# Increasing the Bioactive Compound Content of Olive Oil by Acidification of Olive Paste
## 4 Discussion
### Phenolic Compounds and Antioxidant Capacity
Only \(t\)-ferulic acid shows a notable increase in solubility in the oils, reaching levels nearly three times higher than those in the control oils. In a study examining the impact of cultivar on olive oil phenolic profiles across 80 selected varieties over two harvest seasons [45], the first season yielded average (mg/kg) values of 1.68 for hydroxytrosol (max. 4.89), 3.31 for luteolin (max. 6.25), and 1.87 for apigenin (max. 11.53). The second season's averages were 2.04 for hydroxytrosol (max. 7.57), 3.72 for luteolin (max. 11.35), and 2.98 for apigenin (max. 19.79). Our findings indicate that several of our experiments achieved or exceeded the maximum phenolic contents observed in the first season for all three compounds, and surpassed the second-season averages, although we did not reach the second-season maximums. These exceptionally high values in the cited study likely resulted from specific, highly favorable conditions. All secoiridoids are derived from the hydrolysis of oleuropein and ligtroside (Table 4). Among these compounds, oleuropein derivatives were predominant across all oil samples, with oleacein (3,4-DHPEA-EDA) and its precursor, oleuropein aglycone (3,4-DHPEA-EA), being particularly abundant. In contrast, ligtroside derivatives, including oleocanthal (\(p\)-HPEA-EDA) and its aglycone (\(p\)-HPEA-EA), were detected at significantly lower concentrations. Table 4 shows that the oleacein content is higher in all acid-treated oils compared to the control, especially in the oils obtained from pastes treated with 1% ascorbic acid, where the content is the highest among all treatments, nearly doubling that of the control. The oleuropein aglycone content, however, is lower than in the control in all oils except those extracted from pastes with 1% ascorbic acid. Regarding ligtroside derivatives, the content of both oleocanthal and its aglycone is lower than in the control in all oils, except for oleocanthal in samples obtained from pastes treated with 1% ascorbic acid. Table 4 confirms that oils extracted from 1% ascorbic acid pastes have higher oleacein and oleocanthal content than all other oils, including the control samples. As evidenced by the data presented in Table 4, no discernible correlation between secoiridoid compound content and the pH of the vegetation waters was observed. Table 4 also presents the total phenolic compound content and antioxidant capacity of the oils. Phenolic content generally decreases as acid concentration increases, with the exception of citric acid, which shows no significant effect. At lower acid concentrations, a higher phenolic content was observed compared to the control oils, particularly in oils extracted using 1% ascorbic acid, which correlates with the elevated secoiridoid levels in these samples. The antioxidant capacity trend mirrors that of oleacein, peaking in oils produced with 1% ascorbic acid. The oils obtained with 1% ascorbic acid exhibit the highest phenolic compound content and antioxidant capacity, 37.2% and 66.9% greater, respectively, than the control oils. Regarding the phenolic compounds discussed previously, neither the total phenolic content nor the antioxidant capacity exhibited a statistically significant correlation with the pH of the vegetation waters. Consequently, it is inferred that the observed variations in phenolic compounds within the oils are not attributable to pH, but rather to other factors beyond the scope of this study. Based on the experimental results, it is concluded that the acids introduced into the pastes do not function as technological coadjuvants, as they fail to alter extraction yields or other process-dependent oil parameters. However, they can be categorized as chemical coadjuvants due to their ability to modify the paste pH and, critically, to enhance the \(\beta\)-_glucosidase_-mediated hydrolysis of oleuropein and ligtroside into their respective derivatives, thereby indirectly enriching the oils with secoiridoid compounds, which is the primary objective of this study.