## 3 Results and Discussion
### Volatile Compounds (VCs)
During our study, \(n\)-alkanes, such as \(n\)-decane (C\({}_{10}\)) and \(n\)-undecane (C\({}_{11}\)), were detected only in oil produced from control olives (at 1.75 \(\pm\) 0.05% and 0.71 \(\pm\) 0.08%, respectively) because of the slow ripening process. These compounds were detected earlier in virgin olive oils by other authors [35; 36; 37]. As regards the commercial oil sample, it was characterized by the highest levels of \(E\)-hex-2-enal (44.55 \(\pm\) 1.63%) and \(Z\)-2-hexen-1-ol (2.76 \(\pm\) 0.13%). Figure 4 presents, the total C\({}_{6}\) VCs in the commercial oil which were 50.00 \(\pm\) 1.62% (88.41 \(\pm\) 0.12% of total VCs detected). At the same time, no C\({}_{5}\) VCs were detected in the commercial oil sample. In the commercial oil sample, the green attributes were positively correlated with \(Z\)-3-hexen-1-ol following the same pattern of the sum C\({}_{6}\) alcohols and \(E\),\(E\)-2,4-hexadienal [11]. The \(E\),\(E\)-2,4-hexadienal has also been detected earlier in olive oil [11; 36; 38]. \(E\)-\(\beta\)-Ocimene is also present in virgin olive oil as reported in previous studies [13; 35; 36; 37; 39; 40] and was detected only in commercial oil sample at a low concentration (0.81 \(\pm\) 0.16%). \(\alpha\)-Copaene is a mono-unsaturated tricyclic sesquiterpene (C\({}_{15}\)). The highest percentage appeared in the commercial oil sample (2.18 \(\pm\) 0.03%), followed by the oil produced from control olives (0.87 \(\pm\) 0.09%) and, finally, the oil produced from CO\({}_{2}\)-processed olives (0.55 \(\pm\) 0.05%). This compound was also reported earlier in virgin olive oil [11; 13; 35; 36; 39; 40; 41]. \(E\),\(E\)-\(\alpha\)-Farmesene a tetra-unsaturated acyclic sesquiterpene (C\({}_{15}\)) was detected only in the commercial oil sample in a low amount (0.91 \(\pm\) 0.02%). This compound has already been reported to be part of virgin olive oil by other authors [11; 21; 35; 36; 39; 40; 41]. (+)-Cyclosativene, a tetracyclic sesquiterpene (C\({}_{15}\)), was detected during our study only in commercial oil sample (0.25 \(\pm\) 0.01%). It was also reported to be part of virgin olive oil [11; 35; 40; 41]. Cyclosativene, generated through the sesquiterpene synthase enzyme under the farnesyl pyrophosphate [42], has antioxidant and anticarcinogenic properties [43]. Most terpen have substantial pharmacological bioactivity due to their anti-inflammatory, anticancer, antidiabetic, antioxidant, or antibacterial activity [44]. In the oil produced from CO\({}_{2}\) atmosphere-processed olives, only \(E\)-hex-2-enal (1.05 \(\pm\) 0.04%) out of the other C\({}_{6}\) compounds was detected. This happened possibly because \(E\)-hex-2-enal (the main VC in most European virgin olive oils) decreases (as observed for most of the aldehydes formed from the LOX pathway) with the increase of ripeness [45]. Additionally, ethyl esters such as ethyl 3-hydroxybutyrate (0.28 \(\pm\) 0.02%) were detected only in oil produced from CO\({}_{2}\)-processed olives. In the biosynthesis of cholesterol, acetoacetate is further reduced to D-3-hydroxybutyrate in the mitochondrial matrix [46]. The fresh green fruity notes are brought on by these C\({}_{6}\) VCs, which are also present in the aroma of many other vegetable products [15; 18]. According to Figure 4, in the oil from CO\({}_{2}\)-processed olives, the total C\({}_{6}\) VCs were 1.82 \(\pm\) 0.02% (2.17 \(\pm\) 0.04% of total VCs). The oil from CO\({}_{2}\)-processed olives greatly differs (\(p\) < 0.05) from the other oils in the percentage of C\({}_{6}\) VCs content. The aldehyde and ester levels in the olives, which bestow a pleasant aroma, reduce when olives are stored. VCs that cause bad odors are produced when olives or oil are stored for an extended time [12; 20]. C\({}_{5}\) VCs have a sensory behavior quite similar to that of C\({}_{6}\) VCs. The level of C\({}_{5}\) compounds (such as \(Z\)-2-penten-1-ol) was found to be lower in comparison to the C\({}_{6}\) compounds.