosphate buffer was

added to the autoxidized samples. The solution was

mixed and heated at 9095 1C for 10 min and then cooled

in an ice bath. To extract the DETBA-reactive substance,

8 mL of ethyl acetate was added and the mixture was

shaken on a cyclomixer. The supernatant was pipetted

out and passed through a bed of sodium sulfate and the

fluorescence intensity of the ethyl acetate layer was

measured at an excitation wavelength of 515 nm and an

emission wavelength of 555nm using a Perkin Elmer

fluorometer (Model L 30). A control containing no

additives represented 100% lipid peroxidation and wasused as a blank. Lipid peroxidation was calculated using

the following formula:

% lipid peroxidation Sample reading

Blank reading 100.

A low lipid peroxidation level indicated a high

antioxidative activity. All data are expressed as

mean7SD of values from three independent replications

of the experiment.

3. Results and discussion

Fig. 1 shows the extent of lipid peroxidation brought

about by different concentrations of extracts from

unirradiated cashew nuts and that after immediate

irradiation at 0.251.00 kGy. Fig. 2 shows similar data

after 2 months of storage at a room temperature of

2830 1C. Data were also collected after 4 and 6 months

of storage (figures not shown). In order to understand

the effect of irradiation on the antioxidant activity,

regression equations correlating percentage of lipid

peroxidation with the concentration of the nut extract

was developed, from which the concentration required to

ARTICLE IN PRESS

M.G. Sajilata, R.S. Singhal / Radiation Physics and Chemistry 75 (2006) 297300298

7/29/2019 1-s2.0-S0969806X05002112-main

3/4

inhibit 50% lipid peroxidation was calculated. This was

done for control cashew nuts and those irradiated at

0.251.00 kGy for the entire storage period of 6 months.

The results are compiled in Table 1. As can be seen, the

antioxidative activity of cashew nuts decreased immedi-ately on irradiation and further decreased on subsequent

storage. The decrease in antioxidant activity in irradiated

cashew nuts could be potentiated by the combined effects

of irradiation and storage at room temperature in air.

Irradiation is known to produce free radicals, and

antioxidants from foods have been shown to scavenge

free radicals. In the present work, immediately after

irradiation, there was a decline in antioxidative activity,

which further decreased during storage. Since cashew

nuts are rich in fats (47%) and proteins (20%), the stable

radicals could be contained chiefly in the lipid and

protein fractions. Fats are particularly susceptible to

changes in odor and flavor. The food processing

industry has been able to resolve some of the issues

relating to changes in the quality of foods by lowering

processing temperatures to refrigeration or freezing

levels, and/or by excluding oxygen (Diehl, 1979) from

foods to be processed with the use of vacuum packaging

or packaging in nitrogen atmosphere. Cashew nuts are

reported to contain antioxidants such as vitamin E.

Tocopherols have been shown to be very sensitive to

irradiation in the presence of oxygen, which could be

contributing to the decrease in antioxidant activity

(Urbain, 1986). Diehl (1981) reported the loss of a-

tocopherol in stored irradiated (1 kGy) rolled oats to be

greater than that in non-irradiated oats under the same

conditions. The substantial loss of antioxidative activityshown by the nuts after irradiation and subsequent

storage could be ascribed to free radical scavenging by

the naturally occurring antioxidants, and also loss of

vitamin E due to storage in the presence of oxygen.

4. Conclusion

Irradiation and subsequent storage of cashew nuts

showed a decrease in antioxidative activity indicating

free radical damage.

ARTICLE IN PRESS

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Cashew nut extract (ppm)

%

lipidperoxidation

Control 0.25 kGy 0.5 kGy 0.75 kGy 1 kGy

Fig. 1. Percent lipid peroxidation brought about by different

concentrations of cashew nut extracts from unirradiated and

irradiated cashew nuts at 0 months of storage. Results are

expressed as mean7SD%.

