## 2 Results and Discussion
### Effect of Attenuated UV Radiation on Three Major Classes of Volatiles
#### 2.1.3 Effect on Fatty Acid-Derived Volatiles  
Aliphatic volatile compounds include short-chain aldehydes and alcohols that are either straight or branched. They are yielded from fatty acid oxidation and/or amino acid degradation [37]. Straight-chain aliphatic volatiles result from the enzymatic splitting of polyunsaturated fatty acids (mainly linoleic and linolenic acid), and therefore they are also classified as fatty acid-derived volatiles. In grapes, straight-chain alcohols, aldehydes, esters, acids, and ketones belong to straight-chain aliphatic volatiles. In this study, 18 alcohols were identified (Supplementary Table S1). Their total concentration had an increase with grape maturation, and then followed a slight decrease at harvest (Figure 5). The UV1-A and the UV1-B treated grapes had significant lower concentration of straight-chain alcohols compared with the control at 5 waf, 8 waf, and at harvest. This indicated that UV radiation attenuation down-regulated the biosynthesis of straight-chain alcohols in Cabernet Sauvignon grapes. No significant differences were observed in the concentrations of alcohols among the UV2 treated, the UV3 treated, and the control grapes. Straight-chain aldehydes are primary constituents of fatty acid-derived volatiles, and thus determine the evolutionary trend of this group of volatiles. Seventeen aldehydes were detected in the 2010 vintage grapes (Supplementary Table S1). Aldehyde volatiles showed the highest level at 11 waf, followed by a decline at the ripening stage (Figure 5). This was consistent with the report of [PERSON] _et al_. (2009) [9]. Compared with the control, the UV3 treatments resulted in a decrease in the aldehyde concentrations in the grapes at 14 waf. However, this impact disappeared at harvest (17 waf). The UV1 treatments also induced the reduction of aldehyde concentrations in the whole development period. Particularly at the onset of veraison and at harvest, this reduction was statistically significant (Figure 5). The UV1-B treatment resulted in the grapes with much lower concentration of alcohols and aldehydes compared to the UV1-A treatment (Figure 5), suggesting that the impact of UV radiation reduction could be dose-dependent. Esters are usually at low levels in grapes with limited flavor contribution. Seven straight-chain esters were identified (Supplementary Table S1). The concentration of ester volatiles showed a gradually decreasing trend. [PERSON] _et al_. (2009) also reported the similar pattern on the ester volatile evolution, which was mainly explained by the loss of ester synthesis ability in grapes at the beginning of veraison [9]. At pre-harvest, the UV1 and the UV3 treated grapes exhibited a larger reduction in the concentration of straight-chain esters compared with the control (Figure 5). Therefore, the concentration of esters in the UV1 and the UV3 treated grapes were significantly lower than the control at harvest (Figure 5). This suggested that UV radiation attenuation might more rapidly trigger grapes to lose ester synthesis activity at the late development stages of grapes. Figure 5: Effect of attenuated UV radiation on the concentration of fatty acid-derived volatiles in developing “Cabernet Sauvignon” grapes. For more information, please refer to the explanation in Figure 2.  
Three straight-chain acids were identified from the samples (Supplementary Table S1). Their total concentration decreased overall. In the UV3-A and the UV3-B treated grapes, the concentration of acid volatiles dropped much more than the control, resulting in lower concentration of these compounds at harvest. The UV1 treatments also markedly decreased the concentration of straight-chain acids of the grapes at the early development stages (5 waf and 8 waf) (Figure 5). However, this decrease impact did not remain consistent by berry harvest. Five straight-chain ketones were identified in the 2010 vintage grapes (Supplementary Table S1). The total concentration of these volatiles reached the highest level at 8 waf and subsequently decreased.