The efficacy of phenolics compounds with different polarities as antioxidants from olive leaves depending on seasonal variations

Recent studies suggest that olive leaf is a significant source of bioactive phenolic compounds compared to olive oil and fruits. Identifying appropriate extraction methods is thus an important step to increase the yield of such bioactive components from olive leaf. In the present study, the antioxidant activity of olive leaf extracts from the Tunisian cultivar Neb jmel harvested at two different times, using solvents of increasing polarity (hexane, chloroform, ethyl acetate and methanol) was evaluated using DPPH and ABTS⁺ radical-scavenging assays. The total pigment and anthocyanins as well as total phenolics and flavonoids from leaves of Olea europaea L. cultivar Neb jmel were also evaluated. Besides, a seasonal pattern variation study was performed. The extracts were found to have different levels of antioxidant properties in the test solvent used. The efficiency of the solvents used to extract phenols from the olive leaves varied considerably. Total polyphenol and flavonoid contents were significantly higher in methanol extract than hexane, chloroform and ethyl acetate fractions (p<0.05). Chloroform and ethyl acetate extracts in the leaves of the first harvest was found to be rich in flavonoids (104.83 and 129.24 CEQ/100g DW, respectively). Statistically, a seasonal pattern was observed for the total phenols, o-diphenols and flavonoids between the leaves harvested at two stages. Differences were observed in pigment and anthocyanin contents at the two different stages. A relationship was observed between the potential antioxidant activity, total phenolic and flavonoid levels of the extracts. Principal component analysis revealed the inter-correlation of the variables DPPH, ABTS, flavonoids, total phenols and o-diphenols.