## 3 Results and Discussion
### Volatile Aroma in Grape Juice and Skin
Regarding the grape juice, the total terpenoid content accounted for 25.07 \(\mu\)g kg\({}^{-1}\) (free and bound forms combined) in the NS samples, and 35.9 \(\mu\)g kg\({}^{-1}\) in the CS samples. With regard to the SS grape sample, the sum of the terpenoids in the skins accounted for 14.81 \(\mu\)g kg\({}^{-1}\) (free and bound forms combined), and in the juice the total content was 43.64 \(\mu\)g kg\({}^{-1}\). As known, the concentration of terpen in grapes is affected by their sun exposure. Several authors have studied the effect of light on terpene concentration in grapes [36], and the general conclusion that emerges is that the concentration of monoterpenes increases according to the level of sun exposure [14]. Moreover, [PERSON] et al. [37] have highlighted the role of grape maturity on the content of glycosylated terpen, which tend to increase during maturation. In our case, the SS sample was characterized by the highest sugar content with respect to the NS and CS samples, in agreement with the literature data. The benzene derivatives identified in the studied samples were represented by benzaldehyde, benzyl alcohol, and 2-phenylethanol. The latter is a derivative of phenyl propanoid metabolism and produces a rose-like aroma. This compound was absent in the bound volatiles of the juice, whereas it ranged from 12.5 to 34.3 \(\mu\)g kg\({}^{-1}\) and from 0.0 to 10.3 \(\mu\)g kg\({}^{-1}\) in the skin (free and bound forms, respectively), and from 7.7 to 23.5 \(\mu\)g kg\({}^{-1}\) in the juice (free form only). The concentration of benzyl alcohol (free form) was significantly higher (\(p<0.05\)) in the skin and juice samples from the north of Sardinia with respect to the samples collected in central Sardinia (Table 3). The highest value was reported for the SS grape juice (81.8 \(\mu\)g kg\({}^{-1}\)). The same trend (\(p<0.05\)) was also observed for the free form of 2-phenylethanol in the skins. This latter result could suggest a slight influence of the terror on the shikimic acid biosynthetic pathway of benzene derivatives. As reported by [PERSON] and [PERSON] [11], their concentration increases during the final grape maturation step. Moreover, it was recently reported that foliar fertilization with an aqueous water solution of phenyl alanine increases the concentration of some benzene derivatives [38], confirming that the common intermediate in the reaction pathway of the biosynthesis of benzenoids volatiles is the amino-acid phenyl alanine. Although the results for the free and bound compounds (Tables 3 and 4, respectively) reveal great variability between the samples in relation to the concentrations of individual compounds, as observed by the maximum and minimum values (with the exception of very few compounds), no significant differences (\(p\geq 0.05\)) were found in the mean concentrations for the main group of volatiles between the regions investigated (data pertaining to southern Sardinia were not considered in the statistical analysis since only one sample was studied). This conclusion agrees with the results reported by [PERSON] et al. [39], who studied the effect of seasonal variability and region of cultivation on the green aroma compounds present in _Vitis vinifera_ L. Merlot in California. The authors detected great variability in the production of green aroma compounds, such as C6 compounds and methoxypyrazines, according to seasonal variability, whereas no significant variation was observed according to the region of vineyard cultivation. On the contrary, [PERSON] et al. [37] found that the amount of alcohols, acids, and ketones in the Pais cv grape was influenced by vineyard location. The same occurred in relation to terpene content. In general, they observed that the bound aroma fraction was mostly influenced by location, whereas the level of grape maturity achieved had a greater influence on the free aroma profile.