Q

26 27

15-hydroxy-(E)-8ß(17)-epoxylabd-12-ene-16-al Galanolactone

Figure 3.4 Diterpenoids of labdane type identified in ginger (adapted from Kikuzaki [2000]).

Figure 3.4 Diterpenoids of labdane type identified in ginger (adapted from Kikuzaki [2000]).

Capsaicin

Capsaicin (28) is an artifact in ginger essential oil (Rosella et al., 1996).

Characteristic Flavor and Odor in Ginger

Odor quality of the oils for several imported and Australian commercial varieties of ginger have been compared by Mathew et al. (1973). Hot-air drying was the best method for the raw ginger products. The identification and evaluation of the flavor-significant components of ginger essential oil was made by Bednarczyk (1974) and Bednarczyk and Kramer (1975). They used stepwise multiple regression analysis, taking into account individual peak intensities and taste panel scores for ginger flavor intensity as a dependent variable. Taste panel evaluation of the isolated components indicated that ß-sesquiphel-landrene and ar-curcumene are the prime contributors to the characteristic ginger attribute. a-Terpineol, neral, and geranial contribute to the lemony aroma of ginger oil, and may therefore be desirable additives to whole ginger oil to intensify its lemony or citrus character. Nerolidol contributes to the woody or soapy flavor and does not appear to be a good potential additive to ginger oil. A trained sensory panel judged a mixture of a-terpineol, neral, geranial, ß-sesquiphellandrene, ar-curcumene, and nerolidol to be characteristic of ginger oil.

Kostrezewa and Karwawska (1976) investigated the characteristic flavor and odor of a Polish extract of ginger by comparing the yield of the essential oil and its levels of a-zingiberene and zingiberol as well as total gingerols and shogaols with two foreign extracts.

Pusrseglove et al. (1981) and Heath and Reineccius (1988) reported the impact compounds of ginger. Organoleptic properties of ginger oils from various origins have been described by Akhila and Tewari (1984).

Aromagrams and key compounds of various spices including ginger have been outlined and relation between their chemical structure and flavor have been described by Ney (1990a, b). Chemically speaking, ginger contains 2-methoxyphenols (or 4-substituted guaiacols). From the study of Nishimura (2001), it can be concluded that flavor dilution factors (FD), according to Grosh (1994), of compounds identified in fresh ginger are the highest for 1,8-cineole (15), linalool (20), citronellyl acetate (16), borneol (16), geranial (17), and geraniol (20), which are the most important contributors to the odor of ginger. Enantiomer separation of the characteristic odor compounds in Japanese fresh rhizomes of ginger was described in an excellent work of Nishimura (2001). Using multidimensional gas chromatography (MDGC) and chiral analytical HRGC/olfactometry (or sniffing), the odor character of each enantiomer was confirmed.

The fresh rhizomes of ginger were fractionated into a hydrocarbon fraction (hexane extract) and an oxygenated hydrocarbon fraction (methylene chloride extract). This latter fraction was subjected to chiral GC/olfactometry (GC/O) and GC/MS analyses. It was considered that monoterpenoids such as linalool, 4-terpineol, isoborneol, and borneol as well as geranial and neral might contribute to the characteristic odor of the fresh ginger. Each enantiomer was easily separated using the off-line MDGC system. The odor character of each enantiomer was confirmed by GC/O. The values are reported in Table 3.25.

Unfortunately, odor units which are the ratio between the concentration of each product in the oil and the corresponding threshold olfactive values, have not been measured.

Chemometrics

Fingerprint analysis of ginger oils by chemometrics methods using individual peak quantities as independent variables and their flavor intensities as dependent variables was performed by Bednarczyk and Kramer (1975). a-Terpineol, neral, and geranial, ß-sesquiphellandrene, ar-curcumene, nerolidol, and «s-ß-sesquiphellandrol accounted for 85% of the panel's flavor response. Identification of each isolated peak was carried out by IR, 1H-NMR, and MS data and comparison with authentic samples. Unfortunately, a-zingiberene was not included in this study. Organoleptic evaluation included:

1. Tasting the mixture of compounds in each peak, individually

2. Tasting combinations of the mixtures

Table 3.25 Composition and odor description of enantiomers of four potent odor components of Japanese fresh ginger2

Compounds

Configuration

(%)

Odor

Linalool

R-(-)

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