Microwave Hydrodistillation Based on Deep Eutectic Solvent for Extraction and Analysis of Essential Oil from Three Amomum Species Using Gas Chromatography-Mass Spectrometry

Deep eutectic solvent has been gaining much attention in recent years due to its various novel properties. The present study develops a novel microwave-assisted hydrodistillation method based on pretreatment using deep eutectic solvent, for the extraction of essential oil (EO) from dry fruits of Amomum kravanh, Amomum tsaoko, and Amomum villosum, respectively. The process is optimized by single-factor experiments taking the improvement in the essential oil yield of A. kravanh as the target. The results indicate that using the reaction product of choline chloride and ethylene glycol as the deep eutectic solvent with 7:1 of mass ratio to fruit powder, the optimal conditions are (1) pretreatment stage: 500 W of microwave power, 50 A degrees C of temperature, and 7 min of duration; (2) fast heating stage: 600 W of microwave power, 110 A degrees C of temperature, and 5 min of duration; (3) hydrodistillation stage: 300 W of microwave power, 110 A degrees C of temperature, and 30 min of duration. Under these conditions, the EO yields of A. kravanh, A. tsaoko, and A. villosum are 3.64, 2.16, and 1.62%, respectively. The EOs are analyzed by gas chromatography-mass spectrometry, with totally 63 compounds identified. In most cases, the new method brings about more identified compounds than the traditional methods. Moreover, the relative contents of hydrocarbons in most essential oils are improved by applying the new method. Thus, the approach based on deep eutectic solvent has been proved superior in the enhancement of essential oil production.