Abstract
This study investigated the formation of angiotensin-converting enzyme (ACE) inhibitory peptides from koro kratok beans tempe during gastrointestinal digestion. The absorption of bioactive peptides was also investigated in this study. Koro kratok was fermented by commercial culture including Rhizopus oligosporus for 48 h. Gastrointestinal digestion was simulated sequentially by hydrolysis of tempe protein extract with pepsin and pancreatin for 240 min. The peptide content, degree of hydrolysis, molecular weight distribution, and ACE inhibitory activity were analyzed. The absorption of ACE inhibitory peptides was evaluated using the inverted gut sac of Sprague Dawley rats. Results showed that some amino acids, such as Arg, Lys, Asp, Glu, Phe, and Leu, were predominantly found in tempe. After the hydrolysis process, cooked tempe exhibited the highest ACE inhibitory activity (90.05%). Although the ACE inhibitory activity of nonfermented koro kratok was lower than that of tempe, the increase in its inhibitory activity was too large (23.03%). The ACE inhibitory peptides from tempe showed a predominance of peptides with a molecular weight of < 1 kDa and could inhibit ACE activity by 84.34%. The majority of ACE inhibitory peptides from tempe was absorbed in the jejunum and exhibited an ACE inhibitory activity of 81.59%. Based on these results, it can be concluded that the fermentation and boiling process of koro kratok beans improved the release of ACE inhibitory peptides during the gastrointestinal digestion process and had an impact on its absorption.