Ultrasonic assisted natural deep eutectic solvents as a green and efficient approach for extraction of hydroxytyrosol from olive leaves

In this study, an ultrasonic assisted natural deep eutectic solvent (DES) was used to extract hydroxytyrosol (HT) from olive leaves. The optimal extraction conditions of the MaPa-4 concentration, extraction time and solid–liquid ratio were obtained by single factor experiments. The formation mechanism of MaPa and its interaction with HT were analyzed by FTIR, ¹H-NMR and density functional theory (DFT) calculation. Then, MaPa-4 and water extracts obtained under the optimal extraction conditions were selected for a series of efficacy tests. MaPa-4 extract demonstrated low cytotoxicity, good biocompatibility, and excellent anti-inflammatory and bacteriostatic properties. Overall, MaPa-4, as an environmentally friendly and efficient solvent, was combined with ultrasound treatment to develop an efficient, green and feasible method to extract HT from olive leaves.