Antioxidant and biochemical properties of protein hydrolysates prepared from Silver carp (Hypophthalmichthys molitrix)

The antioxidant and biochemical properties of enzymatically hydrolyzed silver carp (Hypophthalmichthys molitrix) protein were studied. The molecular weight of the main peaks of the hydrolysates by both Alcalase and Flavourzyme was lower than 5000 Da. The hydrolysates treated by Alcalase for ?1.5 h (hydrolysis time) showed that the relative proportion of <1000 Da fraction was more than 60%. For the biochemical properties, hydrolysis by both enzymes increased protein solubility to above 75% over a wide pH range; and when the hydrolysis time was prolonged (>3 h), the colour of the hydrolysates turned yellowish. The protein hydrolysates exhibited significant hydroxyl radical-scavenging activity and inhibited linoleic acid peroxidation. For Alcalase treatment, the hydroxyl radical-scavenging activity and the inhibition of linoleic acid peroxidation of hydrolysates appeared to reach a maximum level for 1.5, 2.0 h of hydrolysis, respectively; and their antioxidant activity was close to that of α-tocopherol in a linoleic acid emulsion system, and carnosine in the 2-deoxyribose oxidation system. The hydrolysate with lower molecular weight distribution possessed stronger Fe²⁺ chelation ability at a sample concentration of 5.0 mg/mL. The results suggested that the antioxidant activity of silver carp protein hydrolysates were related to its degree of hydrolysis (DH), hydrolysis time and molecular weight.