Proteolytic oligopeptides as molecular markers for the presence of cows' milk in fresh cheeses derived from sheep milk

The possibility of using short peptides in cheeses, derived from the proteolysis of milk caseins, as molecular markers for the origin of the milk (cows' or sheep) in fresh sheep milk cheeses has been explored. By using a liquid chromatography/mass spectrometry (LC/MS) technique, two peptides generated during the proteolytic process (fragments 1-14 and 1-23 from αS1 casein), which are slightly different in sheep and cows, were detected separately. The method easily allowed for the detection of casein-derived peptides from cows' caseins even when cows' milk was present at very low concentrations, thus revealing the presence of undeclared cows' milk. This method is a possible simpler alternative to the official electrophoretic methods.