Abstract: To optimize the extraction process of total flavonoids from the tubers of Stephania kwangsiensis H. S. Lo and explore its in vitro antioxidant activity, based on single-factor experiments, an orthogonal test method was used to investigate the effects of ethanol concentration, solid-liquid ratio, extraction temperature, and ultrasonic time on the extraction rate of total flavonoids. The optimal extraction process was determined, and the in vitro antioxidant activity of total flavonoids was further studied. The results showed that the optimal extraction condition for total flavonoids from the tubers of Stephania kwangsiensis H. S. Lo was ethanol concentration of 70%, solid-liquid ratio of 1∶; 35 (g/mL), extraction temperature of 50 ℃, and ultrasonic time of 50 min. Under this condition, the yield of total flavonoids content could reach up to 5.45 mg/g. The total flavonoids from Stephania Kwangsiensis H. S. Lo exhibited strong antioxidant activity, with the scavenging rate against 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals reaching up to (84.39±; 0.61)%. In this study, the ultrasound-assisted extraction process of total flavonoids coupled with ultraviolet spectrophotometry was simple and yielded reliable results. Given that the total flavonoids possessed good antioxidant properties, this method could provide a sound theoretical reference for the extraction, development, and application of total flavonoids from Stephania kwangsiensis H. S. Lo.

Key words: Stephania kwangsiensis H. S. Lo, total flavonoids, extraction process, orthogonal test, antioxidant activity