Conclusion
Plant essential oils are natural and aromatic compounds that are found in small amounts in plants and have many interesting applications as flavors and fragrances in perfumery, cosmetics, pharmaceutical, food, agriculture, industry and etc. Research on essential oils extraction methods has aroused great interest for scientists. as evidenced in this review, essential oils can be produced by various techniques including conventional, novel and biotechnology methods. Novel or green methods can be a good alternative to conventional methods due to their advantages such as higher efficiency and quality, short extraction time, non-degradable compounds due to heat, no pollution and etc. But due to the problems that are observed in common and even new green methods, including climate conditions, supply shortages, natural disasters, plant diseases and etc. recently scientists have chosen biotechnology methods for the preparation of natural compounds. In this method, in addition to the fact that there are no problems of the other extraction methods, finally, a high quality and efficient product is obtained. Production of natural products and volatile through biotechnology can be an appropriate response to consumer demand in relation to the consumption of natural products and move towards ”green processes” and environmentally friendly.