## 3 Results and Discussion
### Free Amino Acid Profiles of Grape Berries  
Amino acids were linked with fruit aroma by acting as precursors for the biosynthesis of aroma-forming volatile compounds. Table 3 showed the free amino acid profiles from CK and other treated vines by regulating the training system. A total of 15 types of free amino acids were detected in the grape berries. Glu, Ala, Val, Pro, and Phe were the most abundant amino acids in all the grape berries. Glu is preferably utilized by Saccharomyces cerevisiae during fermentation. Val can be converted into isobutanol, propanol, isoamyl alcohol, and active amyl alcohol in the process of wine brewing. These higher alcohols can also be further formed into higher alcohols acetic ester, which are the main fermented flavor components in wine. Pro is a plant compatible osmotic agent, which is beneficial to resist osmotic stress [32]. Phenylalanine is an \(\alpha\)-amino acid and a substrate of the phenylalanine ammonia lyase enzyme (PAL) that catalyzes the conversion of phenylalanine into cinnamic acid as the first step of the biosynthesis of plant phenolic compounds [33]. In addition, certain volatile compounds such as 2-phenylethanol and 2-phenylethyl acetate are formed by this aromatic amino acid due to the enzymatic activity of yeast, which contributes to the floral wine aroma [34]. In terms of above five types and total free amino acids, T3 treatment could significantly increase the content at harvest (\(p<0.05\)).  
Figure 3: (**A**) Percentage stacked bar chart showing the volatile compounds of the different training system of ‘Cabernet Gernischt’ (_Vitis vinifera_ L.) during grape maturity. (**B**) Four aromas related genes under the different training system of ‘Cabernet Gernischt’ (_Vitis vinifera_ L.). Different letters denote significant differences separately for individual factors by [PERSON]’s test at \(p<0.05\).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Free Amino Acid** & **CK** & **T1** & **T2** & **T3** \\ \hline Asp & 0.038 \(\pm\) 0.003 b & 0.045 \(\pm\) 0.014 b & 0.044 \(\pm\) 0.003 b & 0.099 \(\pm\) 0.002 a \\ Glu & 0.1 \(\pm\) 0.006 b & 0.094 \(\pm\) 0.005 b & 0.1 \(\pm\) 0.008 b & 0.289 \(\pm\) 0.007 a \\ Ser & 0.044 \(\pm\) 0.002 b & 0.041 \(\pm\) 0.003 b & 0.047 \(\pm\) 0.002 b & 0.08 \(\pm\) 0.001 a \\ His & 0.037 \(\pm\) 0.001 b & 0.038 \(\pm\) 0.003 b & 0.037 \(\pm\) 0.002 b & 0.058 \(\pm\) 0.004 a \\ Gly & 0.025 \(\pm\) 0.004 b & 0.036 \(\pm\) 0.007 b & 0.032 \(\pm\) 0.003 b & 0.097 \(\pm\) 0.003 a \\ Thr & 0.04 \(\pm\) 0.002 b & 0.035 \(\pm\) 0.003 b & 0.039 \(\pm\) 0.002 b & 0.061 \(\pm\) 0.002 a \\ Arg & 0.086 \(\pm\) 0.002 a & 0.08 \(\pm\) 0.001 b & 0.081 \(\pm\) 0.001 b & 0.037 \(\pm\) 0.003 c \\ Ala & 0.225 \(\pm\) 0.05 b & 0.207 \(\pm\) 0.006 c & 0.261 \(\pm\) 0.03 a & 0.212 \(\pm\) 0.001 c \\ \hline \hline \end{tabular}
\end{table}
Table 3: Free amino acid content (%) in grape berries at harvest under different training systems. All parameters are performed with their standard deviation (\(n=3\)). For each parameter, with the same column, different letters indicate significant differences between treatments by Tukey HSD (\(p\leq 0.05\)).