Hydrolysis of κ-casein in solution by chymosin, plasmin, trypsin and Lactobacillus -proteinases

Abstract

The aim of this study was to examine the enzymatic hydrolysis of K-casein by isolating and identifying the released peptides. The enzymes employed in the study were chymosin, plasmin and trypsin, as well as a cell-free extract from three Lactobacillus helveticus and nine Lactobacillus casei strains.The findings showed that the bond most sensitive to the proteolytic activity of chymosin was the Phe 105-Met 106. After 24 hours of hydrolysis a few other bonds in the casein macropeptide were also cleaved. Plasmin was found to have weak proteolytic activity under the conditions of this study. When the enzyme-substrate ratio was raised from 1:200 to 1:50, a few peptides were released from the N-terminal region. Trypsin was found to hydrolyze several K-casein bonds, and peptides were released from almost all regions of the protein.The proteases ofLactobacillus had less effect than chymosin, plasmin or trypsin. The strains could be divided into three categories. L. helveticus strains had activity on bonds in the mid-section and C-terminal region, L casei strains EB, P 3, P 8 and A 1 had activity on bonds in the N-and C-terminal regions, while L. casei A 5 and M 9 had activity only on bonds in the C-terminal region.