The rates of extraction of [6]-ginger01 from ground dried Jamaican ginger rhizomes were determined in supercritical carbon dioxide over the pressure range 128-197 bar (1850-2850 psi) and the temperature range 5045°C. The CO;! densities varied from 0.415 to 0.775g cmV3. First-order plots showed two approximately linear sections with an initial intercept. The first linear section corresponded to a relatively fast initial extraction stage while the last 20% or so of the gingerol was extracted in the much slower subsequent stage. Reducing the ginger particle size by a factor of 3 increased the rate constant of the fast stage nine-fold. Despite the low viscosity of the supercritical fluid, the rate constants of the fast stage were much smaller than in extractions with organic solvents. Only when the C02 density was increased to 0.775g cm-3 did the rate constant of the fast stage rise to a value comparable with, but still smaller than, those in organic solvents of similar density. The rate constants of the later slow extraction stage were also somewhat smaller than the corresponding values in organic solvents at 30°C.
Ground sieved Jamaican ginger rhizome has been treated with acetone under various conditions and, in each case, the concentration of [6]-ginger01 extracted was measured as a function of time. The results could be expressed by two intersecting first-order plots and an initial intercept, representing very rapid initial extraction, followed by a fast stage and a subsequent slow stage. At 30°C the rate constant of the slow stage was c. 95 times smaller than that of the fast stage and its activation energy was 3.6 times larger. The fast stage was not affected by solvent flow into the ginger particles, or by an increase in the stirring speed. These findings, together with the fact that both first-order rate constants were inversely proportional to the square of the radius of the particles, pointed to [6]-ginger01 diffusion through the solid ginger as the rate-determining step. The data could also be fitted by the equation of So and MacDonald (1986). The relevance of the research to the industrial production of ginger oleoresin is pointed out.
Equations have been derived for the direct and indirect methods of determining partition constants for constituents extracted from food and other natural materials. A careful distinction is drawn between mass and volume partition constants. The direct method has been applied to the extraction of [6]-gingerol from Jamaican ginger rhizome with supercritical carbon dioxide and the indirect method to its extraction with acetone, dichloromethane. ethanol and isopropanol. The resulting average mass partition constants were 0.29 and 0.3u, respectively. The content of [6]-ginger01 in the original ginger rhizome was found to be 31-32 pmol g-' . The extent of oleoresin extraction from the ground ginger and the degree of swelling and organic solvent uptake were also measured.
The kinetics of extraction of [6]-ginger01 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]-ginger01 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]-ginger01 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]-ginger01 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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