Quality Factors of Fruits and Vegetables - ACS Publications

Chapter 25

Irradiation Processing of Fruits and Vegetables Status and Prospects

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch025

James H. Moy Department of Food Science and Human Nutrition, University of Hawaii, 1920 Edmondson Road, Honolulu, HI 96822

Ionizing radiation can be e f f e c t i v e l y applied to f r u i t s and vegetables f o r : (a) d i s i n f e s t a t i o n as a quarantine treatment at 0.15 kGy or above, a process more e f f i c a c i o u s than thermal, chemical or cold treatment; (b) delaying ripening i n selected f r u i t s , and i n h i b i t i n g sprouting i n tubers and bulbs at 0.02 to 0.75 kGy; (c) decontamination of vegetable seasonings at 10 to 30 kGy; and (d) product improve ment i n dried products such as dried vegetables and beans at 0.30 to 5.0 kGy. Between 1963 and 1986, the U.S. FDA has cleared s i x food groups f o r i r r a d i a t i o n . To date, 36 countries have cleared 42 foods or food groups f o r i r r a d i a t i o n with 19 countries commercially i r r a d i a t i n g 20 food items. The prospects f o r commer cial radiation processing of selected f r u i t and vegetable products are promising. I r r a d i a t i o n i n a combined process f o r synergistic e f f e c t s should be explored.

A l l fresh f r u i t s and vegetables are perishable and have a limited marketable l i f e due to post-harvest insect i n f e s t a t i o n , microbial i n f e c t i o n , physiological changes and breakdown, and environmental factors such as storage temperature and humidity. Various food processing and preservation techniques such as dehydration, canning, freezing or p i c k l i n g can extend the marketable l i f e of these com modities but often change t h e i r sensory and nutrient q u a l i t i e s . This i s because of the rather drastic applications of heat, cold or a c i d i t y to the f r u i t s and vegetables. Since fresh f r u i t s and vegetables are an enjoyable part of our d i e t , extending their marketable l i f e and expanding t h e i r markets to d i f f e r e n t parts of the world are always the goals of the food industry. Proper c h i l l i n g and packaging between harvest and the markets are e f f e c t i v e ways of achieving these goals. For some export markets, insect-infested products would require quarantine treatments p r i o r to shipment. Additional means to slow down the 0097-6156/89/0405-0328$06.00/0 ο 1989 American Chemical Society

In Quality Factors of Fruits and Vegetables; Jen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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Irradiation Processing of Fruits and Vegetables

329

ripening and senescence of the climacteric group of f r u i t s and vegetables during shipment and storage are also desirable. Some of these techniques include chemical fumigation and atmospheric modification respectively. Coming into play i s the p o s s i b i l i t y of application of low doses of i o n i z i n g radiation to f r u i t s and vegetables. The tech nology of radiation preservation of foods has been studied for more than three decades around the world. A great deal of research findings suggest that the technology i s simple, v e r s a t i l e , and efficacious when compared with some of the established food preser vation techniques. This chapter w i l l attempt to summarize several b e n e f i c i a l applications of i r r a d i a t i o n to f r u i t s and vegetables, the processing variables and chemical factors that should be considered, the current status of the technology with respect to the food industry, the market and the consumer, and the technical and com mercial prospects of using t h i s technology on f r u i t s and vegetables i n the foreseeable future. Technical E f f i c a c i e s of I r r a d i a t i o n Technical e f f i c a c y of any food processing technology suggests that the process i s capable of achieving a c e r t a i n desirable technical e f f e c t , such as k i l l i n g some or a l l of a microbial population, or inactivating insects i n various stages. In addition, the process should have a high e f f i c i e n c y to achieve that technical e f f e c t . The combination of effectiveness and e f f i c i e n c y makes a process e f f i c a cious. Examples w i l l show that food i r r a d i a t i o n i s e f f i c a c i o u s as well as v e r s a t i l e . Radiation Disinfestâtion. For fresh f r u i t s and vegetables infested by insects, i o n i z i n g radiation, often i n the form of gammaradiation, can inactivate various stages of insects and serve as a quarantine treatment when the commodities are to be shipped from an infested area to non-infested market places. F r u i t f l y eggs i n papayas, oranges and grapefruits, seed weevils i n mangoes, and codling moths i n apples and cherries can be inactivated with an applied doses of 0.15-0.35 k G y ( ) ( l ) . The q u a l i t i e s of these irradiated f r u i t s are completely retained Ç2, 3). The time required to treat Hawaii grown papayas by i r r a d i a t i o n i s about 10 to 20 minutes as compared to more than one hour by the double-dip hot water treatment and 6-9 hours by the vapor heat treatment. The enzymes f o r ripening the papayas are sometimes inactivated i n the double-dip hot water treatment (42°C, 30 min., 49°C, 20 min.) causing the f r u i t not to ripen normally. a

