Natural deep eutectic solvents and ultrasound-assisted extraction for the recovery of antioxidant phenolic compounds from orange pomace

• Green extraction of antioxidant phenolic compounds from orange pomace by UAE-NaDES. • Choline chloride-lactic acid in a 1:3 M ratio was the most efficient NaDES. • Optimal conditions were 3 % (v/v) water content, 60 % ultrasound amplitude in 14 min. • Composition of the antioxidant extracts studied by HPLC-DAD-QTOF-MS. • Hydroxycinnamic acids, flavanones, flavones, flavonols, and limonoids identified. Fruit and vegetable processing produces substantial waste, with the citrus industry discarding about 50–60 % of the fruit’s total weight. However, orange waste is rich in biologically active secondary metabolites, including phenolic compounds. Natural deep eutectic solvents (NaDES) have emerged as a sustainable and cost-efficient alternative to conventional organic solvents. In this study, a sustainable extraction method combining ultrasound-assisted extraction (UAE) with NaDES was developed to efficiently extract antioxidant phenolic compounds from orange pomace. Five different NaDES were assessed to identify the optimal solvent for extracting levels of proanthocyanidins with antioxidant capacity. Results indicated that choline chloride-lactic acid in a 1:3 M ratio was the most efficient NaDES, yielding the highest antioxidant extracts. A Box-Behnken experimental design was used to optimize key UAE parameters: water content, ultrasound amplitude, and extraction time. The optimal conditions for extraction were found to be 3 % (v/v) water content, 60 % ultrasound amplitude, and 14 min. Hydroxycinnamic acids, flavanones, flavones, flavonols, and limonoids were identified in the orange pomace extracts using high-performance liquid chromatography coupled with diode array detection and quadrupole-time of flight mass spectrometry (HPLC-DAD-QTOF-MS). This study demonstrates the potential of UAE-NaDES as an environmentally friendly approach for the valorization of orange pomace, supporting the development of bioactive-rich extracts for potential applications in the elaboration of nutraceuticals and functional foods.