## 3 Results and Discussion
### Behavior of Volatile Compounds during Storage  
Table 3 presents the composition of volatile compounds of EVOO at baseline and after 12 months of storage for the five conditions. The profile of Arbequina var. EVOO volatile compounds at baseline were characteristic of fresh EVOO, in which the major compounds were aldehydes, alcohols, and esters, the volatile compounds produced by lipoxygenase pathway [8]. (_E_)-2-hexenal, hexanal, 1-hexenol, and (_E_)-2-hexenol were among the most abundant compounds. Following storage of EVOO under different conditions, an increase in volatile compounds such as hexanal and (_E_)-2-hexenal was observed. In addition, there were significant increases in compounds produced by the autoxidation of EVOO, such as propionic and acetic acids and (_E_)-2-nonenal, temperature appearing to be an accelerating factor in the formation of these compounds. The largest increase in propionic acid from 0.21 to 0.56 mg/kg was observed during the highest storage temperature (C5). The presence of acids in olive oil has been attributed to the oxidation of aldehyde compounds previously formed by the autoxidation of unsaturated fatty acids [41]. Thus, the increase of propionic acid may be the result of autoxidation of linolenic acid through the formation of 16-hydroperoxide, to yield propanal, which by oxidation would then form propionic acid [8; 42]. An odor threshold of 0.72 mg/kg was previously reported for propionic acid and imparts defective sensory notes to VOO, such as sour and moldy, although these levels were not reached in our study [7]. (_E_)-2-nonenal increased in nearly all storage conditions, with temperature being the most relevant factor for its formation, increasing in the C5 condition from 0.12 mg/kg to 4.58 mg/kg after 12 months of storage. Light was another contributing factor in the formation of (_E_)-2-nonenal, as room temperature with light (C2) reached 1.93 mg/kg and room temperature without light (C3) reached just 0.47 mg/kg after 12 months of storage. Room temperature storage with light was also similar to storage at 30 \({}^{\circ}\)C in darkness (C4), with levels reaching 2.03 mg/kg in the latter. Appreciable levels of volatiles were produced in soybean oil containing chlorophyll only under light compared to in the dark [34]. In general, the increased levels of volatile compounds during the storage could be explained by the decomposition of hydroperoxides formed during the autoxidation and photooxidation of olive oils subjected to temperature and light conditions, respectively. [PERSON] et al. [43] reported that the hydroperoxide decomposition rate of crude herring oil stored at 50 \({}^{\circ}\)C in the dark was higher than the formation rate of hydroperoxide. The (_E_)-2-nonenal in darkness conditions could be formed from the decomposition of the 9-hydroperoxylineic acid via a homolytic cleavage mechanism, resulting in the formation of a hydroxyl radical (HO \({}^{\bullet}\)) and an alkoxy radical (RO \({}^{\bullet}\)). \(\beta\)-scission of the C9-C10 linkage would then form an olefin, which would then form the compound (_Z_)-3-nonenal [8], followed by isomerization to yield (_E_)-2-nonenal [44]. In light condition (C2) (_E_)-2-nonenal could be formed from the decomposition of 10-hydroperoxylineic acid [30]. The homolytic \(\beta\)-scission was identified as the most important free radical reaction, leading to breakdown products causing flavor deterioration in fats [8; 34]. [PERSON] et al. [45] reported the formation of (_E_)-2-nonenal from an omega-7 monounsaturated fatty acid such as palmitoleic acid (16:1\(\omega\)-7), through the formation of 8-hydroperoxylineic acid. This volatile was reported to have an odor threshold of 0.90 mg/kg [8] and results in defective sensory notes in olive oil such as paper-like, fatty, penetrating, waxy, beany, and rancid notes [8; 31]. In our study, the level of (_E_)-2-nonenal did indeed exceed the odor threshold.