Shelf L i f e Extension. Applying radiation doses of 0.02-0.15 kGy w i l l i n h i b i t the sprouting of potatoes, onions and g a r l i c f o r 6 months or longer, while doses of 0.12-0.75 kGy w i l l delay the ripening of t r o p i c a l f r u i t s such as papayas, mangoes and some v a r i e t i e s of bananas. Some delay i n senescence was found i n

(a) Units of absorbed dose:

1 Gray = 100 rad = 1 j/kg 1 kGy = 100 krad = 1 kJ/kg


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QUALITY FACTORS OF FRUITS AND

VEGETABLES


papayas, apricot and sweet cherries at doses varying from 0.75 to 2.0 or 3.0 kGy (4). However, i t i s believed that doses of 2.0 to 3.0 kGy would exceed the tolerance doses for apricots and sweet cherries and might cause softening of the f r u i t and thus make the process technically impractical. Decontamination. Vegetable seasonings are often contaminated with various pathogens and other unwanted organisms. Spices and vegetable seasonings are routinely fumigated with ethylene oxide, a toxic, carcinogenic and explosive gas that could be hazardous to the operators and consumers. I r r a d i a t i o n at 10 to 20 kGy could be an e f f e c t i v e substitute for fumigation. (In A p r i l , 1986, the U.S. Food and Drug Administration raised the allowable upper dose f o r decontamination of spices and seasonings from 10 to 30 kGy, although spices currently being i r r a d i a t e d i n the United States receive less than 20 kGy.) Product Improvement. In the 1960s, Lipton Co., Inc. i n the United States found that i r r a d i a t i n g dehydrated vegetables could reduce the cooking time of dry soup mixes several f o l d s , e.g. from 10 to 3 minutes. The dose required varied from 0.30 to 5.0 kGy dependent upon the types of vegetables. The decrease i n time for rehydration and cooking was probably due to some depolymerization by i r r a d i a t i o n , thus softening of the vegetables. A study of i r r a d i a t e d soy beans at the University of Hawaii (5) showed that an optimal dose of 2.5 kGy on germinating soy beans with subsequent drying substantially reduced the gas producing factors (oligosaccharides) i n the beans, and also made the beans cook faster and taste better. I r r a d i a t i o n Processing Variables In order to i r r a d i a t e f r u i t s and vegetables for useful purposes mentioned above, several variables should be considered and caref u l l y controlled: Host Tolerance to I r r a d i a t i o n Treatment. Every f r u i t and vegetable responds d i f f e r e n t l y to i o n i z i n g radiation because of i t s inherent chemistry and biochemistry. One of the f i r s t variables to be determined should be the tolerance dose, which can be defined as the "maximum dose below which a f r u i t or vegetable exhibits no external or i n t e r n a l symptoms of i n j u r i e s or changes." I f a f r u i t or vegetable i s i r r a d i a t e d above i t s tolerance dose, symptoms of phytotoxicity such as off-aroma, o f f - f l a v o r , softening, scalding, or decrease i n nutrient content could occur. Of course other processes such as thermal process could cause similar changes. In f a c t , the general observation has been that among various processes, the responses of a host (food) to i r r a d i a t i o n and thermal processing are more similar to each other than are other processes. Variation of c u l t i v a r . Response to i r r a d i a t i o n may d i f f e r due to v a r i a t i o n of c u l t i v a r of a f r u i t or vegetable. An example i s banana. Delay i n ripening occurs i n some v a r i e t i e s of bananas after i r r a d i a t i o n . In others, no changes i n ripening occur. Yet i n s t i l l


