Ultrasound-assisted extraction of phenolic compounds from blueberry leaves using natural deep eutectic solvents (NADES) for the valorization of agrifood wastes

The food industry demands novel green solvents for the extraction of bioactive compounds, particularly from residues of the agrifood industry. Herein, an ultrasound-assisted method has been developed for the environmentally friendly extraction of phenolic compounds from blueberry leaves using natural deep eutectic solvents (NADES). After the screening of multiple NADES, the best extraction efficiencies in terms of total phenol content and antioxidant activity were provided by NADES composed of lactate, sodium acetate, and water (3:1:2), and of choline chloride and oxalic acid (1:1). Using a Box–Behnken experimental design, the optimal extraction conditions were achieved by sonicating for 45 min at 65 °C and using solvent:sample ratios of 15 and 75 (v/w) for the NADES based on lactic acid and choline, respectively. Compared with conventional organic solvents, the use of these NADES composed of lactic acid and choline provided superior performance for the recovery of phenolic compounds (1.6-fold and 2.2-fold greater efficacy, respectively) and antioxidant compounds (1.6-fold and 2.8-fold greater efficacy, respectively). The chromatographic characterization of the extracts obtained under these optimized conditions evidenced that the lactic-based NADES enabled the extraction of a wide range of hydroxycinnamic acids and flavonol derivatives, whereas the choline-based NADES was selective towards the extraction of anthocyanins. These results indicate that the proposed method could represent an excellent green alternative for the recovery of phenolic compounds from plant materials and agrifood wastes, with improved extraction efficacy and/or selectivity compared to that provided by traditional organic solvents.