Abstract: The ultrasonic-assisted alkaline extraction of duck liver protein was optimized by response surface methodology, and the antioxidant activity of duck liver protein extracted with and without ultrasonic treatment was compared. For the ultrasonic-assisted extraction, the optimum conditions were determined as follows: ultrasonic power, 256 W; ultrasonic exposure time, 43 min; and pH value, 11, where the maximum yield of duck liver protein equal to 73.1% was achieved. Antioxidant activity tests showed that IC50 values for scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS+·) and hydroxyl free radicals were 1.97, 0.168 and 0.529 mg/mL of the ultrasonically extracted duck liver protein, respectively, suggesting stronger scavenging activity against ABTS+· than other free radicals, which also had high reducing power. Moreover, its antioxidant activity was significantly higher than that of the conventional alkali-extracted protein (P < 0.05). The current study may provide a scientific basis for intensive processing of duck liver.

Key words: duck liver protein, ultrasonic-assisted alkaline extraction, response surface methodology, antioxidant activity