Position of The American Dietetic Association:
Recognition is given to the following for their contributions:
Olivia Bennett Wood, MPH, RD, and Christine M. Bruhn, PhD
Dean O. Cliver, PhD; John W. Erdman, PhD; William C. Morris, PhD; Claire Regan, MS, RD; Anita Wilson, PhD, RD
The American Dietetic Association (ADA) and qualified dietetics professionals have a responsibility to educate consumers on issues related to food and nutrition. One such issue of importance to professionals and consumers is food irradiation. Food irradiation offers one solution for addressing the growing concerns associated with food safety.
It is the position of The American Dietetic Association that food irradiation is one way to enhance the safety and quality of the food supply. The ADA encourages the government, food manufacturers, food commodity groups, and qualified dietetics professionals to continue working together in educating consumers about this technology.
Although the US food supply has achieved a high level of safety, microbiological hazards exist. Because foods may contain pathogens, mishandling, including improper cooking, can result in foodborne illness. About 6.5 to 33 million cases of foodborne illness are estimated to occur annually in the United States; about 9,000 of these result in death (1). Recent outbreaks of illness and death caused by Escherichia coli O157:H7 have focused attention on this emerging pathogen, which is estimated to affect 7,000 to 20,000 Americans yearly at a cost of $174.3 to $467.7 million (2). Irradiation has been identified as one solution that enhances food safety through the reduction of potential pathogens and has been recommended as part of a comprehensive program to enhance food safety (3-6).
The Food Irradiation Process
Irradiation exposes food to radiant energy. (See Figure 1 for definitions of food irradiation terminology.) Food is passed through an enclosed chamber - an irradiator - where it is exposed to an ionizing energy source (Figure 2). Although the sources of ionizing energy may be gamma rays from cobalt 60 (60Co) or cesium 137 (137Cs), x-rays, or electrons generated from machine sources (7,8), food irradiation in the United States relies exclusively on the use of (60Co) (9,10), which is contained in stainless-steel rods placed in racks. The gamma rays emitted are very short wavelengths, similar to ultraviolet light and microwaves. Because gamma radiation does not elicit neutrons (ie, the subatomic particles that can make substances radioactive), "meltdown" and chain reactions cannot occur, and irradiated foods and their packaging are not made radioactive (8,10-12). The (60Co) gamma energy penetrates the food and its packaging but most of the energy simply passes through the food, similar to the way microwaves pass through food, leaving no residue. The small amount of energy that does not pass through the food is negligible and is retained as heat.
The duration of exposure to gamma energy, density of food, and amount of energy emitted by the irradiator determine the amount or dose of irradiation to which the food is exposed (8,10,11,13). Regulated doses are set at the minimum levels necessary to achieve specified purposes or benefits (Figure 3). Radiation doses allowed by the US Food and Drug Administration (FDA) are the most restrictive of all countries in which irradiation is allowed (10). Low doses (up to 1 kiloGray [kGy]) control the trichina parasite in fresh pork; inhibit maturation in fruits and vegetables; and control insects, mites, and other arthropod pests in food. Medium doses (up to 10 kGy) control bacteria in poultry, and high doses (above 10 kGy) control microorganisms in herbs, spices, teas, and other dried vegetable substances (14).
Food irradiation does not replace proper food handling. The lower doses of irradiation permit microorganisms to survive (8). Therefore, the handling of foods processed by irradiation should be governed by the same food safety precautions as all other foods. Food irradiation cannot enhance the quality of a food that is not fresh, or prevent contamination that occurs after irradiation during storage or preparation.
