STABILITY OF PEPSIN (EC 3.4.23.1) DURING IN VITRO PROTEIN DIGESTIBILITY ASSAY2

To maximize the efficiency of utilization of pepsin and estimate the contamination of pepsin for in vitro protein digestibility assays, the specific activity decay and peptide bond hydrolysis of pepsin incubated at different pH and concentration were studied with the bovine hemoglobin method and the o-phthaldialdehyde method, respectively. It was found that increase of pH and concentration of pepsin increased pepsin's half-life for both specific activity decay and peptide bond hydrolysis. The half-life for specific activity decay was not extended by the presence of a substrate protein. The results indicated the time needed to maximize pepsin utilization depended on pH and the concentration of pepsin. At the time when all specific activity of pepsin was lost, the average size of pepsin autolysates was between 6.9 and 12.1 amino acid residues, suggesting most peptic protein would be fractionated as digestible protein.