# Free Monoterpene Isomer Profiles of _Vitis Vinifera_ L. cv. White Wines
## 4 Discussion
Many terpene volatiles are direct products of terpene synthases in grapes [51], therefore the groupings based on monoterpene isomers could be linked to grape variety genetic information. The eight grape varieties selected are some of the most cultivated varieties in the world [8; 18]. To date, the parentage information and genetic associations among these grape varieties are very limited. Torrontes possessed a distinct Muscat flavor and is the second most widely planted white grape cultivar in Argentina. It is very possible that Torrontes was the progeny of a cross between Muscat of Alexandria and Mission [52; 53]. Consequently, Torrontes could contain some similar genetic information with Muscat that is responsible for monoterepne biosynthesis. This would explain our results, with similar monoterepne isomers in Torrontes and Muscat wines. Research using microsatellite markers has shown that Sauvignon blanc is progeny from Cabernet Sauvignon (2018). Gewurztraminer originates from Italy and is a mutation of Sauvignon blanc (2018). Riesling originates from Germany, descended from the mother plant Heunisch Weiss (2018). Chardonnay and Pinot gris originate from France and are both progeny of Pinot norir (2018). Restriction fragment length polymorphism analysis showed that Chardonnay is 80% similar with Riesling, 76% with Sauvignon blanc, and 77% with Viognier (2018). To some extent these parental information do explain the groupings that are based on monoterepne isomers in this study. However, further parentage information related to these varieties cannot be traced from available resources. The differences found in monoterepne content that cannot be explained by possible grape genetics may be linked to winemaking practices and known chemical stability at wine conditions ([PERSON], 2018; [PERSON], 2018). Monoterpene formation can occur through different pathways, including grape biosynthesis ([PERSON], 2018), biotransformation by bacteria or fungi ([PERSON], 2018; [PERSON], 2018), alcoholic fermentation ([PERSON], 2018; [PERSON], 2018), and aging ([PERSON], 2018). The low monoterepne content of Chardonnay wines may be due to de novo production of monoterepne by _Saccharomyces cerevisiae_([PERSON], 2018). Further research in to the source of monoterepne in neutral wines is needed to determine if monoterepne content is due to grape variety or yeast. All other varieties in this study had one or more monoterepne at concentrations above those found by [PERSON] et al. (2018), supporting the fact that monoterepnees originate from grapes. Additionally, the profiles of monoterepnees are known to change due to chemical rearrangement ([PERSON], 2018). Polyols such as 3,7-dimethylocta-l,5-diene-3,7-diol, 3,7-dimethylocta-l,7-diene-3,6-diol, 3,7-dimethyl-l-ene-3,7-diol, and 3,7-dimethyl-lene-3,6,7-triol found in grape varieties can be non-enzymatically rearranged under conditions at grape juice pH of 3.2 ([PERSON], 2018). The rearrangement results in formation of other monoterepnees, such as nerol oxide and funanoid linalool oxide, which are highly reactive ([PERSON], 2018). It is well known that certain pairs of enantiomers possess different sensory characteristics that could alter aroma perception in wines. However, there have not been any studies to date on the EFs of monoterepnees in wines. The fitted lines in the X-Y scatterplots of enantiomer pairs had high \(R^{2}\) values for most of varietal wines (Table 4). It implied that the enantiomer difference of each compound is similar in wines from the single variety although these wines were collected from different wineries, regions, vintages and storage conditions. Our work showed that the majority of \(R^{2}\) values were at 0.8 or higher, suggesting that low variation in enantiomeric differences based on variety.