# To What Extent Are the Effects of UV Radiation on Grapes Conserved in the Resulting Wines?
## 3 Discussion
### Wine VOCs  
The radiation regime significantly affected 15 out of 30 wine individual VOCs (50%), among which eight (27%) increased in wines made from grapes exposed to UV-A, UV-B, or both. In other studies, the proportions of compounds affected by UV radiation were similar: seven out of 27 (26%), among which six compounds (22%) increased under high UV-B [16], and 13 out of 50 (26%), although only three (6%) increased under ambient UV [22]. Given the importance of VOCs for wine aroma, these overall figures are promising for the potential manipulation of UV as a technological tool in grapevine cultivation and winemaking. Total esters showed a specific effect of UV-A alone, and their concentrations increased in PA in comparison with the remaining samples, whose values were similar. Although most esters are by-products of yeast metabolism during fermentation, they can be modified by the grape composition [22], which in turn can be influenced by UV radiation. This would explain the significant influence of UV-A on wine esters in our study. Additionally, the presence of UV-B (PB, PAB, and PAB\(\dagger\) samples) seemed to have some overall inhibitory effect on total ester accumulation. Thus, UV-B would counteract the promoting effect of UV-A. Nevertheless, one major (ethyl octanoate) and two minor (ethyl decanoate and methyl octanoate) individual esters showed higher concentrations in wine samples made from grapes exposed to both UV-A and UV-B, in comparison with wines made from non-exposed grapes, which brings into question the inhibitory role of UV-B. The effects of the UV received by grapes on the esters of the resulting wines are controversial. The concentrations of seven esters in wines made from Pinot noir grapes exposed to ambient UV (both UV-A and UV-B), were lower than those made from grapes exposed to UV-deprived solar radiation [22]. This would agree with a potential inhibitory role of UV-B against ester accumulation. However, the total esters did not change in wines made from Tempranillo grapes exposed to high UV-B, and three individual esters even increased [16]. The influence of variety, UV treatment, and unification process may explain these differences, but further research is needed to better understand the effect of UV-A and UV-B on wine esters. Esters are important because they contribute to fruity aroma in wines; specifically, ethyl octanoate has been considered an indicator of red wine quality [21]. Wine samples made from grapes that had received some UV (mainly PA and PAB\(\uparrow\) samples) showed higher concentrations of three fatty acids (hexanoic, octanoic, and nonanoic acids). Hexanoic acid also increased in wines made from grapes exposed to high UV-B [16], but octanoic acid decreased in wines made from grapes exposed to ambient UV [22]. Thus, the influence of UV on wine straight-chain fatty acids is far from clear. These compounds are produced during wine fermentation and their excessive presence in wine is associated with fatty, cheesy, and rancid aromas, although low concentrations contribute to aroma complexity [22]. Hence, a potential increase in these compounds under UV should be carefully monitored. The major alcohol 2-methyl-1-butanol significantly increased in PAB\(\uparrow\) samples, but was not influenced by UV radiation in other studies [16; 22]. Given the importance of alcohol concentrations in wines, the elevation of 2-methyl-1-butanol under supplemental UV-B warrants more study. The last VOC increasing in wines under UV radiation was the hydrocarbon tetradecane, showing higher concentrations in PAB\(\uparrow\) than P and PB samples. No comparative results are available for this compound, but, being a minor component of our wines, its increase would potentially have a low impact on wine quality. Other comprehensive VOC variables (total alcohols, hydrocarbons, and fatty acids), as well as many individual VOCs, showed unclear or non-significant responses to UV radiation.