engleski

Effect of the extraction solvent on the oleuropein content and antioxidant properties of olive leaf (cv. Oblica, Lastovka and Levantinka) extracts

In last few decades numerous studies proved that olive leaf is a rich source of bioactive phenolic compounds, mainly oleuropein and its derivatives. The aim of this study was to investigate the influence of the extraction solvent on the phenolic and oleuropein content in the leaf extracts of Dalmatian autochthonic olive cultivars: Oblica, Lastovka and Levantinka. The antioxidant activity of leaf extracts was determined using FRAP method and by metal chelating activity evaluation. The extraction yield obtained using alcoholic solvents was higher than the water solvents. The highest share of total phenols and oleuropein was detected in alcoholic extract of Lastovka, while almost two-fold lower amounts were obtained using water extracts, both hot water and room temperature water. The extremely significant correlation between the FRAP and oleuropein/phenolic content point out the importance of this compound in total reducing activity of the extracts. All tested extracts provided good chelating activity probably due to the high concentrations of oleuropein but also the presence of other compounds with catechol structure, which is the most important structural feature for strong chelating activity. According to the obtained results we can conclude that the extraction of polyphenols from olive leaves, especially from Lastovka cultivar, could represent an interesting means of increasing the value of this cheap plant material that often remains unused after the harvest.

olive leaf ; oleuropein ; HPLC ; reducing ability ; chelating activity

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