Food irradiation

Food irradiation is one means of food preservation that may not be familiar to many, but it has been in development since the early decades of the twentieth century. If properly applied, irradiation can be an effective way to treat a variety of problems in our food supply, such as insect infestation of grains, sprouting of potatoes, rapid ripening of fruits and bacterial growth. However, it has not yet obtained a significant place in the U.S. food industry. This apparent hesitancy is caused in part by very vocal and active opponents who provide inaccurate information to instill fear about food safety into the public's minds. Many factors of economic feasibility seem to hinge on food industry as well as consumer acceptance, and in turn, have hindered the potential for widespread commercial success of food irradiation.

Radiation is not a modern, man-made creation. We get natural radiation from the sun and other natural components of our environment such as gases and deposits of uranium ore in rock structures. In the 1890s, radioactive substances and X-rays were discovered. Intense research about the biological effects of these radiations began immediately and beneficial uses of these substances were soon found. The biggest contribution of man's use of radiation has been in the medical field -- medical and dental X-rays, detection and treatment of diseases, sterilization of medical equipment, medical devices, pharmaceutical products, and home products, and production of sterilized food for special hospital diets. It is also interesting to note that for many years precious stones have been irradiated to increase their brilliance, as with diamonds, or to change their appearance, as with topaz, in which irradiation produces a smoky-like appearance in the crystal.

Despite these known benefits of irradiation and the technologies to control its use, consumer acceptance and concern for nuclear issues have hindered the potential for widespread commercial success in this country. However, more than 30 countries have approved and are using food irradiation technologies to ensure food safety. Countries utilizing food irradiation for various purposes include Japan, China, the Soviet Union, the Netherlands and France. In the U.S., irradiated foods have been used by astronauts, the military and hospital patients, but the adoption of the technology for other purposes has been slow despite approvals from the Food and Drug Administration (FDA). For example, the process to control trichinosis in pork, approved in 1985, is still not used. With the recent approval of irradiation for controlling bacteria on red meats, attention was again focused on food irradiation. The U.S. may be the closest it has ever been to seeing irradiation accepted for more widespread use, due to recent outbreaks from E. ColiO157:H7.

History of the Irradiation Preservation of Food

Early in the 1920s, a French scientist discovered that irradiation could be used to preserve food. This technology was not adopted in the U.S. until World War II. At this time there was a need to feed millions of men and women in uniform. The U.S. Army sponsored a series of experiments with fruits, vegetables, dairy products, fish and meats. In 1963, the U.S. saw its first approval of food irradiation when FDA approved its use to control insects in wheat and wheat flour. In 1964, additional approval was given to inhibit the development of sprouts in white potatoes.

In 1983, approval was granted to kill insects and control microorganisms in a specific list of herbs, spices and vegetable seasonings. (The approved list of food products has been increased with later changes.) Then, in 1985, treatment of pork to control trichinosis was added to the list of approvals. In the same year, approval was granted to control insects and microorganisms in dry enzyme preparations used in fermentation-type processes. In 1986, approval was granted to control insects and inhibit growth and ripening in such foods as fruits, vegetables and grains.

Approval was granted in May, 1990, for irradiation of packaged fresh or frozen uncooked poultry. FDA supports it as an effective control of microorganisms responsible for a major portion of foodborne illness, including Salmonella, Yersinia, and Campylobacter. This approval was the first approved process to "pasteurize" solid foods, such as poultry. The process reduces but does not eliminate all bacteria. Therefore, processed poultry are safe longer than unprocessed poultry, but still require refrigeration.

The latest approval for irradiation in the U.S. was granted in December 1997, for red meat. A maximum dose of 4.5 KGy was approved for uncooked, chilled red meat and meat product, and 7.0 KGy for frozen red meat and products. These approvals are for the purpose of controlling microorganisms, including pathogens such as E. Coli 0157:H7. Just as with irradiated poultry, irradiated red meats still require refrigeration or freezing. Higher doses that sterilize frozen and packaged meats were approved in 1995 for use by NASA only. Legislation to allow the irradiation of seafood is being developed.

What is "Irradiation?"

