Scheme 3.3 Synthesis of (6)-shogaol 3b and (6)-paradol 1i from (6)-gingerol 1b (from Connell ).
being recovered when the SF ratio was less than 2. The SF ratio was found to be the major factor affecting the composition of ginger extract. The temperature had little effect on the composition within the range 9 to 35° C. Extraction of the sample with supercritical CO2 revealed that solubility was the dominant limiting factor in the extraction procedure. Introducing small amounts of ethanol as a cosolvent increased the overall yield from liquid CO2 and the recovery of ginger oleoresin.
Used in perfumery and cosmetics, the essential oils of ginger have been widely studied in producer countries. These studies have been reviewed by several workers (Guenther, 1952; Gildemeister and Hoffman, 1956; Connell, 1970; Masada, 1976; Lawrence, 1983, 1984, 1988, 1995, 1997; Afzal et al., 2001).
Before 1970 (Connell, 1970) and the use of packed columns, the number of identified compounds remained low. The main components were the sesquiterpene hydrocarbons, (—)-a-zingiberene, ( + )-ar-curcumene, P-bisabolene, P-sesquiphellandrene, farnesene, 7-selinene, P-elemene, and P-zingiberene. Other compounds identified at this time were monoterpene hydrocarbons: a-pinene, P-pinene, myrcene, P-phellandrene, limonene, ^-cymene, cumene and oxygenated compounds: 1,8-cineole, d-borneol, linalool, neral, and geranial, bornyl acetate, in addition to some aliphatic aldehydes (nonanal, decanal), ketones (methylheptenone), alcohols (2-heptanol, 2-nonanol), esters of acetic and caprylic acid, and chavicol. After 1967, the development of capillary GC and its coupling with MS and data banks has provided a suitable technique for a good separation and identification of a greater number of compounds.
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