When foods are exposed to ionizing radiation under conditions envisioned for commercial application, no significant impairment in the nutritional quality of protein, lipid and carbohydrate constituents was observed. Irradiation was no more destructive to vitamins than other food preservation methods. Protection of nutrients is improved by holding the food at low temperature during irradiation and by reducing or excluding free oxygen from the radiation milieu. 'Deceased. Kennedy (1965) observed little change in nutritive value of animal feeds (protein concentrates) when 0.5 and 1.0 Mrad doses were appliedand no nutritional changes with frozen eggs irradiated at 0.5 and 5.0 Mrad. Ley (1972Ley ( , 1975 noted excellent results with radappertized feed for germ-free rat and mouse colonies which were maintained for 5 years. Radappertization and radicidation have been used in preference to thermal sterilization to sustain germ-free and specific-pathogen-free rats, mice, pigs and chickens (Sato 1970;Schoen and Hiller 1971;Udes et al. 1971;Ley et al. 1969;Coates et al. 1963). Others have reported that both the biological value of proteins, and the metabolizable energy value, of composite rodent diets are unaltered by radappertization a t 5.6 Mrad (Raica and Howie 1966;Read et al. 1961;Kraybill 1960).
erator at 2-5°C overnight (15 hr) prior to enzyme-inactivation. A study was undertal:en to compare the effect of ionizing radiation and thermal processing on the thiamin content of pork. Ground pork was either then rally processed in cans or, after enzyme-inactivation, irradiated in l'ouches with electrons or gamma rays. Thiamin in treated and untre;.ted samples was measured by the thiochrome method. The results ;how that thiamin retention in pork decreases as the irradiation doss increases, but that retention increases as the temperature of irrac.iation decreases. Moreover, irradiation with gamma rays (low dare-rate) leads to lower retention than irradiation with electrons Ihigh dose-rate). Results also show that conventional thermal processing causes loss of thiamin comparable to or greater than irradiation at effective processing conditions for sterilization.The enzyme-inactivation was accomplished in a steam-heated cookhouse, utilizing the cooking cycle shown in Table 1. This process brings the internal temperature of the rolls to the range 75-77'C, at which point, the steam is discontinued to reduce the dry bulb temperature to 74'C when an additional heat treatment of 3 to 4% hr is given to allow each roll to reach an 88% yield. During this time, the internal temperature of the rolls remained 75-77°C. The rolls are then removed from the cookhouse and chilled to 2-5°C by refrigerating overnight.The final steps include cutting and packaging. By removing the end pieces, the chilled pork rolls were trimmed to 45 cm lengths and then sliced into 13 mm sections. For the irradiation, representative samples of each rollwere vacuum packaged in flexible pouches 11.5 x 17.8 cm in size, as described by Killoran et al. (1979).
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