## 3 Results and Discussion
### Phenolic Compounds

Table 2: Phenolic composition (mg/kg) of VOOs extracted with different values of oxygen flow during the crushing phaseThe results obtained agree with [PERSON] et al. [65], who detected a higher loss of phenols, particularly for oleupropein derivates, when a higher amount of oxygen (60%) in the crushing phase was applied. In that study, it was also possible to identify the cultivar influence on the oxidation of the phenolic compounds. However, the oxidation detected was more relevant in the oils coming from olives with higher concentrations of phenols, as was observed in the present study for oils from Coratina olives. The results obtained agree with previous works focused on the malaxation phase and the role of oxygen in modifying the oil composition. Thus, [PERSON] et al. [41] detected that the oxygen added during the malaxation phase also reduced the quantity of phenols in oils due to the activities of the enzymes involved in the oxidation process of phenols. In that work, it was hypothesized that peroxydase (POD) and polyphenodoxidase (PPO) performed phenol oxidation due to the catalysis of the reaction in the presence of oxygen [23; 73]. The reduction of phenols was also observed by [PERSON] et al. [73], who reported that oleacein and oleuppein aglycone were considered to be the preferred choice in terms of substrate for activity in oxidative reactions carried out by PPO and POD. In the present study, the higher concentration of ligstroside derivatives detected in all the Coratina virgin olive oils made with the addition of oxygen during crushing, compared with the control test, seems to confirm the hypothesis above. The observed effect of oxygen is supported by previous studies in which oxygen consumption and reactivity were measured during malaxation. In these studies, the oxidation activity of the enzymes that use oxygen as a co-factor was also evidenced. Thus, [PERSON] et al. [34], referring to the malaxer's head space gas composition, showed that there is a rapid decrease in oxygen concentration, followed by a gradual reduction of its consumption inside the malaxer. The initial oxygen loss was attributed to the enzyme oxidation activities of PPO, POD, and LOX. Then, only in a second moment, the consumption of oxygen due to the cellular respiration process during all the rest of the malaxing phase can take place. Although there are not similar studies carried out during crushing, oxygen consumption can be due to analogous processes. Concerning CO2, in all the cases analyzed by [PERSON] et al. [34], any significant increase of this gas was only observed after the first eight minutes of malaxation. Thus, it is possible to hypothesize that the increase in oxygen concentration during the crushing phase can also promote the activity of PPO and POD with an effect on the phenol composition of the virgin olive oil, according to the data shown in Table 2. Nevertheless, considering that virgin olive oil phenols are first-type antioxidants, their higher concentration can be related to their antioxidant activity to avoid lipid oxidation. The protective effect of the phenolic compounds on the lipid matrix is confirmed by the non-significant variation of the quality parameters when oxygen is applied. The different effects observed in the individual phenols can also be related to their antioxidant activity. Referring to this, several studies demonstrated that ortho-di-phenols such as hydroxytyrosol, oleacein 3,4-DHPEPA-EDA, and oleuppein aglycone are the most reactive substances and have the maximum antioxidant power, especially if compared with derivates of ligstroside and lignans [67; 68]. The results of this work confirm the different reactivity of these phenols reported in these studies.