Natural deep eutectic solvent for efficient extraction of polyphenols from dendrobium residue: optimization, characterization, and enhanced antioxidant activity

This study optimized the extraction of polyphenols from Dendrobium residue using a natural deep eutectic solvent (NADES). A Box-Behnken design determined the optimal conditions: a choline chloride to glucose molar ratio of 2.4:1, solid-to-solvent ratio of 1:61 g/mL, water content of 35.7%, temperature of 80 °C, and duration of 120 minutes. This yielded a polyphenol content of 1.381 ± 0.071%, which was 2.93 to 38.36 times higher than conventional organic solvent methods. Fourier transform infrared (FTIR) spectroscopy was used to characterize the hydrogen bonding changes in the NADES system, while scanning electron microscopy (SEM) was employed to examine the morphological differences of Dendrobium residues before and after extraction treatment. Ten compounds were identified from the NADES extract, namely Prunin, Schaftoside, Apigenin-6,8-di-C-α-l-arabinopyranoside, Batatasin III, Moscatilin, Dihydroresveratrol, Hesperetin, Naringenin, Dendrophenol, and Erianin, which exhibited important pharmacological activities. Ultra-performance liquid chromatography(UPLC) analysis revealed a great variety and quantity of polyphenols in the NADES extract. Furthermore, the extract exhibited superior antioxidant activity: at 1.00 mg/mL, DPPH scavenging was 90.615 ± 0.92%, ABTS scavenging was 96.095 ± 0.44%, and FRAP value was 1.048 ± 0.03 mmol/L. These results highlight the green and efficient nature of this NADES-based protocol for industrial applications in food and herb residue processing.