Microwave-assisted extraction (MAE)
This green method was first proposed in 1986 [86]. Microwaves radiations include X-ray and infrared ray radiations which are characterized by frequencies between 300 MHz to 300 GHz. In this method which also called ”dielectric heating” or ”high-frequency heating”, electromagnetic energy due to ionic conductivity and the molecular dipole rotation within the electric field is converted to heat (figure 14). So, the only dielectric materials and solvents with permanent dipoles can be heated under microwave.
In fact, MAE due to electromagnetic waves Causes changes in cell structure. As a result, it differentiates itself from other common methods [87]. In this method, heat transfer occurs inversely from inside to outside compared to normal heating. Parameters such as solvent, temperature and exposure time, pressure, sample viscosity, microwave power output and physicochemical properties of materials affect the quality and efficiency of the final product [7, 88, 89, 90]. The advantages of this method over other common methods include reducing the extraction time and volume of solvent, low temperature, energy saving and increasing the yield produced essential oil [7].