Essential oils extraction from Anoectochilus roxburghii using supercritical carbon dioxide and their antioxidant activity

In order to obtain the highest possible yield of essential oils from Anoectochilus roxburghii, the response surface methodology (RSM) was employed to optimize the conditions of supercritical fluid carbon dioxide extraction (SFE) of the essential oils from A. roxburghii. The chemical compositions of the essential oils extracted by SFE were compared with those obtained by hydro-distillation (HD) and Soxhlet extraction (SE). Furthermore, the antioxidant activities of essential oils extracted by SFE were compared with those obtained by HD and SE employing the DPPH free radical assay and the ABTS assay. The optimum SFE conditions were found to consist of a temperature of 37.6 °C, a pressure of 35 MPa, an extraction time of 150 min and a CO2 flow rate of 8 L/h. Applying these conditions, the mean extraction yield of essential oils was 1.677%. The essential oils obtained by SFE and SE were found to contain a significant proportion of carboxylic acids and carbonyl compounds. The antioxidant activities decreased as follows: SFE > SE > HD. The study showed that RSM was successfully applied for SFE optimization of the essential oils from A. roxburghii. The pressure and CO2 flow rate had significant effect on essential oils yield produced by SFE.