Research Progress on Extraction, Separation, and Purification Methods of Plant Essential Oils

Essential oils (EOs), also called liquid gold, are known for their wide range of applications and biological activities. The modern use of EOs has received increasing attention for more than 60 years. The precious EOs have been refined from plant raw materials using a variety of methods. Since the extraction, separation, and purification methods determine the type, quantity, and stereochemical structure of EO molecules as well as the final yield and quality of EOs, the selection of an appropriate method is crucial. The traditional and emerging extraction methods (hydrodistillation, steam distillation, organic solvent extraction, etc.), as well as separation and purification methods (chromatography, macroporous resin, chemical reaction, etc.), of plant EOs and their main volatile compounds were shown. Our review focused on the principles, processes, characteristics, and applications of these methods, so as to better understand the preparation of pure plant EOs and further guide their large-scale use.