VARIATIONS IN THE BINDING OF BETA-CASEIN TO OIL-WATER INTERFACES DETECTED BY TRYPSIN-CATALYZED HYDROLYSIS

Trypsin-catalyzed proteolysis has been used to investigate the influence of the oil phase on the topography of interfacial β-casein in soya oil-water and tetradecane-water emulsions. In both emulsions, the initial step in the hydrolysis is the removal of the N-terminal peptide(s). The rate of this reaction is considerably faster than that of the formation of the C-terminal peptide (three-fold in soya-oil, five-fold in tetradecane), indicating that the charged N-terminal region is more accessible to the protease. As with β-casein in solution, certain of the trypsin-sensitive bonds are not readily hydrolyzed at the tetradecane-water interface. However, these bonds are hydrolyzed at the soya oil interface, suggesting that the protein possesses different conformations in the two emulsions. Surface area coverage measurements confirm that the protein covers a larger surface area on the triglyceride. The effect of the nature of the oil phase on the structure of the adsorbed protein is discussed with reference to the relative hydrophobicities of the oils. © 1992.