In Vitro Hydrolysis of Skim Milk and Pea Proteins by Pepsin and Rennin

Abstract

In vitro hydrolysis of skim milk (SM) powder, pea protein concentrate (PPC) and pea protein isolate (PPI) was determined with pepsin and rennin under experimentally established conditions. The hydrolysis of the three proteins, particularly by rennin, followed their in vivo digestibility, i.e., SM>PPI>PPC. In vitro digestibility of PPI by pepsin was also greater than that of PPC. The PPC contained both albumin and globulin proteins while PPI contained mostly globulin proteins. The SDS-electrophoresis showed SM to contain fewer and lower molecular weight proteins than PPC or PPI. The PPC contained more protein bands than PPI. The SM contained 769, PPI 584 and PPC 561μM of tyrosine, tryptophan and phenylalanine per g protein, the amino acid residues preferentially hydrolyzed by pepsin and rennin. Nitrogen solubility and differential scanning calorimetry showed SM to be denatured and PPC and PPI partially denatured. Further denaturation of SM, PPC and PPI by thermal treatment at different temperatures, pH or treatment with urea, guanidine-HCl, 2-mercaptoethanol, and dithiothreitol failed to improve their in vitro digestibility.