## 3 Results and Discussion
### Volatile Free Aroma Compounds  
The effects of berry thinning on the profiles of free volatile aroma compounds of Shine Muscat grapes are presented in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Classification**} & \multirow{2}{*}{**Aroma Compounds**} & \multirow{2}{*}{**RT (min)**} & \multirow{2}{*}{**Identification**} & \multicolumn{2}{c}{**The Level of Berry Thinning (\%)**} \\ \cline{5-6}  & & & **0** & **30** & **50** \\ \hline \multirow{7}{*}{Alcohols} & (E)-2-Hexen-1-ol & 17.36 & Mass spectrum & 533.3 \(\pm\) 133.1 \({}^{\rm a}\) & 505.4 \(\pm\) 55.1 \({}^{\rm a}\) & 298.3 \(\pm\) 59.0 \({}^{\rm b}\) \\  & (E)-3-Hexen-1-ol & 15.45 & Standard & 1 \(\pm\) 0.3 \({}^{\rm a}\) & 0.3 \(\pm\) 0.02 \({}^{\rm b}\) & 0.9 \(\pm\) 0.2 \({}^{\rm a}\) \\  & (Z)-2-Pentent-1-ol & 13.55 & Standard & 0.5 \(\pm\) 0.1 \({}^{\rm b}\) & 0.5 \(\pm\) 0.1 \({}^{\rm b}\) & 1.5 \(\pm\) 0.2 \({}^{\rm a}\) \\  & (Z)-3-Hexen-1-ol & 16.29 & Standard & 39.9 \(\pm\) 5.1 \({}^{\rm b}\) & 52.1 \(\pm\) 4.2 \({}^{\rm a}\) & 28.9 \(\pm\) 0.7 \({}^{\rm c}\) \\  & 1-Heptanol & 19.32 & Standard & 0.3 \(\pm\) 0.1 & 0.4 \(\pm\) 0.1 & N.D \({}^{\rm a}\) \\  & 1-Hexanol & 15.09 & Standard & 323.4 \(\pm\) 77.6 \({}^{\rm a}\) & 265.1 \(\pm\) 34.1 \({}^{\rm a}\) & 294 \(\pm\) 57.31 \({}^{\rm a}\) \\  & 1-Nonanol & 27.42 & Standard & 0.2 \(\pm\) 0.02 \({}^{\rm a}\) & 0.1 \(\pm\) 0.03 \({}^{\rm b}\) & 0.1 \(\pm\) 0.01 \({}^{\rm b}\) \\  & 1-Octanol & 23.51 & Standard & 0.5 \(\pm\) 0.03 \({}^{\rm a}\) & N.D & 0.4 \(\pm\) 0.05 \({}^{\rm b}\) \\  & 1-Octen-3-ol & 19.29 & Standard & 0.2 \(\pm\) 0.02 \({}^{\rm a}\) & 0.2 \(\pm\) 0.03 \({}^{\rm a}\) & 0.1 \(\pm\) 0.03 \({}^{\rm a}\) \\  & 2-Ethyl-1-hexanol & 20.85 & Standard & 4.1 \(\pm\) 0.4 \({}^{\rm b}\) & 5 \(\pm\) 0.4 \({}^{\rm a}\) & 5.2 \(\pm\) 0.5 \({}^{\rm a}\) \\ \hline \multirow{7}{*}{Aldehydes} & (E)-2-Heptenal & 13.16 & Mass spectrum & 0.8 \(\pm\) 0.1 \({}^{\rm b}\) & N.D & N.D \\  & (Z)-3-Hexenal & 6.01 & Standard & 4.8 \(\pm\) 0.1 \({}^{\rm b}\) & 4.9 \(\pm\) 0.5 \({}^{\rm b}\) & 8.4 \(\pm\) 0.1 \({}^{\rm a}\) \\  & (E)-2-Hexenal & 9.00 & Standard & 1140.3 \(\pm\) 90.9 \({}^{\rm a}\) & 1149 \(\pm\) 287.2 \({}^{\rm a}\) & 1419.7 \(\pm\) 104.6 \({}^{\rm a}\) \\  & Benzaldehyde & 21.47 & Standard & 2.8 \(\pm\) 0.2 \({}^{\rm b}\) & 4.1 \(\pm\) 0.2 \({}^{\rm a}\) & 1.3 \(\pm\) 0.6 \({}^{\rm c}\) \\  & Hexanal & 4.14 & Standard & 749.3 \(\pm\) 91.4 \({}^{\rm b}\) & 983.2 \(\pm\) 15.2 \({}^{\rm b}\) & 1538.5 \(\pm\) 20.0 \({}^{\rm a}\) \\  & Nonanal & 16.46 & Standard & 0.3 \(\pm\) 0.05 \({}^{\rm a}\) & 0.4 \(\pm\) 0.03 \({}^{\rm a}\) & 0.2 \(\pm\) 0.05 \({}^{\rm b}\) \\ \hline C13- & \multirow{2}{*}{(E)-\(\beta\)-Damascenone} & 32.48 & Standard & 0.6 \(\pm\) 0.1 & 0.2 \(\pm\) 0.002 & N.D \\ \cline{1-1}  & & & & & & \\ \end{tabular}
\end{table} 
Table 2: Effects of berry thinning on the composition and concentration of volatile free aroma compounds in Shine Muscat grape juices. Figure 4: Effects of berry thinning on the composition and concentration of phenolic compounds in Shine Muscat grape skins. Different letters on the bars with the same color indicate statistically significant differences at \(p\) < 0.05. TPC, total phenolic concentration expressed in mg gallic acid/g dry weight; PAC, proanthocyanidin concentration expressed in mg catechin/g dry weight; PTC, polymeric tannin concentration expressed in mg tannic acid/g dry weight. A total of 42 volatile compounds, including 10 alcohols, 6 aldehydes, 1 C13-norisoprenoids, 2 esters, 5 ketones, and 18 monoterpenes were identified. Berry thinning decreased the alcohol concentration while increasing the aldehyde concentration. Four C6-alcohols, (E)-2-hexen-1-ol, (E)-3-hexen-1-ol, (Z)-3-hexen-1-ol, and 1-hexanol constituted the majority of the total alcohol concentration. Among them, only (E)-2-hexen-1-ol was found to be an active odorant in all the sample groups. Three C6-aldehydes, (Z)-3-hexenal, (E)-2-hexenal, and hexanal, were the most abundant volatile aldehydes and were active odorants in all the sample groups.