Elettrochemical sensor and biosensor for polyphenols detection in olive oils

The aim of the work was to compare different techniques, in evaluating the phenolic content of an extra-virgin olive oil with varying storage time and storage conditions. A disposable screen-printed sensor (SPE) was coupled with differential pulse voltammetry (DPV) to determine the phenolic fractions after extraction with a glycine buffer; DPV parameters were chosen in order to study the oxidation peak of oleuropein, which was used as reference compound. A calibration curve of oleuropein was performed in glycine buffer 10 mM, pH = 2, NaCl 10 mM (D.L. = 0.25 ppm oleuropein, RSD = 7%). Moreover a tyrosinase based biosensor operating in organic solvent (hexane) was also assembled, using an amperometric oxygen probe as transducer. The calibration curves were realised using flow injection analysis (FIA) with phenol as the substrate (D.L. = 4.0 ppm phenol, RSD = 2%). Both of these methods are easy to operate, require no extraction (biosensor) or rapid extraction procedure (SPE), and the analysis time is short (min). The results obtained with these two innovative procedures were compared with a classical spectrophotometric assay using Folin-Ciocalteau reagent and HPLC analysis. Other extra-virgin olive oil quality parameters were investigated using classical methods in order to better define the alteration process and results are reported.