# From Vine to Wine: Non-Colored Flavonoids as Fingerprints
## 4 Discussion
### Univariate Analyses
#### 4.1.1 Cultivar  
Regardingflavanols, the predominance of epicatechin over catechin and their concentrations in our red wine samples align with previous findings for Syrah red wines [28]. Epicatechin is known to be more prevalent in condensed tannins and contributes significantly to wine astringency and potential aging [29] This pattern might be due to differences in the chemical structure of tannins, grape skin composition, and seed-derived flavanols. In agreement with previous research, most of the concentrated flavonoids in our study were those derived from quercetin (Quer, Q3 gu), while kaempfer and laricitrin were found in lower concentrations [22]. This predominance of quercetin derivatives may be attributed to its greater natural abundance in grape skins [25]. Interestingly, in the red wines analyzed, GFlo were generally found at higher concentrations than their aglycone counterparts, which are in agreement with most of the studies that indicate that flavonoids in wines are predominantly present in their glycosylated forms [30; 31; 32]. In contrast, results obtained for Australian red wines [22] found higher contents of the free flavonoids or aglycones. This discrepancy could be explained by differences in unification techniques between both regions or to variations in enzymatic activity during fermentation. Specifically, differences in the activity of \(\beta\)-glucosidase and other hydrolytic enzymes, which cleave glycosidic bonds and release aglycones, might result in a higher retention of glycosylated flavonoids in the Canary red wines [32]. Additionally, factors such as pH, fermentation temperature, and maceration time could influence the relative abundance of glycosylated versus the corresponding free flavonoids [31]. For instance, acidic conditions can promote hydrolysis, leading to the release of aglycones [33]. When the non-visible flavonoids (flavanols and flavonoids) were compared with visible flavonoids (anthocyanins) obtained in our previous study [15], it was observed that, in general, flavanol content exceeded anthocyanin content, except in highly pigmented cultivars (S, C, and R), where anthocyanin concentrations were nearly double those of flavanols. This suggests that anthocyanin biosynthesis and accumulation might vary more significantly by grape cultivar than flavanol production, possibly influenced by genetic factors and ripening conditions. T cultivar exhibited the highest flavanol concentration, which could result in red wines with more structured tannins and an increased astringency. Flavanols, particularly catechins and epicatechins, are precursors to condensed tannins (proanthocyanidins), which impact the texture, mouthfeel, and aging potential of red wines [34]. On the other hand, the flavonoid concentrations were lower than anthocyanin concentrations for red wines produced from most of the cultivars, except for N cultivar. This unusual profile obtained in N cultivar could be explained by differences in grape skin thickness or similar specific varietal traits that could favor a higher flavonoid accumulation than anthocyanins [35]. Additionally, differences in anthocyanin stability, polymerization, and degradation during winemaking and aging in this cultivar may also play a role in its differential behavior observed. The variation in GFlo according to grape cultivars observed in this study confirms a strong cultivar influence on flavonol biosynthesis in single-cultivar red wines. This aligns with previous findings that flavonoid accumulation is highly dependent on genetic factors and environmental conditions, particularly UV exposure [26]. Notwithstanding this genetic variability, flavonoid concentrations measured in red wines produced from the Canary Islands autochthonous cultivars align with the typical ranges documented in existing literature [1]. Wines derived from international grape cultivars generally exhibited elevated levels of most flavonoids compared to those from local cultivars.