Small Peptides Isolated from Enzymatic Hydrolyzate of Fermented Soybean Meal Promote Endothelium-Independent Vasorelaxation and ACE Inhibition

Fermentation of soybean is a process in which soy proteins are broken down into small peptides to exert various physiological functions beyond their nutritional value and to improve food source bioactive components responsible for health benefits. Enzymatic hydrolysis could speed up the degradation of proteins during fermentation of soybean, thus resulting in higher peptide production. In the present study, fermented soy meal (fermented with Bacillus subtilis from Douchi) was hydrolyzed by thermolysin, and the water extraction was then separated into four fractions using ultrafiltration membranes. Their vasorelaxation activities were screened, and the most potent fraction was further isolated and purified to obtain four peptides. Briefly, three peptides exerted a dose-dependent vasorelaxation (0.01–4.10 μM) in the phenylephrine preconstricted thoracic aorta ring of Sprague–Dawley rat (relaxation actions were all endothelium-independent), while one peptide induced vasoconstriction. Furthermore, an independent causal relationship between vasorelaxation and angiotensin converting enzyme (ACE) inhibition activities was found.