Isolation of a glycopolypeptide fraction with Lactobacillus bifidus subspecies pennsylvanicus growth-promoting activity from whole human milk casein.

Human milk casein samples were digested with trypsin and chymotrypsin, and a glycopolypeptide fraction was isolated from the soluble portion of the digests by a series of gel filtration steps. The glycopeptide fraction stimulated the growth of Lactobacillus bifidus subspecies pennsylvanicius to the same extent as a whey glycopolypeptide fraction previously isolated (Pediat. Res. 10: 1, 1976). It contained between 60 and 70% carbohydrate consisting of galactose, galactosamine, glucosamine, fucose, and sialic acid. This, along with its apparent molecular weight of near 30,000 was also similar to the respective parameters of the whey glycopolypeptide. It is proposed that human milk casein may serve a dual function: that serving the nutritional needs of the breast-fed infant, and that stimulating the growth of L. bifidus subspecies pennsylvanicus. Additionally, the whey glycopolypeptide may arise from casein through proteolysis by an endogenous milk protease.