Comparison of in vitro systems of protein digestion using either mammal orfish proteolytic enzymes

Hydrolysis of three different proteins by either crude fish digestive extra cts or purified mammal proteases was assayed using two different in vitro s ystems. The closed system was a modification of the pH-stat method includin g a previous acid digestion. The open system used a digestion cell containi ng a semi-permeable membrane which allowed continuous separation of the fin al products of hydrolysis with a molecular cut-off of 1000 Da. Assays in bo th systems resulted a similar arrangement of the tested proteins in relatio n to their ability to be hydrolyzed, with casein > fish meal greater than o r equal to soybean meal. With the exception of casein, no significant diffe rences were found between results produced by any of the enzyme sources usi ng the closed system. In constrast, significantly higher hydrolysis of all proteins was produced by mammal enzymes under conditions operating in the o pen system. Differences in the rate of release of amino acids measured in t his latter system were related both to the type of protein and the origin o f the enzymes. When using purified mammal enzymes, release of lysine or phe nylalanine from casein and soybean was high, but low from fishmeal, Isoleuc ine and valine present in fishmeal were preferentially hydrolyzed by commer cial enzymes, but glycine and proline by fish enzymes. (C) 2001 Elsevier Sc ience Inc. All rights reserved.