Towards green analysis of virgin olive oil phenolic compounds: Extraction by a natural deep eutectic solvent and direct spectrophotometric detection

The determination of phenolic compounds in extra virgin olive oils (EVOO) by means of rapid, low-cost, environment-free methods would be a desirable achievement. A natural deep eutectic solvent (DES) based on glucose and lactic acid was considered as extraction solvent for phenolic compounds in EVOO. DESs are green solvents characterized by high availability, biodegradability, safety, and low cost. The spectrophotometric characteristics of DES extracts of 65 EVOO samples were related to the total phenolic content of the oils, assessed by methanol-water extraction coupled to the Folin-Ciocalteu assay. A regression model (ncalibration = 45, nvalidation = 20), including the absorbance at two wavelengths (257, 324 nm), was obtained, with an adjusted R2 = 0.762. Therefore the DES could provide a promising and viable approach for a green screening method of phenolic compounds in EVOO, by means of simple spectrophotometric measurements of extracts, even for on-field analysis (for example in olive mills).