Changes in Available Lysine and Digestibility of Proteins Accompanied with Lipid Oxidation: Experiments with a Model System

Abstract

The effect of lipid oxidation on the nutritive value_??_ proteins was investigated using a model system _??_mposed of protein-ethyl linoleate-sugar. The mix_??_re was kept at 50°C, RH 80.4% for 1_??_2 weeks _??_der fluorescent light. Available lysine and di_??_estibility in vitro by pepsin and trypsin were_??_ easured with defatted proteins.
1. The effect of sugars on casein: The decreases _??_the quantity of available lysine and the digesti_??_lity by trypsin were remarkable with glucose or _??_alactose in comparison with sucrose, lactose, cellu_??_se or corn starch. No differences were observed on _??_e digestibility by pepsin though it was decreased.
2. The effect of the amounts of lipid on casein: he extents of the decreases in the three paraeters measured were remarkable with the increasg amounts of lipid. Even without lipid but glu_??_se was presented, there was a considerable _??_terioration of casein.
3. The effect on different proteins: The extent deterioration of casein was remarkable in com_??_rison with that of gluten or soy-bean protein.