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others, ripening i s accelerated a f t e r i r r a d i a t i o n . Generally, only the ripening of climacteric f r u i t s and vegetables would be affected by i r r a d i a t i o n . The non-climacteric group i s not affected. Maturation at Time of Treatment. The general rule for i r r a d i a t i n g f r u i t s and vegetables i s that the more ripe they are, the better they can tolerate i r r a d i a t i o n . Often i f a f r u i t i s harvested too early, i t s f u l l flavor may not develop l a t e r and i t may be prone to radiation i n j u r i e s . For climacteric f r u i t s and vegetables, the i r r a d i a t i o n must be done p r i o r to the onset of the climacteric process i n order to delay ripening. For d i s i n f e s t a t i o n of papayas, i r r a d i a t i o n i s e f f e c t i v e at a l l stages of ripeness beyond the mature-green stage. The double-dip hot water treatment, however, requires that the papaya be less than one-quarter r i p e at the time of treatment. The i r r a d i a t i o n process therefore allows the f r u i t s to ripen to an optimal degree on the tree before harvest and t r e a t ment, resulting i n higher quality f r u i t s for the consumer. Pretreatment and Conditioning. Since radiation doses f o r insect d i s i n f e s t a t i o n have l i t t l e or no effect on the fungi on f r u i t s and vegetables, fungicidal or thermal treatment p r i o r to i r r a d i a t i o n i s often b e n e f i c i a l and necessary to control fungal diseases. Sometimes i r r a d i a t e d c h i l l e d f r u i t s can be damaged due to moisture condensation during i r r a d i a t i o n . To avoid moisture conden sation, temperature of such f r u i t s should be allowed to r i s e pass the dew point of the ambient a i r p r i o r to i r r a d i a t i o n . For sprout i n h i b i t i o n of onions and potatoes by i r r a d i a t i o n , conditioning of bulbs and tubers at optimal temperatures and r e l a t i v e humidities and for a time period u n t i l they are at the dor mant stage would make the i r r a d i a t i o n process more e f f e c t i v e (6). White potatoes must be held after harvesting f o r a period suf f i c i e n t to enable the healing of "wounds" r e s u l t i n g from harvesting handling. Onions must be i r r a d i a t e d promptly a f t e r harvesting and p r i o r to s i g n i f i c a n t internal bud growth i n order to minimize the black internal "spot" that results from the radiation-caused death of t h i s tissue. Post-Irradiation Storage. For sprout i n h i b i t i o n of bulbs and tubers by i r r a d i a t i o n , proper p o s t - i r r a d i a t i o n storage i s also important (6) If irradiated potatoes are for culinary use or chip ping, i t i s not necessary to store them at low temperature. However, low temperature (5-10°C) and a r e l a t i v e humidity of 95% or higher are recommended i f an extended storage period a f t e r i r r a d i a t i o n i s anticipated. For i r r a d i a t e d onions, storage at low temperature i s recommended, but high r e l a t i v e humidity was found to contribute to r o t t i n g . For both i r r a d i a t e d potatoes and onions, good v e n t i l a t i o n i n the storage area i s also necessary. Tropical f r u i t s such as papayas tend to become more sensitive to low temperature storage, e.g., 7°C, after i r r a d i a t i o n . They would keep better i f stored at a few degrees higher, e.g., 10°C. Packaging and Transport. A very challenging task f o r i r r a d i a t e d f r u i t s and vegetables i s to f i n d suitable i n d i v i d u a l and bulk packaging to maximize their q u a l i t i e s and marketable l i f e a f t e r



