Partial enzymatic hydrolysis of whey protein by trypsin

Partial enzymatic hydrolysis of whey protein by trypsin increased solubility of this protein in water. Water-insoluble, heat-denaturated whey protein was solubilized fully by trypsinization. Optimal conditions for the enzyme reaction, established by the pH-stat technique, were: digestion at pH 8.0 and 55 C for approximately 3 h, at an enzyme-substrate ratio of 1 : 100. Under these conditions, 500 mumoles of titratable protons were liberated per g of substrate in the course of the reaction. Digestion at 40 C generated only about 400 mumoles of acid. Predenaturation of the substrate by heat did not improve digestibility. The extent of hydrolysis reached approximately 8% of all peptide bonds in the protein. Fractionation of the digest on Sephadex G-50 showed it was composed of a major fraction of highly water soluble peptides, ranging in molecular weight from approximately 500 to 5000. The gel excluded a minor fraction of larger, aggregated peptides. This aggregate was dissociated in the presence of urea and a reducing agent. All amino acids in the digest, except some lysine and arginine, were peptide bound.