Comparative studies on "acid-stable, heat-stable polypeptides" of ovine, caprine and bovine milks

"Acid-stable, heat-stable polypeptides" (previously called proteose-peptone) of three milk species have been studied. Analysis by polyacrylamide gel electrophoresis revealed that all fractions showed similar patterns. Only bands with the lowest mobilities showed the presence of carbohydrates when stained with Schiff's reagent. These bands had a lower mobility in ewe's and goat's milk than in cow's milk. Gas chromatography/mass spectrometry analysis showed the presence of fucose, mannose, glucose, galactose, glucosamine and galactosamine in the three fractions studied. Acid-stable, heat-stable polypeptides of bovine milk had the lowest carbohydrate content (4 mg/100 mg protein), whereas the highest content was found in ewe's milk (7.30 mg/100 mg protein) mainly as a result of the high galactose, mannose and glucosamine content. The sialic acid content was lower in ewe's and goat's milk (2.68 and 2.98 mg/100 mg protein respectively) than in bovine milk (2.06 mg/100 mg protein).