Natural polysaccharides from Glycyrrhiza uralensis residues with typical glucan structure showing inhibition on α-glucosidase activities

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Two neutral Glycyrrhiza polysaccharide (GP), named GP-LA and GP-HA, with molecular weights of 3.023 × 105 and 1.291 × 105, respectively, were extracted from Glycyrrhiza residues by hot acid extraction (HA) and low-temperature acid extraction (LA) and purified by column chromatography. Comprehensive analysis showed that the backbone of GP was composed of →4)-β-D-Glcp-(1→. For GP-LA, the side chain probably composed of β-L-Araf-(1→, →5)-β-L-Araf-(1→, →4)-β-D-Xylp-(1→, β-D-Glcp-(1→, →3,4)-α-D-Glcp-(1→, →4,6)-α- D-Glcp-(1→, and for GP-LA, the side chain probably composed of→6)-β-D-Galp-(1→, -α-D-Glcp-(1→, →3,4)-α-D-Glcp-(1→, →2,4)-α-D-Glcp-(1→, →4,6)- D-Glcp-(1→. The GP had a triple helix conformation and numerous irregular spherical particles with smooth surfaces. Atomic force microscopy (AFM) confirmed that GP-HA possessed single-branched structures and GP-LA possessed cross-linked network structures. X-ray diffraction (XRD) analysis revealed that GP-LA had both crystalline and amorphous structures, but GP-HA had no crystal structure. Furthermore, the results indicated that GP-LA and GP-HA exhibited certain inhibition activity on α-glucosidase. CD spectra and fluorescence intensity measurements confirmed that the secondary structure of α-glucosidase changed with the addition of GP.