## 3 Results and Discussion
### Volatile Compounds (VCs)
One of the amyl alcohol isomers, 3-methylbutan-1-ol was detected only in the oil produced from CO\({}_{2}\)-processed olives (3.63 \(\pm\) 0.11%). The \(n\)-6(S)-hydroperoxylinolenic acid is cleaved anaerobically by the LOX to produce a C\({}_{13}\)-oxoacid (13-oxo-12,9-tridecadienoic acid) and a C\({}_{5}\) alcohol (\(Z\)-2-penten-1-ol), according to the study of [PERSON] et al. [18]. An integral component of the olive oil aroma is the C\({}_{5}\) VCs that bestow fruity and sweet aromas [18]. Hexanal, \(E\)-hex-2-enal, hexan-1-ol, and 3-methylbutan-1-ol are the main VCs of olive oil that contribute to the positive aroma characteristics (fruity, spicy, and bitter) [14]. In addition, Figure 4 presents the total C\({}_{5}\) VCs in the oil from CO\({}_{2}\)-processed olives which were 3.63 \(\pm\) 0.11% (4.33 \(\pm\) 0.17% of total VCs detected). The quality of the oil is also directly correlated with the presence of short-chain alcohols in virgin olive oil. Since small amounts of these alcohols may occur during the ripening of olives, low levels of methanol and ethanol are acceptable. Especially, ethanol has also been detected in low concentrations [12; 36; 37; 47]. On the other hand, significant amounts of ethanol are produced during the fermentation processes, which primarily occur during the storage of olive fruit [48; 49]. Additionally, hydroxytyrosol, tyrosol, and ethanol are produced as a result of the hydrolysis of oleuppein during the preservation of olive oil [50]. During our experiments, ethanol was detected only in oil produced from CO\({}_{2}\)-processed olives. It had higher concentrations than reported in previous studies and the highest concentration among the VCs (50.75 \(\pm\) 2.07%). Substantially, ethanol is a cellular fermentation product from continuous emissions of CO\({}_{2}\) in olive fruit storage [51]. Aromatic alcohols have been also detected earlier in olive oil [47; 52]. Benzyl alcohol and 2-phenylethan-1-ol are constituents of the olive oil volatile fraction [2]. In our case, benzyl alcohol (2.12 \(\pm\) 0.17%) was detected only in the oil produced from CO\({}_{2}\)-processed olives. 2-Phenylethan-1-ol was detected at a significantly higher level (\(p<\) 0.05) in oil produced from CO\({}_{2}\)-processed olives (14.69 \(\pm\) 0.21%) in comparison to the oil produced from control olives (0.54 \(\pm\) 0.02%). Another odorant, guaiaicol (2-methoxyphenol), is already found in green olives but appears in higher concentration as the fruit ripens [52]. Guaiaicol and 2-phenylethan-1-ol are the aroma compounds that are important for the fusty flavor [47]. These specific volatile phenols were found in high concentrations in olive oils that had strong fusty, musty, and muddy defects. Their concentration is significantly correlated with the duration of storage and with sensory evaluation, suggesting that they could be used as analytical indices of the oxidation of olive fruits during storage, most likely reflecting the activity of microorganisms [53]. Perhaps this is why it was detected only in oil produced from CO\({}_{2}\)-processed olives but in a very low concentration (0.84 \(\pm\) 0.13%). Olive-pomace oil contains many more aliphatic alcohols than other olive oils, including dodecan-1-ol [54] and, therefore, it was also detected in oil produced from CO\({}_{2}\)-processed olives in a very low concentration (0.16 \(\pm\) 0.02%). Hexanoic acid and ethanol condense to form the ester known as ethanol hexanoate. The formed ethyl hexanoate was detected only in oil produced from CO\({}_{2}\)-processed olives in a low amount (1.47 \(\pm\) 0.07%). The fatty acid ester ethyl octanoate, sometimes referred to as ethyl caprylate, is created when ethanol reacts with the caprylic acid (a saturated fatty acid labeled 8:0). Ethyl octanoate was detected only in oil produced from CO\({}_{2}\)-processed olives and also in a low percentage (1.46 \(\pm\) 0.04%). A fatty acid ester called ethyl decanoate,  
Figure 4: % Peak area of the total, C\({}_{6}\), and C\({}_{5}\) VCs in different olive oils.