Optimization of extraction of essential oil from white pepper ( Piper nigrum L.) by simultaneous ultrasonic-microwave assisted extraction

The optimal conditions for simultaneous ultrasonic-microwave assisted extraction ( UMAE) of essential oil from white pepper ( Piper nigrum L.) were established by single factor experiments and response surface analysis as follows: Extraction temperature 100 ℃, ratio of plant material to water 1 ∶ 10 ( g/m L) , that microwave and ultrasonic powers were 500 W and50 W, respectively, and extraction time 7 min. Under such optimal conditions, the yield of essential oil was 3.80% ± 0.08%.Meanwhile, UMAE was compared with single microwave assisted extraction ( MAE) and ultrasonic assisted extraction ( UAE) , the extraction yield of essential oil by UMAE was significantly higher than those of single MAE ( p < 0.001) and UAE alone ( p <0.001) . The results from scanning electron microscope showed that when ultrasonic wave and microwave worked in coordination, the cell walls of white pepper could be broken more thoroughly, which was helpful for the essential oil to dissolution.Conclusion: Using UMAE technique to extract the constituents of essential oil, the extraction efficiency of essential oil is significantly superior to the conventional extraction methods.