## 3 Results and Discussion
### Amino Acid Profiles of Grape Berries and Wines  
Amino acids are the main precursors for secondary metabolites, including flavonoids, in grapes [11], and are also a nitrogen source for yeast during alcoholic fermentation [28; 29]. The amino acid profile of grape berries affects the production of polyphenol compounds, ethanol and glycerol [30]. The amino acid profiles of the grape berries and wines in the current experiment are shown in Tables 2 and 3, respectively. Chromatograms of the amino acid are shown in Figure S1. According to amino acid biosynthesis pathways, 17 of the amino acids present in grape berries and wines can be classified into five families, including serines (Cys, Ser, and Gly), aromatic amino acids (Phe and Trp), aspartate (Ile, Asp, Lys, Met, and Thr), glutamates (Arg, Glu, His, and Pro), and pyruvate (Leu, Ala, and Val) [31]. For the serine family, serine was the most abundant amino acid in grape berries, accounting for 50% of the amino acids from this family (Table 2). RDI-3 treatments significantly increased the levels of serine in both years; lower levels of serine were detected in the RDI-2 treatment group. The highest levels of cysteine were found in 2015 wines produced from RDI-3-treated wines; however, RDI-1 and RDI-2 treatments decreased cysteine values in both vintages of wine (Table 3). Phenylalanine and tryptophan are the main aromatic amino acid families in grape berries and wines. RDI-1 and RDI-3 treatments significantly increased tryptophan levels in the two vintages; however, the lowest tryptophan levels were detected with the RDI-2 treatment for both years (Tables 2 and 3). The highest levels of phenylalanine were detected in the RDI-3 group for both years, which means that the RDI-3 treatment might give wine more rose, floral, and honey flavors [2]. The concentration of phenylalanine amino acid in berries with the RDI-2 in 2016 was higher compared to the control group. Higher values of aspartic acid in grape berries after RDI-3 treatment might provide more nitrogen for yeast [30; 32]. The RDI-1 and RDI-2 treatments decreased the levels of methionine and lysine in berries; however, increased levels of methionine and lysine were found in berries after the RDI-3 treatment (Table 2). Methionine is the precursor of glutathione [29], and the RDI-3 treatment increased the level of methionine in the two vintages wines, which was consistent with a high level of glutathione. In contrast, the RDI-1 and RDI-2 treatments decreased the level of methionine in the two vintages wines, which was consistent with a low level of glutathione (Table 3 and Figure S2). Threonine was the most abundant member of the aspartate amino acid family in berries. For the glutamate family, proline and arginine were the most abundant amino acids in grape berries (Table 2). Proline plays an important role in enhancing plant tolerance to water deficits [32; 33]. The RDI treatments enhanced proline biosynthesis in both vintages, which was consistent with previous reports [32]. Argin levels were enhanced in berries after the RDI-3 treatment; however, the RDI-2 treatment decreased the arginine levels in both vintages. The levels of arginine were lower in the wines than the berries, which might be due to yeast consuming arginine during fermentation [2]. The leucine and valine levels increased in berries and wines from the RDI-3 treatment for both vintages. The RDI-2 treatment increased the levels of leucine and valine in the 2016 grape berries; however, higher leucine and valine levels were only found in the 2015 wines.