## 2 Results
### Wine Characterization  
Recursive analysis extracted and identified 77, 75, 78 and 73 metabolites in wines from La Changa 2017 and 2018 and Los Dolores 2017 and 2018, respectively (Table 1). PCA included 101 metabolites (Table 1), where the first three components explained 86.71% of total variance (data not shown); furthermore, using the first two components (67.02% of total variance) allowed the clustering of wines by vineyard and vintage (Figure 3a) with a metabolite distribution shown in Figure 3b (PCA loadings). To elucidate PC1 and PC2's meaning, a closer glance at metabolites near to wine-clustering areas was required; PC1 appears to be related to variables depending upon vintage, while PC2 allows the separation of wines by typology, and therefore is associated with wine quality or/and sensorial profile. Figure 3: Principal component analysis (PCA). (a) grouping vineyards (blue: Los Dolores, yellow: La Changa) and vintages (\(\blacksquare\): 2017, \(\blacktriangle\): 2018); and (b) compound distribution, identifying those that contributed greatly to sample differentiation. Figure 2: PCA of quality-control samples, PW (yellow), PWS (red) and samples (blue). Regarding PC2 (Figure 3), some of its positive loadings such as 4-ethylguaiacol (compound #88 Table 1) and 4-ethylphenol (#94) contribute with undesirable aromas and have been reported in wines affected with Brettanomyces [35]. However, 2-undecanol (#64), 4-methylbenzaldehyde (#55), furfuryl ethyl ether (#18), methyl salicate (#72) and translinalo oxide (#38) have been associated with spicy notes or found in spices, with roasted nuts, cooked beef and blackberry aromas; isoamyl acetate (#10) has banana and balsamic notes and \(\alpha\)-terpineol (#62) has anise and citrus. At the same time, some of its negative PC loadings--metabolites such as monoethyl succinate (#101), ethyl nonanoate (#44), acetoin (#20), diphenyl ether (#87) and isobutyl hexanoate (#26)--have desirable sensorial properties and are reported as sweet and fruity [36]. Further analysis on PCA-loading distribution (Figure 3b) showed that metabolites at PC1- and PC2-negative loadings have fruity and citrus descriptors; those at PC1-negative and PC2-positive loadings are described as fresh, sweet, floral and fruity; while those at PC1-positive and PC2-negative loadings are predominantly floral and sweet notes. PC1- and PC2-positive loadings are less desirable, with descriptors such as alcoholic, balsamic and phenolic [36]. Based on these descriptors it could be inferred that the 2018 vintages from both vineyards have frutier, more citrus, sweeter and fresher notes than the 2017 vintage, and Los Dolores 2017 presents floral notes. According to these results, La Changa 2017 could be the most-balanced wine as it is positioned almost at the center of the PCA (Figure 3a); however, sensorial analysis is required to confirm these assumptions. In addition, some putatively identified (level 2) and unknown (level 4) components have potential use as biomarkers for vineyard and vintage classification; consequently, their elucidation is required [7]. Additional data analysis (Figure 4) showed five potential markers for vintage differentiation. Compounds cis-2-Hexen-1-ol (#33), Unknown 38.9824 (RI 1432; ions 43.0543, 71.0852, 57.0699, 70.0774, 55.0543 \(m/z\); C6H12O) and Unknown 41.3476 (RI 1754; ions 163.1114, 145.1008, 164.1161, 73.0645, 45.0335 \(m/z\); C11H12O3) were unique to 2017 wines. Ethyl lactate (#27) and octyl ether (#68) were only present in 2018 wines (Figure 4 and Table 1). Interestingly, 54 compounds are shared by vineyards and vintages, which ideally, could indicate a metabolomic fingerprint of Santo Tomas Valley; however, extensive sampling and further analysis is needed to conclude this. Nevertheless, 24 of those compounds (Table 2) were decisive in vintage differentiation (\(p<0.05\)).