Supercritical CO2 extraction of oregano and clove buds mixture-synergistic effect and chemical composition of extract

The goal of present study was to investigate kinetics of supercritical carbon dioxide (SC CO2) extraction of essential oils from dried clove buds and oregano leaves. Total extract yields after exhaustion of plant material at 10 MPa and 40°C (after consumption of 94.3 kgCO2/kg plant material) were 18.2% and 1.0 %, respectively. Synergistic effect in the extraction process was also investigated using mixture of clove buds and oregano leaves with initial mass ratio of clove buds to oregano leaves of 1:18.2. This mass ratio was applied assuming that it will give the extract with equivalent masses of clove and oregano extract (50:50) and that expected total yield will be 1.89 %. However, the experimentally determined total yields of extract in three repeated experiments were in the range of 2.10-2.66 % and it was higher than expected. The experimental data of extract yield versus CO2 consumption were used to obtain the parameters of Sovová model and to propose logical interpretation of SFE extraction from oregano leaf and clove bud mixture. Chemical analyses of extracts were accomplished by GC/FID and GC/MS analytical methods. Extract obtained by SFE from mixture of oregano leaf and clove bud contains a lower amount of less and higher amount of heavier soluble monoterpene and sesquiterpene type compounds (eugenol, eugenol acetate and trans-caryophyllene) than expected on the basis of separate SFE from oregano and clove buds. Such results indicate that some synergistic effect in the SFE process really exists.