Quantitation of oleuropein and related metabolites in decoctions of Olea europaea leaves from ten Greek cultivated varieties by HPLC with diode array detection (HPLC-DAD)

An extraction procedure and chromatographic methodology for the simultaneous quantitation of four major constituents in the boiling water extracts (decoctions) of Olea europaea leaves has been developed. The four studied constituents were oleuropein, elenolic acid, hydroxytyrosol, and tyrosol. The quantitation was performed using HPLC-DAD, whereas qualitative data were acquired using LC-MS. The developed methodology was applied in the study-of ten Olea europaea varieties commonly cultivated in Greece. The chromatographic analysis revealed important differences among the varieties. The decoction of variety gaidouroelia was identified as the best source of oleuropein, but it was completely lacking of elenolic acid. The decoction of variety koronaiiki was the best source of hydroxytyrosol, whereas the variety mastoides was the best source of tyrosol and elenolic acid. In addition, the methanol and acetone extracts of one of the studied varieties (koranaiiki) were investigated, in order to compare the concentration of oleuropein in the extracts and the decoction. Interestingly, only a very low percent of the total oleuropein is present in the traditionally prepared decoction, while elenolic acid, which is a minor constituent of the extracts, was found to be one of the major constituents of the decoction.