Historical Summary of Food Irradiation
Food irradiation has the longest history, more than 40 years, of scientific research and testing of any food technology before approval (10). Research has been comprehensive, and has included wholesomeness, toxicological, and microbiological evaluation. In 1955, the Army Medical Department began to assess the safety of types of foods commonly irradiated in the US diet (15). Petitions to the FDA for approval of specific foods for irradiation soon followed - wheat and wheat powder received the first approval in 1963 (Figure 3). In the early 1970s, the National Aeronautics and Space Administration adopted the process to sterilize meats for astronauts to consume in space, and this practice continues today (16). The first products approved by the FDA were wheat and white potatoes in the 1960s. During the 1980s, FDA approved petitions for irradiation of spices and seasonings, pork, fresh fruits, and dry or dehydrated substances. Poultry received approval in 1990. Currently, petitions for seafood, ground beef, and eggs are pending approval. Worldwide, 38 countries permit irradiation of food, and more than 28 billion lb of food is irradiated annually in Europe (6,17). The United States has 40 licensed irradiation facilities; most are used to sterilize medical and pharmaceutical supplies, but 16 also irradiate spices for wholesale use, and several others irradiate food. Food irradiation has an impressive list of national and international endorsements: ADA, American Council on Science and Health, American Medical Association, Council for Agricultural Science and Technology, International Atomic Energy Agency, Institute of Food Technologists, Scientific Committee of the European Union, United Nations Food and Agricultural Organization (FAO), and the World Health Organization (WHO).
Benefits of Food Irradiation
Treating foods with gamma rays offers benefits to consumers, retailers, and food manufacturers such as improved microbiological quality, replacement of chemical treatments, and extended shelf life. The benefits depend on the treatment used (Figure 2). The microbial count in spices can be lowered through irradiation, and the process substitutes for use of the fumigant ethylene oxide. Compared with other quarantine treatments, irradiation results in a higher-quality fruit. Pathogens in raw poultry or meat can be reduced by 99.9% by a low "pasteurization" dose of radiation (13). Use of still lower doses can disinfest grain and produce and can retard natural senescence of fruit and vegetables. This all results in the reduced use or elimination of chemical treatments. Irradiated foods closely resemble foods in their fresh state (8,12).
Effect of Irradiation on Nutritive Value of Food
Irradiation has been compared with pasteurization because it destroys pathogenic bacteria. Because irradiation does not substantially raise the temperature of the food being processed, nutrient losses are small and are often substantially less than nutrient losses associated with other methods of preservation, such as canning, drying, and heat pasteurization and sterilization (7,8,10,11). The relative sensitivity of different vitamins to irradiation depends on the food source, and the combination of irradiation and cooking is not considered to produce losses of notable concern (8). Proteins, fats, and carbohydrate are not notably altered by irradiation (7,8,12). In general, those nutrients most sensitive to heat treatment, such as the B vitamins and ascorbic acid, are those most sensitive to irradiation. Diehl (8) and Thorne (12) compared nutrient losses from irradiation with those associated with other traditional methods of preparation. Vitamin losses from pure solutions are larger than losses when the vitamin is in a food (8). Nutrient losses can be further minimized by irradiating food in an oxygen-free environment or in a frozen state (8,12). Fox and coworkers (18) derived a formula to calculate predicted losses in cooked pork and chicken on the basis of data on quantities of these items from the second National Health and Nutrition Examination Survey in the US diet and irradiation doses allowed by FDA. Predicted losses for thiamin, riboflavin, and niacin in pork and thiamin in chicken ranged from 0.01% to 1.5%. Earlier reports regarding losses of ascorbic acid in potatoes, due to a shift to dehydroascorbic acid, are no longer considered valid as they failed to consider that dehydroascorbic acid also has vitamin activity (8). In a study of the ascorbic acid content of oranges, Nagai and Moy (19) found no significant differences between irradiated and control fruit at dose levels up to 1.0 kGy and throughout a 6-week storage period.
Sensory qualities such as appearance and flavor have been evaluated in the laboratory (8,17,19,20) and in market studies with consumers (15,20). Consumers consistently rate irradiated fruit as equal or better than nonirradiated fruits in appearance, freshness, and taste (15,20,21).