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i r r a d i a t i o n . For example, i r r a d i a t i o n of strawberries at 2.0 kGy e f f e c t i v e l y controls several fungi, but the f r u i t s suffer from transport damage due to abrasion, decreasing the amount of marketable f r u i t s (7). A recent trend i n marketing fresh f r u i t s i s to wrap each f r u i t i n d i v i d u a l l y . I t should improve the f r u i t ' s appearance and minimize abrasion between f r u i t s . However, t h i s would require finding a f i l m with the optimal permeability f o r a i r , water vapor, ethylene and carbon dioxide between the f r u i t and the surrounding atmosphere so as to slow down the f r u i t ' s r e s p i r a t i o n rate, and to maintain the proper r e l a t i v e humidity. If i r r a d i a t i o n and a fungicidal agent can be incorporated into the process and packaging, i t should further extend the s h e l f - l i f e of the f r u i t substantially. Chemical and Quality Factors To determine the a p p l i c a b i l i t y and effectiveness i n using i o n i z i n g radiation to preserve fresh f r u i t s and vegetables, the following factors should be evaluated: Phytotoxicity/Tolerance. These two terms express opposite results of radiation treatment. If a f r u i t or vegetable i r r a d i a t e d at a certain dose l e v e l exhibit no detectable or measurable external or i n t e r n a l changes or i n j u r i e s , then the f r u i t or vegetable i s said to be tolerant to i r r a d i a t i o n at that dose. The maximum dose a f r u i t or vegetable can tolerate before phytotoxicity occurs should be determined. Age or ripeness of the commodity, i t s temperature, and the condition of the atmosphere at the time of i r r a d i a t i o n should be reported with the dose applied. Quality Indices. Measuring the aroma, flavor, color and texture of i r r a d i a t e d f r u i t or vegetable against the non-irradiated controls w i l l reveal whether or not these q u a l i t i e s are affected by i r r a d i a t i o n and at what does l e v e l . Current Status Food i r r a d i a t i o n has been defined i n the United States as a food additive according to the 1958 M i l l e r amendment of the Federal Food, Drug, and Cosmetic Act. Each food item allowed f o r commercial i r r a d i a t i o n must f i r s t be petitioned to the FDA for clearance on the basis of data and evidence supporting technical e f f e c t s , safety and sometimes user i n t e r e s t . A regulation permitting the use i s issued by the FDA, and i n some cases, by other government agencies. Update on the U.S. and World Situation. A limited number of food products have been cleared since the early 1960s by the U.S. Food and Drug Administration for commercial i r r a d i a t i o n and marketing. Table I l i s t s these products (8). These clearances represent several applications of food i r r a d i a t i o n with d i s i n f e s t a t i o n the leading potential application.


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Irradiation Processing of Fruits and Vegetables Table I.

Clearance of food products i n the U.S.A. for commercial i r r a d i a t i o n

Disinfestation

0.20-0.50

Date of Clearance August 1963

Potatoes

Sprout

0.15

June 1964

Enzymes (Dried)

Decontamination and d i s i n f e s t a t i o n

10

June 1985

Pork

D i s i n f e s t a t i o n of parasites

0.30-1.0

July 1985

Fresh foods

D i s i n f e s t a t i o n and Delay of maturation

1.0

A p r i l 1986

Product Wheat and wheat f l o u r


333

Purpose

inhibition

Spices and Decontamination Seasonings (a) Clearance f o r 10 kGy i n July 1983.

