Effect of enzymatic modification on the biological activity and nutritive value of cow and buffalo casein

Buffalo and cow milk caseins were submitted to hydrolysis either with alpha-chymotrypsin or with pepsin. Enzymatic peptide modification (EPM) was carried out by using L-methionine ethyl ester in the reaction mixture. As catalyst, alpha-chymotrypsin or pepsin was used. The incorporation of methionine in to the peptide chains in the presence of alpha-chymotrypsin showed an optimum value at 0.14 g Met added to the reaction mixture/1 g hydrolysate in both cases. In the case of pepsin used as catalyst, the optimal Met-enrichment was at 0.14 g Met added to the reaction mixture/1 g buffalo casein hydrolysate and at 0.34 g Met/1 g cow casein hydrolysate. The covalent nature of the amino acid incorporation was confirmed by SDS - polyacryl amide gel electrophoresis in the presence of urea. Electrophoretic patterns of the products indicate that transpeptidation plays an essential role in the EPM reaction. Antigenic character of the EPM-products was investigated in vitro by competitive indirect ELISA. Enzymatic peptide modification with methionine enrichment seems to be an efficient method for the reduction of the antigenic/potential allergenic character and for the improvement of the nutritive value of buffalo and cow milk caseins.