Determination of the Antioxidant Properties of the Syrian Olive Leaves Extracts and Isolation Oleuropein by HPLC Techniques

The phenolics of Syrian olive leaves were determined in alcoholic and aqueous extracts by the ultrasonic bath. The total phenolic and flavonoids contents were compared, and the IC50 values of olive leaves extracts were calculated for the inhibition of the free radical of 2,2- diphenyl-1 picrylhydrazyl (DPPH.), and free monocation radical of 2.2,-azino-bis-[3-ethyl benzothiazoline-6-Sulfonic Acid] (ABTS+.) and the results were compared with vitamin C and oleuropein standard values. Oleuropein content was quantified in extracts using highperformance liquid chromatography (HPLC), and isolated by TLC, then it was detected by HPLC-MS. The results showed that the total phenolic content and total flavonoids content for alcoholic extracts were higher than those in aqueous extract contents, with significant differences in the statistical study. There were no significant differences in their ability to inhibit DPPH., opposed to the result of the monocation radical (ABTS+.), where the inhibition capacity of the ethanolic extract was greater than that in the aqueous medium. The study also showed that the alcoholic extract contains a higher concentration of oleuropein (88.50 ± 9.67 mg g-1) compared to the aqueous extract (37.60 ± 6.84 mg g-1), allowing the use of Syrian olive leaves extracts as natural antioxidants. The isolated oleuropein yield by TLC was 0.43-0.1 mg g-1 in ethanolic and aqueous extracts as well.