Abstract: The scavenging activity of enzymic hydrolysates of the soy protein isolates on hydroxyl radical (•OH)of Fenton reaction was studied by colorimetric.The results showed that the hydrolysates could scavenge •OH.The hydrolysates of hydrolyzed SPI by using papain for 15min showed the strongest scavenging activity as 56.5%.The mixed hydrolysates were fractionaled with a sephdes G-50 resin with considerable variations in antioxidant actvity existed among different peptide fractions.Molecular weights of the fractions were measured by sodium dodecyl sulfate-Polyacrylamide gel electrophoresis,and showed that the polypeptides at 11.355KD～5.154KD had the best antioxidant activity with the sangnging activity on hydroxyl radical as 60.4%.

Key words: Soy protein isolates , Enzymic hydrolysates , Hydroxyl radical , Scavenging activity