Soy protein isolate hydrolysate was separated by ultrafiltration membranes with different relative molecular weight cut-offs. The effects of operation pressure, mass concentration of feed, ultrafiltration time on ultrafiltration membrane flux were studied. Then the scavenging capacities on ·OH and DPPH·of different ultrafiltration fractions were studied. The results showed that the optimal ultrafiltration conditions were determined as follows: operation pressure 0.2 MPa, mass concentration of feed 50 g/L, ultrafiltration time 80 min for ultrafiltration membranes with relative molecular weights of 10, 3, 1 kD, ultrafiltration time 100 min for ultrafiltration membrane with relative molecular weight of 5 kD. The soy peptide of relative molecular weight less than 3 kD had higher radical-scavenging rate, and the scavenging rate of ·OH and DPPH· showed some degree of correlationship. |