The olive fruit intended for oil extraction was inoculated by Lactobacillus plantarum to evaluate the anti-oxidative effect. Results showed that orthodiphenols, in particular dialdehydic form of decarboxymethyl of elenolic acid linked to hydroxytyrosol (Hy-EDA) increased their concentration in oils issued from the olive fruits inoculated by Lactobacillus. Among non-orthodiphenols, the tyrosol increased their concentration. Oil quality issued from inoculated olive fruits had a higher quality. The difference between the acidity, K-232 and K-270 indices and sensory quality shows clearly the positive effect of Lactobacillus on olive oil quality. Beside, aqueous phase showed a higher concentration of phenolics when the olive fruits were inoculated with Lactobacillus plantarum. Storage of the aqueous phase showed that phenolic compounds concentration has decreased. (c) 2005 Elsevier Ltd. All rights reserved.