Microwave and Ohmic Heating Impact on the In situ Hydrodistillation and Selective Extraction of Satureja macrosiphonia Essential Oil

The aerial parts of Satureja macrosiphonia were extracted through microwave-assisted hydrodistillation (MAHD) and ohmic-assisted hydrodistillation (OAHD) methods and compared to conventional hydrodistillation (HD). The aim of this study was to evaluate the essential oil extraction kinetics, chemical constituents, physical properties and leaves' structural changes for the three above processes. Relative energy consumption and CO2 emissions during various extraction methods were also compared. Significant differences were observed in rate and time for the extraction methods; however, the values of extraction yield were insignificant, with no adverse changes in the essential oil composition. The more selective extraction of cis-sabinene hydrate (29.65%) and linalool (22.38%), however, was obtained through MAHD and OAHD, respectively. The relative electrical energy consumption for the OAHD and MAHD were almost one half and one quarter of that recorded for HD, respectively. Based on equivalent CO2 emission, OAHD and MAHD may be considered as green technologies. Practical ApplicationsIn order to reduce the drawbacks of the conventional extraction techniques, emerging thermal technologies such as ohmic and microwave heating has been introduced to essential oil extraction. In this study, ohmic- and microwave-assisted hydrodistillation were used to extract the essential oils from Satureja macrosiphonia. There are some desirable advantages of the newly introduced extraction methods over the conventional methods, which were observed in the present study, such as effective heating and fast energy transfer, which in turn results in a faster extraction process along with time saving and low operating costs. Moreover, no adverse alterations in chemical compositions have been observed. According to the results of the present study, selective extraction of oxygenated and hydrated components were achieved by MAHD, compared to OAHD and HD, although OAHD presented a slightly better extraction of components in contrast to HD.