## 3 Results and Discussion
### Phenolic Compounds  
Table 2 shows the phenolic composition of the oils produced by adding different concentrations of oxygen during the crushing phase. For the two cultivars, the addition of different concentrations of oxygen (particularly 0.4 and 0.8 L/min) during the crushing phase resulted in a significant decrease in the total phenol concentration (\(p<\) 0.05) compared with the control test. In both cultivars, the maximum decrease in total phenolic concentration was detected in the virgin olive oils produced by adding 0.8 L/min of oxygen during crushing. Thus, in the case of Ogliarola, the total concentration of phenols decreased 13% with respect to the control oil, from 645 mg/kg to 562 mg/kg. In addition, the phenolic compounds that are more influenced by the addition of oxygen in crushing are those with higher antioxidant activity, which are the oleupopein derivates [(67; 68)]. Thus, the sum of oleupopein derivatives (hydroxytrosol, oleacein, and oleupopein aglycon) decreased from 489 mg/kg (control oil) to 419 mg/kg in the case of 0.8 L/m of oxygen addition (Table 2). However, oleacein and oleupopein aglycone underwent a reduction of 14% and 16%, respectively, in their concentration. The reduction in the concentration of oleupopein derivatives can be related to an enzyme oxidation activity promoted by peroxidase and polyphenolidase, which use oxygen as a co-factor [(69; 70; 71; 72)]. Furthermore, for the test adding 0.8 L/min of oxygen, a similar concentration decrease of the ligtroside derivates was detected, including tyrosol, oleocanthal, and ligtroside aglycon. This decrease accounted for 14% of the difference compared with the concentration of ligtroside derivatives in the control test, mainly due to the reduction of the concentration of oleocanthal (17%). On the contrary, the concentration of lignans did not show any significant variation. When 0.4 L/min of oxygen was added, the concentration of total phenols underwent a 5% reduction, from 645 mg/kg in the control test to 611 mg/kg. In this case, the higher effect of reduction was also detected for the derivates of oleupopein and ligtroside. For example, a decrease of 5%, 10%, and 7% was observed for oleacein, oleupopein aglycon, and oleocanthal, respectively, in comparison with the control test. Finally, the treatment with 0.2 (L/min) of oxygen during crushing led to a non-significant reduction of only 2% in the total concentration of phenols. The data for Coratina oils shows the same trend as the oil from the Ogliarola cultivar. Thus, the sum of total phenols showed its maximum value in the control test with no oxygen added. In Coratina oils, the maximum decrease of phenols was also observed with the addition of 0.8 (L/min) of oxygen. This oxygen treatment resulted in a significant (\(p<\) 0.05) decrease of 31% in total phenol concentration, from 856 mg/kg for the control test to 591 mg/kg for the test with 0.8 (L/min) of oxygen addition. This reduction percentage was higher than that observed in the Ogliarola cultivar (13%). The most relevant effect of oxygen addition was also identified for the oleupropin derivates, especially for oleacein (52% reduction percentage). For the other concentrations of oxygen addition, a significant decrease of total phenolic compounds in comparison with the control test was observed: 11% and 2% of concentration decrease, respectively, for 0.4 L/min and 0.2 L/min of oxygen addition. The concentration of oleacein in the control test (555 mg/kg) underwent a reduction of 15% and 5% when oxygen was added at 0.4 L/min (472 mg/kg) and 0.2 L/min (527 mg/kg), respectively. On the contrary, an increase in the concentration of hydroxyytrosol and tyrosol was registered, although this change was not identified as significant. Derivates from ligtroside and lignans did not show significant variations for all the oils produced from Coratina olives, which contrasted with the results obtained with Ogliarola oils (Table 2).