Phenolic compounds and antioxidant activity of Olea europaea L. fruits and leaves

Extracts of leaves, fruits and seeds of olive tree cultivars of TrAs-os-Montes e Alto Douro (Portugal) were analysed by reverse phase HPLC with diode array detection and mass spectrometry (MS). This methodology allowed the identification of some common phenolic compounds, namely, verbascoside, rutin, luteolin-7-glucoside, oleuropein and hydroxytyrosol. Moreover the hyphenation of HPLC with MS enabled the identification of nuzhenide in olive seeds. An oleuropein glucoside was also detected in olive tree leaves. The total phenolic content was determined with the Folin Denis reagent and the total antioxidant activity with the ABTS' method. There is a correlation between total antioxidant activity and total phenolic content with the exception of the seed extracts analysed. The apparent high antioxidant activity of seed extracts may be due to nuzhenide, a secoiridoid that is the major phenolic component of olive seeds. These results suggest a possible application of olive seeds as sources of natural antioxidants.