Dynamic ultrasound-assisted extraction of oleuropein and related biophenols from olive leaves

A continuous approach for the ultrasound-assisted extraction of olive biophenols (OBPs) from olive leaves is proposed. Multivariate methodology was used to carry out a detailed optimisation of extraction. Under the optimal working conditions, complete extraction of the target analytes (namely, oleuropein, verbacoside, apigenin-7-glucoside and luteolin-7-glucoside with LODs 11.04, 2.68, 1.49 and 3.91 mg/kg, respectively) was achieved in 25 min. The extract was injected into a chromatograph–photodiode array detector assembly (HPLC–DAD) for individual separation–quantification. No clean-up or preconcentration steps were required. Gas chromatography–mass spectrometry (without derivatization of the analytes) was used to identify OBPs at concentrations below the LODs obtained by HPLC–DAD. The efficacy of ethanol–water mixtures to extract OBPs from olive leaves has been demonstrated and compared with that of a conventional method which requires 24 h for complete extraction; so these mixtures can substitute toxic extractants used to date.