Abstract: Response surface methodology (RSM) was used to optimize the ultrasonic-assisted extraction process of total saponins from stems and leaves of Pairs polyphylla var. yunnanensis (Franch.) Hand. Mazz.Furthermore,the antioxidant activity of the total saponins was analyzed in vitro. Based on single-factor tests,a five-level four-factor response surface test was developed by Box-Benhnken design.The optimal extraction conditions were determined to be the solid-liquid ratio of 1:12 (g/mL),extraction temperature of 54 ℃,ultrasonic power of 210 W,and extraction time of 2 h.Under these conditions,the extraction yield was 2.360%,while the predicted extraction yield was 2.385%,with relative error of 1.04%.The maximum inhibition rates of DPPH,hydroxyl radical and superoxide anion of the total saponins were 98%,58% and 64%,respectively.The IC₅₀ values of those antioxidant activities were 2.223 mg/mL,6.782 mg/mL and 4.638 mg/mL,respectively.

Key words: stems and leaves of Pairs polyphylla var. yunnanensis (Franch.) Hand.Mazz.;total saponins;response surface method;ultrasonic-assisted extraction, antioxidant