Abstract: This study aimed to reveal whether the difference in hypotensive activity between animal and plant proteins could be caused by the angiotensin conversion enzyme (ACE) inhibitory activity of peptides present in protein digests. The ACE inhibitory activity of peptides derived from in vitro digestion of plant and animal proteins was assessed. The in vitro digestion of plant proteins (rice, oat, soybean, and pea), red meat proteins (pork and beef), and white meat protein (chicken) was carried out by using a two-step process of hydrolysis with pepsin and trypsin. The hydrolysis degree, relative molecular weight distribution, amino acid composition and ACE inhibition rate of the obtained peptides were determined. The results showed that the inhibition percentage of ACE activity by protein digests increased with the increase in the degree of hydrolysis and consequently the decrease in the relative molecular weight. Among all protein digests, the ACE inhibition rate of plant protein digests was the highest (60.41%), while the lowest value (40.13%) was observed for red meat protein digests. The amino acid composition of protein digests showed that the levels of hydrophobic amino acids in both plant protein and white meat protein digests were significantly higher than in red meat protein digests. The higher the concentration of hydrophobic amino acids in protein digests was, the higher the ACE inhibitory activity was. It was suggested that the high content of hydrophobic amino acids may be one of the main causes of the ACE inhibitory activity of plant protein-derived peptides.

Key words: plant protein, red meat protein, white meat protein, in vitro digestion, angiotensin converting enzyme (ACE)