## 3 Results and Discussion
### Volatile Composition of Olive Oil
Other alcohols found in the literature  
relatively high levels were ethanol, 2-penten-1-ol, 1-hexanol and 2-hexen-1-ol, responsible for the green, fruity and floral notes of olive oil [8]. The most quantitatively important aldehydes were (E)-3-hexenal followed by (E)-2-hexenal and hexanal, which provide the typical \"green note\" of olive oil aroma [12]. According to [PERSON] et al. [33], hexanal, (E)-2-hexenal and 1-hexanol are the major volatile compounds of olive oil, which is in agreement with our results. 2,4-Hexaional and nonanal are among the aldehydes identified and have been associated with the oxidative status of EVOO [12]. Small amounts of C5 ketones and pentene dimers also positively affect olive oil aroma [34] that is characterized as sweet. In the current study, 3-pentanone was identified in abundance (CRE: 8.10%, PEL: 12.27%, LES: 15.75%, \(p<0.05\)) and 1-penten-3-one in lower levels but significantly higher in LES samples (6.06%, \(p<0.05\)%). (Z)-3-Hexenyl acetate, which derives from LOX pathway [8; 35; 36], was the most prominent ester in the olive oil samples from the CRE and PEL regions (10.12% and 10.80%, respectively). Relatively high concentration of this ester has also been reported by other researchers [12; 23], and it contributes to the pleasant green and banana notes of olive oil [37]. On the contrary, samples from LES displayed lower levels of (Z)-3-hexenyl-acetate (3.77%, \(p<0.05\)). This could be attributed to a reduced activity of alcohol acetyl transferase (AAT), an enzyme that catalyzes the transformation of alcohols to esters [35], a process which seems to be affected by environmental growth conditions, cultivar and oil extraction processing parameters [24; 35]. Ethyl acetate was the most prominent ester (5.08%, \(p<0.05\)) in the LES samples. It is commonly found in various olive oils [11; 38] and related to aerobic fermentation [36]. Among the carboxylic acids, acetic acid was the dominant one in our samples (CRE: 4.62%, PEL: 3.04%, LES: 5.43%), out of nine acids identified. Carboxylic acids, such as acetic acid, have been suggested to derive from sugar fermentation [38] but are also linked with sensory defects (pungent, like acetic acid) resulting from bacterial growth during olive fruit storage [8]. As far as hydrocarbons are concerned, 4-methyl-2,6-octadiene was the most abundant one displaying slightly lower levels in samples from PEL (CRE: 4.71%, PEL: 2.75% and LES: 3.89%, \(p<0.05\)), followed by 3-ethyl-1,5-octadiene. It is noteworthy that (E)-4,8-dimethylnona-1,3,7-triene, a monoterpene, was present in relatively high levels in samples deriving from CRE. This compound has been reported by only a few researchers [12; 34]. Miscellaneous compounds were generally found in low levels (<0.12%). The total relative content (%) of each chemical class according to geographical origin and cultivar is presented in Figures 1 and 2, respectively. Figure 1: Comparison of the relative content (%) of the chemical classes of volatile compounds identified in EVOOs originating from various growing locations (CRE: Crete; PEL: Peloponnese; LES: Lesvos). The error bars indicate standard errors at 95% confidence level. Data in the same class with different lowercase letters differ significantly (\(p<0.05\)). It is evident from Figure 1 that alcohols were the dominant chemical class within samples of the three geographical origins (\(\sim\)40-45%), followed by ketones (\(\sim\)12-22%), esters (\(\sim\)12-18%) and aldehydes (\(\sim\)8-12%). The content of the remaining chemical classes was lower (\(<\)9%). The content of alcohols was similar (\(p\) > 0.05) between samples from PEL and LES (43.9% and 44.5%, respectively), whereas a lower value (39.5%, \(p\) < 0.05) was observed in CRE samples. The opposite trend was evident when the content of aldehydes was examined. Samples from PEL and LES did not differ significantly (9.29% and 7.60%, respectively; \(p\) > 0.05), and samples from CRE displayed higher levels of aldehydes (12.1%, \(p\) < 0.05).