## 3 Results and Discussion
### Volatile Composition
#### 3.3.1 Free Volatile Compounds
This group of compounds had a higher content in the white varieties, 'Caino Blanco' being the variety that showed the highest value. C\({}_{13}\) -norisoprenoids are varietal aroma compounds positive to the aroma of wines [37] because of their powerful odor, as the result of their low odor threshold [38]. In this study, \(\alpha\)-damascenone was the major norisoprenoid in most of the studied varieties (Tables 6 and 7). \(\beta\)-damascenone was also present in 'Caino Blanco', 'Caino Bravo', 'Souson' and 'Verdello Blanco'. 'Loureira' was the grape variety that showed the highest number of different C\({}_{13}\)-norisoprenoids identified, with \(\alpha\)-ionone, \(\alpha\)-damascenone, \(\delta\)-damascone, ionone and \(\beta\)-damascone. The importance of this group of volatile compounds is also due to their positive aroma descriptor, such as sweet, floral, and fruity for \(\alpha\)-damascenone [39], and sweet and apple nuances [40] for \(\beta\)-damascenone. \(\beta\)-ionone is defined with different descriptors such as floral, dark berry or red berry aroma [37] and violet aroma [41], depending on the wine matrix. The presence of \(\alpha\)-ionone together with \(\beta\)-ionone is associated with sweet floral notes [42]. Terpenes are important grape-derived compounds mainly responsible for the characteristic aroma of muscat or related aroma wines, but also of other non-muscat varieties [28]. Relative recent published data showed the wide range of monoterpene content among different varieties and wines, a reason why there are thought to be good varietal compounds [43]. The presence and content of terpenes were also applied to differentiate grapevine varieties using them as varietal markers. In this study, 'Loureira', 'Verdello Blanco' and 'Albarifio' were the white grape varieties with the higher terpene content and also showed a higher number of different terpenoid forms, 46, 43 and 31, respectively. Nevertheless, it should be considered that probably only a part of those terpenes will have an important implication in wine aroma [44]. Among the red varieties, 'Caino Longo 2' showed the highest terpene level as well as a high terpene compound diversity, with 27 different compounds identified along the three years studied. Total average terpene concentrations per variety are shown in Tables 2 and 3. Tables 6 and 7 show that \(\alpha\) -terpineol, with a descriptor of anise [41], was the terpene that reached the highest concentration in 'Albarifio', 'Caino Blanco', 'Caino Longo 2' and in 'Caino Bravo'. In this last variety, \(\alpha\) -terpineol was present in similar content to nerol, that was indeed the major one. Similar results for this variety were obtained by [PERSON] et al. [36] and [PERSON] et al. [45] of this terpene in free and glycosidic fraction, respectively. Terpenyl acetate was the main terpenoid compound identified in 'Caino Tinto', 'Castafal' and 'Souson' while \(\alpha\) -citronellol, with a citrus descriptor, was identified as the highest concentration terpene in 'Caino Longo 1'. Unlalythranilate was the terpene with the highest content in 'Brancellao' and 'Loureira'. This compound is described with fresh linalool, gardenia and orange-like aroma [46]. Nerol was the terpene with the highest concentration in 'Brancellao Blanco', 35 ug\(\cdot\)L\({}^{-1}\), with rose, fruity and floral descriptors [44]. Finally, 'Verdello Blanco' showed linalool as the highest concentration terpene, characterized with floral, lavender and citrus odor [44]. Most of these terpenes were already highlighted by [PERSON] [28] for being the most prominent terpenes in aroma-related cultivars. Sesquiterpenes (C\({}_{15}\)) are the other major important terpene group with balsamic, spicy and woody aroma descriptors [47]. Nevertheless, their contribution to the wine and grape aroma is low, given that their concentrations are usually below their corresponding odor threshold [48]. Sesquiterpenes have also been added in functional foods or cosmetics due to their bioactive and preservative health properties [49].