# Changes in Biochemical and Volatile Flavor Compounds of Shine Muscat at Different Ripening Stages
## 3 Results and Discussion
### Free Volatile Aroma Compounds

Table 2: Volatile aroma compound profiles of Shine Muscat grape berries at different ripening stages. Monoterpenes are a major volatile constituent of Muscat grape varieties [6]. The importance of monoterpenes in the flavor characteristics of Muscat grape varieties has been emphasized in previous studies [6; 27], and many experimental attempts have been made to elucidate the effects of their composition and concentration on the flavor intensity and aromatic profile of Muscat grape varieties [7; 28; 29]. Monoterpenes, in particular linalool, geraniol, nerol, citronellol, and \(\alpha\)-terpineol, are a major constituent of the floral and fruity flavors of Muscat grape varieties [1]. A total of 17 different monoterpenes have been identified (Table 2). The concentrations of linalool and its oxidized forms (linaly oxide and linalyl acetate) were found to be much higher than that of the other monoterpene compounds in all experimental groups. The concentrations of linalool were 76.3 and 78.8 \(\upmu\)g/kg in the RS1 and RS2 groups, respectively, and increased rapidly to 181.5 \(\upmu\)g/kg in the RS3 group (Figure 6). The occurrence of linaly oxide and linalyl acetate in the RS3 group seemed to result from the oxidation of linalool [11]. The two oxidized forms of linalool were assumed to be found in ripe grapes, only because of their higher oxidation levels compared to linalool [6]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Volatile** & \multicolumn{3}{c}{**Concentration (\(\upmu\)g/kg)**} \\ \cline{3-5}  & **Compounds** & **1 RS1** & **RS2** & **RS3** \\ \hline \multirow{4}{*}{C13-norisopenroids} & Damascenone & - & 6.5(1.8) a  & 1.3(0.3) b  \\ \cline{2-5}  & 2-Methyl-\(\upbeta\)-ionone & 0.2(0.04) b  & 0.4(0.1) a  & - \\ \cline{2-5}  & Subtotal & 0.2 & 6.9 & 1.3 \\ \hline \multirow{2}{*}{Esters} & Ethyl octanoate & - & 1(0.4) & - \\ \cline{2-5}  & Subtotal & 0 & 1.0 & 0 \\ \hline \multirow{4}{*}{Esters} & Geraniol & - & 1.5(0.2) a  & 1.4(0.2) a  \\ \cline{2-5}  & Hotrienol & - & - & 3.4(1.0) \\ \cline{2-5}  & Limonene & 2.8(0.3) b  & 1.5(0.1) c  & 5.5(1.3) a  \\ \cline{2-5}  & Linalool & 76.3(8.7) b  & 78.7(13.8) b  & 181.5(4.5) a  \\ \cline{2-5}  & Linalyl oxide & - & - & 1.5(0.3) \\ \cline{2-5}  & Linalyl acetate & - & - & 20.4(4.6) \\ \cline{2-5}  & Nerol & 1.7(0.3) b  & - & 3.3(0.2) a  \\ \cline{2-5}  & \(\alpha\)-Terpinene & - & 0.2(0.02) & - \\ \cline{2-5}  & Rose oxide & 0.3(0.1) a  & 0.3(0.02) a  & - \\ \cline{2-5}  & Terpinen-4-ol & & - & 0.2(0.1) \\ \cline{2-5}  & Sabinene & 0.4(0.1) & - & - \\ \cline{2-5}  & \(\alpha\)-Phellandrene & - & - & 2.4(0.4) \\ \hline \multirow{2}{*}{\(\alpha\)-Terpineol} & 0.9(0.3) c  & 2.3(0.7) b  & 19.4(3.9) a  \\ \cline{2-5}  & \(\beta\)-Citronellol & 1.8(0.5) & - & - \\ \cline{2-5}  & \(\beta\)-Myrcene & 5.3 (0.6) a  & 0.9(0.1) b  & - \\ \cline{2-5}  & \(\beta\)-Ocimene & - & - & 8.1(2.8) \\ \cline{2-5}  & \(\gamma\)-Terpinene & 1.3(0.2) a  & 0.5(0.1) b  & 0.6(0.1) b  \\ \cline{2-5}  & Subtotal & 90.8 & 85.87 & 247.65 \\ \hline \multirow{2}{*}{Total} & Total & 136.9 & 123.0 & 260.5 \\ \cline{2-5}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._Geraniol and nerol, which are geometrical isomers and \(\beta\)-Citronellol, were observed at very low concentrations. The highest concentration of geraniol was observed in Muscat grape varieties before veraison, after which the concentration decreased to low levels before disappearing at maturity [6]. In this study, geraniol was found at very low concentrations in the RS2 and RS3 groups (1.5 and 1.4 \(\mu\)g/kg, respectively) (Table 2). Nerol was observed in the RS1 and RS3 groups (1.7 and 3.3 \(\mu\)g/kg, respectively), while \(\beta\)-Citronellol was only observed in the RS1 group (1.8 \(\mu\)g/kg) (Table 2). The low concentration or disappearance of these two isomers and \(\beta\)-Citronellol in the experimental groups was associated with the ripening degree of the berries, since all berries entered the ripening stage after the onset of veraison, regardless of group.