Abstract

This study aimed to fractionate water-soluble antihypertensive peptides from fermented African oil bean condiment and evaluate their antioxidant properties and inhibitory effects on enzymes associated with hypertension. The condiment was prepared using traditional methods, oven-dried, and extracted in distilled water (200 g/L) for one hour, followed by filtration through a 0.45 μm membrane filter. Subsequently, the filtrate was fractionated using molecular weight cut-off (MWCO) membranes with pore sizes of 1 kDa, 3 kDa, and 10 kDa. The resulting peptide fractions yielded 1.05% (1 kDa), 7.16% (3 kDa), 10.53% (10 kDa), and 80.36% (>10 kDa) by dry weight of the condiment. The antioxidant properties of the fractions were assessed through ferric reducing antioxidant power (FRAP), DPPH radical scavenging, ABTS+• scavenging, nitric oxide (NO•) scavenging, and Fe²⁺-chelating assays. Additionally, the inhibitory effects of the fractions on arginase and angiotensin-I converting enzyme (ACE) – key enzymes linked to hypertension – were evaluated in vitro. The results demonstrated that all peptide fractions exhibited potent radical scavenging abilities (>60%), with the 1 kDa fraction showing the highest scavenging activity for all tested radicals. However, no significant difference (P > 0.05) was observed in the FRAP assay among the fractions. Furthermore, the 1 kDa fraction also displayed the strongest inhibitory effects on arginase and ACE activities in vitro. In conclusion, this study revealed that fermented African oil bean condiment is a potential source of bioactive peptides with significant antioxidant and antihypertensive properties. Among the fractions, the 1 kDa fraction emerged as the most potent and could be incorporated into functional food formulations aimed at managing hypertension.