Optimization of ultrasonic extraction of flavonoids from Moringa stenopetala leaves and their antioxidant activities

Response surface methodology( RSM) was firstly used to optimize ultrasonic- assisted extraction( UAE) of total flavonoids from Moringa stenopetala leaves. Based on the yield and oxygen radical absorbance capacity( ORAC) of flavonoids,the four single factors including ethanol concentration,solid-liquid ratio,ultrasonic time and temperature were optimized.The optimal conditions were enthanol concentration 70%( v / v),solid- liquid ratio 1∶ 27( g /m L),ultrasonic time 46 min and temperature 50 ℃.Under the condition,the yield and ORAC value were( 48.93± 0.44) mg rutin equivalent( RE) / g and( 2747.17 ± 301.51) μmol trolox equivalents( TE) / g,respectively,which had no significant differences with the predicted values( 49.23 mg RE / g,2853.99 μmol TE / g). The crude extract was then purified by polyamide resin,the flavonoids content and ORAC value were increased to 65.89% and( 5923.48 ±228.65) μmol TE / g.The crude and purified extracts showed strong DPPH and ABTS radical scavenging activities.The EC50 values of crude extract were 0.45 mg / m L and 0.10 mg / m L and the EC50 values of purified extract were0.26 mg / m L and 0.05 mg / m L.These results demonstrated that UAE was a highly effective way to extract flavonoids from Moringa stenopetala leaves and the polyamide resin could significantly increase flavonoids content and antioxidant activity of flavonoids extract.