| Curdlan is an exopolysaccharide composed entirely of β- (1,3)- D-glucosidic linkages which is produced by bacteria. The unique features of Curdlan, thermic gels and its special molecular structure has attracted the extensive attention of the food industry, light industry, medicine and healthcare. In this study, the new mutant strain for Curdlan was induced and its characters for Curdlan fermentation were studied, the ideal culture medium and fermentation conditions were investigated. The rheological property and oxygen mass transfer were both studied in Curdlan broth, and the batch process and dynamics model were determined , the progresses of isolation, purification and separation of Curdlan from fermentation broth were studied. The structure of the purified Curdlan which was separated and purified from fermentation broth was analyzed, and the process for its structure modification was also studied. The main results were as following:1. The cells and protoplasts of initial strain, whose name was Alcaligenes Species var. GM-24 , were treated by 60Co γ radiation respectively for the first time, while both of the mutants from protoplasts and cells had improved their productivity of Curdlan , the productivity and genetic stability of former were much greater than those of the latter.In contrast with the strain GM-24, the final mutant A38, which was induced by 60Co γ radiation from protoplast of the GM-24, had greatly improved its productivity properties. Its rate of sugar transmission was increased to 58.2% from 38.7% , the productivity of Curdlan was increased to 15.35 g.L-1 from 22.3 g.L-1, meanwhile , the fermentation term was reduced 18%.The genetic properties of strain A38 were very stable, so it was choosed as fermentation strain in follow-up study.2. The single factor experiments for the composition in culture medium indicated that glucose was the optimal carbon resource, while sucrose, molasses and solubility starch could be also used to produce Curdlan , and that yeast extract was the optimal nitrogen resource . Furthermore, reasonable calcium carbonate could not only promote the Curdlan yield but maintain the pH of fermentation broth.The result of orthogonal test indicated that the effect of four principal factors on Curdlan fermentation was: glucose > yeast extract > MgSO4 7H2O > KH2PO4 . As an assistant factor in culture medium, uracil had greaterinfluence on Curdlan production than citrate kalium.The composition of fermentation culture medium optimized with respond surface methodology(RSM )was (g.L-1): glucose 49.5, yeast extract 7.64, KH2PO4 0.22, MgSO4 7H2O 0.31, uracil 0.32, citrate kalium 0.2, CaCO3 2.0. The Curdlan yield was 26.32gL-1 when the strain A38 was cultured in optimized medium, it was 18% higher than that in culture medium before being optimized .The result of fermentation indicated that Curdlan produced by strain A38 was associated partially with cell growth , The Curdlan had not to be yielded from the cells until the nitrogen resource was almost consumed up and the cells entered stationary phase.3.The optimal culture conditions for Curdlna production selected by single factors experiments was as following : the inoculum age and inoculum size were 10h and 10%(v/v) respectively; the optimum charge quantity was 100-125ml culture medium in 500ml flask; and the optimum temperature , 30-32 shaker rotation speed, 200 rpm; initial pH, 7.0 ;and pH for Curdlna, yielding 5.2-6.0; fermentation time was around 72 hours . PPE and rap oil could help oxygen to dissolve in the fermentation broth and promote Curdlan production.The optimal conditions for Curdlan fermentation with RSM was: inoculum age , 9.9h; inoculum size , 9.8%(v/v); shaker rotation speed , 208rpm; initial pH 7.0; pH for Curdlna yielding , 5.2; fermentation temperature, 30 fermentation term,70.9 hours. Curdlan production reached the maximal point 29.88g.L-1 under the optimal culture conditions, this was 13.6% higher than that before the culture conditions were optimized .The op...
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