## 3 Results and Discussion
### Behavior of Phenolic Compounds during Storage  
Table 2 shows the changes in levels of phenolic compounds following 12 months of storage. Arbequina variety EVOO had a total phenol content of 247 mg/kg of oil at the beginning of the storage period. This total phenol amount is in the expected range found for this variety and depends on other variables such as agroclimatic and processing factors [28]. As shown in Table 2, the simple phenols tyrosol and hydroxytyrosol, and elenolic acid increased during storage as a likely result of the hydrolytic degradation of the secoiridoid compounds [36]. The largest increases were observed after 12 months of storage at room temperature with light (C2), and at higher temperatures in darkness (C4 and C5). The increase in tyrosol and hydroxytyrosol was not proportional to that of elenolic acid (molar ratio), possibly due to the active role of both phenols as antioxidants, which can trap free radicals formed under different storage conditions. [PERSON] et al. [9] proposed hydroxytyrosol as a reliable marker to detect aged EVOOs and blends prepared with aged EVOOs. Following 12 months of storage, no significant change was observed in the content of total phenols (\(p>0.05\)). Nevertheless, a significant increase in the content of total oxidized phenols was detected under conditions C2, C3, C4, and C5, reaching a value of 63 mg/kg in the latter, equivalent to 24% of the total phenols. The increase in oxidized phenols may be due to the oxidation of secoiridoid compounds, pleuropein, and ligustroside derivatives, predominant compounds present in fresh EVOO [37], which were oxidized at between 10 and 50% relative to their initial content. The decarboxymethylated compounds derived from oleuropein (oleacein) and ligustroside (oleacein) were the most oxidized (Table 2). This large degradation could be explained by the chemical structure and reactivity of secoiridoid derivatives. Oleacein and oleocanthal, with two aldehyde functional groups in an open configuration, possess larger reactivity than monoaldehyde oleuropein aglycone isomers, which are mainly present in a closed configuration [9]. [PERSON] et al. [12] has proposed oleocanthalic acid formed by oxidation of oleocanthal as a marker of EVOO aging. In a study of EVOO storage in darkness and room temperature for 24 months, [PERSON] and [PERSON] [11] reported that the decrease in secoiridoid derivatives gives rise to simple phenols (hydroxytrosol and tyrosol) and the formation of oxidized products and attributed these changes to hydrolytic and oxidative effects, respectively. Figure 2 shows the degradation of the total secoiridoid compounds, of the decarboxymethylates, oleacein, and oleocanthal, and the formation of oxidized phenols, under C2 (Figure 2a), and C5 (Figure 2b) conditions. The C5 condition resulted in the highest degradation of these compounds, with temperature seemingly being the preponderant factor. Levels reached 48 and 35% of retention percentage for total secoiridoid compounds  
and decarboxymethylate derivatives, respectively. Secoiridoid compounds and the decarboxymethylated forms, oleacein and oleocanthal, resulting from the C5 condition followed a kinetic degradation of zero-order (k = \(-\)6.3491 \(\pm\) 0.7157 mg/kg \(\times\) months\({}^{-1}\); \(\dot{\mathbf{r}}^{2}\) = 0.9608), (k = \(-\)5.8785 \(\pm\) 0.5923 mg/kg \(\times\) months\({}^{-1}\); \(\dot{\mathbf{r}}^{2}\) = 0.9629), respectively, with no significant differences (\(p\) > 0.05) between them. In the C2 condition, the largest degradation was observed in decarboxymethylated derivatives, reaching a retention percentage of 59% at 12 months of storage, while secoiridoid compounds reached retention percentage values of 71%. The highest levels of oxidized phenols were present in the highest temperature condition (C5), with a value of 63 mg/kg. [PERSON] [9] reported degradation of total phenols in a range of 22 to 61% in EVOO subjected to 20 \({}^{\circ}\)C in darkness for 12 months. Another study conducted by [PERSON] et al.