Pulsed ultrasound-assisted deep eutectic solvent-mediated stabilization and bioactivity enhancement of hydrolysable tannins from chestnut (Castanea mollissima) burrs

A pulsed ultrasound-assisted deep eutectic solvent (DES) strategy enabled high-efficiency tannin extraction from chestnut burr waste, yielding 104.40 ± 4.31 mg TAE/g DW—2.1-fold higher than conventional aqueous extraction. Comprehensive mechanistic investigations revealed synergistic effects: DES components enhanced hydrogen bonding and electrostatic attraction with tannins, while a favorable solvation energy barrier (ΔG = −85.15 kcal/mol) facilitated extraction. Advanced spectroscopic analysis (FT-IR, HPLC-IT-TOF-MS 2 ) demonstrated DES-induced structural stabilization of hydrolysable tannins, with key components exhibiting a 3.1-fold increase in relative abundance. Specifically, DES was found to suppress water activity while forming protective tannin-DES complexes, as evidenced by characteristic upfield 1 H NMR shifts (Δδ = −0.19 ppm) and distinct vibrational frequency changes. The sustainability of this method was validated through five successful recycling trials and comprehensive green metric assessments. DES-extracted tannins demonstrated >1.2-fold enhanced antioxidant capacity and superior antibacterial activity compared to aqueous extracts. This work establishes an innovative method for agroforestry waste valorization and advances green extraction technologies.