## 3 Results and Discussion
### Volatile Compounds

Table 3: Volatile composition (ug/kg) of VOOs extracted with different values of oxygen flow during the crushing phaseAdditionally, virgin olive oils obtained by the addition of oxygen during the crushing phase showed significant variation (\(p<0.05\)) in the composition of volatile compounds that come from LOX activity compared to the control test (no oxygen added). The test carried out under an oxygen flow of 0.2 L/min showed the highest concentration of aldehydes compared with all the other tests. This trend was detected in the oils from the two cultivars, with 19% and 8% of them increasing for Ogliarola and Coratina cultivar, respectively. The virgin olive oil produced by the Ogliarola cultivar with a 0.2 L/min addition of oxygen showed a sum of C5 and C6 aldehydes of 21,146 ug/kg, which was significantly higher compared with the value of the control test (17,798 ug/kg) (Table 3). The most relevant increase was detected for (E)-2-hexenal, this compound being strictly related to \"green grass\" and \"green fruity\" aromas [4; 74; 75; 76; 77; 78]. Unlike aldehydes, esters and alcohols showed a decreasing trend. Then, a significant decrease (\(p<0.05\)) was detected for these two clusters of compounds, expressed as a decreasing of the sum of the C5 and C6 alcohols and, for the esters, a decrease of hexyl acetate and cis-3-hexenyl acetate. The lower concentration of these compounds may have an effect on the sensory profiling of the oils, given the reported sensory impact of alcohols and esters [78; 79; 80]. The oils obtained using an addition of 0.4 L/min of oxygen have a higher concentration of aldehydes (18,059 ug/kg) compared with the control oil (Table 3). However, this increase in concentration was only significant for (E)-2-hexenal. Regarding alcohols and esters, the oxygen under this flow reduced the concentration of these compounds by a significant amount. In the case of alcohols, it was also relevant to reduce some individual compounds by 20%. That was the case with 1-penten-3-ol, (E)-2-penten-1-ol, (Z)-2-penten-1-ol, 1-hexanol, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, (E)-3-hexen-1-ol, and (Z)-3-hexen-1-ol. The production of oil under an oxygen addition of 0.8 L/min during crushing resulted in the lowest mean concentration for all the clusters of volatile compounds (Table 3). However, the concentrations were significantly different from those in the control oil in the case of alcohols and esters. The concentration of alcohols showed the most relevant reduction (1407 ug/kg compared with 2057 ug/kg). Similar results were observed in the oils from the Coratina cultivar. These oils also showed a significant increase in the sum of aldehydes, especially when oxygen was added at 0.2 L/min. Regarding the concentrations for each cluster, the values were different between the two cultivars (Table 3), thus pointing out that the oxygen effect was strongly modulated by the cultivar effect. The differences found in the volatile concentrations are explained by the particular enzyme activity in the volatile compound production (LOX) associated with each cultivar [78; 81; 82]. On the other hand, the enzyme activity is also modulated by the availability of oxygen during crushing, considering that it is a co-substrate of some enzymes that are involved in the LOX pathway. The results confirm that, under the studied conditions, the best concentration of oxygen addition during the crushing phase was 0.2 L/min, considering the rise of aldehydes, particularly (E)-2-hexenal, and the effect on the other volatile compounds. In order to check if there is a better concentration of oxygen addition while also considering the cultivar and the extraction technology, it should be useful to make a sort of calibration line near this value. Considering the low quantity of oxygen used, and the interesting results also for sensory profiling, it could be useful in the future to have a recommended quantity of oxygen for each cultivar at a fixed condition of extraction technology.