## 3 Results and Discussion
### Volatile Substances  
In this study, a selection of volatile molecules among those detected in the EVOOs investigated, has been considered, based on their recognized relation with positive or negative sensory attributes of an olive oil. Their relative quantification has been performed in terms of peak area percentage, and significant differences between the cvs. were highlighted in each of the two years investigated (Table 2), with some features seeming to be peculiar of the cultivar, as suggested by an identical trend in both years. Volatile substances are key compounds concerning the sensory properties of an EVOO where they can provide positive sensory notes as the green, fruity, almond and many other desirable attributes. However, some of the volatiles (e.g., ethanol, acetic acid, some aldehydes) are also responsible for negative sensory attributes of the oil (e.g., rancid, winey, yeast). Thus, the profile of the volatile substances can be related to the quality of an EVOO highlighting some peculiarities of the specific olive cultivar from which the oil has been obtained. The lipoxygenase pathway is the key biochemical process leading to formation of a series of volatile molecules, mainly having five or six carbons, that are aldehydes, alcohols, or their ester derivatives with acetic acid. (_E_)-2-Hexenal, which is one of the main compounds formed in the lipoxygenase pathway, is a key molecule in EVOO flavor, which contributes with sensory notes of green leaves, grass, and fruit and is commonly found to be the most abundant volatile detected. Other aldehydes are present in EVOO and their presence, referring in particular to longer chain aldehydes, as e.g., 2-heptenal, nonanal, and decanal [30], which is due to autoxidation phenomena leading the oil to lose its sensory and nutritional quality, beyond its safety. Pentene dimers are a group of isomers formed during lipoxygenase pathway, which have been associated with positive sensory attributes of the oil [31]. Terpenes (e.g., \(\alpha\)-farnesene, \(\alpha\)-copaene) are also commonly found in EVOO and their presence has been related to the olive cultivar, which has molecules already present in the olive fruit and are partially transferred to the oil during the production. \(\alpha\)-Copaene is a tricyclic sesquiterpene whose presence in the fruit has been reported to contribute to an increase in the susceptibility of olive fruits to attack by _Bactrocera oleate_ females [32]. Methanol and ethanol are produced to a large extent in undesirable fermentation processes occurring during prolonged olives storage before processing and higher levels are generally found in oils having lower quality [33; 34; 35]. In the present study, oils from the cultivar ASC were characterised by a high average percent of the C5 compounds 1-penten-3-one and 1-penten-3-ol, by (Z)-3-hexen-1-ol and 3-hexen-1-ol acetate and by a low relative percentage of (_E_)-2-hexenal (Table 2). MIG had a high percent of 3-hexen-1-ol and hexanol acetates, pentene dimers, and \(\alpha\)-farnesene, which was highest in MIG in each of the two years even if statistical significance was not reached in 2016. On the other side, MIG was relatively poor of 1-penten-3-one and 1-penten-3-ol, (_E_)-2-hexenal, hexanal, and \(\alpha\)-copaene. In both years investigated, RAG was the cultivar with the highest average percentage of (_E_)-2-hexenal, \(82.2\pm 4.6\%\) in 2015 and \(72.1\pm 10.3\%\) in 2016, which is significantly higher than its average percentage of content in MIG and in ASC in both years. The absolute content of the molecule, measured in terms of peak area units, has the same trend, with RAG having the highest average value, as compared to the other cvs. in both years, and differing significantly from MIG in both years. MOG variety was characterised by the highest percent content of \(\alpha\)-copaene in each of the two years, with significant differences among the groups investigated, which points at \(\alpha\)-copaene as a possible marker for the variety.