Just a mention of the word irradiation usually sparks strong objections, usually based on misunderstanding of the process involved and its effects on foods. Very simply, food irradiation is a process of exposing foods, either prepackaged or in bulk, to very high-energy, invisible lightwaves (radiation). The process controls the amount of radiation the food absorbs.

Food irradiation is a means of preservation; it is used to extend product shelf life. The radiation energy used is able to cause changes in molecules, such as breaking chemical bonds. At small irradiation doses, properties of the food, such as sprouting and ripening can be modified (usually inhibited). Higher doses can alter molecules in microorganisms so they can no longer cause spoilage or human illness. The microorganisms may be killed or genetically altered so they can't reproduce. It takes lower doses to damage microorganisms and insects than to alter enough molecules in the food to damage it.

For those who want to know more about the radiation that is used and its relationship to other types of energy, it is necessary to look at the electromagnetic spectrum. Food irradiation uses gamma rays, X-rays or electron beams that are part of the invisible lightwaves range of the electromagnetic spectrum. Ultraviolet light (radiation) is also in the invisible range of the spectrum, although the waves of ultraviolet light are not as short as those of X-rays and gamma rays. The shorter the wavelength, the greater the amount of energy per unit.

High energy radiation can break molecules into smaller fragments that may be either electrically charged (ions) or neutral. The electrically charged ions are radioactive. Ultraviolet, X-ray and gamma radiation can break stronger bonds than visible light and even expel electrons from atoms. This is why they may also be called ionizing radiation or ionizing energy.

Other types of radiant energy with longer wavelengths and less energy per unit are infrared and microwave radiation. Thus, conventional cooking methods such as broiling and baking also use radiant energy, but in the infrared range. Cooking with microwaves is accomplished by microwave radiation, energy of yet another wavelength. Microwave radiation is also used to detect speeding cars, to send television and telephone communications, to treat muscle soreness, to dry and cure plywood and to raise bread and doughnuts.

 Sources of Radiation (Ionizing Energy)

There are three types of energy that can be used for irradiation of food: X-rays, electron beams and gamma rays. Machines called "electron accelerators" are used to produce beams of electrons to which food can be exposed. If the electrons from the accelerator are stopped by a metal target (such as tungsten foil) first, X-rays are produced and the food is exposed to X-rays. The amount of energy produced by electron beams can be adjusted.

Gamma rays are produced by radioactive substances (called radioisotopes) that continuously emit the high energy gamma rays. The approved sources of gamma rays for food irradiation are cobalt- 60 (the most common) and cesium-137.

Doses and Effects of Radiation

In food irradiation, the radiation "dose" that a food receives should not be confused with something added to the food. The "dose" for food irradiation is the amount of radiation absorbed by the food and it is not the same as the level of energy transmitted from the radiation sources. The dose is controlled by the intensity of radiation and the length of time the food is exposed.

Terms used to describe this "dose" or amount of absorbed radiation, are unfamiliar and confusing to most people. In the past, the term used was rad, short for "radiation absorbed dose," which is 100 ergs absorbed by 1 gram of matter. The rad has been replaced by the gray (Gy). One gray is equal to 100 rads or 0.00024 Calorie (i.e., diet calorie) per kilogram of food. (0.00024 Calorie per kilogram equals 0.0001 Calorie per pound.) The FDA's regulations describe radiation levels in terms of the kilogray (kGy), equal to 1000 Gy.

The dose (number of kGy) permitted varies according to the type of food and the desired action. Treatment levels have been approved by FDA as follows:

1. "Low" doses - (up to 1 kGy) designed to
1. control insects in grains
2. inhibit sprouting in white potatoes
3. control trichinae in pork
4. inhibit decay and control insects in fruits and vegetables
2. "Medium" doses - (1-10 kGy) designed to
1. control Salmonella, Shigella, Campylobacter, Yersinia and E. Coli in meat, poultry and fish
2. delay mold growth on strawberries and other fruits
3. "High" doses - (greater than 10 kGy) designed to
1. kill microorganisms and insects in spices
2. commercially sterilize foods, destroying all microorganisms of public health concern (e.g., to sterilize food to the same degree as if they were thermally sterilized (canned); however, no commercial applications of this dosage have been approved by FDA for use in the U.S. with the exception of some special hospital diets for immune-deficient patients.)

