Microwave Assisted Extraction: The Effects mechanisms and application selection

The application of solvent free microwave extraction (SFME) and microwave assisted extraction (MAE) of the effective compounds from selected plant matrices was investigated. The effective diffusion coefficients (Deff ) of saikosaponins under MAE was determined. The effect of microwave irradiation on microstructure of plant tissues was observed using scanning electronic microscopy (SEM) technique.;SFME of essential oil from pomelo peels, and sequential MAE of pectin from oil extracted peels were performed. The results showed that SFME was superior to the conventional hydrodistillation (HD) method in terms of extraction efficiency and the yield. The extraction time of MAE of pectin was also significantly shorter than that of the conventional method. The sequential extraction of essential oil and pectin from pomelo fruit peels by SFME and MAE was a feasible processing method.;In the study of MAE for extraction of saikosaponins from Radix Bupleuri, the effects of microwave power, irradiation time, temperature, ethanol concentration, solvent-to-sample ratio, and sample particle size were evaluated. Compared with conventional extraction methods, MAE can significantly reduce the extraction time, resulting in better extraction efficiency. The optimum MAE conditions for extracting saikosaponin a, c, and d simultaneously were found by desirability function approach to be at the microwave power of 360--400 W, ethanol concentration of 47--50 %, temperature of 73--74 °C and time of 5.8--6.0 min. At these conditions, the yields from the verification experiments were 96.18--96.91 % for saikosaponin a, 95.05-95.71 % for saikosaponin c, and 97.05--97.25 % for saikosaponin d, which were in good agreement with the predicted values from the fitted models.;The diffusion coefficients of saikosaponins through the solid matrix under MAE were determined using a Fick's second law-based model. It was found that the Deff increased as a result of the increase in microwave power, and were significantly higher than those extracted with the conventional extraction method. SEM results indicated that microwave heating caused the explosion of oil glands and rupture of parenchymal cells of the selected plant materials. As a result, better extraction efficiency and significantly reduced extraction time for extraction of the effective compounds were obtained using MAE.