Inhibitory Properties of Kidney Bean Protein Hydrolysate and its Membrane Fractions Against Renin, Angiotensin Converting Enzyme, and Free Radicals

Kidney bean hydrolysate (KBH) was obtained by alcalase hydrolysis of the seed globulin protein followed by membrane ultrafiltration to produce peptide fractions that differ in molecular sizes (<1, 1?3, 3?5, and 5?10 kDa). Evaluation of potential antihypertensive properties of the peptides showed that the <1 and 5?10 kDa fractions exhibited significantly highest (p<0.05) renin inhibition. In contrast, the KBH and peptide fractions showed similar and non?significant (p<0.05) inhibitory activities against angiotensin converting enzyme. The antioxidant power of the hydrolysates was evaluated through free radical scavenging activities (DPPH and hydroxyl radical), inhibition of iron activities (metal chelation and ferric reducing antioxidant power) and inhibition of linoleic acid peroxidation. The <1 and 5?10 kDa peptide fractions showed significantly (p<0.05) higher ability to scavenge DPPH free radical, inhibit peroxidation oflinoleic acid and reduce Fe3+ to Fe2+. Generally the fractions with <1 and 5?10 kDa peptides showed better potential as antihypertensive and antioxidant peptides, probably due to their slightly higher contents of hydrophobic aminoacids. It was concluded that kidney bean protein hydrolysate and some of the peptide fractions could potentially serve as useful ingredients to formulate functional foods and nutraceuticals against hypertension and oxidative stress.