Characterization and Purification of Phenols From Olea europaea L. and Assay Against Xylella fastidiosa Subsp. pauca

The present study reports the characterization of main glucoside secoiridoid phenols from olive and of the respective aglycones as well as the bioassay of these compounds against Xylella fastidiosa, a pathogen microorganism responsible for a serious olive phytosanitary event occurred in Apulia (Italy) since 2013. The assayed secoiridoids were two native secondary metabolites, namely oleuropein and demethyloleuropein isolated and purified from leaves and from ripe drupes, respectively. Moreover, the corresponding aglycones were prepared in an easy, sustainable, and bio-based way, by adding olive juice drops on buffered solutions of oleuropein and demethyloleuropein. The secoiridoids oleuropein and demethyloleuropein were obtained with 80% chromatographic purity. The aglycones obtained from native compounds were respectively a mixture of isomers derived from oleuropein and oleacein derived from demethyloleuropein. These purified compounds were assayed against X. fastidiosa subsp. pauca at a starting concentration of 1 and 2 mM after 10-, 100-, and 1000-fold dilutions. Relevant activities were observed also towards the biofilm form of X. fastidiosa, especially for aglycones, after 100 (0.01 and 0.02 mM) and 1000 dilutions (0.001 and 0.002 mM). The data of the present study can pave the way for a sustainable method to face the relevant problem of X. fastidiosa infection.