Abstract:

We report the response surface optimization of the process of extracting total flavonoids from Wikstroemia indica (Linn.) C.A.Mey with an ultrasonic-microwave synergistic extractor and the subsequent evaluation of antioxidant activity of the extract. Based on a series of one-factor-at-a-time investigates, Box-Behnken experimental design was employed to provide experimental data for developing a regression model with the extraction yield of total flavonoids as dependent variable and three process conditions, namely ethanol concentration, length of extraction and microwave power as independent variables, and the interactive effects of the three independent variables on the dependent variable were analyzed. The optimum process conditions for extracting total flavonoids from Wikstroemia indica (Linn.) C.A.Mey were determined as follows: ethanol concentration, 70%; length of extraction, 123 s; and microwave power, 419 W. Under such conditions, the experimental value of extraction yield of total flavonoids was 1.172%, in substantial agreement with the predicted value of 1.162%. This demonstrates that the developed regression model could give an accurate prediction of extraction yield of total flavonoids. The total flavonoid extract in concentration ranges from 13.16 to 78.96μg/mL and from 0.43 to 52.64μg/mL could scavenge both DPPH and hydroxyl free radicals in a significant concentrationdependent way, with scavenging ratios ranging from 20.87% to 71.11% and from 9.04% to 52.21%, respectively.

Key words: Wikstroemia indica (Linn.) C.A.Mey., total flavonoids, ultrasonic-microwave synergistic extraction, response surface methodology, antioxidant activity