Pressure effect on ginger essential oil extraction by supercritical carbon dioxide and steam distillation

Ginger is a plant with Asian origin and it is widely used in food and pharmaceutical industries. Its essential oil obtained by supercritical fluid extraction (SFE) or steam distillation (SD) is composed mainly of α-zingiberene, among a series of monoterpenes, terpenoids and sesquiterpenes compounds that present many antioxidant and antibacterial activity. This study aims to find the best conditions for the extraction of Zingiber officinale essential oil using the SFE and SD techniques, regarding the maximum oil yield and aromatic potential. Principal Component Analysis (PCA) is used to evaluate the similarity between the composition of the essential oil in different pressures and extraction methods. The SD extractions were performed in a pilot unit at three different pressures (1, 2 and 3 bar) using 2 kg of ginger rhizome. On the other hand, the SFE method was evaluated screening the process pressure (80, 90, 100 and 110 bar), maintaining the temperature fixed at 40 °C, using CO2 as solvent and 0.2 kg of rizhome. Firstly, the plant was milled and submitted to the SFE with known humidity and all the experiments were performed in triplicate. A curve of accumulated mass versus extraction time was plotted and three different mathematical models (first order kinetics, Crank and Reverchon) were fitted for both methods, obtaining the relevant mass transfer parameters. The essential oil compounds were identified by gas chromatography coupled with mass spectrometry (GC-MS), with α-zingiberene as the main component with different contents (from 11.9 to 28.9%). The obtained data indicate that the best condition for the SFE is 100 bar, 40° C (0.0697 goil/gplant) with 19.34% of α-zingiberene and for the SD extraction the one performed at 3 bar (133° C) (0.007 goil/gplant) with 28.9% of αzingiberene, measured on a dry basis.