Preparation Of Xanthan Gum With High Thermal Stability

Xanthan gum(XG) is a widely used microbial polysaccharide. To produce XG, Xanthomonas campestris 1.1781 was used as production strain, sucrose is the most frequently used carbon sources. The following studies were done aimed at solving a sevies of problems such as improving the production rate of XG, decreasing the cost of extraction, unstabilities at high temperatures.Which implys XG is easily degraded , the viscosity of that is reduced ,and the worse thermal stability.The fermentation conditions of XG were studied. The effects of different factors, including carbon source, calcium carbonate, and inoculum volume on the production rate of XG and absorbency of fermentation broth were studied by monofactonal experiments. Then the optimum production conditions were obtained by orthogonal design:Saccharose 50.0g/L, peptone 5.0g/L, K₂HPO₄·3H₂O 4.0g/L, MgSO₄·7H₂O 0.2g/L,citric acid2.0g/L, CaCO₃ 3g/L, pH7.0. The results showed that under such optimum conditions the production rate was 32.38 g/Kg , absorbency of fermentation was 0.338.The planting methods were investigated."Two-Staged Fermentation":â‘ culture mediumâ… : Saccharose 25.0g/L, peptone 5.0g/L, CaCO30g/L,K₂HPO₄·3H₂O 4.0g/L, MgSO₄·7H₂O 0.2g/L, citric acid 2.0g/L, (NH4)2SO4 2.0g, pH7.0.â‘¡culture mediumâ…¡: Saccharose 50.0g/L, peptone 5.0g/L, CaCO₃ 3.0 g/L,K₂HPO₄·3H₂O 4.0g/L, MgSO₄·7H₂O 0.2g/L, citric acid2.0g/L, pH7.0.Dilution rate was 5. After 87 hours later, the production rate was 34.26 g/Kg ,which increased by 5.81% compared with the basic culture conditions, and the viscosity of fermentation broth was 16750 mPa·s; XG biosynthesis was studied in a 5L stirred reactor. The production rate was 37.86 g/Kg, which enhanced by 11.69%. From this, we can known that stirred reactor is feasible.Many methods of pretreatment on fermentation broth were tested. The results were: XG precipitation using ethanol was simple and convenient, but the cost was too high, this method was just adapt to use in laboratory; Deposition with 20% potassium chloride, the production rate can arrive at 43.21g/Kg.The variations of the planting methods and extraction methods used in production were factors that can influence the molecular weight of XG,equal to other XG products'; The orthogonal test was developed, then XG with high thermal stability was obtained.This paper mainly studies on the influence of potassium chloride , guar gum , sodium hyposulfite, sodium borohydride and crosslinking agent upon XG thermal characteristics. The results proposed the optimum conditions for XG thermal stability are: sodium hyposulfite of 1.5g/L , crosslinking agent of 4mL/L ,under 121℃,with 3 hours of heat processing. The viscosity stabilizer of XG solution can be respectively enhanced by 1.85 and 7.80 times.The concentration of wall materials(XG) and sodium hyposulfite, crosslinking agent were also analysed . The results were: the ratio of XG was 10%; XG with high thermal stability was obtained by entrapping into sodium hyposulfite, which advanced 1.85 times. But the effect of crosslinking agent was unsatisfactory. The thermal stability of XG was analysed by thermogravimetric apparatus(TGA).The experiments indicated that sodium hyposulfite as viscosity stabilizer of XG can improve the thermal stability. Thermal stability of XG whih were fermented by stirred reactor is better than that of USA XG.