Extraction of Australian ginger root with carbon dioxide and ethanol entrainer

Ginger oil, containing both essential oil and oleoresin components, was obtained from the dried roots of crushed Australian-grown ginger by extraction with liquid and supercritical carbon dioxide containing up to 2% w/w ethanol as co-solvent. Temperatures ranged from 9 to 35 degrees C, pressures 6 to 10 MPa and mass velocity of CO2 in the extractor from 0.17 to 0.46 kg m(-2) s(-1). Particle size averaged 250 mu m. The proportions of essential oil and oleoresins in the extract depended on extraction conditions. The recovery of oleoresin was greater with entrainer, high solvent:feed ratio and higher pressure, but showed little variation with temperature over the range studied. Extraction curves revealed three distinct stages of mass transfer control, a characteristic not previously reported. The rate of extraction in the first stage was highest, linear and lasted for typically 35% of total oil yield. The second stage was also linear but at a reduced rate. The third stage showed typical diffusion-controlled characteristics. Gas chromatographic analyses revealed that later fractions of extract contained a higher proportion of oleoresin components. The refractive index of the extracts increased with solvent/feed ratio, as extract colour changed from straw yellow to dark orange/brown. The results demonstrated the variety of flavour extracts that could be produced under different extraction conditions and that the use of ethanol co-solvent maintained recoveries at pressures lower than those required with pure carbon dioxide. (C) 1998 Elsevier Science B.V.