Detection of phenolic compounds from olive oil using green extraction with deep eutectic solvent, cyclic voltammetry

In this study, it has been shown that the deep eutectic solvent containing lactic acid, water and glucose can be used to efficiently extract phenolic compounds (PC) from olive oils. No organic solvents were used for the extraction, making the method environmentally friendly. Further, these total PC (TPC) have been electrochemically determined using a novel screen-printed carbon electrode (SPCE) based on carbon nanofibers (CNFs), using cyclic voltammetry (CV) as a electroanalytical technique. Three different PC, namely p-coumaric, chlorogenic and gallic acid were solubilized in deep eutectic solvent (DES) and analyzed with the electrochemical sensor. For the individual PC excellent detection limits were obtained in the range from 0.0105 mu M for gallic acid to 0.0253 mu M for chlorogenic acid. After that, a series of six extra virgin olive oils (EVOO) samples and six pomace olive oil (POO) samples were used extract PC by liquid-liquid extraction in DES. The signals registered with the sensor by CV immersed in DES extracts were related to the PC amount of the samples. One of the novelties of this work consists in the use of CVs data for the classification of the EVOO and POO samples and to predict the PC content by PLS1 regression model. Furthermore, Folin-Ciocalteu method has been employed to determine the TPC of the DES extracts of olive oils. Excellent correlations between the voltammetric and spectrophotometric methods results have been obtained demonstrating that the applied methodology could be a considered green method for extraction and detection of PC from olive oils.