Renin and angiotensin converting enzyme inhibition with antioxidant properties of African yam bean protein hydrolysate and reverse-phase HPLC-separated peptide fractions

Enzymatic hydrolysate of African yam bean seed proteins was prepared by treatment with alcalase. The African yam bean seed protein hydrolysate (APH) was further separated into six fractions (F1–F6) on a C12 reverse-phase HPLC column. With exception of F6, amino acid composition analysis showed increase in content of hydrophobic amino acids as residence time on the column increased. Some of the peptide fractions had significantly higher (p < 0.05) superoxide and DPPH radical scavenging activities as well as higher inhibition of linoleic acid oxidation when compared to the unfractionated APH. Iron-chelating ability of APH and peptide fractions was positively related to inhibition of linoleic acid oxidation, which suggests the role of metal-catalyzed reactions during lipid peroxidation. However, peptide fractionation had no effect on ferric reducing antioxidant power. F4 and F6 fractions had significantly higher ACE- and renin-inhibitory properties, respectively. The results showed that a higher residency time on the column (reflecting stronger net hydrophobic character) enhanced peptide-induced renin inhibition but lower net hydrophobic character was better for ACE inhibition. There was no direct relationship between ACE and renin inhibitions, indicating different modes of enzyme-catalyzed reactions. We concluded that the APH and peptide fractions may have potential uses as antioxidants and modulators of the renin–angiotensin system for the management of oxidative stress and cardiovascular disorders, respectively.