| Xanthan gum is an extracellular heteropolysaccharide, which is produced through the aerobic fermentation by Xanthomonas campestris. Xanthan is composed of pentasaccharide repeating units, containing D-glucose, D-mannose, D-glucoronic acid (at a ratio2:2:1), acetal-linked pyruvic acid and D-acetyl groups. Due to its excellent stability, rheological property, thickening property, suspensibility and emulsifying property, xanthan gum is used in many applications, mainly in food, medicine, oil, chemical industry, and so on. Xanthan gum is the world’s largest microbial polysaccharides production. However, the xanthan gum production of our country is relatively backward, still has many problems, including low yield, low oxygen solubility caused yield reduction in late fermentation and blank in high purity research.The study is based on industrialization, choosing inexpensive raw materials, optimizing carbon sources, nitrogen sources, organic acid, and inorganic salt with single factor experiments, optimizing the medium component:potato starch6%, soybean powder0.40%, CaCO30.40%, MgSO40.20%, MnCl20.012%, sodium glutamate0.10%. The optimal fermentation condition:inoculum concentration7%, outfit fluid amount60mL/250mL, temperature30℃. The xanthan gum yield reached27.30g/kg, increased by24.09%than before optimization.In order to achieve the maximum yield of xanthan gum, genetic engineering transformation has been applied. A cluster of12genes are involved in the biosynthesis of xanthan. A number of homologous gum genes have been detected in the genome sequence. The gumD protein catalyses the first step of xanthan production, and is responsible for the addition of the first glucose molecule to the isoprenoid acceptor molecule. This study overexpressed gumD in Xanthomonas campestris58(Xc58), resulted in the engineering bacterium Xc58-D, which improved the yield to31.21g/kg, increased by11.19%than Xc58, and increased the Mr and acetyl content. With product accumulation during fermentation process, the high viscosity of the fermentation solution becomes a big hurdle for liquid mass transfer rate and oxygen content. To solve this problem, the pBBR-gumD-vgb was transferred to Xc58to achieve the Xc58-DV strain. Through fermentation in flasks and10L fermenters, gum yields increased in the low oxygen content conditon, reduced ventilatory capacity, and lowed the cost. However, the optimization of engineering strain needs further study.The research also studied surfactant and vegetable additives’s effect on the production of xanthan gum in flasks. Adding0.06%Triton X-100at0h,0.09%Tween-20at48h during the fermentation, the yield reached35.22g/kg, increased by17.87%than the control group. Adding1.17%-1.50%corn oil, the yield reached34.04g/kg, increased by17.10%than the control group. However, if the additives can be applied in industry will need to be researched continually.This study investigated purification protocol of xanthan gum, using the orthogonal design for the steps of diatomite, activated carbon, and alcohol precipitation, and optimizing purification process parameters:diatomite DP-20, final concentration of3‰, temperature80℃; alkali protease, add50g/1×106g, temperature45℃, pH8; activated carbon767, final concentration of5‰, temperature55℃, pH6; temperature of alcohol precipitation at50℃, addition1.5times as many as the gum solution, pH5, twice. The samples were detected according to the standards of pharmaceutic adjuvant and sodium hyaluronate injection drug levels, and all the parameters were confirmed. This served the basis for later research on xanthan gum injection for aesthetic surgery and articular cavity injection. |
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