Polyphenols from Grape Skin:Optimization of Ultrasonic-assisted Extraction Process by Response Surface Methodology and Antioxidant Activity Evaluation

Response surface methodology was employed to optimize the ultrasonic-assisted extraction of polyphenols from grape skin as a byproduct of wine making.On the basis of one-factor-at-a-time experiments,through which the optimal ultrasonic power and ethanol concentration were found to be 100 W and 40%,respectively,polyphenol yield was investigated by response surface methodology with respect to liquid-to-material ratio,extraction time and temperature at three levels.The optimal levels of liquid-to-material ratio,extraction time and temperature were determined to be 16:1(mL/g),57 min and 50 ℃.Under such conditions,the yield of grape skin polyphenols was(42.51 ± 1.21) mg/5 g.The antioxidant activity in vitro of the obtained extract was evaluated by DPPH free radical scavenging assay and potassium ferricyanide reduction assay using water-soluble VE as the control.Grape skin polyphenols were found to have powerful DPPH free radical scavenging capacity and reducing power in a linear dose-dependent manner.