Abstract:The aim of this study was to optimize the process of extracting polyphenols from Dendrobium officinale leaves using response surface methodology and to investigate the free radical scavenging ability of polyphenols from D.officinale leaves.The following extraction conditions were found to be optimal：ethanol concentration，50%；ultrasonic power，350 W；extraction time，37 min；liquid-solid ratio，36∶1（mL/g）；extraction temperature，60 ℃；and times of extractions，2.Under these optimized parameters，the yield of polyphenols from D.officinale leaves was 34.15 mg/g.Moreover，the polyphenols from D.officinale leaves effectively scavenged hydroxyl radicals，superoxide anion radicals，and 2，2-diphenyl-1-picrylhydrazyl（DPPH）free radicals.The free radical removal rate increased with increasing polyphenol concentration.The half-maximal scavenging concentrations（IC50）of the polyphenols toward hydroxyl radicals，superoxide anion radicals，and DPPH free radicals were 0.554，0.775 mg/mL and 0.596 mg/mL，respectively.However，the antioxidant capacity of the polyphenols was weaker than the antioxidant capacity of vitamin C at the same concentration.