Oxidative-Gelation Engineering of <i>Euglena gracilis</i> β-1,3-Glucan: A Green Route to a High-Performance Antioxidant Hydrogel

A green oxidative-gelation strategy was developed to transform water-insoluble paramylon (β-1,3-glucan) from Euglena gracilis into an off-white hydrogel (EPG) without cross-linkers. Alkaline dissolution, acid-neutralization, and mild H2O2 oxidation (8%, v/v, 5 h) disrupted crystallinity and reduced molecular weight while preserving the β-1,3-glycosidic backbone and triple-helix conformation. Systematic optimization based on dry weight recovery, viscosity, and SEM morphology identified 5 h as the optimal oxidation time. EPG exhibited superior antioxidant capacity compared to native paramylon, scavenging 88.1% of DPPH and 98.0% of ABTS radicals at 2.5 mg·mL–1. Oral administration in mice confirmed the safety and efficacy of EPG in enhancing hepatic antioxidant enzyme activity (SOD increased by 165%, MDA decreased by 52.6%). This solvent-free approach provides a scalable route for producing clean-label, high-performance polysaccharide hydrogels suitable for food and biomedical applications.