Pigment Composition Responsible for the Pale Yellow Color of Ginger (Zingiber officinale) Rhizomes

The ginger rhizome (Zingiber officinale) is known to show a pale yellow color. However, the compounds responsible for the color are not known. In this study, 62 kinds of ginger rhizomes originating from different cultivars or different cultivation locations were collected for analysis of yellow pigment compounds. Ultra-performance liquid chromatography profiles at 420 nm for each sample were used for principal component analysis. Curcumin, demethoxycurcumin, and 6-dehydrogingerdione were identified as the main common compounds contributing to the yellow color, and their average amounts were 2.2 +/- 0.1, 1.6 +/- 0.1, and 20.0 +/- 1.1 mg/100 g fresh weight, respectively. Curcumin and demethoxycurcumin were contained in cv. Kintoki samples at higher levels. However, their variation suggested that the yellow pigment of ginger rhizome is more dependent on the cultivation conditions and less on the cultivar. Comparative analysis of these amounts and the b-value between mature seed rhizomes and immature rhizomes from the same lines suggested that yellow pigments were synthesized during rhizome maturation.