SUSCEPTIBILITY OF PROTEINS USED IN CALF MILK REPLACERS TO HYDROLYSIS BY VARIOUS PROTEOLYTIC ENZYMES

Abstract

An in vitro study was conducted to assess the hydrolytic susceptibility of various milk and non-milk proteins (soybean, rapeseed, fish) used in calf milk replacers to endogenous and commercial proteolytic enzymes. Extent of protein hydrolysis (%) was calculated from the reduced amount of protein precipitated by 10% trichloroacetic acid following enzyme treatment. All of the enzymes tested hydrolyzed the milk proteins more extensively than the non-milk proteins both at their optimum pH, and at the pH (6.1) of calf abomasal contents immediately after feeding. At both optimum pH and pH 6.1, the highest average hydrolysis value for all protein substrates was obtained with pronase followed by papain, trypsin, pancreatin, chymotrypsin, Mucor miehei rennet andchymosin (calf rennet). All substrates were hydrolyzed extensively by pepsin at pH 2.0 but, as expected, very little hydrolysis occurred with this enzyme atpH6.1.