# Changes in Biochemical and Volatile Flavor Compounds of Shine Muscat at Different Ripening Stages
## 3 Results and Discussion  
### Sugar Content, Acidity, Color and Pigments  
The \(a\) value, indicating the level of redness or greenness, showed no significant difference between the RS1 and RS2 groups (\(-9.64\) and \(-10.04\), respectively) (Table 1). On the other hand, the \(a\) value of the RS3 group was significantly lower (\(-6.06\)) than those of the other groups (Table 1). The reduced \(a\) value in the RS3 group indicates that the greenness of the grape skin faded as ripening progressed. The \(b\) value, which is responsible for the level of yellowness or blueness, was significantly higher in the RS2 and RS3 groups compared to RS1. The \(b\) value was found to be slightly higher in the RS2 group compared to the RS3 group (22.50 and 20.44, respectively), but no significant differences between them (Table 1). The higher \(b\) values in the RS2 and RS3 groups indicate that the berries in these groups were more yellowish than in the RS1 group. For a more comprehensive indication, the entire yellowness was expressed as yellowness index (YI). The YI values were 45.1, 49.4, and 50.2 for the RS1, RS2, and RS3 groups, respectively (Table 1). The YI values of the RS2 and RS3 groups were significantly higher than that of the RS1 group. The compact green color of grape berries changes during the period of veraison or ripening. In particular, white varieties gradually become transparent, and eventually golden. The grape berries of the RS1, RS2, and RS3 groups were dark green, pale green, and yellowish green, respectively (Figure 2). Changes in the skin color of the grape berries were regarded as a good indicator of the degree of ripening [17]. During the period of veraison and ripening, changes in the skin color are biochemically associated with the metabolism of chlorophylls and carotenoids [18]. In particular, chlorophylls are known to be a major pigment determining the skin color of white grape varieties, including Shine Muscat [19]. The chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll contents tended to decrease as ripening progressed (Figure 3). The total carotenoid content showed a similar tendency as that of chlorophyll. This result is in agreement with the results reported by [PERSON] et al. [20], who observed decreases in the \(\beta\)-carotene and lutein contents in three grape varieties during ripening. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Group**} & \multicolumn{4}{c}{**Skin Color**} \\ \cline{2-5}  & **L** & **a** & **b** & **2 YI** \\ \hline \({}^{1}\) RS1 & \(38.18\pm 1.71\)\({}^{\text{b}}\) & \(-9.64\pm 0.88\)\({}^{\text{b}}\) & \(18.18\pm 1.68\)\({}^{\text{b}}\) & \(45.1\pm 2.3\)\({}^{\text{b}}\) \\ \hline RS2 & \(48.35\pm 1.69\)\({}^{\text{a}}\) & \(-10.04\pm 0.17\)\({}^{\text{b}}\) & \(22.50\pm 0.66\)\({}^{\text{a}}\) & \(49.4\pm 0.4\)\({}^{\text{a}}\) \\ \hline RS3 & \(47.13\pm 1.84\)\({}^{\text{a}}\) & \(-6.06\pm 0.9\)\({}^{\text{a}}\) & \(20.44\pm 1.05\)\({}^{\text{a}}\) & \(50.2\pm 1.2\)\({}^{\text{a}}\) \\ \hline \end{tabular} \({}^{1}\) RS: ripening stage, \({}^{2}\) YI: yellowness index. Different letters in the same column indicate a statistically significant difference (\(p<0.05\)).  
\end{table} 
Table 1: The change in skin color of Shine Muscat grape berries at different ripening stages. The total sugar content had a tendency to increase significantly as ripening progressed (Figure 4). Glucose and fructose are the most abundant sugars in grapes, rapidly accumulating in the vacuoles of grape berries during ripening [21]. On the other hand, titxtatable acidity had a tendency to decrease as ripening progressed, though there was no significant difference between the RS1 and RS2 groups (Figure 2). The titxtable acidity, however, showed a marked decrease in the RS3 group. This decrease in titxtatable acidity led to the low \({}^{\circ}\)Brix/acid ratio value of the RS3 group. The titxtable acidity of grape berries decreases from 2.0\(\sim\)1.5% at veraison to 0.7\(\sim\)0.5% at maturity, depending on the grape varieties [22].