Optimization of the ultrasound- assisted extraction of flavonoids from propolis and its antioxidant activity

The flavonoids of propolis were extracted by ultrasound assisted method,the extracted conditions were optimized by response surface methodology,and the antioxidant activities of flavonoids extracted by pulsed ultrasound were analyzed by DPPH and FRAP assay.First,the optimal frequency of ultrasound was selected.On the basis of single variable experiment,the extracted conditions of flavonoids in propolis were optimized by4- variable,3- level Box- Behnken experimental design. The optimized ultrasound frequency was 20 k Hz,the order of other factors affecting the total flavonoid content was the duty cycle > liquid height > extraction time > the power of ultrasound.The optimized parameters were as follows: extraction time 18 min,the power of ultrasound 100 W,duty cycle 75% and liquid height 4 cm. The extraction yield of flavonoids were( 39.06 ± 0.48) mg / g. At these conditions,the flavonoids extracted by pulsed ultrasound assisted method showed great DPPH and FRAP antioxidant activities.