Protein Digestion in vivo: Peptides and Free Amino Acids in the Jejunum of Rats Fed Different Dietary Proteins

Abstract

To understand the relevance of peptide release and absorption during protein digestion to its quality, digestibility of a few animal (AP) and plant proteins (PP) was studied in trained rats. Some differences were observed between proteins in their digestion in vivo and absorption (as assessed by recovery of fed nitrogen). We observed that rats fed AP diets had a greater proportion of peptides (total, large (PI) and small (P2) including dipeptides) in their jejunal luminal supernatants than those fed PP diets, which had a greater proportion of free amino acids (AA). AA fractions always had a higher essential amino acid (EAA) content than peptide fractions; and among peptide fractions, the PI fraction had a greater content of EAAs than the P2 fraction. Protein quality was correlated positively with the proportion of peptides (total, PI, P2, and dipeptides) in the jejunal luminal supernatants and negatively with that of AAs. Incorporation of some of these in vivo digestion indices increased the correlation between chemical and animal growth indices of protein quality, suggesting their relevance to protein nutritional quality. © 1987, SOCIETY FOR FREE RADICAL RESEARCH JAPAN. All rights reserved.