Quantitative Determination of the Main Phenolic Compounds, Antioxidant Activity, and Toxicity of Aqueous Extracts of Olive Leaves of Greek and Spanish Genotypes

Olive leaves are rich in phenolic compounds, which give them antioxidant properties that are associated with a lower incidence of disease. Therefore, the aim of this work was to determine the phenolic content, antioxidant activity, and toxicity of the aqueous extracts of olive leaves of the main Spanish and Greek cultivated and wild genotypes. For these purposes, 'Picual' and 'Arbequina' leaves from Spain and 'Koronoeiki' and 'Kalamon' leaves from Greece were collected, as were wild olive leaves from both countries. The aqueous extracts of these genotypes were analyzed by HPLC-DAD, and the DPPHGreek ano teleia, ABTSGreek ano teleia(+) Folin-Ciocalteu, and Microtox(R) methods were also used. 'Picual' had the highest oleuropein values, followed by wild olive leaves from both countries and 'Arbequina'. The latter was reflected in the antioxidant activity measured by DPPHGreek ano teleia and ABTSGreek ano teleia(+), which positioned the leaves of 'Arbequina', 'Picual', and the wild genotypes as having the most antioxidant activity. As expected, these leaves also had the highest total phenol content, as measured by Folin-Ciocalteu. Regarding the inhibition of the bioluminescence of Aliivibrio fischeri of the aqueous leaf extracts measured by Microtox(R), the EC50(15) ranged between 11.82 and 82.50 mg/mL, demonstrating similar behavior to other herbal infusions.

Automated summary

The study aimed to determine the phenolic content, antioxidant activity, and toxicity of olive leaves from different genotypes of Spain and Greece. HPLC-DAD analysis, as well as DPPHGreek ano teleia, ABTSGreek ano teleia(+), Folin-Ciocalteu, and Microtox(R) methods were used. The results showed that 'Picual' had the highest oleuropein content, followed by wild olive leaves and 'Arbequina'. The antioxidant activity of 'Arbequina', 'Picual', and wild genotypes were the highest, and they also had the highest total phenol content. The aqueous leaf extracts of olive showed similar behavior to other herbal infusions in terms of their inhibitory effects on the bioluminescence of Aliivibrio fischeri, with EC50(15) ranging from 11.82 to 82.50 mg/mL.