Development and characterization of natural deep eutectic solvents for optimized extraction of olive pomace phenolics

The extraction of olive oil generates substantial amounts of by-products, accounting for approximately 80 % of the olive's weight. Olive pomace, a largely underutilized by-product of this process, holds significant potential as a source of bioactives for various applications. In order to improve their extraction, in this study, we explored different raw materials for the synthesis of Natural Deep Eutectic Solvents (NADES). A total of 16 different NADES were synthesized, using 8 distinct types of solvents and two water concentrations. These solvents were characterized regarding their physicochemical, spectroscopic, and thermal properties, and their extraction capacities were evaluated, alongside a cost analysis of their production. Differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy analyses confirmed the formation of eutectic mixtures, which displayed a wide range of pH values (0.26–12.23), shear viscosities (7.06–492.30 mPa·s), but a low range of polarity. Sugar-based NADES were the most promising solvents for phenolic compounds extraction due to their low production cost; however, the NADES synthesized from choline chloride and urea exhibited the best extractive potential. • NADES synthesized showed eutectic properties, confirmed by DSC, FTIR, and Raman. • NADES 3 and 8 achieved the highest phenolic extraction, outperforming ethanol/water. • Viscosity and polarity influenced NADES performance in phenolic recovery. • Water dilution improved extraction efficiency while reducing viscosity and cost. • Sugar-based NADES were cost-effective and efficient for bioactive extraction.