## 2 Results  
### Acidity, Total Sugars, Amino Acids, and GABA  
Acidity and total sugars were used as a proxy for the staging of berry ripening progression in treated and control samples. Total titratable acidity and total sugars were measured at each time point during both vintages (Figure 1). The treatment with DYE did not induce significant differences in terms of total sugar content or in the acidity of berry juice, except for acidity at TP2 in 2020, which appeared to be transiently higher in the treated samples. This effect was not confirmed in 2021. In fact, at H, both treated and control samples showed no differences in these parameters. The complete amino acid profile, as well as GABA (gamma-aminobutyric acid) and other secondary metabolites, have been determined at TP2 and at H in both 2020 and 2021 (the complete dataset is provided in Table S1). The collective average data is shown in Figure 2.  
According to Figure 2A, the greatest differences among samples were observed between control samples at TP2 and at H. The effect of ripening was in fact evidenced by higher contents of cysteine, proline, hydroxyproline, phenylalanine, pipecolic acid, cis- and trans-piceid, and viniferin, and by lower contents of methionine, asparagine, and GABA, independently from the treatment. At H, the DYE application resulted in higher levels of valine, leucine, methionine, isoleucine, and tryptophan and a less marked decrease of arginine, asparagine, and GABA, or, conversely, a less marked increase of cis- and trans-piceid and viniferin. For some of these compounds (valine, tryptophan, and cysteine), this effect was already evident at TP2. At maturity, as a consequence of these amino acid trends, the arginine to proline ratio, a commonly used marker for evaluating berry maturity [17], was higher in treated berries (2.7-fold) in comparison to the control ones (1.4-fold) in the 2020 season. Figure 1: Total acidity (**A**) expressed in g/L of tartaric acid and total sugars (**B**) expressed in \({}^{\circ}\)Brix, determined in the samples of Sauvignon Blanc berries in the years 2020 and 2021 that had been collected from treated (orange lines) and control untreated (green lines) vines. Sugars were measured for each experimental condition individually on 60 berries belonging to each replica/treatment at each sampling date. The EL stages at each time point (TP1, TP2, and Harvest, H) were identified on the basis of the average sugar levels according to the modified EL system described by [PERSON] (1995) [16] as EL36, 37, and 38, respectively. Aidity was determined by titration of the juice obtained from 20 randomly collected berries. The significant differences (*) were determined with a \(t\)-test with a \(p\)-value < 0.05. Figure 2A was confirmed by PCA analysis, which highlighted the separation of samples according to their ripening stage along dimension 1 (accounting for 43.0% of variability) and positioning samples at H on the left side and TP2 samples on the right side of the graph (Figure 2B). Conversely, the second dimension (describing 25.4% of variability) of the PCA enabled the separation of control and treated samples at H, while treated and untreated samples grouped together at TP2, consistent with the previous analysis (Figure 2B). Figure 2C reports the loading plot driving the observed sample clustering, showing that the metabolites contributing the most to the separation of the grouping samples collected at H from the ones sampled at TP2 were the secondary metabolites viniferin, _cis_- and _trans_-piceid and pipecolic acids, and the amino acids proline, hydroxyproline, and phenylalanine. On the contrary, leucine, isoleucine, tryptophan, valine, histidine, and methionine were the amino acids contributing the most to the separation of treated and control samples at H along the y axis.