Structural Characterization,selenylation And Physiological Activities Of Polysaccharides From Wheat Bran

Wheat is one of the important food crops in many countries with a large annual output.Wheat bran is the main by-product of wheat processing and contains many kinds of active substances.In general,wheat bran is used as a low-value feed product,resulting in a waste of resources.To increase the value of wheat bran,in the present study,the polysaccharides were isolated from wheat bran by sequential extraction with water and alkaline solution,and the structural characterization,selenization modification and physiological activities of polysaccharides were studied.Firstly,the two crude polysaccharide fractions?WXA and AXA?from wheat bran were obtained by sequential ultrasound-assisted water extraction and alkaline extraction processes,and two polysaccharide fractions?W2 and A2?were obtained by DEAE cellulose-52 anion exchange chromatography eluted with 0.1M Na Cl solution.Then,W2 and A2 fractions were further purified by a Sephacryl S-400 gel permeation chromatography,and two homogeneous polysaccharides fractions were obtained and named as WXA-1 and AXA-1,respectively.The structures of WXA-1 and AXA-1 were characterized by monosaccharide composition,methylation analysis,periodate oxidation,Smith degradation and NMR.The total sugar,pentosan and ferulic acid contents of AXA-1 were higher than those of WXA-1,but the molecular weight was lower than that of WXA-1,and only WXA-1 contained uronic acid.Both WXA-1 and AXA-1 were composed of glucose,galactose,xylose and arabinose,their molar ratios were5.30:4.47:2.30:1.00 and 0.05:0.08:2.35:1.00,respectively.The backbone of WXA-1 was?4)-?-D-Xylp-?1?,which was substituted at O-3 positions by arabinose,glucose and galactose residues,while the backbone of AXA-1 was?4?-?-D-Xylp-(1?,which was mainly substituted at O-3 positions by arabinose residue.Both WXA-1 and AXA-1exhibited triple-helical structures,but there were significant differences in apparent morphology.In addition,two wheat bran polysaccharide fractions?W2 and A2?were selenylated by using HNO₃-Na₂Se O₃ method,their Se-enriched products?Se W2s and Se A2s?with different selenylation degrees were obtained.W2 and A2 were successfully selenylated by the determination of selenium content,FT-IR and XPS.The monosaccharide composition,SEM and Congo red experiments showed that the structure of selenylated polysaccharide was changed compared with that of natural polysaccharide.The results of AFM and CLSM showed that the aggregation of selenylated polysaccharide in aqueous solution was weaker than that of natural polysaccharide.Thermodynamic experiments showed that both natural polysaccharides and selenylated polysaccharides had good heat resistance.The results of viscosity and rheology determination showed that the viscosity of polysaccharide can be reduced by selenization modification.At last,the physiological activities of Se-polysaccharides were studied,and the results showed that Se-polysaccharide had good antioxidant activity,including strong hydroxyl radical scavenging ability,reduction ability of iron ions and chelating ability of iron ions,and the antioxidant activities were proportional to the content of selenium.Animal experiment showed that Se W2-3 and Se A2-3 had better liver protective activities by reducing the activities of AST,ALT,LDH,and AKP in mice serum,decreasing the acitivies of caspase-3,caspase-8 and the content of MDA in the liver,enhancing the activities of antioxidant enzymes in the liver,and reducing the levels of TNF-?and IL-1?in mice serum.These results showed that Se W2-3 and Se A2-3 had strong liver protective activities.