Extractions of the flavonoids from barks and leaves of Eucommia ulmoides Oliver by simultaneous ultrasonic/microwave assisted extraction

To improve the extraction yields of flavonoids from Eucommia ulmoides Oliver by simultaneous ultrasonic/microwave assisted extraction(UMAE)method. The degummed E. ulmoides bark and leaf powders were taken as raw materials. The single factor experiment and response surface analysis were used to optimize the extraction conditions by UMAE. Furthermore,the flavonoids in the barks and leaves of E. ulmoides were also compared using HPLC combined standards. The results showed that the optimal conditions were as follows:ethanol concentration,the ratio of plant material to liquid,extraction temperature,microwave power and extraction time were 58%,70:1 (mL:g),75℃,420 W and 6 min. Under these optimal conditions,the yield of flavonoids was 11.80%±0.09%.Meanwhile,the present simultaneous extraction method was compared with microwave assisted extraction(MAE)and ultrasonic assisted extraction(UAE),and the mechanism of the present extraction method was also discussed. By comparison,the extraction yield of flavonoids from E. ulmoides by UMAE was significantly higher than MAE and UAE(p<0.01),which also showed higher DPPH free radical scavenging ability(p<0.01). The results from scanning electron microscope(SEM)indicated that the extraction efficiency of UMAE was higher,since the superiority of UMAE was simultaneously acted and mutually reinforced by ultrasonic and microwave. Consequently,UMAE could crush the plant cells more thoroughly than MAE and UAE,leading to more sufficient extraction,and thus the extraction rate and efficiency were significantly improved. Furthermore,it was found that flavonoids such as rutin,quercetin and kaempferol were significantly higher in leaves than barks,revealing E. ulmoides leaves could be used as better extraction materials for flavonoids than barks.