# Part II--Aroma Profile of Twenty White Grapevine Varieties: A Chemotaxonomic Marker Approach
## 3 Results & Discussion
### Volatile Composition
#### 3.3.1 Free Volatile Fraction  
Regarding the aromatic profile, which provides the contribution of each family to the global aromatic potential of each variety, it can be seen in Figure 1 that C6, acids, ketones, PAHs and thiol compounds appeared mostly in higher percentages in the free fraction. Lactones and norisoprenoids were detected almost exclusively in the free form, with some exceptions, such as in 'Garrido Fino', with a higher percentage of norisoprenoids in its glycosidic fraction. It can also be noticed that there was almost no presence of phenols or esters in their free fraction, contrary to the glycosidic one. Significant differences between varieties are shown in Table 2 for terpen, with 'Pirixileira' showing the lowest mean value (3.66 ug\(\cdot\)L\({}^{-1}\)), while 'Italia' showed the highest one (9169 ug\(\cdot\)L\({}^{-1}\)). The mean content of total free volatiles also showed significant differences, with 'Italia' being the variety showing the highest mean value (11,059 ug\(\cdot\)L\({}^{-1}\)), while 'Batoca' showed the lowest one (2398 ug\(\cdot\)L\({}^{-1}\)). It is considered that the high deviation between the data obtained in the different years of the study is what has prevented us from obtaining greater statistical significance between families of compounds, except for terpen, being, therefore in this fraction of aromatic compounds and in this specific study, the family that will allow us to obtain clear differentiation between varieties together with the mean total free volatile content. Terpenes are the compounds of grape-origin that mainly determine the characteristic wine aroma and muscat wines, with linalool, geraniol, hotrienol, nerol and \(\alpha\)-terpineol being some of the most extended terpenes in muscat and other aroma-related grapes. Their different compositions among varieties could be used for varietal differentiation [49]. Nevertheless, their chemical structure is highly variable reason why there is a broad terpene diversity, being monoterrepoids, sesquiterpennoids and triterpenols only found in determined species [50]. In this study, they were detected in their free form in every variety studied but in very different contents, with the olfactory impact of these compounds being synergistic [51]. As it could be easily appreciated in Figure 1, those varieties with higher percentages were 'Albilla do Avia', 'Branco Lexitimo', 'Dona Branca', 'Fernao Pires', 'Italia' and 'Moscatel de Bago Miudo', which also showed similar terpene percentage contributions in their glycosidic fraction. Of these, 'Italia' and 'Moscatel de Bago Miudo' differed statistically from the rest in terms of their contents, with 9169 ug\(\cdot\)L\({}^{-1}\) and 6361 ug\(\cdot\)L\({}^{-1}\), respectively, with linalool being the major terpene detected (Supplementary Table S2), which could contribute to citric, sweet, and floral aromas [52]. Compared to them, 'Pirixileira' and 'Planta Fina' were the varieties that showed the lowest contents (3.66 and 8.31 ug\(\cdot\)L\({}^{-1}\) respectively), with m-cymene, a geometric p-cymene isomer [53], and \(\beta\)-cyclodextrin, with minty as descriptor [54], as the major terpen detected. Sesquiterpennes are C15 terpene compounds enriched in grapes' external layer wax [55]. More than 60 sesquiterpennes were identified in grapes [56] and could be used for varietal discrimination [57]. Their biological functions are thought to be involved in grape defense strategies against biotic and abiotic stress factors, as well as in grape quality [58]. In this study, they were detected in 11 of the 20 varieties studied in their free form, having a low percentage contribution to their aromatic profiles, as shown in Figure 1, involving up to 1% of the total profile. 'Dona Branca' showed the highest average value. C13-norisoprenoids are interesting compounds, as their odoriferous properties are well-known to contribute to the perception of wine's aroma, derived from the breakage of carotenoids [51].