Microwave-assisted extraction of O. vulgare L. spp. hirtum essential oil: Comparison with conventional hydro-distillation

Abstract Microwave-assisted hydro-distillation (MAHD) at different power levels has been applied for the extraction of essential oil from O. vulgare L. ssp. hirtum. Hydrolats and residual extracts, which present by-products, were also collected. A comparison was done with conventional hydro-distillation (HD) in terms of extraction time, extraction yield, the chemical composition of essential oils and environmental impact. MAHD proved to be a technique with many advantages compared to conventional HD. MAHD had shorter extraction time (24–45 min) compared to HD (136 min), better yields of essential oil (2.55–7.10 % for MAHD compared to 5.81 % for HD), higher content of oxygenated compounds (78.89–85.15 % for MAHD compared to 76.82 for HD), and a more environmentally friendly approach (electrical consumption was from 0.135–0.240 kW h for MAHD compared to 1.360 kW h for HD). The main component in all essential oils, as well as in hydrolats, was carvacrol. MAHD at the power level of 600 W may be considered as the most promising among the tested power levels with respect to all investigated parameters. Residual extracts after HD and MAHD showed to be valuable by-products rich in phenolic compounds, with rosmarinic acid as dominant.