## 3 Results and Discussion
### Determination of Phenolic and Other Compounds in Olive Leaf Samples by HPLC-ESI-TOF-MS
This is due to the polar nature of simple phenols that make them water soluble, and water is more efficient in solvent extraction than ethanol [29]. In addition, the highest content of simple phenols was obtained in the extraction time range of 5-22.5 min and a temperature of 100-150 \({}^{\circ}\)C.  
With regard to secoiridoids, a total of 18 phenolic compounds were quantified. Of these, oleupreein isomer a was the most abundant, with a high content of 60.00 \(\pm\) 0.27 mg g\({}^{-1}\) d.w. in MAE 4 (150 \({}^{\circ}\)C, 100% EtOH and 22.5 min). In addition, MAE 4 conditions resulted in the best total secoiridoids content. Therefore, this result showed that an increase in temperature provides an increase in the concentration of secoiridoids. This can be attributed to the increase in the solubility of oleupreein at high temperatures and 100% of ethanol [30]. A total of 14 of flavonoids were found and the highest content was obtained at 100 \({}^{\circ}\)C, 50% EtOH and 22.5 min. The most concentrated flavonoid was luteolin glucoside isomer a (0.16 mg g\({}^{-1}\) d.w.-0.55 mg g\({}^{-1}\) d.w.). These results suggest that the content of flavonoids increases with the temperature up to 100 \({}^{\circ}\)C. Thus, temperatures higher than 100 \({}^{\circ}\)C decreased the content of flavonoids because these compounds are thermosensitive, especially flavonoids glycosides. This decrease was attributed to the thermal oxidation of the hydroxyl groups of glycoside [31]. Regarding phenolic acids, four compounds were quantified and 100 \({}^{\circ}\)C, 50% EtOH and 22.5 min were the best conditions for maximizing phenolic content. Hence, an increase in the temperature up to 100 \({}^{\circ}\)C increases the content of these compounds, whereas an increase in the extraction time from 22.5 min to 40 min decreases elenolic acid content. This can be due to overexposure to microwave radiation, which leads to overheating and results in thermal degradation and oxidation of elenolic compounds [32]. Finally, it is important to note that the lowest total content of compounds was 21.02 \(\pm\) 0.02 mg g\({}^{-1}\) d.w., which was obtained in MAE 9 (50 \({}^{\circ}\)C, 50% EtOH and 5 min) and 21.84 \(\pm\) 0.37 mg g\({}^{-1}\) d.w. in MAE 8 (50 \({}^{\circ}\)C, 0% EtOH and 22.5 min), whereas the highest total content was 74.24 \(\pm\) 0.50 mg g\({}^{-1}\) d.w. which was obtained in MAE 4 at 150 \({}^{\circ}\)C, 100% ethanol and 22.5 min. Therefore, the highest content of total compounds was obtained at the maximum temperature and percentage of ethanol. This is because oleupreein, which is the most abundant secoiridoid in olive leaves, was extracted in the highest quantity at 100% of ethanol. Ethanol has the capacity to absorb the microwave radiation and heats up faster, thus, the increase in temperature improves the solubility of phenolic and elenolic compounds in ethanol and improves matrix penetration due to a decrease in surface tension and solvent viscosity [33]. In addition, the highest content of total compounds was obtained at 22.5 min. However, the total content decreased in extended extraction times of 40 min because overheating the solvent can lead to the degradation of most compounds [34].