Probing Relative Ordered Structure Of Polysaccharides From Edible Fungi

Edible fungi are abundant in nutritional values with various biofunctions.Polysaccharides,as one of the main active ingredients of edible fungi,are not only involved in growth of edible fungi,but also have a variety of bioactivities.According to modern pharmacology research,edible fungi polysaccharides have huge potentials to develop as drugs featured with significant efficacy and high safety.The activity of edible fungi polysaccharides is closely associated with their physicochemical properties and chemical structures.Polysaccharides have large molecular weight and complex structure,which brings great challenges to the determination of their structures and conformation.In this paper,crude polysaccharides were obtained from Dictyophora rubrovolvata,Agrocybe cylindracea,Hypsizygus marmoreus and Termitomyces albuminosus by water extraction or alkali extraction,respectively.On the basis of “The relative ordered structure of polysaccharides” theory,it is processed with systematic separation and purification to get a series of homogeneous fractions.Their structural characteristics and solution properties are compared and analyzed,and the structural and conformational order of edible fungi polysaccharides were summarized.Main research contents and findings in the present work are as follows:(1)18 kinds of polysaccharides with high homogeneity were prepared from four kinds of common edible fungi,and their chemical compositions were systematically studied.The extracellular polysaccharides,as well as those within the cell wall were isolated from the fruiting bodies of four edible fungi using hot water and alkali solution.The simple but effective gradient ethanol precipitation method and the gel column chromatography were combined to purify the crude polysaccharides,in order to obtain most components of polysaccharides as possible and further analyzed their structures in detail.Results of monosaccharides composition indicated that common monosaccharides in crude polysaccharides before purification mainly included Glc,Gal,Fuc and Man.All purified polysaccharides could be classified into three main categories,including homoglucan,heterogalactan and heteroglucan.(2)The structural characteristics of homoglucan in edible fungi were compared and investigated: Among 18 kinds of homogeneous polysaccharides in edible fungi,there were 9 kinds of homoglucan,including five kinds of β-glucan and four kinds of α-glucan.β-glucan was classified into β-(1→3)-glucan and β-(1→6)-glucan: The main chain of the former was composed of β-(1→3)-glucan,whose substitution was located at the position of O-6 of Glcp,and the side chain was only β-T-Glcp residues in DRP-20(Water-extracted polysaccharides from Dictyophora rubrovolvata);The main chain of β-(1→6)-glucan consisted of β-(1→3)-glucan,the branches were substituted at the position of O-3 of Glcp,and the side chains contained β-(1→3)-Glcp and β-T-Glcp residues in JACP-50 p,JACP-80 and JACP-80r(Alkali-extracted polysaccharides from Agrocybe cylindracea)and HMAP-70(Alkali-extracted polysaccharides from Hypsizygus marmoreus).The other four kinds of α-glucan corresponded to α-(1→4)-glucan.Their main chains were mainly α-(1→4)-Glcp residues.There were branches substituted at the position of O-6 of Glcp,the side chain was α-T-Glcp in DRP-20r(Water-extracted polysaccharides from Dictyophora rubrovolvata),SHMP-10,SHMP-20 and SHMP-40(Water-extracted polysaccharides from Hypsizygus marmoreus).(3)The structural characteristics of heterogalactan in edible fungi were compared and characterizated: Among 18 kinds of purified fractions from edible fungi,there were four kinds of heterogalactan.The first one was a glucofucogalactan observed in JACP-30(Alkali-extracted polysaccharides from Agrocybe cylindracea),whose backbone was α-(1→6)-galactan.The branches were β-T-Glcp and α-T-Fucp,which were linked at the position of O-2 of Galp.The second kind of heterogalactan was a fucomannogalactan existing in SHMP-70p(Water-extracted polysaccharides from Hypsizygus marmoreus),whose backbone was α-(1→6)-galactan.The terminal residues,including α-T-Fucp and β-T-Manp were linked at the position of O-2 of Galp.The third kind of heterogalactan is glucomannogalactan,which was found in MAWP-70(Water-extracted polysaccharides from Termitomyces albuminosus).It contained α-(1→6)-galactan as the main chain,and β-(1→6)-Manp and β-T-Glcp as side chains,which were substituted at the position of O-2 of Galp.The fourth kind of heterogalactan was mannogalactan containing α-(1→6)-Me-Galp,which only occurred in MAWP-60p(Water-extracted polysaccharides from Termitomyces albuminosus).Its main chain comprised α-(1→6)-Galp and α-(1→6)-Me-Galp(5～12%)residues,and the side branches,including mostly β-Manp and a small amount of β-(1→6)-Glcp,were attached at O-2 of Galp.(4)The structural characteristics of heteroglucan in edible fungi were identified and compared: There were five kinds of heteroglucan among 18 kinds of purfied polysaccharides,manifesting into two main forms including fucogalactoglucan and galactoglucan.On the one hand,fucogalactoglucan mainly existed in ACWP-40 and ACWP-80(Water-extracted polysaccharides from Agrocybe cylindracea),whose main chains contained β-(1→6)-Glcp and a few α-(1→6)-Galp residues.Low degree of branches distributed at the O-2 of Galp,which were composed of β-T-Glcp and α-TFucp-(1→.On the other hand,the backbone of galactoglucan showed the presence of a majority of β-(1→6)-Glcp and minor α-(1→6)-Galp and/or →2,6)-α-Galp-(1→ in SHMP-80(Water-extracted polysaccharides from Hypsizygus marmoreus),MAWP-80(Water-extracted polysaccharides from Termitomyces albuminosus)and MAAP-70(Alkali-extracted polysaccharides from Termitomyces albuminosus).Their side branches mainly included β-T-Glcp and β-(1→3)-Glcp residues connected at O-2 of Galp.(5)The effects of the structural characteristics of edible fungi on their solution properties and morphology were elucidated.The molecular weight of polysaccharides is directly proportional to their viscosities.The viscosity significantly became higher as the molecular weight increased.The high-viscosity samples possessed more filamentous structures and less spherical structures in their surface by SEM technique.In addition,not all the fungi polysaccharides showed peculiar and representative conformational features.Among 18 kinds of polysaccharides,only DRP-20(Waterextracted polysaccharides from Dictyophora rubrovolvata)exhibited the rigid chains and strong intermolecular and intramolecular hydrogen bonds in aqueous solution.Other polysaccharide fractions adapted random coil conformation.