Optimization of antihypertensive and antioxidant hydrolysate extraction from rice bran proteins using ultrasound assisted enzymatic hydrolysis

In this study, antihypertensive and antioxidant protein extraction by means of ultrasound-assisted enzymatic hydrolysis was optimized in order to increase the added value of rice bran, which is a byproduct of rice milling. For this purpose, ultrasound treatment optimization was carried out with protein yield as response and solid/liquid ratio, time and power as independent factor using the response surface methodology (RSM). However, degree of hydrolysis (DH), ACE inhibitory activity, DPPH radical scavenging activity were selected as responses and solid/liquid ratio together with time as independent factors during alcalase pepsin and trypsin treatments. Three fractions depending on the molecular weight were separated by ultrafiltration. In enzyme treatments; the increase in solid/liquid ratio resulted in an increase in DH. On the other hand the impact of solid/liquid ratio and treatment time on antihypertensive and antioxidant properties varied. Differences of ACE inhibitory activity between ultrafiltrated protein fraction is not significant statistically. However, 5-10 kDa ultrafiltrated fraction is different for DPPH, hydroxy radical scavenging activity and trolox equivalent antioxidant capacity. Furthermore, the highest bioactivity values were obtained from 5-10 kDa ultrafiltrated fraction as 11.10% for DPPH, 6.20% for hydroxy radical scavenging activity and 8.19 mu g trolox/mg sample for trolox equivalent antioxidant capacity.