Radiation Preservation of Food

Abstract

SOON after World War II, studies sponsored by the Atomic Energy Commission disclosed that ionizing radiation could be used to preserve foods, and a new concept of food processing appeared. Preservation of food promises to be one of the most important peaceful uses of atomic energy. Since food spoilage bacteria can be destroyed effectively by radiation with only a small rise in temperature, not more than 100 C., and with remarkable speed, it is conceivable that irradiated foods can be made to surpass in flavor and texture foods preserved by other methods. Current research, sponsored largely by the Department of the Army, is directed toward this goal, as well as the demonstration of safety and nutritional adequacy. Although many problems regarding the quality of certain irradiated foods remain to be solved, radiation treatment presently offers several interesting possibilities for increasing the supply of perishable food and safeguarding health. At levels much lower than the 2 or 3 million rep (roentgens equivalent physical) necessary for sterilization, radiation inhibits sprouting of potatoes (10,000-30,000 rep), destroys trichina in pork (30,000 rep), increases the keeping quality of perishable foods under refrigeration (50,000-100,000 rep), and destroys insect infestation (50,000-100,000 rep). Either gamma or electron sources are used for radiation preservation of food. Mixed fission products (spent fuel rods from nuclear reactors) and cobalt-60 are the sources of gamma rays. Resonant transformers, Van de Graaff generators, and linear accelerators are the electron sources. Penetration of radiation from a gamma source is greater than that from an electron source, but a gamma source has the disadvantage of requiring continuous shielding. An electron source can be turned off and oni. Since pasteurization or sterilization of food requires rather high levels of radiation, higher than the level required for lethal effects against mammals and insects but lower than that for viruses and enzymes (fig. 1), it might be anticipated that rupture of chemical bonds would occur during processing. This has been found to be true. The molecular alteration in fat, protein, and carbohydrate in food produces certain noticeable changes in odor, color, flavor, and texture (1). The effect of radiation on meat, which has been studied extensively, may be summarized as follows: *Protein change: Increase in creatinine. * Production of sulfur compounds: Hydrogen sulfide and mercaptanls produced at 70,000 rep. * Pigmental changes: Oxymyoglobin and metmyoglobin formed. * Enzyme inactivation: Proteinases inactivated at 1.6 x 106 rep. Much of the current research work is concentrated on improvement of texture and flavor in an effort to increase acceptability of irradiated food. Foods sensitive to radiation undergo changes in sulfur-containing compounds, proteins, and unsaturated fatty acids as a result of interactions with free radicals during irradiation. One method of counteracting these effects would be the introduction of comDr. Kraybill is chief of the chemistry division, Army Medical Nutrition Laboratory, Fitzsimons Army Hospital, Denver, Colo. This article is based on a paper he presented at Pennsylvania's Fifth Annual Health Conference, held August 21, 1956, at Pennsylvania State University, University Park.