Research On Preparation And Characteristics Of Bacterial Exocellular Polysaccharides

In nature, exocellular polysaccharide (EPS) are widely present in higher plants, alga, bacteria and animals. Recently, EPS from microorganism have received more and more attention of people and was applied to in many fields. So, it has important theoretical and practical significance for extending the application field of EPS to obtain the new EPS strains with high EPS yield and good characteristics.In our work, the bacteria with EPS-producing was screened from the traditional yogurt of Xinjiang. The strains with EPS-producing is Bacillus ginsengihumi by16S rDNA. Then it was compared with that of kept in laboratory. The result showed that the bacillus subtilis4-3kept in laboratory has higher EPS yield. The bacillus subtilis4-3was used as the tested strain, the work is to optimize culture medium and fermentation condition for Bacillus subtilis4-3EPS production. Then EPS was collected and its characteristics was studied.EPS production was used as the indexes, the optimum culture medium for EPS production from the Bacillus subtilis4-3was primarily studied in single factor experiment method and the response surface method. The results indicated that the composition of optimum culture medium was as follows:25.4g/L sucrose,15.2g/L peptone bacto,3.0g/L trisodium citrate,3.Og/Lbeef extract,1.0g/L magnesium sulfate,3.0g/L sodium chloride. It was primarily studied by the single factor and orthogonal test that the optimum production condition for Bacillus subtilis4-3EPS. The results indicated that the optimum fermentation condition was as follows:liquid volume36mL/100mL, initial pH5.0, cell age10h, inoculum size3%, temperature37℃, wave bed speed160r/min, fermentation time36h. At the optimum condition, the EPS yield was4.1g/L.In order to improve extraction of EPS, the extraction condition of EPS was optimized. The result showed that the best method for EPS extraction is precipitation using95%ethanol3times the volume of fermentation broth. It is the best way to remove the protein of EPS by Sevag method for three times, deproteinization rate was70%and the loss porportion of EPS was20%.It was studied that the characteristics of EPS produced from reforming broth medium and PDA broth medium by Bacillus subtilis4-3, including antioxidative activity, hygroscopicity, moisture rerention and flocculating activity. The results showed that the EPS from different mediums had reductive ability, antioxidative activity, and eliminated effect on the radical·OH and O-· The EPS from different mediums had good hydroscopicity in relative humidity (RH) of81%,43%and had good moisture retention in relative humidity (RH) of43%and dry silica gel environment. The EPS from different mediums had different flocculating activity. Flocculating activity of the EPS from PDA broth medium was overmatch the EPS from reforming broth medium. The optimum flocculating activity of the EPS from PDA broth medium was as follows:20℃, pH5.0, presence of Ca2+...