Shogaols

artifacts can be formed either by hydrolysis of labile esters or by isomerization (or rearrangement) of some hydrocarbons. In the headspace technique, these artifacts will be greatly diminished (Van Beek, 1991). Examples of artifact formation by chromatographic techniques (GC, LC, GC/MS) have been reviewed by Garnero and Tabacchi (1987).

To conclude this section, it should be pointed out that packed columns should be strongly discouraged owing to the limited number of separated compounds (about 40). This problem can be partially alleviated by using better performance capillary columns of two different polarities and specific detectors for compounds containing nitrogen and sulfur atoms. Even in this case, some peaks overlap. Thus, it is necessary to proceed to a prefractionation of the ginger oil on a short column of silica gel in a hydrocarbon and an oxygenated fraction using pentane (or hexane) and pentane/ether (2:1 v/v) as solvents, respectively. Each fraction is again analyzed by GC and GC/MS. The method does not require a large amount of product (20 to 50 ^L).

Gas Chromatography/Mass Spectrometry Coupling (GC/MS)

Since 1967, HRGC and GC/MS coupling have been successfully used in the analysis of essential oils in general, and particularly in the analysis of ginger oils. The most important papers are summarized in Table 3.8.

Table 3.8 Principal publications on ginger (Zingiber officinalis Roscoe) essential oils according to their origin

Origin

Extraction/Identification methods*

Author(s) (year)

India

Steam distillation/GC/MS

Nigam et al. (1964)

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