Characterization of an immobilized digestive enzyme system for determination of protein digestibility

Porcine pepsin, trypsin, alpha -chymotrysin, and intestinal mucosal peptidases, covalently immobilized on porous glass beads, were used to determine the digestibilities of a number of proteins from both plant and animal sources. Immobilized pepsin was used in a separate reactor maintained at low pH, whereas trypsin, chymotrypsin; and intestinal peptidase were placed in a single reactor operated at pH 7.5. Digestibilities determined with pepsin alone were lowest for those proteins having high structural stability such as lysozyme, ovalbumin, and beta -lactoglobulin. Nevertheless, combination of pepsin pretreatment with proteolysis by pancreatic and intestinal enzymes indicated more rapid initial digestion rates by the latter enzymes as a result of the pretreatment of structurally stable proteins. The complete system gave digestibilities in agreement with in vivo studies. Correlation (r super(2)) of digestibilities with FAO and literature values for in vivo digestibilities for a number of plant and animal proteins was 0.83.