A two part study was designed to investigate radiation-induced structural and nutritional changes in food proteins. Model systems composed of 0.1-10% myoglobin, lactalbumin or BSA were used and the effects of propyl gallate, ascorbic acid, air or nitrogen, pH 5, 6 or 7 citrate or phosphate buffer, and addition of glucose and SDS were investigated. We found that 0.02-0.04% propyl gallate (PG), alone or in conjunction with other solutes, inhibited protein aggregation after irradiation to 0.5 and 1.0 megarad and subsequent -20 C storage for 3-6 months. PG alone at 0.04% yielded up to 90% retention of myoglobin after 0.5 megarad and up to 94% retention of lactalbumin after 1.0 megarad as compared to unirradiated controls. BSA appeared more radiation sensitive than other proteins, and use of 0.02% PG yielded retention of only 10% of the original protein after 1.0 megarad. Use of synergists such as glucose or SDS together with PG allowed up to a two-fold increase in protein retention, while use of 0.02% ascorbic acid led to lower retention compared to samples irradiated alone in control buffer. Irradiations at pH 5 and 6 yielded greater protein retention than at pH 7. Isoelectric focusing of myoglobin revealed acidic shifts in protein pI with new bands at pH 4.9-5.2 after irradiation at pH 6 with glucose and PG. A similar acidic shift was seen in focusing lactalbumin, with major new bands forming at pH 3.7-4.0 after irradiation in pH 6 phosphate with 0.04% PG. BSA showed a bipolar pattern of pI shifts after irradiation in pH 6 phosphate. Mice fed irradiated lactalbumin in factorial studies grew slightly faster and ate more than unirradiated controls, while those fed protein irradiated with 0.02% PG showed slightly decreased rates of gain and feed consumption. Amino acid analysis revealed a 35% decrease in lysine, as compared to control, in diets prepared with protein irradiated to 1.0 megarads in 0.05 M phosphate, pH 6 with 0.02% PG. The negative effects of PG on feeding and growth were reduced when protein was irradiated at 22.5% rather than 15% (w/v). Liver to body weight ratios among animals fed protein irradiated with PG were decreased by 18% in contrast to control animals fed identical, though unirradiated, diet. (Abstract shortened with permission of author.)