The nutritional value of irradiated casein-fat mixtures-effect of anaerobic conditions, storage time, added vitamin E and degree of unsaturation of lipids.

The effect of oxygen elimination during irradiation (5 Mrad) and subsequent storage, storage time (12 weeks), degree of lipid-unsaturation and added antioxidant (vitamin E) in protein-lipid mixtures (casein : fat - 11.1 : 4) on the nutritive value of protein was studied during 8-day nitrogen balance trials in 12 groups of 6 weanling rats each. When casein-cocofat-cornoil mixtures were irradiated and stored under aerobic conditions a reduction of NPU appeared upon prolonged storage time, which was prevented by excluding oxygen during irradiation and storage. When the lipid component consisted entirely of cocofat no loss in NPU occurred under aerobic processing and storage conditions throughout the 12 week storage period. Replacement of cocofat through sunfloweroil resulted in a drastic reduction of NPU and in growth inhibition, which was not prevented by the addition of vitamin E (0.05 g/100 g lipid). Irradiation of casein-lipid mixtures resulted in a significant increase of carbonyl compounds. A further increase was effectively prevented by elimination of oxygen during irradiation and storage. A drastic increase of carbonyl compounds as well as a significant reduction of available lysine occurred in casein-sunfloweroil mixtures. Added vitamin E afforded only limited protection against these changes.