Isolation of essential oil from the leaves of Polygonum viscosum Buch-ham. using microwave-assisted enzyme pretreatment followed by microwave hydrodistillation concatenated with liquid–liquid extraction

Microwave-assisted enzyme pretreatment followed by microwave hydrodistillation concatenated with liquid–liquid extraction (MEP-MHDE) was developed in this work for the efficient separation of essential oil from the leaves of Polygonum viscosum Buch-ham. The modified hydrodistillation concatenated with liquid–liquid extraction apparatus included conventional oil-water separation process and another extraction process for essential oil components from the hydrosol using an organic solvent. A comparison of the types of enzymes implied that the composite enzyme of cellulase and pectinase (1/1, w/w) performed better than the others. The optimum conditions derived were a microwave irradiation time of 17 min, a microwave irradiation power of 503 W, and an incubation temperature of 42 °C, which were evaluated through single factor experiments and Plackett–Burman design for selecting significant parameters as well as Box–Behnken design for optimizing the conditions. Based on these conditions, high yields of essential oil in the first separation column (3.66 ± 0.11 g/kg) and second separation column (1.02 ± 0.03 g/kg) were achieved. The developed MEP-MHDE method performed better regarding obtaining a higher yield of essential oil using a shorter time than other methods, which was mainly attributed to the influence of the combination of microwave irradiation, enzyme pretreatment and the hydrodistillation concatenated with liquid–liquid extraction apparatus. Through GC–MS analysis, more oxygenated compounds of the essential oil were achieved in the second separation column than in the first one, thus providing more valuable essential oil. Thus, the developed MEP-MHDE method is an efficient method for separation of high-value essential oils from natural plants and crops.