| Polysaccharides are an important class of active components from Pleurotus eryngii with potential biological activities. Scince structure and functions are intimately related, an in-depth study of Pleurotus eryngii polysaccharides would be of interest. In this work, crude polysaccharides were extracted from Pleurotus eryngii by hot water and were further fractionated to give two new polysaccharide fractions termed WPP1and WPP2. They were subjected to structural identification by means of UV, HPLC, GC, IR, GC-MS, NMR, CD, ESEM and AFM. Meanwhile, Pleurotus eryngii polysaccharides were modified by chemical methods. In addition, their antioxidant and anti-diabetic activities were evaluated in vitro. The results are as follows:1. The results showed that the protein, mineral elements, polysaccharides, trehalose, crude fiber, Ca, Zn and Se were present in significant concentrations, whereas crude fat was found in lower ones, and the compositions of amino acid meet the FAO/WHO ideal model. The polysaccharides, trehalose and crude fat were extracted using the optimum extraction technology. A small amount of nucleic acid was detected in both crude polysaccharides and trehalose by UV-spectrophotometer. The IR spectrometry results showed that the peaks at around914,796and610cm-1of crude polysaccharides is characteristic of pyranose, the peak near833-855cm-1suggest the presence of a-D-glucopyranosyl in trehalose. The Study confirmed that Pleurotus eryngii is a nutrient-rich and weight-loss healthy food, Pleurotus eryngii polysaccharides is a pyran-glucan, and Pleurotus eryngii trehalose is composed by a-D-glucopyranosyl.2. The average molecular weight of WPP1was determined by HPGPC to be about2.871×104Da. The structure analysis results indicated that WPP1was composed of3-O-Me-galactose, mannose and galactose with a molar ratio3.31:9.35:8.35, had a backbone of (1â†'6)-linked β-D-Manp,(1â†'6)-linked α-D-Galp,(1â†'4,6)-linked β-D-Manp and (1â†'2,6)-linked a-D-Galp. The branches were mainly composed of (1â†'6)-linked a-D-Galp, and terminated withβ-D-Manp residues. Unusual (1â†'6)-linked3-O-Me-a-D-Galp were distributed in branches and backbone with a smaller amount. The particle size and AFM analysis indicated that WPPl existed as aggregation conformation in aqueous solution with a mean effective diameter1487.0nm. Congo red reaction indicated that WPPl have no the triple-helical structure in aqueous solution.3. The results revealed that WPP2is rich in Glc with an average molecular weight of about4.499×105Da. The main chain of WPP2is made up ofâ†'1,3)-β-D-Glcp,â†'1,6)-β-D-Galp, andâ†'1,3)-β-D-Manp with two side chains.â†'1,6)-β-D-Glcp,â†'1,6)-β-D-Galp and terminal residueâ†'1)-β-D-Glcp are linked to form side chains bearingâ†'1,2,3)-β-D-Manp andâ†'1,2,6)-β-D-Manp residues as branched points; Congo red reaction indicated that WPP2have the triple-helical structure in aqueous solution; The multi-branched structure of WPP2was detected at the nanometer scale for the first time by ESEM and AFM.4. The biological activity of Pleurotus eryngii polysaccharides had improved significantly according to different chemically modified. The sulfation and carboxymethylation Pleurotus eryngii polysaccharides have stronger scavenging activity to a-amylase, and the phosphorylation Pleurotus eryngii polysaccharides have certain inhibitory activity to a-glycosidase at a concentration of2mg/mL, particularly, the phosphorylation Pleurotus eryngii polysaccharides have the strongest antioxidant activity. The results suggested that the Pleurotus eryngii polysaccharide could potentially be used as a new natural medicine, but the relation of structure and functions need further study. |
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