# Changes in Biochemical and Volatile Flavor Compounds of Shine Muscat at Different Ripening Stages
## 3 Results and Discussion
### Free Volatile Aroma Compounds  
The variation of volatile flavor compounds in grape berries is closely related to the biochemical changes of berries [11]. The total ion chromatograms of free volatile flavor compounds and their profile are presented in Figure 5 and Table 2. The concentration of total alcohols had a tendency to decrease as ripening progressed. The concentration of most alcohols also tended to decrease, while that of 1-dodecanol tended to increase as ripening progressed. The concentration of 1-hexanol showed a decreasing trend as ripening progressed. C6-compounds, such as C6-aldehydes (hexanals and hexenals), alcohols (hexanols and hexenols), and esters (hexyl acetates), are synthesized via complex enzymatic reactions, namely, the lipoxygenase pathway, during ripening [23]. In addition, [PERSON] et al. [11] found that (\(Z\))-hexenal, a C6-aldehyde, could be converted into (\(E\))-2-hexenal and (\(E\))-2-hexenal acetate. However, our results showed a constant decrease of C6-alcohols during ripening, which was inconsistent with the results of previous works [11; 23; 24]. Different C6 compound profiles are observed depending on the grape varieties and their cultivation regions [2]. The concentration of C6-alcohols, including 1-hexanol, showed different trends depending on the cultivation regions. A decrease in C6-alcohols concentration in grapes was related to differences in the activity of enzymes involved in the lipoxygenase pathway and in a reduction of unsaturated fatty acids, which are precursors of C6-compounds during ripening. Thus, decreasing 1-hexanol observed in this study may be associated with reduced lipoxygenase and alcohol dehydrogenase activity, since their activity reached a maximum during the second week after veraison [25]. The decrease in aldehydes may also be related to the activity of these enzymes. The decrease in C6-alcohols and aldehydes during ripening is favorable to the consumer's sensory perception, since their herbaceous characteristics give an unpleasant odor [11]. The variation of volatile C13-norisoprenoids is related to the degradation of carotenoids, which are precursors of volatile C13-norisoprenoids [26]. In this study, damascenone and 2-methyl-\(\beta\)-ionone were identified. Damascenone was identified in the RS2 and RS3 groups (Table 2), while 2-methyl-\(\beta\)-ionone was identified in the RS1 and RS2 groups. The concentration of total C13-norisoprenoids was the highest in the RS2 group, followed by RS3 and RS1, in agreement with previous studies [11; 24]. In regards to carotenoid degradation (Figure 3), the rapid reduction of the total carotenoid concentration in the RS1 group seemed to correspond to a rapid increase in the concentration of damascenone and 2-methyl- \(\beta\)-ionone. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Volatile** & \multicolumn{3}{c}{**Concentration (\(\mu\)g/kg)**} \\ \cline{3-5}  & **Compounds** & \({}^{1}\) **RS1** & **RS2** & **RS3** \\ \hline \multirow{5}{*}{Alcohols} & 1-Dodecanol & 4.6(1.6) \({}^{\text{b}}\) & 9.3(2.7) \({}^{\text{a}}\) & 11.2(0.4) \({}^{\text{a}}\) \\ \cline{2-5}  & 1-Hexanol & 9.8(2.0) \({}^{\text{a}}\) & 2.8(0.5) \({}^{\text{b}}\) & 0.2(0.1) \({}^{\text{c}}\) \\ \cline{2-5}  & 1-Octen-3-ol & 1.5(0.2) & - & - \\ \cline{2-5}  & 2-Ethyl-1-hexanol & 1.5(0.3) \({}^{\text{a}}\) & 0.7(0.1) \({}^{\text{b}}\) & - \\ \cline{2-5}  & 3-Methyl-1-butanol & 8.8(0.8) \({}^{\text{a}}\) & 3.1(0.3) \({}^{\text{b}}\) & - \\ \cline{2-5}  & Subtotal & 26.0 & 15.9 & 11.4 \\ \hline \multirow{5}{*}{Aldehydes} & 3-Methylbutanal & 8.9(2.4) & - & - \\ \cline{2-5}  & Hexanal & 9.1(2.2) \({}^{\text{a}}\) & 10.9(1.5) \({}^{\text{a}}\) & 0.2(0.1) b \\ \cline{2-5}  & Pentanal & - & 1.2(0.1) & - \\ \cline{2-5}  & Benzaldehyde & 1.1(0.1) & - & - \\ \cline{2-5}  &
\begin{tabular}{c} Phenyl \\ acetaldehyde \\ \end{tabular} & 0.9(0.3) \({}^{\text{a}}\) & 1.2(0.2) \({}^{\text{a}}\) & - \\ \cline{2-5}  & Subtotal & 19.9 & 13.3 & 0.2 \\ \hline \hline \end{tabular}
\end{table}