Irradiation is the process of exposing materials to radiation to achieve a technical goal, such as for medical applications, plastics, automobile parts, and even gemstones. When applied to food, food irradiation is the process of exposing food to ionizing radition to destroy bacteria, viruses, or other microorganisms. Food irradiation is one of the most extensively and thoroughly studied methods of food preservation. Although many countries permit the use of this technology, the full potential of this technology has yet to be achieved. 
The use of irradiation to kill microbes in food was evaluated in the US in 1921, when the Department of Agriculture reported that it would effectively kill trichinae in pork.  Irradiation has then become a very standard technique to sterialize consumer and medical products, from adhesive strips to surgical implants. The high energy rays emit from a particular energy source, which then hits the food directly. The energy rays directly damange the DNA of the living organisms in the food, such as bacteria. However, there has been some reluctance from the public to accept irradiated foods because radiation is often associated with cancer and unhealthiness. Surveys conducted in early 2000s by the Food Marketing Institute and FoodNet sites showed that 50% of the population is ready to buy irradiated foods. 
Three different techniques have been developed by the sterilization industry: gamma irradiation, electron beam irradiation, and x-irradiation. Gamma irradiation uses high energy gamma rays emitted by cobalt (Co) 60 or cesium (Cs) 137. These sources have a very long half-life, which makes them useful for commercial installation. Food or other products are put into a heavily-shielded room and exposed to gamma rays for a specified period of time. When the source is not in use, it is stored in a pool of water which turns it off. Because the gamma ray contains high energy, they can penetrate deeply, making it possible to treat bulk foods. 
The electron beam technology uses beta rays, which is a stream of electrons, that are emitted from an electron gun. Electrons can only penetrate a few centimeters of food, so this technique is only applicable to thin layers of food. Thin layers of metal shielding from the treatment cell is sufficient to protect the operator. When not in use, the electron source is turned off by switching the electric currnet. No radioactivity is involved. This technique is much more convenient than the gamma irradiation, but also less effective due to the power of the electron being less than that of the gamma rays. 
The X-irradiation is the most recently developed technology, which combines the properties of the two techniques above. High energy X-rays can be produced if an electron beam hits a thin metal foil. Like gamma rays, X-rays can penetrate foods to much greater depth than electron beams can and require heavier shielding for the operator. However, X-rays sources can be switched on and off and do not require the use of a radioactive source. 
Food irradiation has been more thoroughly evaluated than any other food processing technology. It is an important food safety tool in fighting food borne illness. It can be used to improve the shelf-life of some foods as well as kill potential disease-causing microbes in our food before it is consumed by the public. However, although irradiation itself is safe to the human body and helps prevent diseases, it is not completely foul-proof. Even with irradiation, precautions should still be taken when handling food. 
© Chun-Kai Kao. The author grants permission to copy, distribute, and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 B. R. Thakur and R. K. Singh, "Food Irradiation - Chemistry and Applications," Food Reviews International 10, 437 (1994).
 E. S. Josephson, "An Historical Review of Food Irradiation," J. Food Safety 5, 161 (1983).
 P. D. Frenzen et al., "Consumer Acceptance of Irradiated Meat and Poultry in the United States," J. Food Protection 64, 2020 (2001).
 Robert V. Tauxe, "Food Safety and Irradiation: Protecting the Public from Foodborne Infections," Emerging Infectious Diseases 7, 516 (2001).
 K. M. Shea, "Technical Report: Irradiation of Food," J. Am. Acad. Pediatrics 106, 1505 (2000) [Retired by J. Am. Acad. Pediatrics. 115 1438 (2005)].