When radiation energy is absorbed by food, it causes a variety of chemical and physical reactions. The amount of energy the food absorbs is controlled so the changes produced have desirable food preservation effects while maintaining the safety, quality, and wholesomeness of the food. The food itself does not become radioactive.

Perishable foods treated with all but high doses, however, must still be refrigerated. Refrigerated storage life is extended, but the need for cold storage is not replaced by irradiation. Microorganisms are destroyed by radiation more easily than enzymes which lead to food deterioration (color, flavor and texture changes, for example). Many enzymes survive the current levels of radiation processing, although refrigeration can slow down many enzymatic changes. In addition, not all microorganisms are destroyed. The process does not protect the food against reinfestation or contamination. Therefore, irradiated perishable foods are still considered perishable.

Facilities

Facilities for irradiating food are similar to those in operation for sterilizing medical equipment and do not resemble nuclear reactors in any way. There are no explosives or materials that could cause widespread dissemination of radioactive material. Facilities using cobalt do not use materials from nuclear defense industries. Facilities used, however, must comply with plant and worker safety requirements of the Nuclear Regulatory Commission and the Occupational Safety and Health Administration.

 

At an irradiation facility, the radiation source (usually the cobalt-60) is contained in slender pencil- like stainless steel casing about 18 inches long by 3/8 inch diameter. The casings, in turn, are contained in a lead-lined chamber. Packaged food travels in pallets on a conveyor between 6-1/2 foot thick concrete walls into and through a chamber where it is exposed to the radiation source (gamma rays if cobalt-60 is used). Pallets may be turned to allow uniform exposure over the route. Radiation dosage is controlled by a computerized rate of passage (conveyor speed) through the chamber.

As of June 1989, there were three facilities in the U.S. which irradiated food on a commercial scale. Those in operation have been facilities for sterilizing medical and other supplies, and who sometimes divert to irradiate bulk loads of spices. One hospital in Seattle is approved for irradiating special diets for immune-deficient patients mentioned previously.

Adoption of the Technology

Although some food radiation treatments have been approved in the U.S. since 1963, there has been only infrequent use in test markets other than use on spices. The food industry is slow to invest in this technology because of uncertainty over the public acceptance of food. In 1986, 2 metric tons of mangoes irradiated in Puerto Rico were test marketed in Miami, FL. In 1987, irradiated Hawaiian papaya were tested in Anaheim and Irvine, CA. These test market studies as well as others in France, Argentina and South Africa indicated good consumer acceptance and willingness to buy.

Worldwide, over 30 countries approve some form of irradiation and many groups of consumers readily accept these products. As of 1986, Japan irradiated over 10,000 pounds of potatoes annually. The Netherlands irradiated 2 tons of food daily, and Belgium irradiated 1 ton daily. South Africa routinely irradiates mangoes, papaya, and other vegetables. Canada has a facility dedicated to irradiating potatoes.

Labeling of Irradiated Foods

 

Because the beneficial effects of irradiating foods are not discernable to consumers, labeling has been considered essential if consumers are to be adequately informed. After much debate, the FDA approved initial labeling requirements in April, 1986. The regulations required that all produce be labeled at the packing/wholesale and retail levels. Suggested wording and an international symbol (logo) were provided.

At the retail level, the label was required to bear the symbol plus one of these statements: "treated with radiation" or "treated by irradiation." In addition, the manufacturer was allowed to add a phrase which truthfully described the primary purpose of the treatment, such as "treated with radiation to control spoilage." For unpackaged fruits and vegetables, labels could be on each piece, on the shipping container placed in prominent consumer view, or on a sign near the commodities identifying the use of the treatment.

For irradiated foods sold at the wholesale level, the logo and the wording were still required. In addition, however, they were to be accompanied by the caution "do not irradiate again." Irradiated spices sold in the U.S. do not need to carry the logo if they are in packaged foods where they constitute one small ingredient. Most packaged spices in stores are usually treated by chemical fumigation, not by irradiation. New legislation in November 1997 (The FDA Modernization Act of 1997, Public Law 105-115) contained food provisions that direct FDA to review its labeling rule for irradiated foods. The agency was told to revise the rule so the disclosure statement is not more prominent than the declaration of ingredients. The ruling does not, however, exclude making a disclosure of irradiation through use of the radura.

