♦According to Pellerin (1991)
♦According to Pellerin (1991)
These results show a great difference in the sesquiterpene hydrocarbons percentages between steam distillation and supercritical CO2 extraction, particularly for a-zingiberene. Several cooked dishes (soup, fish, poultry) were seasoned with ginger prepared by the same three methods. Tasters commented favorably on the flavor balance and fresh characteristics of food seasoned with a supercritical CO2 extract of ginger. In a study of a Fijian ginger oil extracted with CO2, the content of gingerols increased with rising CO2 pressure (Zhou et al., 1994). A two-stage separation of (6)-gingerol was proposed by Yonei et al. (1995). The first step was carried out under various pressures of 7.9 to 10.9 MPa at a constant temperature of 333°K and the second step conditions were kept the same as those for the first stage step, that is, extraction by high-pressure CO2 from the dried rhizome. Roy et al. (1996) studied the extraction rate of oil from freeze-dried ginger with supercritical carbon dioxide as a function of solvent, flow rate, particle size, temperature, and pressure. The extraction curves were independent of flow rate in a plot of oil yield versus extraction time. This indicated that the extraction process is controlled by intraparticle diffusion within a particle of ginger root. The extraction rate increased as the particle size decreased due to a decrease in the diffusion path. The higher temperature favoured the extraction at 10.8 MPa (crossover effects). Extraction of Australian ginger root with CO2 and ethanol entrainer was carried out by Badalyan et al. (1998). The proportion of oleoresin 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 (9 to 35° C). GC analyses revealed that latter fractions of extracts contained a higher proportion of oleoresin components. The use of ethanol as cosolvent maintained recoveries at pressures lower than required with pure CO2.
A method comprising drying of ginger, crushing to obtain ginger powder, subjecting it to supercritical CO2 fluid extraction at 32 to 65° C and 12 to 40 MPa, and separating to obtain ginger oil resin containing active ingredients (i.e., gingerols, shogaols, and gingerone), was patented by Li (1999). Another procedure using a series of separators was patented by Yao et al. (2000). The effective components from 435 g ginger powder were extracted by supercritical CO2 at 80° C and 45 MPa.
The separation conditions were as follows:
1. 60° C and 25 MPa in the first separator (1.1 g of ginger wax was obtained).
2. In the second separator, temperature and pressure were 70° C and 20 MPa, respectively (2.1 g of hot gingerin was obtained).
3. In the third separator 9.2 g of ginger essential oil was isolated at 60° C and 14 MPa, and in the final separator, 33.5 g water was separated at 15° C and 3.5 MPa.
The effects of extraction pressure (25 MPa), temperature, time (2 hours), CO2 flow rate (0.09 l.h-1), water control (15%), and material size (40 to 60 ^m) on the extraction rate of ginger oleoresin from China were explored under industrial conditions (Zhang et al., 2001). Other methods have been published by Yu et al. (1998) and Wen et al. (2001).
In conclusion, the supercritical carbon dioxide extraction has many advantages over normal extraction methods for the following reasons:
1. Shorter extraction time
2. Lower energy consumption
The selective solubility of components in CO2 enables it to extract all the useful aromatics from a flavoring source. However, according to Van Beek (1991), its use should be limited in the industry because of the high pressures needed and the high cost of the appropriate apparatus.
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