Characterization of polysaccharide fractions from Allii macrostemonis bulbus and assessment of their antioxidant

In order to comprehensive understanding of the active substances of Allii macrostemonis bulbus (AMB), this study conducted the extraction, purification, structure and antioxidant activity of AMB polysaccharides. The crude polysaccharides were obtained by hot water and ethanol precipitation extraction, and five purified polysaccharide fractions were obtained (AMBP-1, AMBP-2, AMBP-3, AMBP-4 and AMBP-5) with different molecular weights. Structural characterization of five fractions by chromatography, spectroscopy, TGA and Zeta potential analysis. AMBP-1, AMBP-2 and AMBP-3 were primarily composed of mannose, glucose and galacturonic acid. Whereas AMBP-4 and AMBP-5 were primarily composed of mannose, glucuronic acid, galacturonic acid, glucose, galactose, arabinose, xylose. Five fractions possessed differences in characteristic morphology, thermal stability and Zeta potential. Further investigated,the results revealed that five fractions comprised of 1 → 4、1 → 6 linked d-glucopyranose as the main chain with different branch by using methylation with GC-MS and 1D-NMR. Any one of AMB polysaccharides displayed the ability to scavenge free radicals, chelate iron with a dose-effect relationship. Among which AMBP-5 displayed the strongest antioxidant contribute to its rich uronic acid, monosaccharide composition and large molecular weight. This study has enriched the research on the chemical composition of AMB and provides a theoretical basis for developed as a functional food.