An easy and green tool for olive oils labelling according to the contents of hydroxytyrosol and tyrosol derivatives: Extraction with a natural deep eutectic solvent and direct spectrophotometric analysis.

Natural deep eutectic solvents (NADES) are a green, promising class of solvents. Phenolic compounds are among the targets of NADES' use in foods. A health claim is admitted by European Regulations for olive oils (OOs) containing at least 250 mg kg-1 of selected polyphenols (hydroxytyrosol and its derivatives, included tyrosol, HTD), but their determination involves analytical issues that are being currently debated. A NADES based on glucose and lactic acid was here used to develop a green and rapid tool for correct labelling of OOs. 163 OOs were submitted to liquid/liquid extraction with the NADES. Regression and classification approaches were adopted to relate features of the UV spectra of extracts to HTD content. The models allowed to assess HTD content for screening purposes (R2prediction = 0.84, RMSEP = 35.5 mg kg-1). For labelling purposes, oils could be labelled according to health claim limits with an error of 0.6%.