Supercritical CO2 Extraction Optimization of Onion Oil Using Response Surface Methodology

Response surface methodology was employed to optimize the conditions of supercritical CO2 extraction of the oil from freeze-dried onion powder. The effects of pressure, temperature and extraction time on the yield of oil were investigated. The maximum extraction yield of 4.69 +/- 0.04g/kg dry basis was achieved at a pressure of 20.6?MPa, a temperature of 40.6 degrees C, a time of 260?min, a CO2 flow rate of 22?L?h1, and an entrainer ratio of 0.1?mL absolute ethanol per gram dry basis. The chemical composition of the oil was analyzed by gas chromatography-mass spectrometry. The most representative compounds of the essential oil were organosulfur-containing compounds and, among these, the main constituents were methyl 5-methylfuryl sulfide (18.30?%), methyl 3,4-dimethyl-2-thienyl disulfide (11.75?%) and 1-propenyl propyl disulfide (9.72?%).