Continuous subcritical water extraction as a useful tool for isolation of edible essential oils

A method for extraction of oregano oil based on the use of subcritical water is proposed. Ground oregano (ca. 1.8 g accurately weighed) was extracted with water at 2.0 MPa, 125 °C and 1 ml min−1 for 24 min. The extracted compounds were removed from the aqueous extract by a single extraction with 4 ml hexane, determined by gas-chromatography-flame ionisation (GC-FID) and identified by mass spectrometry (MS). Hydrodistillation was performed on 30 g of ground oregano with 500 ml water for 3 h for comparison of the results with those provided by the proposed method. The subcritical water extraction-based method is clearly quicker and more efficient than the conventional: yields from the former for eight of the 11 major compounds in the extract are higher after 15-min extraction than after hydrodistillation for 3 h. This enables substantial cost savings of both energy and raw material. In addition, the proposed method has the possibility of manipulating the composition of the oil and thus its quality. The aqueous-oil extract was investigated for essential oil preparative purposes and several fast, cheap and clean alternatives for breaking the emulsion and separating the phases are proposed.