Irradiation does cause changes in food, all of which have been found to be benign. More than 40 years of multispecies, multigenerational animal studies have shown no toxic effects from eating irradiated foods (22). Additionally, human volunteers consuming up to 100% of their diets as irradiated food have shown no ill effect (8). Irradiation produces so little chemical change in food that it is difficult to design a test to determine whether a food has been irradiated (23).
A small number of new compounds are formed when food is irradiated, just as new compounds are formed when food is exposed to heat. Early research described these new compounds as "unique radiolytic products" because they were identified after food was irradiated (8). Subsequent investigations have determined that free radicals and other compounds produced during irradiation are identical to those formed during cooking, steaming, roasting, pasteurization, freezing, and other forms of food preparation (8,10,12). Free radicals are even produced during the natural ripening of fruits and vegetables (22). All reliable scientific evidence, based on animal feeding tests and consumption by human volunteers, indicates that these products pose no unique risk to human beings. In fact, people requiring the safest food, hospital patients receiving bone marrow transplants, are routinely given irradiated foods. Furthermore, because spices, being of tropical origin, are often microbe laden, irradiated spices are preferred for routine use in hospital foodservice for patients. Thus, as with pasteurization, the evidence suggests that food irradiation can make a quality food supply better.
The American Medical Association's Report of the Council on Scientific Affairs on Food Irradiation (10) agreed with a WHO policy statement (4,24) released in 1992:
"Irradiated food produced under established Good Manufacturing Practices is to be considered safe and nutritionally adequate because: i) the process of irradiation will not introduce changes in the composition of the food which, from a toxicological point of view, would impose an adverse effect on human health; ii) the process of irradiation will not introduce changes in the microflora of the food which would increase the microbiological risk to the consumer; iii) the process of irradiation will not introduce nutrient losses in the composition of the food,which, from a nutritional point of view, would impose an adverse effect on the nutritional status of individuals or populations (10)."
Environmental Safety of Food Irradiation
Strict regulations govern the transportation and handling of radioactive material. Irradiation facilities are constructed to withstand earthquakes and other natural disasters without endangering the community or workers. Radioactive material is transported in canisters tested to withstand collisions, fires, and pressure. Worker safety is protected by a multifaceted protection system within the plant (11).
The 60Co used by US commercial facilities is specifically produced for use in irradiation of medical supplies and other materials. It is not a waste product of any other activity, and it cannot be used to make nuclear weapons. It is estimated that all the spent 60Co to date could fit in an office desk (8,9). Disposal of 60Co is carefully arranged by the producer.
US Regulation of Food Irradiation
Congress defined the sources of ionizing energy as food additives and included them in the Food Additives Amendment to the Federal Food, Drug, and Cosmetic Act (25), thus delegating the main regulatory responsibility to the FDA. Additionally, two agencies within the US Department of Agriculture (USDA) are involved in the process: the Food Safety and Inspection Service, which develops standards for the safe use of irradiation on meat and poultry products, and the Animal and Plant Health Inspection Service, which monitors programs designed to enhance animal and plant health (eg, using irradiation as an insect quarantine treatment in fresh produce) (25).
All irradiated foods in the United States must be labeled with a radura, the international symbol for irradiation (Figure 4),and the words "treated by irradiation" or "treated with radiation." Products that contain irradiated ingredients, such as spices, are not required to be labeled. A continuing area of research is identifying scientific detection methods to verify that unlabeled foods have not been irradiated and that labeled foods have received the intended dose (23). An international general standard for irradiated foods and facilities was adopted by the Codex Alimentarius Commission, a joint body of the WHO and the FAO. The standards are based on the findings of the Joint Expert Committee on Food Irradiation convened by the FAO, WHO, and International Atomic Energy Agency (10).
Food categories currently approved for irradiation in the United States are listed in Figure 3. The US facilities currently in operation process spices, citrus fruits, tropical fruits, strawberries, tomatoes, mushrooms, potatoes, onions, and poultry.
