Study On The Extrcation Of Microbial Polysaccharide-Welan Gum

Welan gum (S-130), a kind of soluble extracellular hetero-polysaccharide produced by Alcaligenes sp. ZW-3 in an aerobic submerged fermentation. It is one of the most market prospective microbial polysaccharides developed by C.P.Kelco, division of Huber Company in American. As reported that welan gum's unique molecular structure gives excellent rheological properties of its aqueous media, it is widely used in concrete construction industry, oilfield drilling fluids, and have in the cosmetics, food, medicine and other areas of potential applications as thickening agent, drilling agent, suspending agent, emulsifying agent.In this study, separation and precipitation technology of welan with ethanol were investigated, and then determined the best drying process, as well as explored influce of the technological conditions on the rheological properties of welan, which was form flask-shaker fermentation with Alcaligenes sp.ZW-3. The main works and research results are as follows:(1) Reduced pH of welan solution can promote its precipitation with ethanol. There is no obvious destroy to rheological characters of welan gum when pH> 2.0, but lower pH is not conducive to keeping the good rheological properties of welan. Adding the salt ions can promoted welan precipitation, comparing to monovalent salt ions, the role of divalent salt ions, especially CaCl2,is the most significant.(2) The optimal conditions for welan recovery from fermentation broth were as follows: 2.5mol/L of CaCl2 was added until Ca2+ concentration reached O.lmol/L, pH was adjusted to 2.0 and the ethanol concentration in the bulk mixture was 37.6%. Welan gum was effectively precipitated and separated from the fermentation broth and the recovery yield achieved 92.5%. Moreover, the rheological properties of the welan gum were robustly kept, and 73.3% ethanol dosage was economized as compared to the control experiments.(3) A method of vacuum drying was used for welan drying and a reasonable drying technology parameter was determined in this article. The experiment of single factor for vacuum drying, conducted under different conditions, explored the effect of vacuum drying parameters (drying temperature, vacuum, material thickness) on moisture content of welan, vacuum drying time and drying velocity. According to orthogonal analysis, we concluded the optimal technological parameters for vacuum drying:60℃(drying temperature),0.06MPa (vacuum),2mm (material thickness).In vacuum thin-layer drying process of welan gum, drying temperature and vacuum were the most important factors which can affect drying rate. The dying rate increased significantly with the drying temperature and vacuum rising.(4) The vacuum thin-layer drying Model of welan, described the variation trend of relative moisture ratio of welan along with drying time, and met the Page equation.The precipitation characteristics of welan gum in the ethanol-water solution were clarified. The influence of ethanol concentrations, pH, salt types and salt concentrations on welan precipitation and its rheological properties were investigated. We also studied vacuum drying process parameters of welan and constructed the vacuum thin-layer drying model. These results have important practical application value for the industrial production of welan.