Dose, kGy

3 0

(a)

A p r i l 1986

Currently i n the United States, some spices such as black peppers, ground paprika and some blend of spices are i r r a d i a t e d f o r the wholesale market and f o r some s p e c i a l i t y foods such as pastrami. The purpose i s decontamination at a dose range of 10 kGy and higher. These spices and seasonings have been i r r a d i a t e d i n the past few years at commercial i r r a d i a t i o n plants i n New Jersey, C a l i f o r n i a and elsewhere. The quantities i r r a d i a t e d i n the past two years are estimated to be around 1,000 to 2,000 metric tons per year. On the international scene, 36 countries have approved 42 foods or food groups to be i r r a d i a t e d f o r various purposes f o r commercial marketing, most of which on an unconditional basis, with a few i n several countries f o r test marketing only. Nineteen countries are currently i r r a d i a t i n g some 20 food items commercially: Belgium, B r a z i l , Chile, China, Cuba, Denmark, Finland, France, German Democratic Republic, Hungary, I s r a e l , Japan, Republic of Korea, Netherlands, Norway, South A f r i c a , the United States, USSR, and Yugoslavia. Ten other countries are either constructing or i n an advance stage of planning commercial or large-scale demonstration i r r a d i a t o r s f o r treating food and non-food items: A u s t r a l i a , Bangladesh, Canada, Cote D'Ivoire, I t a l y , New Zealand, Pakistan, Poland, Thailand, and Vietnam (9). Table II shows the number of countries that have approved the i r r a d i a t i o n of f r u i t s and vegetables f o r three d i f f e r e n t a p p l i c a tions, and the number of countries currently i r r a d i a t i n g f r u i t s and vegetables on a commercial scale. Industry Interest and Consumer Acceptance. To advance the use f o r food i r r a d i a t i o n , interest for whatever prupose and a p p l i c a t i o n must be shown by the food industry which i s a major beneficiary of a l l the research that has been carried out worldwide. However, over the years, the food industry i n the United States has not taken a very active role i n food i r r a d i a t i o n research and development. There may be several reasons f o r t h i s :



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ο Needs for i r r a d i a t i o n The needs for i r r a d i a t i o n have not always been c l e a r l y i d e n t i f i e d or well defined. There are other processing technology available to manufacture and provide the consumer with a wide variety of processed foods. ο Concerns for large c a p i t a l investment By most estimates, a commercial i r r a d i a t o r to be b u i l t i n the United States would cost three to four m i l l i o n d o l l a r s . The economic f e a s i b i l i t y may or may not exist i f a company does not have a large enough throughput to keep the i r r a d i a t o r busy. ο L o g i s t i c s of using i r r a d i a t i o n Even i f several companies pool t h e i r resources together and build an i r r a d i a t o r , the l o g i s t i c s of trucking products to and from the i r r a d i a t o r plant would present problems i n manpower allocations and plant operations. Optimal and e f f i c i e n t scheduling i s possible with computers, but company management might s t i l l worry about the products not being kept under the best conditions. ο Consumer acceptance A l l segments of the food industry i n the United States are con cerned about consumer acceptance of i r r a d i a t e d foods. The fact remains that p u b l i c i t y over the past four decades about negative aspects of nuclear energy such as nuclear weapons, nuclear reactor leakage tends to overshadow the benefits and safety of food i r r a d i a tion by a large margin. Anti-nuclear a c t i v i s t s , including those who oppose food i r r a d i a t i o n , f u e l the s i t u a t i o n by spreading a great deal of misinformation to the public. Inadequate public education plus the misinformation on food i r r a d i a t i o n cause the industry to hesitate i n considering the use of t h i s technology.

Table I I .

Countries Approved 29

Number of Countries Approved and Using I r r a d i a t i o n of F r u i t s and Vegetables for Three A p p l i c a t i o n s ^ )

Countries Using

Disinfes tation 13

19

1

Shelf-Life Extension 26 7

Decontam ination 20 13

(a) Some countries approved or are using only one application while some others approved or are using more than one applications (9).

