Angiotensin I-converting enzyme inhibitory and antioxidant properties of rapeseed hydrolysates

This study investigates the angiotensin I-converting enzyme (ACE) inhibitory and antioxidative activities of protein hydrolysates prepared from industrial defatted rapeseed meal using various proteolytic enzymes. The hydrolysate generated by Alcalase displayed the highest ACE-inhibitory activity (IC50 0.02 mg/ml) as well as high inhibitory capacity against lipid oxidation in a liposomal model. The Alcalase hydrolysate was fractionated using stepwise solid-phase extraction into three fractions (SP10, SP30, SP60), of which the hydrophobic fractions possessed the highest ACE-inhibitory activity. Subjecting these fractions to ultra filtration with 3000 Da molecular weight cut off (MWCO) membrane revealed that ACE-inhibitory activity was concentrated in the permeate. The ACE-inhibitory peptides in Alcalase hydrolysate exhibited good stability in an in vitro digestion model using human gastric and duodenal fluids. Kinetics studies gave moderate Ki values (0.2–0.3 mg/ml) and an uncompetitive pattern of ACE inhibition for the Alcalase hydrolysate and peptide fractions. Our results indicate the defatted rapeseed meal is a potential source of ACE-inhibitory compounds for use in functional foods.