Preliminary structural characterization and in vitro radical-scavenging activity of a high molecular weight, glucan-enriched polysaccharide from Alpinia officinarum Hance

A high molecular weight polysaccharide fraction (AOP-1A) was isolated from edible Alpinia officinarum rhizomes through hot-water extraction, ethanol precipitation, ion-exchange, and gel-filtration chromatography. SEC–MALS–RI showed a predominant population with an apparent Mw of 2.73 × 106 Da. GC–MS analysis revealed a glucose-enriched composition with an approximate Glc:Man:Gal relative proportion of 9.85:0.06:0.09, while methylation analysis identified →4)-Glcp-(1→ as the predominant linkage, with terminal and substituted glucopyranosyl residues. FT–IR and one-dimensional NMR supported a glucan-enriched polysaccharide with multiple glycosidic environments. No Congo-red-detectable helical transition was observed under the tested conditions. AOP-1A exhibited concentration-dependent DPPH and ABTS•+ radical scavenging activities, but lower activities than crude polysaccharide preparation (AOP) at 1.0 mg/mL. These findings provide preliminary structural characterization of a high molecular weight, glucan-enriched fraction and indicate that high molecular mass and glucose predominance alone are insufficient to predict chemical radical-scavenging responses. Further studies are required to establish detailed structure–property relationships and food-related functions.