Hydration-driven structural engineering via enzymatic glycation: Sustained quercetin release in pullulan-zein coatings for extended walnut preservation

This study developed pullulan-based edible coatings incorporating quercetin-loaded glycated zein nanoparticles (gZein I–III-Que) to mitigate oxidative rancidity in walnuts. Enzymatic glycation-driven hydration engineering modulated interfacial interactions between zein and pullulan, forming structurally homogeneous nanocomposites. The optimized intermediate glycation coating (gZein II-Que@Pul) resolved incompatibility between hydrophobic antioxidants and hydrophilic matrices through uniform nanoparticle dispersion (PDI 0.19 ± 0.02) and enhanced mechanical strength (28.48 ± 0.52 MPa). Hydration-mediated structural reorganization balanced molecular mobility and diffusion resistance, sustaining antioxidant release via non-Fickian kinetics (Korsmeyer-Peppas n = 0.55). The coatings reduced oxygen permeability to 0.10 ± 0.02 kg m⁻²·s⁻¹ and demonstrated high antioxidant efficiency (I₅₀ = 1.4 mg/mL) alongside cytocompatibility exceeding 80 % cell viability. Applied to walnuts, gZein II-Que@Pul extended shelf life by 528 ± 25 % at 25 °C, retaining 91.76 ± 1.17 % omega-3 and 95.22 ± 0.76 % omega-6 fatty acids. MRI spatial analysis visualized lipid oxidation suppression spatially correlated with hydration-driven quercetin release, validated by peroxide value reductions (57.53 ± 2.73 %). By tailoring glycation degree, this work establishes enzymatic hydration engineering as a scalable strategy for sustainable food preservation. The optimized coating harmonizes bioactive delivery and structural integrity through hydration-modulated diffusion kinetics and interfacial stability, leveraging renewable biopolymers to advance plant protein-polysaccharide hybrids as functional barriers for minimizing postharvest losses in lipid-rich foods.