| Schizophyllum commune polysaccharide,also known as schizophyllan,is one of the main metabolites of S.commune and has significant effects on anti-tumor,immune regulation,and moisturizing.Selenium,as an essential trace element in human body,is mainly supplemented by intake of products containing selenium.Among them,selenium polysaccharide,as an existing form of organic selenium,has higher biological activity than natural polysaccharide,and compared with inorganic selenium,selenium polysaccharide has the advantages of low toxicity,high bioavailability,and slow release of selenium element.However,there are few kinds of natural selenium polysaccharides and their content is low in nature,which makes it difficult to meet the daily needs of the human body.Therefore,artificial synthesis of selenium polysaccharides has become a hot research topic.In this study,S.commune selenium polysaccharide was synthesized and prepared by two methods of biosynthesis and chemical synthesis,and the selenium polysaccharide was isolated and purified.The structure and properties of the purified selenium polysaccharide were characterized,and the differences in structure and properties between the biosynthesis and chemical synthesis of selenium polysaccharide were compared,which provided a new idea for the artificial synthesis of selenium-enriched dietary substances.The main research contents and results are as follows:（1）Biosynthesis of S.commune selenium polysaccharideBased on the metabolic characteristics of S.commune,Na2Se O3 was added in the liquid fermentation process for the biosynthesis of selenium polysaccharide.First,the amount of selenite was optimized to determine the optimal concentration of Na2Se O3 in the medium.By observing the extracellular polysaccharide,reducing sugar,biomass,pellet morphology and diameter data after fermentation,we found that the addition of 7.5 mg·L-1 Na2Se O3 significantly inhibited the growth and metabolism of S.commune.Therefore,5 mg·L-1 Na Se O3 was selected as the addition amount of the biosynthesis selenium polysaccharide.After separation and purification,two components BPS-1 and BPS-2 were obtained,with the selenium content of1.313 and 8.080μg·g-1,respectively.（2）Chemical synthesis of S.commune selenium polysaccharideIn this paper,ultrasonic-assisted nitric acid-sodium selenite method was used for the chemical synthesis of S.commune selenium polysaccharide.With the content of selenium in polysaccharide as the index,the ultrasonic time and power for chemical synthesis were optimized to determine the optimal synthesis conditions.The results showed that the crude selenium polysaccharide obtained under the ultrasonic condition of 6,000 Hz for 1 h had the highest selenium content,and the chemical synthesis of selenium polysaccharide under this condition was selected.After separation and purification,two components CPS-1 and CPS-2were obtained,with the selenium content of 3.461 and 4.171μg·g-1,respectively.（3）Structural characterization of S.commune selenium polysaccharideThe composition and structure of the purified selenium polysaccharides were analyzed,and the relative molecular mass,monosaccharide composition and selenium content were determined.The result showed that that relative molecular weight of BPS-1,BPS-2,CPS-1 and CPS-2 were 19,125,15,519,2,291 and 1,551 k Da,respectively.The four selenium polysaccharides have that same monosaccharide composition type as the non-selenized polysaccharide,and are all composed of fucose,xylose,mannose,glucose and galactose;and only the proportion of each monosaccharide is chan after selenization.The results showed that BPS-1 had a triple helix structure,while BPS-2,CPS-1 and CPS-2 did not have a triple helix structure.XRD spectra confirmed that BPS-1 and BPS-2 had semi-crystalline structures,while CPS-1 and CPS-2 had amorphous structures.XPS energy spectrum analysis showed that the binding energies of selenium in BPS-1,BPS-2,CPS-1 and CPS-2 were all about 59.8 e V,Selenium in the selenium polysaccharide of S.commune exists in the form of+4 valence.The FSEM showed that BPS-1 and BPS-2 had irregular fibrous and hollow rod-like structures,while CPS-1 and CPS-2 exhibited fibrous sheet-like structures with smooth surfaces and honeycomb cavities.It was found by AFM that the four selenium polysaccharides presented as naturally bent lines in the aqueous solution,without overlapping and stacking,and had good dispersibility.The chain length of BPS-1 and BPS-2 is longer than that of CPS-1 and CPS-2.（4）Physicochemical property and cytotoxicity of S.commune selenium polysaccharideThe thermal stability and rheological properties of four S.commune selenium polysaccharides were analyzed.The results showed that the introduction of selenium did not change the thermal stability of polysaccharides,and the stability of polysaccharides was good at the temperature of 30-210℃.It was found from the analysis of rheological properties that the aqueous solution of selenium polysaccharide was a pseudoplastic fluid with the characteristics of shear thinning,and the shear thinning phenomenon was more significant with the increase of the solution concentration.The cytotoxicity experiment was conducted to verify whether the S.commune selenium polysaccharide was toxic.Cytotoxicity experiments showed that BPS-1,BPS-2,CPS-1 and CPS-2 did not inhibit the growth of mouse macrophage RAW264.7 at the concentration of 0-200μg·m L-1,indicating that selenium polysaccharide was not toxic to mouse macrophages within this concentration range. |
