| Leuconostoc mesenteroides is a representative genus of genus Leuconostoc in lactic acid bacteria.It can not only be used for fermentation of various foods,but also can produce exopolysaccharide(EPS).EPS have been paid much attention in recent years because of their special physiological,biochemical characteristics and biological activities.Therefore,the study took dajiang as the research object,from which a strain of Leuconostoc mesenteroides SN-8,which has high production of EPS,was isolated and purified.Structural analysis and biological activity analysis of the polysaccharides were as follows:In the experiment,a strain with high yield of EPS was first isolated from the dajiang collected in Fuxin City,Liaoning Province by using the viscosity measurement method and polysaccharide content determination.After morphological observation,physiological and biochemical tests,and 16S rDNA sequence analysis,it was identified as Leuconostoc mesenteroides and named Leu.mesenteroides SN-8.The beads were inoculated into De Man Rogosa Sharp-sugar producing(MRS-S),a lactic acid bacteria sugar-producing medium,and cultured at a constant temperature of 28 ? for 48 h to obtain EPS fermentation broth.The crude polysaccharide was obtained by centrifugation,protein removal,alcohol precipitation,dialysis and freeze-drying,and its yield was 2.42 g / L.Further purification steps such as dialysis with purified water,Sephadex G-100 Sephadex G-100 filtration column,rotary evaporation concentration and freeze-drying were used to obtain purified extracellular polysaccharides EPS-8-1 and EPS-8-2.They are 43.12% and 10.24% respectively,and the total output is 1.3 g/L.Then the crude polysaccharide and two purified polysaccharides were analyzed.The reverse high-performance liquid chromatography(HPLC)found that the crude polysaccharide was mainly composed of dextran and contained a small amount of mannose.The gas chromatography(GC)analysis of the purified polysaccharides showed that Consistent with HPLC,the molecular weights of the EPS and EPS-8-1 determined by high performance size exclusion chromatography were 2.07×10~5 Da and 1.46×10~5 Da,respectively.At the same time,further analysis of the structure of different extracellular polysaccharides by fourier infrared spectroscopy and nuclear magnetic resonance shows that the exopolysaccharide is indeed composed of glucan and a small amount of mannose,and the main component is a highly linear dextran.Through the electronic scanning observation,bit was found that EPS had a smooth surface,pores and many branches.Thermogravimetric analysis of the exopolysaccharide and purified polysaccharide,respectively,the thermal degradation temperature of the three kinds of EPS was measured to be about 300 ?,indicating that the thermal stability of the exopolysaccharide is high,which is suitable for thermal processing.The exopolysaccharide and purified polysaccharides EPS-8-1 and EPS-8-2 have good emulsification properties for various oils.Among them,the highest emulsification index of peanut oil with EPS-8-1 is 0.59,and EPS is 0.55.Antioxidation test results show that the exopolysaccharide has a good scavenging effect on · OH free radicals,DPPH free radicals and ABTS free radicals,indicating that it has a certain antioxidant capacity.The biological activity test of purified exopolysaccharide showed that both EPS-8-1 and EPS-8-2 had an inhibitory effect on HepG2 liver cancer cells,and the results of the inverted microscope further indicated this conclusion.For HepG2,the extracellular polysaccharide of 5000 ?g / m L acted for 72 hours,and the inhibition rate was the largest,reaching 68.42%.In summary,Leu.mesenteroides SN-8,a high-yield EPS,was isolated and screened from natural fermented soybean paste in this study,the excellent physical,chemical properties and functional characteristics of the exopolysaccharide were analyzed,it lays a theoretical foundation for the application and industrial production of this exopolysaccharide. |
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