Optimized preparation of ACE-inhibitory and antioxidative whey protein hydrolysate using response surface method

The main aim of the present study was to optimize the hydrolysis conditions of whey protein isolate digested by a protease preparation from Aspergilus oryzae through response surface method (RSM) in order to achieve the maximum angiotensin I-converting enzyme (ACE)-inhibitory activity and antioxidant properties. The effects of hydrolysis conditions including time (2, 13, 24, 35, and 46 h), temperature (40, 45, 50, 55, and 60 °C) and pH (6, 6.5, 7, 7.5, and 8) were investigated on the bioactivity of whey protein hydrolysates. Each process parameter emerged to have a dual effect on bioactivity; that is, increase in all variables promoted bioactive peptide generation through facilitating enzyme access to the primary protein sequence by partial unfolding of the compact globular assemblies of whey proteins. However, prolonged digestion at high temperatures and alkaline pH were concomitant with decreased bioactivity which are attributed to hydrolysate aggregation and splitting of bioactive peptides into biologically inactive counterparts, respectively. Nonetheless, some discrepancies were observed between the trend of ACE-inhibitory activity and that of antioxidant activity changes which was explained in light of their general characteristics. RSM efficiently identified the critical levels of each variable to obtain maximum bioactivity. It was shown that hydrolysate prepared at 56.54 °C and pH 6.04 resulting from digestion for 3.89 h exerted 74% ACE-inhibitory activity, 666.31 μM trolox equivalent/mg antioxidant activity, and 14.03% hydrolysis degree.