Abstract: The objectives of this study were to optimize the ultrasonic-assisted extraction process of total flavonoids from Schnabelia tetradonta with orthogonal design and to determinate its antioxidant activity. The antioxidant activity of S. tetradonta was evaluated by three methods:DPPH radical scavenging,ABTS radical scavenging and FRAP assay,with Vc as the control. The single factor test and orthogonal design were used to select the optimal extraction condition with ultrasonication by studying the effect of ethanol concentration,ultrasonic time,solid-liquid ratio and extraction temperature on the extraction yield of flavonoids. The experimental results revealed that:the optimal extraction conditions were:ethanol concentration of 70%,solid-liquid ratio of 1:30 g/mL,and extracting 2 times at 50 ℃,30 min each time. Under these conditions,the extraction yield of total flavonoids reached up to 4.78%. In addition,total flavonoids of S. tetradonta showed strong DPPH radical scavenging activity (IC₅₀=42.91 μg/mL,the maximum scavenging rate was 88.57%),ABTS radical scavenging activity (IC₅₀=44.61 μg/mL,the maximum scavenging rate was 92.86%) and ferric reducing antioxidant power (AEAC=5380 μmol/g). It is an effective and natural antioxidant.

Key words: Schnabelia tetradonta, ultrasonic-assisted extraction, total flavonoids, DPPH, ABTS, FRAP