Towards more rational techniques for the isolation of valuable essential oils from plants

Attention is drawn to the use of new and clean alternative methods for the isolation of essential oils from plants. A critical overview is presented of conventional methods (based on either organic solvent extraction or distillation) and new alternatives (including microwave-assisted extraction (MAE) as well as supercritical CO₂ (SC-CO₂) extraction and subcritical water extraction). The advantages and disadvantages of each technique are reported and special emphasis is given to the use of continuous subcritical water extraction which emerges as clearly advantageous over conventional techniques (by avoiding the use of organic solvents and considerably shortening the extraction time, as well as increasing the efficiency) and recent techniques, such as MAE (by increasing the efficiency) and SC-CO₂ extraction (by avoiding the co-extraction of cuticular waxes and lipids and the need for a sample drying stage prior to extraction).