Studies On Fermentation Process And Molecule Structure Of Curdlan Polysaccharide

Curdlan is a bacterial polysaccharide composed entirely of (l,3)-p-D-glucosidic linkages produced by fermentation of microorganism. One of the unique features of Curdlan is that aqueous suspensions can be thermally induced to form high-set gels, and this has attracted the extensive attention of the food industry, light industry, medicine and health protection. In this study, the Curdlan producing strain - Alcaligenes faedelis Var. C125 strain was induced and screened, and its characters for Curdlan production was studied. Culture medium and conditions of fermentation was optimized by respond surface methodology(RSM). The progress of isolation, purification and separation of Curdlan polysaccharide from fermentation broth was studied. The structure of the purified Curdlan product (CD-3) which was separated and purified from fermentation broth was analysed and its structure modification was also studied. The main results were as following:1) Glucose, sucrose, molasses and solubility starch can all be used as carbon resource to produce curdlan by single fector experiments by Alcdigenes faedelis Var. C125 strain. However, glucose was the optimal carbon source and its fitting concentration was 45gL-1; yeast extract was the optimal nitrogen source and its fitting concentration was 8.5g.L-1; Reasonable calcium carbonate(2.5g.L-1) could not only promote the Curdlan yield but also maintain the pH of fermentation broth.Carbon source and nitrogen source influenced the Curdlan fermentation significantly by orthogonal test, and mixinorganic salt (K2HPO4+MgSO4 ) influenced Curdlan fermentation significantly less than the former, but kalium citrate hadn't significant influence. Culture medium optimized with orthogonal wasfeL-1) glucose 40; yeast extract 8.5g.L-1; mixinorganic salt 2+0.2, kalium citrate 0.2.The Curdlan yield was 28.22g.L-1 in optimized medium. Uracil and KH2PO4 could also affect Curdlan production greatly. Additonal concentration of KH2PO4 was 2g.L-1 and uracil concentration was no less than 0.3g.L-1.The composition of fermentation culture medium optimized with RSM was (g.L-1): glucose 49.5, yeast extract 7.64, uracil 0.32, KH2PO42.72, (NH4)2HPO4, 1.16; The Curdlan yield was 25.03g.L-1 at 95h in optimized culture medium, similar to that predicted by model. The Curdlan fermented by strain C125 was associated partially with cell growth. The former phase of Curdlan fermentation was logarithm phase of cell growth and did not produce Curdlan polysaccharide. The cells did not start to produce Curdln after it entered stationary phase, until nitrogen source was almost exhausted out2) 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癈; and shaker rotation speed, 200 rpm; initial pH, 6.5; fermentation time was 95h. PPE and rap oil used as assisting dissolved oxygen reagent could modify dissolved oxygen in the fermentation broth and promote Curdlan production. But H2O2was unfitted to be used as assisting dissolved oxygen reagent. The optimal conditions for Curdlan production with RSM was: inoculum age 9.9h; inoculum size 9.8%(v/v); shaker rotation speed 208rpm; initial pH 6.1 and culture 30℃ for 93.9h.Curdlan production reached the maximal point 24.69g.L"1similar to the result predicted by model.The optimized composition of culture medium and the optimized condition were adopted to produce Curdlna in 3.7L automatism fermentor and could continue to optimize using the former result as starting point. The connection between Curdlan concentration and viscosity of fermentation broth were studied, and obtained the model equation that used viscosity of fermentation broth to forecast Curdlan production during fennentation process of Curdlan polysaccharide. So it was simple to inspect Curdlan production and control the culture conditions of Curdlan fermentation process.3) It w...