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G. DEITZ and J. MASEFIELD. STERIS - Isomedix Services, 11 Apollo Drive, Whippany, NJ 07981

During the early 1950s, the U.S. Army undertook the task of developing shelf-stable, ready-to-eat meat products for inclusion as military rations. Meats were cooked for proteolytic enzyme inactivation, packaged, then exposed to gamma energy at very high doses (approximately 45kGy) to sterilize the product. This dose was sufficient to yield a 12 log reduction in pathogenic microorganisms, including spores of clostridium botulinum. This work led to the filing with the U.S. FDA of petitions to irradiate bacon, ham, and for the clearance of a number of packaging materials as food contactants during gamma irradiation. At the same time, it was realized that the irradiation of fresh meat and poultry at doses of up to 3-4kGy was effective in yielding a several log reduction in pathogens such as E. Coli, Listeria, Salmonella, and Yersinia, while at the same time extending the fresh shelf-life of prepackaged products for up to a week or two. For the most part, these findings lay dormant until recently, when industry was spurred by various pathogenic microorganism outbreaks in several fresh- and processed-meat products. Processing with gamma enery, primarily from the radioisotope cobalt-60, has been shown to be a safe and effective radiation-processing method. Gamma rays (which are similar to x-rays) are not themselves radioactive, and are highly penetrating, allowing thicknesses of meats up to 16 in to be processed with reasonable overdose ratios. Gamma radiation technology is widely used in sterilizing disposable medical devices and for reducing microorganism levels in a large variety of consumer products. Today's irradiators, with their proven safety systems based on over 30 years of operational experience, have proven to be highly effective, safe, and reliable. Gamma irradiation will likely be utilized to process packaged meat and poultry products where carton thicknesses generally exceed three in, which is about the upper limit of penetration of two-sided irradiation utilizing electron beam.