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

Two neutral Glycyrrhiza polysaccharide (GP), named GP-LA and GP-HA, with molecular weights of 3.023 x 105 and 1.291 x 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)-beta-D-Glcp-(1 ->. For GP-LA, the side chain probably composed of beta-L-Araf-(1 ->, -> 5)-beta-L-Araf-(1 ->, -> 4)-beta-D-Xylp-(1 ->, beta-D-Glcp-(1 ->, -> 3,4)-alpha-D-Glcp-(1 ->, -> 4,6)-alpha-D-Glcp-(1 ->, and for GP-LA, the side chain probably composed of -> 6)-beta-D-Galp-(1 ->, -alpha-D-Glcp-(1 ->, -> 3,4)-alpha-D-Glcp-(1 ->, -> 2,4)-alpha-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 alpha-glucosidase. CD spectra and fluorescence intensity measurements confirmed that the secondary structure of alpha-glucosidase changed with the addition of GP.