Despite repeated endorsements and regulatory approval, irradiated foods are not widely available in the United States. Although consumers are familiar with food irradiation, many have little knowledge of the process and its advantages (26). When consumers receive science-based information on food irradiation, however, most prefer irradiated to nonirradiated spices, poultry, pork, beef, and seafood (20). In a nationwide survey, consumers indicated that they would pay a premium for irradiated ground beef (26). The increase in cost for irradiated foods is estimated at 2 to 3 cents per pound for fruits and vegetables and 3 to 5 cents per pound for meat products (15,16). Produce has been marketed in some locations without a price premium due to decreased losses and increased shelf life. It has been estimated that the savings from the reduction of foodborne illness are substantially greater than the modest increase in food cost (13).
Marketing studies support the results of attitudinal surveys (20). Mangoes labeled as irradiated sold successfully in Florida in 1986. In March 1987, irradiated Hawaiian papayas, available on a 1-day trial in Southern California, outsold the identically priced nonirradiated counterpart by greater than ten to one. Irradiated apples marketed in Missouri were also favorably received. Record amounts of irradiated strawberries were sold in Florida in 1992, and irradiated strawberries, grapefruit, juice oranges, and other products continue to outsell their nonirradiated counterparts in a specialty produce store in Chicago, Ill. Irradiated poultry, which is available in select markets, has experienced brisk sales. A University of Georgia shopping simulation test (27) showed a significant increase in the proportion of consumers purchasing irradiated ground beef after they participated in an educational program on the benefits of food irradiation. After receiving information, 71% purchased irradiated beef, including 62% of those consumers who originally said they would not purchase irradiated food.
Role of Dietetics and Health Professionals
ADA and qualified dietetics professionals have the responsibility to educate consumers about food and nutrition issues, including new technologies such as food irradiation. As advocates for the public on food and nutrition issues, dietitians are in a unique position to monitor the advancement and further implementation of food irradiation technology.
The greatest need is expanded education for the public and for food retailers. Pilot educational programs could be offered in which health professionals work with food industry representatives to present accurate information about irradiation to the public. Educational materials about food irradiation are available from a variety of resources including colleges and universities and the FDA. A current and validated educational packet (21), which includes a consumer audiovisual, is available through the Agricultural Communication Service, Purdue University, West Lafayette, Ind.
Although the safety and efficacy of irradiation are well established, continued research on the ability of irradiation to destroy new and emerging microbial pathogens is appropriate. With today's demand for high-quality convenience foods, researchers should evaluate the effectiveness of irradiation in combination with other processing methods to enhance the safety of minimally processed foods or extend the quality and shelf life of fresh-cut produce.
In an era of increasing concern about food safety, consumers must understand that irradiation is one method of enhancing an already safe food supply. Health professionals can assist in consumer and food industry education.
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20. Bruhn, CM. Consumer attitudes and market responses to irradiated food. J Food Protection. 1995; 58(2): 157-181.
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24. Kaferstein FK. Food Irradiation: The Position of the World Health Organization. Vienna, Austria: International Atomic Energy Agency; 1992.
25. Pauli GH. Food irradiation in the United States. In: Thorne S, ed. Food Irradiation. New York, NY: Elsevier Science Publishers Ltd; 1991; 235-259.
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27. Resurreccion AVA, Galvez FCF, Fletcher SM, Misra SK. Consumer attitudes toward irradiated food, results of a new study. Presented at the 1993 Annual Meeting of the Institute of Food Technology; July 13, 1993; Chicago, Ill.
ADA Position adopted by the House of Delegates on October 29, 1995. This position is in effect until December 1999. The American Dietetic Association authorizes republication of the position paper, in its entirety, provided full and proper credit is given. Requests to use portions of the position must be directed to ADA Headquarters at 800/877-1600, ext 4896.
The American Dietetic Association
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Prepared Summer 1997 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.