Relationship between In Vitro Digestibility of Casein and its Content of Lysinoalanine and D‐Amino Acids

Alkali and heat induce changes in proteins. These include racemization of L‐ to D‐amino acids and crosslinking via lysinoalanine. Since high‐quality proteins are presumably well‐digested, possible effects of D‐amino acid and lysinoalanine contents on food casein digestibility was examined. The following variables, which were expected to influence all three parameters, were evaluated: (a) pH (8‐14); (b) temperature (25‐75°C); and (c) time of treatment (10 min to 24 hr). An approximately inverse relationship was observed between D‐ammo acid and lysinoalanine content and the extent of proteolysis. Such changes may lower the quality and safety of foods.