Release of peptides and amino acids from dietary proteins during sequential enzymatic digestion in vitro with pepsin, pancreatin + trypsin and erepsin

Abstract

Six plant proteins and five animal proteins were subjected to sequential enzymatic digestion in vitro with pepsin, pancreatin + trypsin and erepsin and the release of peptides and amino acids (aa) was determined after separating the enzymatic digests on columns of copper Sephadex G25. The dipeptide content of the peptide fractions was determined by a simple Biuret method and the amino-acid composition of the different fractions was determined in an automatic amino-acid analyser. There were no significant differences between plant and animal proteins with respect to the quantities of aa released as total peptides and as free aa. However, the release of small peptides (especially the dipeptides) was significantly higher with animal proteins than plant proteins. The quality of the different fractions as judged by their essential amino acids/non-essential amino acids ratios or their essential amino-acid composition indicated the smaller peptide fraction (P 2) of animal proteins to be of better quality than all the other peptide fractions obtained while the free aa fraction was the best. There was a positive correlation between the dipeptide content of the enzymatic digests of proteins and their quality.