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

Abstract

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