Abstract:

In this study, flavonoids were extracted from pomelo peel by ultrasonic extraction method using 70% ethanol as the solvent. The optimum extracting parameters were investigated with quadratic rotation combination design. The mathematical model including the rate of flavonoids extraction, ultrasonic power, ultrasonic time and the ratio of material to liquid was established. Scavenging effects of pomelo peel flavonoids on superoxide anion, DPPH, and hydroxyl radical were studied. The results showed that ultrasonic power, ultrasonic time and the ratio of material to liquid have significantly effects on the yield of pomelo peel flavonoids, and the regression quadratic equation is Y=0.5087+0.0311X1－0.0253X2－0.0289X3 +0.0498X1－0.0238X1X3+ 0.0395X2 + 0.022X2X3 + 0.0233X3, and the optimal conditions are attained through the regression equation as following: ultrasonic power 1250 W, ultrasonic time 10 min and the ratio of material to liquid 1:30 (g/ml). The extraction rate of flavonoids from pomelo peel is 0.734% through experiment and the mathematical model provids a good fit. Moreover, antioxidation experiments showed that flavonoids from pomelo peel have very strong scavenging capabilities for superoxide anion and DPPH free radical, their EC50 values are 0.0906 mg/ml and 0.0161 mg/ml respectively, and are approximately 1.9 times and 3.3 times as much as that of vitamin C respectively. The scavenging capability of pomelo peel flavonoids for hydroxyl radical is weaker than that of vitamin C, and its EC50 is 0.5649 mg/ml, 15.5 times as much as that of vitamin C.

Key words: pomelo peel, flavonoids, ultrasonic-assisted extraction, quadratic rotation combination design, antioxidation