# To What Extent Are the Effects of UV Radiation on Grapes Conserved in the Resulting Wines?
## 3 Discussion
### Wine Phenolic Composition  
Wine total flavonoids, together with four major (three quercetin- and one myricetin-glycosides) and three minor (two kaempferol- and one isorhamentin-glycosides) individual flavonoids, showed the most consistent responses to the UV radiation applied to the grapes. Hence, flavonoids were the phenolic compounds more reliably conserved from grapes to wine. In general, these variables significantly increased in PAB and PAB\(\uparrow\) samples in comparison with the remaining samples, including those whose grapes had received either UV-A or UV-B alone (PA and PB samples, respectively). These consistent responses could be expected, because the accumulation of different flavonoids, especially glycosylated quercetin, is the most reliable response of grapes [6; 8; 10; 15; 23; 25; 26; 27; 28; 29; 30] and the resulting wines [16; 23] to UV radiation, across different grapevine varieties and experimental conditions. Given that flavonoids contribute to wine co-pigmentation by stabilizing anthocyanins [31], and they are also interesting antioxidants and nutraceuticalids [32; 33], their increase under UV radiation can improve the quality of both grapes and wines. It is interesting to highlight that the responses of flavonoids were determined by a synergic effect between UV-A and UV-B, as found in other studies dealing only with grapes [9; 26; 34]. Consequently, this is the first time to our knowledge that this synergy has extended from grapes to the resulting wines, thus proving the effect of UV radiation on grapevines. The response of wine total hydroxcinamic acids to UV was significant, and PA, PAB, and PAB\(\uparrow\) samples showed higher concentrations than P samples. Nevertheless, differences between regimes were relatively low and the response of total hydroxcinamic acids was not clearly reflected in any individual acid. The response of total hydroxcinamic acids, although subtle, was surprising because these compounds do not usually respond to UV radiation, neither in grapes [8; 11; 14; 23; 35; 36] nor in the resulting wines [23]. This lack of response is likely due to the competition between flavonoids and phenolic acids for the same precursors in their synthesis. In addition, some hydroxcinamic acids are produced de novo during winemaking, which can decouple, to a certain extent, the relationship between their contents in grapes and their concentrations in wines. However, high UV-B irradiance increased the total hydroxcinamic acids in both Tempranillo grapes and the resulting wines [16], showing that UV-B levels well over the ambient ones may be needed to induce the accumulation of these phenolic compounds. Given the importance of hydroxcinamic acids and their derivatives to the color, taste, and flavor of wines [21], further research is needed to better understand their responses to UV radiation. Total anthocyanins did not respond to radiation regimes and, among the 15 individual anthocyanins measured, only delphinidin-glucoside showed a consistent response to UV,with higher concentrations in PAB\(\dagger\) than in P and PA wines. Overall, the diffuse response of anthocyanins to UV radiation was expected, being consistent with most previous results obtained in grapes and, occasionally, in wines [16]. Nevertheless, anthocyanins increased in wines made with Pinot noir and Tempranillo grapes exposed to ambient UV [22; 23]. Thus, the responses of grape anthocyanins to UV are complex and may depend on the interaction of internal (variety, berry development) and environmental (temperature, radiation) factors [6]. In addition, anthocyanins can change during winemaking due to polymerization and/or degradation [37], which may limit the relationship between grape and wine anthocyanins. Consequently, although they are crucial compounds for the red coloring of wine, and also have nutraceuticalal properties, the effects of UV radiation on grape and, particularly, wine anthocyanins are not fully understood yet.