0

10

20

30

40

50

60

70

80

90

0 5000 10000 15000 20000 25000 30000

Cashew nut extract (ppm)

%

lipidperoxidation

con trol 0.2 5 kGy 0.5 kGy 0.75 kGy 1 kGy

Fig. 2. Percent lipid peroxidation brought about by different

concentrations of cashew nut extracts from unirradiated and

irradiated cashew nuts after 2 months of storage. Results are

expressed as mean7SD%.

Table 1

Concentration of control and irradiated cashew nuts required to effect 50% lipid peroxidation

S tora ge time (mon ths) Irr adi ation d ose ( kGy)

Control 0.25 0.5 0.75 1

0 1045 1311 1765 2417 2833

2 3144 6820 10 156 13 157 14 500

4 4128 8367 11 235 11 740 13 005

6 5198 8419 14 285 14 513 14 125

M.G. Sajilata, R.S. Singhal / Radiation Physics and Chemistry 75 (2006) 297300 299

7/29/2019 1-s2.0-S0969806X05002112-main

4/4

Acknowledgements

The authors gratefully acknowledge Dr. Arun Behere,

Food Technology Division, Bhabha Atomic Research

Centre, Trombay, Mumbai 400085, for arranging forirradiation of cashew nuts.

References

Ahn, D.U., Olson, D.G., Lee, J.I., Jo, C., Wu, C., Chen, X.,

1998. Packaging and irradiation effects on lipid oxidation

and volatiles in pork patties. J. Food Sci. 63 (1), 1519.

Bhattacharjee, P., Singhal, R.S., Gholap, A.S., Variyar, P.S.,

Bongirwar, D.R., 2003a. Hydrocarbons as marker com-

pounds for irradiated cashew nuts. Food Chem. 80 (2),

151157.

Bhattacharjee, P., Singhal, R.S., Gholap, A.S., Variyar, P.S.,

Bongirwar, D.R., 2003b. Compositional profiles ofg-irradiated cashew nuts. Food Chem. 80 (2), 159163.

Bors, W., Werner, H., Michel, C., Saran, M., 1990. Flavonoids

as antioxidants: determination of radical scavenging effi-

ciencies. Meth. Enzymol. 186, 343355.

Diehl, J.F., 1979. Reduction of radiation-induced vitamin losses

by irradiation of foodstuffs at low temperature and by

exclusion of atmospheric oxygen. Z. Lebensm. Unters.

Forsch. 169, 276280.

Diehl, J.F., 1981. Effects of combination processes on the

nutritive value of food. In: Combination Processes in the

Food Irradiation. International Atomic Agency, Vienna,Austria, pp. 349366.

Furuta, S., Nishiba, Y., Suda, I., 1997. Fluorometric assay for

screening antioxidative activity of vegetables. J. Food Sci.

62 (3), 526528.

Kader, A.A., 1986. Potential applications of ionizing radiation

in postharvest handling of fresh fruits and vegetables. Food

Technol. 40 (6), 117121.

Rainey, C., Nyquist, L., 1997. Nutsnutrition and health

benefits of daily use. Nutr. Today 32, 157163.

Suda, I., Furuta, S., Nishiba, Y., 1994. Fluorometric

determination of 1,3-diethyl-2-thiobarbituric acid-malon-

dialdehyde adduct as an index of lipid peroxidation in

plant materials. Biosci. Biotechnol. Biochem. 58 (1),

16061608.

Urbain, W.M., 1986. Radiation chemistry of food componentsand of foods. In: Food Irradiation. Academic Press Inc.,

Harcourt Brace Jovanonich Publishers, New York, pp.

3782.

Vajdi, M., Nawar, W.W., 1978. Comparison of radiolytic

compounds from saturated and unsaturated triglycerides

and fatty acids. J. Am. Oil Chem. Soc. 55, 849850.

ARTICLE IN PRESS

M.G. Sajilata, R.S. Singhal / Radiation Physics and Chemistry 75 (2006) 297300300