Sustainable extraction of waxberry (Myrica rubra Sieb. et Zucc.) pomace phenolics using deep eutectic solvents with optimization and bioactivity evaluation

To enable more sustainable utilization of waxberry pomace, this study developed an ultrasound-assisted deep eutectic solvent (UAE-DES) method for efficiently recovering total phenolic content (TPC) and total anthocyanin content (TAC). Based on physicochemical properties and extraction efficiency, choline chloride–lactic acid (ChCl–LA, 1:2) was identified as the best system. Low-field nuclear magnetic resonance (LF-NMR) and Fourier-transform infrared spectroscopy (FTIR) revealed the DES's hydrogen-bonding architecture restricted molecular mobility, explaining its superior solvation capacity. Optimization by single-factor and response surface methodology (RSM) gave the optimization conditions, including ultrasonication for 58 min at 360 W (16W/L), a solid-liquid ratio of 1:35 g/mL, and a water volume fraction of 36% (v/v). Under these settings, TPC and TAC reached 44.26 mg GAE/g DW and 6.92 mg C3GE/g DW, respectively. Furthermore, comprehensive UPLC-QTOF-MS profiling identified 11 major bioactive constituents in the extract. In comparative antioxidant assays, the DES extract markedly outperformed the ethanol extract, with IC 50 values of 0.025 mg/mL for DPPH•, 0.038 mg/mL for ABTS• + , 0.114 mg/mL for •OH, and 0.675 mg/mL for total antioxidant capacity (T-AOC). These results indicated ultrasound-assisted ChCl-LA extraction offered a sustainable and tunable strategy that achieved both high phytochemical recovery and preserved antioxidant functionality from waxberry pomace.