Extraction of ginger rhizome: kinetic studies with dichloromethane, ethanol, 2‐propanol and an acetone—water mixture

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Abstract
Summary: The kinetics of extraction of [6]‐gingerol from ground Jamaican ginger rhizome have been determined at 30°C in dichloromethane, ethanol, isopropanol and an 80% (v/v) acetone + 20% (v/v) water mixture. The extractions all proceeded in three stages: an initial ‘washing’ stage, a fast stage and a subsequent much slower stage. The rate of extraction of hexahydrocurcumin in ethanol was found to follow a simpler pattern. From the first order plots, the diffusion coefficients of the extracted solubles within the ginger particles were calculated. They varied inversely with the 0.6 power of the solvent viscosity, which explained why the rates of [6]‐gingerol extraction decreased in the sequence: acetone < acetone + water < dichloromethane < ethanol < isopropanol. These results show that solvents of low viscosity should be chosen to attain fast extraction rates. The diffusion coefficient of [6]‐gingerol was also measured at 30°C in pure acetone, ethanol and isopropanol. The values in these bulk solvents were 13–20 times greater than the diffusion coefficients of [6]‐gingerol within the ginger particles for the fast stage and over 900–1800 times greater than those for the slow stage. These hindrance factors quantify the effect of the ginger matrix environment on internal diffusion.

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