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 isoelectric 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 milk by restricted rennet action produced B-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 B-casein-rich fraction or human casein, this difference was minimized or even reversed at pH4. This was ascribred to the difference in clotting behavior of s1-casein and B-casein, namely a harder clot of the former. Therefore, the difference in clotting and proteolytic properties between human milk 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 s1-case-ins in human milk and cow's milk, respectively.
Nakai, S. and Li-Chan, E.
"Effect of Clotting in Stomachs of Infants on Protein Digestibility of Milk,"
Food Structure: Vol. 6
, Article 8.
Available at: http://digitalcommons.usu.edu/foodmicrostructure/vol6/iss2/8