Abstract: Flavones are important biologically active substances,thus methods to optimize total flavonoid extraction in particular plant species are of significant worth.Response surface methodology (RSM) was performed using five single factors (i.e., ethanol concentration,solid-liquid ratio,ultrasonic power,extraction temperature and extraction time) to optimize experimental conditions for ultrasonic-assisted extraction (UAE) of total flavonoids from Praxelis clematidea, an invasive plant species.In addition,the bacteriostatic activity against Staphylococcus aureus before and after optimization was compared.The result showed that the maximum yield of flavonoids was obtained under optimal extraction conditions of 8 min extraction time,60 ℃ extraction temperature,54% ethanol concentration,a 26 solid-liquid ratio,and 165 W of ultrasonic power.Under these conditions,the actual yield of total flavonoids was 2.385% (relative error,0.022%; predicted value,2.407%).This yield of flavonoids is 1.025% higher than that of previous studies,and the extraction time is shortened 2 hours and 22 minutes.And the antimicrobial difference was not significant(Before:13.898 ± 0.44 mm,After:13.946 ± 0.28 mm; P=0.805 > 0.05)by 100 μL 1.7275 mg/mL total flavonoid extraction.These results indicated that RSM is a credible method for the optimization of total flavonoid extraction from P.clematidea.

Key words: Praxelis clematidea, total flavonoids, ultrasonic extraction, response surface methodology, antimicrobial activity