## 4 Discussion
The higher carotenoid content found in Nebbiolo grapes when compared to other varieties [35; 36; 37; 38], agrees with the levels found so far for cv. Nebbiolo [28]. A peak of lutein concentration, that was proportional to the vine vigor, was noticed after veraison in both seasons. A similar peak was reported for Touriga Franca [21], Nebbiolo, and Barbera [28] and, more recently, for Merlot [36]. Therefore, it is possible that cultivar differences exist in the timing of lutein synthesis and degradation thus, a probable delay in VvCCD1 expression can be hypothesize for these varieties [8]. In the present study, the lutein peak after veraison was more evident in the most vigorous plants. This result may be attributable to the high vigor which often reflects a greater synthesis of chlorophyll so, probably, of carotenoids and/or to the lower degradation of this compound under the cooler conditions of these plants. Furthermore, a higher content of lutein-5,6-epoxide (not quantified in this study) in shaded berries prior the veraison can be presumed; the accumulation of this compound has been shown to be a plant early response to shade conditions [8; 15]. Therefore, a higher transformation of this compound in lutein may occur after veraison. In both years, the peak of lutein after veraison was less evident in SouthV\(-\); high temperatures and a higher exposure to sunlight probably promoted the carotenoid degradation in post veraison, as proposed in literature [39]. Lutein is also reported to be more efficient than violaxanthin in preventing ROS formation, thus, it could be further used by grapevines for photoprotection under stress conditions [40]. This could also explain the lower lutein concentration and its higher rate of degradation under more stressing condition, such as in south facing vineyard and in the warmer periods of the season, where high radiation and temperature (\(>\)35 \({}^{\circ}\)C) were achieved for many hours a day in both years [31]. As regards the other treatments, the west-exposed and the more vigorous plots maintained the highest amounts at harvest. Our findings agree with previous research reporting that grapes grown in shaded conditions [21; 41] had higher carotenoid levels. On the contrary, under high UV-B levels, lower concentrations of total carotenoids were found [27]. In 2012, constant levels for \(\beta\)-carotene were observed during ripening in all experimental plots when results were expressed in \(\mu\)g berry\({}^{-1}\), while a significantly lower amount was registered in SouthV\(-\) in both years at harvest. In 2013, instead, higher contents of \(\beta\)-carotene than in 2012 were highlighted in green berries (three weeks before veraison) and for the south facing vineyards a notable decrease was registered thereafter during veraison. The decline of \(\beta\)-carotene during that period was already observed for Nebbiolo and Barbera grapes and was attributed to the high temperature [28]. According to other studies, instead, \(\beta\)-carotene content in grapes, shows an increase from preveraison to veraison, and a decline thereafter until harvest [23; 25; 36]. In our study, the condition of west facing vineyards, less sunlit and lower temperature than in south ones, likely led to a lower degradation of this compound allowing the maintenance of a constant content (\(\mu\)g berry\({}^{-1}\)) in both years. Other research reported also a greater impact of microclimatic variations on lutein more than on \(\beta\)-carotene [42]. Our results showed a different impact of microclimate on \(\beta\)-carotene if compared to the two xanthophylls since high temperatures of south vineyards in the second year led to a higher degradation of \(\beta\)-carotene during veraison more than at the final stages of ripening.