Influence of pH on the heat-induced proteolysis of casein molecules

Proteolysis of sodium caseinate solution (24.5 g/l) induced by heat treatment at 120 degrees C at different pH values was studied by measuring nitrogen content and relative fluorescence intensity in the 4% trichloroacetic acid filtrates. The low molar mass pepticles corresponding to the soluble nitrogen were identified using liquid chromatography/tandem mass spectrometry. Increase in proteolysis, deduced from the increase in soluble nitrogen content, was observed with heating time (10, 20 and 30 min) and pH (6.0, 7.0, 8.0 and 9.0). The fluorescence measurements showed that the release of peptides containing tryptophan was minimal at pH approximately 7.0. In parallel, eighteen low molar mass peptides were characterized, of which four came from kappa-casein, nine from beta-casein and five from alphas1-casein. Peptides were preferentially released under alkaline conditions.