## 3 Results and Discussion
### Behavior of Antioxidant Compounds  
#### 3.3.1 Phenolic Compounds  
Table 1 presents the composition of phenolic compounds in VOO from fresh and frozen Arbequina variety olives. The VOO from fresh olives presented a content of 413 mg/kg of total phenols, higher than that reported by [PERSON] et al. [33] which had a content of 273 mg/kg, but in the range of other studies [9; 49]. In the VOOs from both types of fruit, a significant decrease in phenolic compounds was observed during ripening, with the oleuropein-derived compounds 3_A_-DHPEA-EDA and 3_A_-DHPEA-EA-AH being the most affected. [PERSON] et al. [50] reported a decrease of phenolic compounds in VOOs of the Arbequina variety between 20 and 35 weeks after flowering. During olive ripening, the concentration of total phenols progressively increases until it reaches a maximum level at the \"cherry\" stage, decreasing abruptly as ripening progresses. The rapid decrease of phenolic content during the black maturation phase has relates to a higher activity of hydrolytic enzymes in this period [51]. When comparing the oils obtained from fresh olives with those from frozen olives, it was observed that the latter presented a higher content of total phenols between June and August, and a higher content of 3_A_-DHPEA-EDA at almost all harvesting times. This behavior would be due to the early action of the endogenous \(\beta\)-glucosidase enzyme on oleuropein in freeze-damaged olive fruits, which would induce the production of oleuropein-derived aglycones. [PERSON] et al. [50] reported the highest affinity of \(\beta\)-glucosidase on oleuropein, resulting in the highest hydrolysis level for oleuropein, followed by ligstroside and demethyloleuropein. In other studies, the content of the main phenolic glycosides, oleuropein and demethyloleuropein, in the olive tissue were severely reduced by freezing, and high levels of hydrolytic secoriidoid derivatives (3_A_-DHPEA-EDA, 3_A_-DHPEA-EA) were found in freeze-damaged fruits [52]. Table 1 further shows an increase in the levels of elenolic acid and hydroxytyrosol in VOOs from freeze-damaged olive fruits as a result of the hydrolytic degradation of oleuropein derivatives. In addition, a decrease in the concentrations of p-HPEA-EDA, and the flavonoids luteolin and apigenin, and an increase in the oxidized fraction of p-HPEA-EDA, were observed. The lower levels of phenols in VOOs from freeze-damaged olive fruits compared with oils from fresh olives would be due to the action of polyphenol oxidase (PPO) and peroxidase (POX) enzymes, which would be released from their sub-cellular compartments by the damage produced during freezing of the fruit and would come into contact with the phenols. PPO is the main enzyme involved in the oxidation of phenols during physiological processes associated with fruit ripening and during any form of manipulation of the fruit involving tissue damage or breakage. The phenol oxidation by PPO includes two different reactions, hydroxylation of monophenols to form orthodiphenols and the oxidation of orthodiphenols to form o-quinones [53]. POX would also act on orthodiphenols in the presence of H\({}_{2}\)O\({}_{2}\) to produce semiquinones, o-quinones, and polymers [53; 54]. [PERSON] et al. [52] described an inactivation of PPO enzymes in olives subjected to freezing for 3 days at -18 \({}^{\circ}\)C; however, POX activity remained unaltered, due to the fact that this enzyme is mainly located in the seed, the tissue of which is rather more resistant to adverse environmental conditions. In the same study, as already mentioned, a marked increase of secoriidoid derivatives was observed in the freeze-damaged olive fruits from the Picusal and Arbequina varieties, and a decrease of these compounds in the VOOs from these varieties. [PERSON] et al. [55] reported a low secoriidoid and high vanillin and vanillic acid content in oils from the Picusal trees grown in areas of Australia with recurrent freezing problems. [PERSON] et al.