Effect of applied voltage and frequency on extraction parameters and extracted essential oils from Mentha piperita by ohmic assisted hydrodistillation

Ohmic-assisted hydrodistillation (OAHD) is a new method proposed for extraction of essential oils in which ohmic heating technology is combined with distillation. In this study, different frequencies (25, 50 and 100 Hz) as well as high and low intensity OAHD (220 and 380 V) were applied on aerial parts of Mentha piperita L. and the results were compared with those of the conventional hydrodistillation (HD). The results showed that high and low intensity OAHD methods had the extraction times of 13.54 and 19.71 min, respectively, while this value was about 1 h for HD. Scanning electron micrographs of mint showed a sudden eruption of essential oil glands for all OAHD samples. GC-MS analysis did not indicate any noticeable changes in the compounds of all extracted essential oils. The results of this study showed that higher applied voltage can speed up OAHD and confirmed this emerging technology as a green technology (considering fossil fuels as the main source of electrical energy). Industrial relevance The quality and quantity of essential oils extracted from herbs and other raw materials are affected by the extraction method. In this research different frequencies (25, 50 and 100 Hz) and also high and low intensity OAHD (220 and 380 V, applicable in industries in many regions) of ohmic-assisted hydrodistillation (OAHD), as an innovative and emerging technology, were used and compared with traditional hydrodistillation in extraction of essential oils from the aerial parts of Mentha piperita L. (peppermint). All OAHD treatments were more economical and more environmentally friendly than hydrodistillation method. In addition, high intensity OAHD method not only can enhance the amount of extracted essential oil but also was the quickest method and consequently can be a valuable industrial alternative for extraction of essential oils.