Covalent conjugation of catechin monomers to corn bran arabinoxylan via DBD plasma and its impact on structural reconstruction and conformational evolution.

A green, non-thermal dielectric barrier discharge (DBD) plasma protocol was established to covalently graft four structurally distinct catechin monomers, epicatechin, epicatechin gallate (ECG), epigallocatechin, and epigallocatechin gallate, onto corn bran arabinoxylan (CAX). Among the synthesized conjugates, ECG-CAX showed the highest grafting yield (72.66 mg/g). Fourier transform infrared spectrum (FT-IR) and ultraviolet-visible (UV-vis) spectroscopy analyses verified phenolic incorporation while preserving the primary polysaccharide skeleton. Two-dimensional nuclear magnetic resonance (2D-NMR), supported by gradient acid hydrolysis, indicated a free-radical-mediated, heterogeneous multi-site conjugation network, with the B- and D-rings of ECG predominantly anchored to the inner xylan backbone. Plasma treatment contracted native CAX from flexible random coils into compact coil conformations, whereas phenolic grafting partially reversed this transition by introducing steric hindrance and promoting chain re-expansion into semiflexible coils. This conformational evolution reduced apparent viscosity and shifted the micromorphology from lamellar sheets to interconnected porous fibrous networks, providing mechanistic insight into plasma-mediated polysaccharide-polyphenol conjugation.