DES-based microwave hydrodistillation coupled with GC-MS for analysis of essential oil from black pepper (Piper nigrum) and white pepper

Deep eutectic solvents (DESs) have been gaining much attention in recent years due to their various novel properties. The present study develops a DES-based pretreatment followed by microwave-assisted hydrodistillation for the extraction of essential oil (EO) from dry fruits of white and black peppers. The process is optimized by single-factor experiments taking improvement in the EO yield of white pepper as the target. The results indicate that by using the reaction product of choline chloride and fructose as the DES with a 3 : 1 DES/powder mass ratio, the optimal conditions are (1) pretreatment stage: 600 W microwave power, 80 degrees C temperature, and 10 min duration; (2) fast heating stage: 600 W microwave power, 110 degrees C temperature, and 5 min duration; (3) hydrodistillation stage: 300 W microwave power, 110 degrees C temperature, and 35 min duration. Under these conditions, the EO yields of white and black peppers are 1.78% and 1.77%, respectively. The EOs are analyzed by using a gas chromatography-mass spectrometer (GC-MS), with a total of 54 compounds being identified. The new method brings about more identified compounds than hydrodistillation. Thus the DES-based approach has been proved superior in the enhancement of EO production, and has the potential of being extended to the analysis of volatile compounds from other plant resources.