Abstract: Response surface methodology (RSM) was employed to optimize the extraction conditions of total flavonoids from Zingiber officinale Roscoe stem and leaves collected from Yongzhou (Hunan province).Based on single-factor tests,Box-Benhnken center-composite experiment was carried out with three factors,including alcohol concentration,extraction temperature and extraction time.RSM was used to determine the effect of prime factors on the yield of flavonoids.Besides,the antioxidant activity of flavonoids from Z.officinale stem and leaves was evaluated.Results showed that the optimal extraction conditions were ethanol concentration 70%,extraction temperature 76 ℃ and extraction time 95 min.Under these conditions,the extraction yield of total flavonoids was 15.42±0.09 mg/g,which was close to the predicted value.Thus,the fitted quadratic regression model was valid.The IC₅₀ of the obtained total flavonoids against hydroxyl radicals were 0.501 mg/mL.The reducing ability and scavenging impact of the radicals of flavonoids from Z.officinale stem and leaves were more effective than those of 2,6-di-tert-butyl-4-methyl phenol (BHT) at the same concentration,but lower than vitamin C.

Key words: response surface methodology, Zingiber officinale Roscoe stem and leaves;flavonoids;extraction;antioxidant activity