Safety of Irradiated Foods

Irradiated food does not become radioactive. At the radiation energy levels used in food processing, only chemical changes are possible, not nuclear changes that would make the food itself radioactive. Over 35 years of research suggest that the chemical by-products of radiation ("radiolytic products") are mostly the same as by-products of conventional cooking or other preservation methods. Animal feeding studies show no toxic, teratogenic or mutagenic effects from irradiated foods. In addition, irradiation leaves no chemical residues in food.

In 1981, the Food and Agricultural Organization (FAO) of the United Nations, the International Atomic Energy Agency (IAEA), and the World Health Organization concluded that "any food irradiated up to an average dose of 1 Mrad or less is wholesome for humans and therefore should be approved without further testing" (WHO, 1981 in IFT, 1987). (A Mrad equals 10 kGy.) Also in 1981, the U.S. FDA concluded that food irradiated with up to 1 kGy is "wholesome and safe for human consumption, even where the food that is irradiated may constitute a substantial portion of the diet," and that food "compromising no more than 0.01% of the daily diet [ex., spices] and irradiated at 50 kGy or less also can be considered safe for human consumption" (FDA, 1981).

Before approving low dose irradiation of foods, the FDA reviewed over 400 toxicity studies, which included animal feeding studies. The U.S. Army Medical Department fed irradiated foods to 41 human volunteers in 15-day tests in 1955-58 and showed no unfavorable effects. More recently, in 1986, the People's Republic of China reported on eight experiments with 439 human volunteers. Their diets included 60% of ingredients irradiated at levels from 0.1-8 kGy. During and after these trials, there were no significant differences in the clinical, physiological and biochemical evaluations between the subjects receiving the irradiated foods and those receiving comparable food without such processing.

Changes in Irradiated Food

Food irradiation is sometimes called a "cold" process; it achieves its effect with little rise in the temperature of the food. There is little if any change in the physical appearance of irradiated foods as they do not undergo the changes in texture and/or color as foods preserved by heat pasteurization, canning or freezing. Food remains close to its original state. Problems that have occurred are some off-flavors in meat and excess tissue softening that has been documented in fresh peaches and nectarines.

As with all preservation or cooking methods, some chemical changes occur in irradiated food. When high energy particles strike matter, electrons are lost from atoms and ions are formed. Newly formed radiolytic products may then interact to create new compounds in the food that were not present before treatment, a few of which could produce off- flavors. (In meat, this can be partly controlled by maintaining low product temperatures during the irradiation process.) The most common chemical reaction during food irradiation is the conversion of water to hydrogen peroxide. Reactions like these occur in all types of food preservation, and those few reactions unique to irradiation are not harmful.

The FDA concluded that "very few of these radiolytic products are unique to irradiated foods; approximately 90% of the radiolytic products...are known to be natural components of food" (FDA, 1986). Some of these are fatty acids just like those that result from the breakdown of triglycerides, amino acids that make up proteins, and compounds (hydrocarbons) commonly found in the waxy coverings of fruits like apples, pears and berries. Others are fatty compounds just like those found from cooking meat by common methods such as grilling. The other 10% of radiolytic compounds are chemically very similar to natural components in food. The chemistry of irradiation is very predictable and the products of an individual component such as proteins are not affected by the type of food or other food components present. Radiolytic products have been critically tested for toxicity and no evidence of hazard has been found.

Radiation does not impair activity of certain nutrients, but overall nutrient retention in irradiated foods is similar to retention with other preservation methods. Vitamin C (ascorbic acid) reduction has been reported, but it is attributed to a shift from ascorbic acid to dehydroascorbic acid, a change that is mostly insignificant from a nutritional standpoint. Tocopherol, which have Vitamin E activity, appear to be very sensitive to irradiation in the presence of oxygen. Vitamin K seems relatively stable. These adverse effects of irradiation on vitamins can be reduced by excluding oxygen and light, keeping the food at a low temperature, and using the lowest dose need for treating (processing) food.

