Medicinal ginger is produced by various processes in Japan and China, e.g., ginger that has been soaked in hot water or steamed is called
kankyo in Japan, and roasted ginger is called
hokyo (
paojiang in Chinese) in China. However, the heating method differs between the two countries, and the quality of processed ginger might be affected by differences in the heating period and strength. The color of ginger changes markedly during heating. Therefore, in this study, we analyzed the color value and pungent compound contents of our processed ginger samples and elucidated the differences in the quality of these samples. In addition, we investigated the relationship between the color values and pungent compound contents of processed ginger samples.
As a result, we found that the
a* value (indicating redness) of steamed (St) ginger was positively correlated with its 6-shogaol to 6-gingerol ratio ([S/G]), the
a* value of ginger soaked in hot water (Soh) remained constant regardless of the [S/G], and the
a* value of ginger heated at 180°C (H180) was correlated on a logarithmic curve with [S/G]. In addition, the
b* values (indicating yellowness) of the Soh, St, and H180 ginger samples were negatively correlated with their 6-shogaol concentrations. Therefore, we confirmed that color values are suitable indices for evaluating the quality of processed ginger because they can be used to evaluate its [S/G] ratio and the processing method by this value.
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