Effect of Clotting in Stomachs of Infants on Protein Digestibility of Milk

Differences in clotting between human and cow's milk in the stomachs of infants are discussed . Gastric pH, after ingesting milk, of an infant up to 6 months of age stays at a pH range of 4-5, near the isoelec tric point of casein, and never reaches the value of 2, which is found in adults. Pepsin C (or gastricsin) can hydrolyze proteins at this pH range. Gastric emptying time is shorter with human milk than with cow's milk which appears to be correlated to the smaller size of human milk clots. Elimination of a readily coagulable fraction of casein from cow's mi1k by restricted rennet action produced a-casein rich milk with similar coagulating properties to that of human milk. Although pepsin digestibility at pH 2 was greater for bovine whole casein than bovine Bcasein-ric h fraction or human casein, thi s difference was minimized or even reversed at pH 4. This was ascribed to the difference in clotting behavior of <Xsl-casein and a -casein, namely a harder c lot of the former. Therefore, the difference in c lotting and proteolytic properties between human mil k and cow's milk in an infant's stomach can be explained from the difference in chemical properties of their major caseins, i.e ., B-caseins and asl caseins in truman milk and cow's milk, respectively. Initial paper received June 3, 1987 Ma!luscript received November 5, 1987 Di:rect inquiries to S. Nakai Te:ephone number: 604 228 4427/5859