Consumer Acceptance

Studies on consumer acceptance have been done with a few irradiated products. Bruhn, Schutz and Sommer (1986) examined change in consumer attitudes toward food irradiation as the result of opportunities to read about and discuss the technology. They found that consumers in general showed a higher level of concern for preservatives and sprays than for food irradiation. "Alternative" consumers who were a vocal segment of ecologically sensitive consumers, were more skeptical about the safety and advantages of the process. They also were initially more aware of food irradiation and their concern increased after educational efforts. After educational efforts, conventional consumers adopted a minor concerned attitude toward irradiation, but a discussion leader knowledgeable in food irradiation reduced concerns of conventional consumers compared with the impact of a non-expert leader. These researchers concluded that the attitudes of conventional consumers can be positively influenced by an educational effort and the influence is most effective when the consumer can interact with someone knowledgeable about irradiation.

Wiese Research Associates (1984) found that less than 25% of a national telephone sample were aware of food irradiation technologies. Among those aware, 75% were concerned, but in general, consumers were more concerned about chemical sprays and preservatives than irradiation. Those with fewer concerns had more formal education and higher levels of awareness.

A market survey of the effects of irradiation on demand for papaya in California in the 1960s suggested that demand would be reduced by 23% if the fruit were treated with irradiation (Huang, et.al., 1987). Acceptance of irradiated produce is quite high in South Africa. Reportedly, 90% of consumers reacted positively to its introduction in the late 1970s. However, the test marketing was accompanied by an extensive educational campaign that involved mass media and supportive consumer organizations (Bruhn, et.al., 1986). A 1992 study revealed that consumers were willing to pay up to $0.81 more per meal to eliminate risk of foodborne illness. This is 10 times more expensive than the actual cost of irradiating food (Olson, 1997).

Even though some test marketing has shown some hope for consumer acceptance, irradiated foods have caused picketing and violent protests in the past. Consumer studies seem to suggest that people are more interested in the safety and wholesomeness of the foods rather than benefits of the process for any specific foods. These and other findings also seem to indicate that as knowledge and awareness of the technologies increase, so might its acceptance. History indicates that consumer acceptance will continue to influence the extent to which irradiation gets adopted as an alternative food processing technology.

Summary

There is no doubt that food irradiation involves many complex issues. If properly applied, irradiation can be an effective method of reducing organisms which cause food spoilage and human illness. Some benefits of food irradiation include:

Reduction of postharvest losses (less foodwaste);

Reduction of chemical residues in foods (could replace fumigants and other pesticides)

Reduction of risks of foodborne illness from bacteria (Salmonella, Campylobacter and Shigella)

Reduction of the risk of trichinosis from pork;

More appealing "fresh" characteristics for foods because it is a relatively "cold" process and foods closely resemble those in their fresh state.

The potential benefits of food irradiation may come closer to realization now that regulatory barriers are beginning to be removed, interest in alternatives to pesticides is high and some studies are demonstrating consumer acceptance of products. See Table 1 for clearances as of August, 1988, for use of ionizing energy on foods in the United States.

Table 1. Summary of Approved Food Irradiation Processes

Date	Food/Product	Dose (kGy)*	Purpose
1963	Wheat and wheat flour	0.2 - 0.5	Disinfestation of insects
1964, 1965	White potatoes	0.05 - 0.15	Inhibit sprouting (and extend shelf life)
1983	Spices and dry vegetable seasonings (38 commodities)	30 maximum	Disinfestation of insects and decontamination
1985	Pork (carcasses or fresh, non-heat processed cuts)	0.3 - 1.0	Control of Trichinella spiralis
1985, 1986	Dry or dehydrated enzymes	10 maximum	Control of insects and/or microorganisms
1986	Fruit	1 maximum	Delay of maturation (ripening) and disinfestation
1986	Fresh vegetables	1 maximum	Disinfestation of insects
1986	Herbs	30 maximum	Control of microorganisms (decontamination)
1986	Spices	30 maximum	Control of microorganisms
1986	Vegetable seasonings	30 maximum	Control of microorganisms
1990	Poultry, fresh or frozen	3 maximum	Control of microorganisms (includingSalmonella)
1995	Meat, frozen and packaged (solely for use in NASA)	44 minimum	Sterilization (destruction of microorganisms)
1995	Animal feed and pet food	2 - 25	Control of Salmonella
1997	Red meat, uncooked, chilled Red meat, frozen	4.5 maximum 7.0 maximum	Control of microorganisms