Evaluation of Antioxidant Activity of Eucommia ulmoides Leaf Extracts by DPPH· Assay

The antioxidant components of Eucommia ulmoides leaves were extracted by ultrasonic-assisted method and their antioxidant activities were investigated by scavenging DPPH·.The extracts obtained from optimum technological conditions were further extracted by different polar organic solvents and the contents of total phenolic compounds,total flavonoids and DPPH radical scavenging activity were determined.The results showed that the optimal parameters of the ultrasonic-assisted extraction were as follows: ethanol concentration 60%,solid to liquid ratio 1∶15,temperature 60℃ and extracting time 30 min.Under these conditions,the clearance rate to DPPH· were 91.01%.The bioactive antioxidants of E.ulmoides leaves were mainly attributed to the ethyl acetate fraction.The percentage of scavenging DPPH radical of the sample of the ethyl acetate fraction with the concentration of 100 μg·mL-1 was 92.28%,stronger than those of BHT(p0.05) and no significant differences compared with those of Vc.The result of correlation analysis showed that the strong antioxidant activity mainly resulted from the high contents of the total phenols and total flavonoids.