Structural Characterization, Chain Conformation And Morphology Of A Polysaccharide Isolated From The Fruiting Body Of Dictyophora Indusiata

Numerous bioactive polysaccharides or polysaccharide-protein complexes from medicinal mushrooms,plants and other resources are reported to enhance innate and cell-mediated immune responses and exhibit antitumor activities in animals and humans.Polysaccharides are also widely used in food industry as functional ingredients due to its special rehological propetties.Many polysaccharides are exploited as thickning,gelling,stabilizaing,emulsifing,and water-binding agents in food industry.The reason that polysacchrides can exhibit large diference in solubility, aggregation,crystallization,viscosity,gel formation,digestibility and biological activities,is because their different primary chemical structures determine the shape that they can adopt in aqueous solution.For example,(1→3)-β-D-glucans with some(1→6)-glucosyl side groups,including Lentinan,Schizophyllan,Scleroglucan, all exist as triple helical chains,form very viscous solution at low concentration,and have potential antitumor activity.Therefore,investigating the primary chemical structure,solution property and chain conformation is very essential for the study of the polysaccharide bioactivity and developing new polysaccharide based food additives.The present work was aimed to investigate the chemical structure,chain conformation and morphology of the triple-helical polysaccharide in aqueous solution. We isolated the triple-helical polysaccharide,characterized its monosaccharide composition by GC,and determined its chemical structure by FTIR and ¹³C-NMR. Viscometry and LLS experiments were carried out to measure its physcico-chemical properties i.e.,intrinsic viscosity[η],weight average molecular mass Mw,radius of gyration(Rg),hydrodynamic radius(Rh) and structural parameter p(Rg/Rh) in water. Rheological measurement and[η]dependence of CNaO.experiments were used to investigate its triple helical conformation and conformation transition.Finally,the morphology of the polysaccharide was directly observed by AFM and TEM methods.The major conclusions and creative points of this work include:(1) Four water-soluble polysaccharides were isolated and purified form the fruiting body of Dictyophora indusiata.Among them,PD3 was selected for further study due to its high viscosity in dilute solution;(2) The chemical structure of PD3 was characterized by GC,FTIR and ¹³C-NMR.And the results indicated that PD3 is a (1→3)-β-D-glucan,with(1→6)-β-glucopyranoside side branches;(3) The weight average molecular mass(Mw),radius of gyration(Rg),hydrodynamic radius(Rh) and intrinsic viscosity([η]) of PD3 in water were determined to be 5.1×10⁵,141nm,44nm, and 1440cm³Â·g^-1,respectively,by LLS and viscometry.The structural parameterρ(Rg/Rh) of PD3 was calculated to be 3.4.These results indicated that PD3 exists as very stiff chain in dilute soltion;the[η]dependence of C_NaoH of PD3 is similar with that of triple helical polysaccahrdies Scleroglucan and Lentinan,suggesting that PD3 exists as triple helical chain conformation in water.This conclusion was further proved by rheological measurement;(4) Morphology study by AFM found that PD3 exist as a rod-like chain in dilute solution and its chain diameter is about 1.2nm, similar with that of Lentinan,further proved the trople-helical chain conformation of PD3 in aqueous solution.With the increasing of concentration,PD3 trends to self-assemble to fibrous aggregates in aqueous solution as measured by TEM.