Optimization of ACE-Inhibitory Hydrolysate Production from Alfalfa (Medicago Sativa L.) Leaf Protein Using Response Surface Modeling

Alfalfa Leaf protein isolates (ALPI) was extracted by direct heating method of alkali solubilization and acid precipitation, and hydrolyzed by six proteases, including alcalase, neutrase, papain, pepsin, trypsin and flavourzyme, were used to obtain hydrolysates. The results indicated that the alfalfa leaf protein hydrolysate (ALPH) prepared by papain exhibited the highest angiotensin I converting enzyme (ACE) inhibitory activity of 79.69%±2.77% at the same concentration. Therefore, papain was employed to hydrolyze ALPI to produce the ACE inhibitory activity peptides. Then, response surface methodology (RSM) was applied to optimize the hydrolysis conditions (including hydrolysis temperature, enzyme to substrate ratio (E/S) and pH value). The minimum ACE inhibitory rate (92.33%±0.30%) was obtained at an E/S of 3%, a pH of 7.5 and an incubation temperature of 55 oC, which agreed with the predicted value estimated by RSM within a 95% confidence interval. It was suggested that alfalfa Leaf protein hydrolysate prepared by papain with good ACE inhibitory activity and could be a potential source of natural ACE inhibitor.