| Lactic acid bacteria exopolysaccharides(LAB EPSs)are the LAB's metabolic products during growth,these polysaccharides have unique rheological properties and physiological activities such as antioxidant,antitumor and immune regulation.According to the medical effects of koumiss,LAB and its metabolites exopolysaccharides are also involved in the medical functions of koumiss.A Lactobacillus plantarum(named NM18),which secretes exopolysaccharides(EPSs)to extracellular matrix,was isolated from koumiss.The EPSs were studied in this experiment,including the isolation,purification,primary structure elucidation,and antioxidant activities in vitro.The main results are as follows:1.The obtained CEPS was purified by anionic chromatography of DEAE-Cellulose 52 and Sepharose CL-6B to acquire six polysaccharide fractions,named with EPS-1A,EPS-1B,EPS-2,EPS-3,EPS-4 and EPS-5,all six EPS showed just a single symmetrical peak on HPSEC with the molecular weights respectively estimated to be 2.11×105 Da,2.04×105Da,2.02×105Da,2.17×105Da,2.09×105Da,1.93×105Da.2.As to CEPS,EPS-1A,EPS-1B3 EPS-2,EPS-3,EPS-4 and EPS-5,polysaccharide content which measured by using the method of phenol-sulfuric acid coloration was 75.25%,96.88%,95.98%,94.67%,80.06%.84.32%,75.38%,respectively.Protein content which measured by applying the method of Bradford was 1.13%.not detected,not detected.inot detected,not detected,7.22%.not detected.respectively.Sulfuric radical content,measured by using the method of gelatin-barium chloride assay,was 1.40%,0.22%,0.31%,0.26%,0.42%,6.30%,0.27%.respectively.Uronic acid content,employing the method of sulfuric acid-cartazoleassay,was 3.24%,0.23%,0.34%,0.25%,0.43%,0.54%,0.85%,respectively.3.The primary structural characterizations of EPS-1A,EPS-1B,EPS-2,EPS-3,EPS-4,EPS-5 were detemined by physical and chemical methods.UV full wavelength scanning showed that EPS-1A,EPS-1B,EPS-2.EPS-3,EPS-5 had no absorption peak in the range of 190?500 nm,and EPS-4 had a strong absorption peak near nm 260?280 nm,which indicated that the protein content of EPS-4 was higher;the monosaccharide composition of EPS-1A,EPS-1B and EPS-2 were mannose,glucose and galactose,the monosaccharide composition of EPS-3 were mannose,glucose,galactose,rhamnose,fucose and N-acetyl-D-glucosamine,the monosaccharide composition of EPS-4 were mannose,glucose,galactose and N-acetyl-D-glucosamine,the monosaccharide composition of EPS-5 were fucose,allose,rmannose,galactose and N,acetyl-D-glucosamine.4.The results of FT-IR spectra of EPS-1A,EPS-1B,EPS-2,EPS-3,EPS-4 and EPS-5 showed that they all had the obvious absorption of polysaccharide,and contained pyranose ring,EPS-1A,EPS-1B and EPS-2 had the similar FT-IR spectra,had the a-D-Galp and a-D-Glcp,EPS-4 had an N-H bending vibration and S=O stretching vibration that showed it had a high content of protein and sulfate group relatively.Methylation and GC-MS analysis showed that EPS-1A and EPS-1B were both composed of ?3)-D-Glcp-(1?,?6)-D-Galp-(1?,?4)-D-Glcp-(1? and ?6)-D-Manp-(1?the terminal residues were Glcp-(1?,EPS-2 was composed of ?6)-D-Galp-(1? and ?6)-D-Manp-(1?,Glcp-(1?was the terminal residues.Combining the results of 1D NMR,sugar ring of EPS-1A,EPS-1B and EPS-2 were all pyranose ring,containing ? and ? glycosidic bond.5.Antioxidant activities in vitro of CEPS,EPS-1A,EPS-1B,EPS-2,EPS-3,EPS-4 and EPS-5 were measured by using the chemical methods.Results showed that all EPSs could scavenge free radicals of ·OH and DPPH·,reduce Fe3+ in vitro,all had some antioxidant activities in vitro,EPS-4 and CEPS exhibited much higher antioxidant activities,and the antioxidant activities of EPS-1A and EPS-1B is closed. |
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