ABSTRACT
It is commonly admitted that the biological value of food and feed proteins is primarily related to their ability to supply, upon hydrolysis by digestive enzymes, free essential amino acids that are subsequently absorbed through the intestinal barrier. A better insight into the hydrolysis of polymethionine chains covalently attached to casein was also gained from in vitro enzyme-digestion studies on radiolabeled poly-l-methionyl casein samples. The covalent attachment of polymethionine to food proteins may be considered as a valuable procedure for improving the nutritional quality of food proteins. The protective effect of polymethionine covalently attached to casein on rumen protein degradation is likely to enhance the amount of methionine as well as most if not all of the other amino acids entering the small intestine. Consequently, the bioavailability of polymethionyl casein, especially that of the covalently linked methionine, is expected to be increased in ruminant species.
