ANTIOXIDATIVE ACTIVITIES OF OLEA-EUROPAEA LEAVES AND RELATED PHENOLIC-COMPOUNDS

Olea europaea leaves, oleuropein, hydroxytyrosol and tyrosol were compared with vitamin E and BHT, with regard to their antioxidative activities, by kinetic studies in model systems. The thermal initiated oxidation of methyl linoleate was performed in homogeneous solution at 60-degrees or 40-degrees with or without antioxidants. Olea europaea extracts, oleuropein and hydroxytyrosol were much more effective than BHT or vitamin E in extending the induction period. Assuming a stoichiometric factor f = 2 for BHT, this coefficient of inhibition reached 5 for hydroxytyrosol, 7 for oleuropein and 10 for O. europaea extracts. These extracts owe their antioxidative properties to their high oleuropein content (19% w/w) and also to a lesser amount of flavonoids (1.8% w/w with 0.8% of luteolin 7-glucoside). Tyrosol showed neither antioxidant nor prooxidant activity. No synergistic effect on the preservation of methyl linoleate was found when vitamin E was used together with tyrosol or O. europaea extracts.