| In this study, the main object is to enhance exopolysaccharide product using corncob as carbon source. In order to do this, the conditions of fermentation of exopolysaccharide by Pseudomonas were researched, and the strain was treated by ultraviolet and low-energy nitrogen ion beam implantation. This strain could utilize glucose, xylose and sucrose to produce exopolysaccharide. Carbon source concentration, nitrogen source concentration and carbon-nitrogen ratio are key roles to produce exopolysaccharide. If carbon-nitrogen ratio was below 3, there was no carbon source to be used to produce exopolysaccharide. As for nitrogen source, low concentration is better than high concentration. Organic nitrogen is prior to inorganic one to get high viscidity, but it had no effect on yield. At last 0.02% ammonium chloride was chose as limited factor to enhance exopolysaccharide product.OD value was still ascending after the stationary phase when medium contain high concentration glucose, and this shows that Pseudomonas began to produce exopolysaccharide in the stationary phase. The colony was concentric circles shaping in solid medium. Exopolysaccharide formed transparent ring outside of colony, which can be used to screen mutants having high yield of exopolysaccharide. In consideration of process of corncob, yielding cost and full using etc, mixing stuff of corncob was chosen, which the distinguishing size is 2.0-eye griddle hole. Meanwhile, exopolysaccharide productivity was double if two-dose material was used in experiment. The yield of exopolysaccharide was 26.96g/L.Calcium carbonate, tween 80 and lemon acid had no effect on polysaccharide production referring to xanthan study. But trace elements could facilitate the yield of exopolysaccharide. The new prescription of trace element solution (g/1000ml) was as following: MnSO4 0.300,CaCl2 0.2,FeSO4 0.8.For producing exopolysaccharide, high air concentration was needed. Pseudomonas sp could grow and produce exopolysaccharide in pH range from 7.5 to 10.0, but could not below pH7.0, and the optimum initial pH is 8.0. Meanwhile, it could grow and produce exopolysaccharide at 28～32℃, but could not below 26 or higher than 35℃. Amount of inoculation had no effect on fermentation, but higher amount of inoculation could shorten producing period. The fermentation period was set five days because of the yield is much higher at this time. The yield was steadiness at day 5, but viscosity still enlarged continually probably because of water evaporation. The optimal fermentation condition was 30h bacterial age, 5% inoculating amount, no more than 20% load, initial pH 8.0, 30℃/180rpm and five days growth.Low energy nitrogen ion beam implantation and ultraviolet light were chosen as mutagens to treat strains. As the result, the UV-bactericidal-curve appearing a routine "shoulder shape". While 10KevN+ radiation was introduced, the survive ratio decrease first, then increase and drop at last. The curve was "saddle shape". Finally, two high yield strains, UVZT122 and UVZT213 were got, the yield of which was enhanced by 10.53% and 9.57% respectively. And two high yield strains, NZTZ07 and NZTZ11 were got by low energy N ion beam implantation, the yield of which was enhanced by 11.02% and 6.83% respectively.Rheology research found that the exopolysaccharide had self-viscosity-improvement and thixotropy, so the exopolysaccharide solution was a pseudoplastic liquid. The exopolysaccharide had good adaptability to environment conditions. The viscidity had no change in the range of pH 1～14, and at 60℃. It could be untouched for 20 minutes. And so did it when NaCl, CaCO3 was added. Additionally, Fe3+ could enhance viscidity of the exopolysaccharide solution. When the ratio of the exopolysaccharide and Fe2(SO4) 3 was 2, the solution of exopolysaccharide became a gel. The hydraylation of exopolysaccharide by acid or base was: HCl＞ NaOH＞ H2SO4. It prevented the viscidity decrease from heating by adding NaCl. |
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