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

[Display omitted] •Microwave-assisted and conventional hydro-distillation has been applied and compared.•Essential oil, hydrolats and residual extracts were collected and analyzed.•Microwave-assisted hydro-distillation proved to be a technique with many advantages. 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 (24–45min) compared to HD (136min), 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 0.135–0.240kWh for MAHD compared to 1.360kWh for HD). The main component in all essential oils, as well as in hydrolats, was carvacrol. MAHD at the power level of 600W 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.