Outlook and Conclusion A large volume of research data amassed over the past t h i r t y years , has demonstrated that radiation preservation and processing of foods at low (up to 1.0 kGy) and medium (up to 10 kGy) dose i s a simple, v e r s a t i l e and e f f i c a c i o u s technology. For f r u i t s and vegetables, the most technically feasible and promising applications include: (a) d i s i n f e s t a t i o n of f r u i t s and vegetables to maintain product quality and as a quarantine treatment at low doses (0.15 kGy or higher), a process more e f f i c a c i o u s than thermal, chemical or cold



25. Μ Ο Υ


treatment; (b) s h e l f - l i f e extension of selected f r u i t s through delaying of their ripening, and of bulbs and tubers such as onions, g a r l i c and potatoes through sprout i n h i b i t i o n at low doses (0.02 to 0.75 kGy); and (c) decontamination of dried vegetable seasonings at medium to high doses (10-20 kGy). By combining i r r a d i a t i o n with other processing and packaging technology to synergize the above applications, the e f f i c a c y and processing costs can be further optimized. History has shown that a new food processing technology such as canning, freezing and microwave heating have taken many years to be accepted by the consumer and to be established i n the industry. Radiation technology for food preservation could take even longer than other established processing technology because of i t s unique relationship with nuclear energy and the controversy generated therein. While 42 foods have been cleared by 36 countries f o r i r r a d i a t i o n to date and 19 of these countries are i r r a d i a t i n g 20 food items commercially, food i r r a d i a t i o n around the world s t i l l faces a number of u p h i l l hurdles which must be overcome before i t can gain a foothold i n the consumer market. These include: (a) clear indication of industry interest and need i n using a p a r t i c u l a r application; (b) positive demonstration of economic f e a s i b i l i t y ; (c) proper selection and s i z i n g of i r r a d i a t i o n plant f a c i l i t y and optimal l o g i s t i c s of i r r a d i a t i o n processing; (d) favorable majority consumer acceptance of i r r a d i a t e d food products; and (e) early establishment of international trade agreements among countries on the import and export of i r r a d i a t e d products. Commercializing food i r r a d i a t i o n has worldwide applications. Some f r u i t s and vegetables may be better preserved, supplies are increased, and export markets can be expanded, a l l of which should benefit the consumer and improve the economy of every country con cerned. To take advantage of this technology and to reach the goals, the challenge ahead would be to launch an e f f e c t i v e consumer education program about the purposes, safety and benefits of food i r r a d i a t i o n and to increase i t s commercial applications gradually and s e l e c t i v e l y through the j o i n t e f f o r t s of the industry, govern ment and researchers.

Literature Cited 1. Moy, J. H. Radiation Disinfestation of Food and Agricultural Products; How. Inst. Trop. Agri. & Human Resources, U. Hawaii: Honolulu, HI 1985; 428 pp. 2. Moy, J. H. Final Summary Rpt to USAEC, Radioisot. Rad. Appl. 1972. 3. Moy, J. H.; Kaneshiro, K. Y.; Ohta, A. T.; Nagai, N. J. Food Sci., 1983, 48, 928. 4. Akamine, Ε. K.; Moy, J. H. In Preserv. of Food by Ionizing Radiation. Josephson, E. S.; Peterson, M. S., Eds., CRC Press: Boca Raton, FL, USA, 1983; Vol. 3, p 129. 5. Hasegawa, Y.; Moy, J. H. Proc. Int'l Symp. Rad. Preserv. of Food, IAEA/FAO, Bombay, 1973. p 89. 6. Matsuyama, Α.; Umeda, K. In Preserv. of Food by Ionizing Radia tion. Josephson, E. S.; Peterson, M. S., Eds.; CRC Press: Boca Raton, FL, USA, 1983, Vol. 3, p 159.


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7. Maxie, E. C.; Sommer, N. F.; Mitchell, F. G. HortScience. 1971. 6, 202. 8. List of Clearances, International Atomic Energy Agency Food Irrad. Newsletter, 1988, 12(1), Supplement, 3-15. 9. Safety and Wholesomeness of Irradiated Foods: International Status - Facts and Figures, International Atomic Energy Agency, Food Irrad. Newsletter, 1987, 11(2), 7.


RECEIVED May 12, 1989


Quality Factors of Fruits and Vegetables - ACS Publications

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