Study On Curdlan Production By Microbial Fermentation

Curdlan is a novel microbial extracellular polysaccharide, One of the unique features of curdlan is that aqueous suspensions can be thermally in-duced to form high-set gels. In this study, the factors in agrobacterium cra-diabacter curdlan fermentation were investigated, and the fermentation pro-cess was optimized:the liquid culture time of 24 hr, broth inoculation vol-ume of 5%, fermentation temperature 32℃, fermentation period 78 hr. Op-timized fermentation medium compositions are:glucose 5%, (NH4)2HPO40.2%, KH2PO40.3%, MgSO4·7H2O 0.1%, CaCO30.2%, corn steep liquor 0.2%, pH7.0. PPE and bean oil were used as anti foam reagent, which could affect dissolved oxygen in the fermentation broth and increase curdlan production.The pilot fermentor of 1000 L was used for fermentation with the opti-mal conditions for the production process:mechanical ventilation fermenta-tion tank stirring speed 180 rpm, ventilation 0～36 hr 0.3 VVM,36-60hr 0.4 VVM,60hr after 0.5VVM, culture temperature 32℃, tank pressure 0.1mpa, fermentation period 78hr, liquid volume 750 L, and the polysaccha-ride yield of 32g/L, sugar conversion rate increased up to 60% were ob-tained.Based on the pilot fermentation results, it is concluded that curdlan fer-mentation process is highly aerobic. Mixing emerge influences greatly on curdlan fermentation. Severe stirring influence greatly on the quality of the product, The combination of two kinds of impellers are suitable for curdlan production. Viscosity changes in curdlan fermentation, which effects the dissolved oxygen. In the production process, ventilation is increased in a se-ries of different of fermentation stages.The extraction conditions for curdlan were explored. Dissolve curdlan (concentration 2.0%) in 0.50mol/LNaOH solution, remove curdlan fermenta- tion broth impurities by using centrifugation. The extraction process can be used to achieve purification in industrial continuous production, with curdlan extraction yield of more than 90%. This research solve a series of industrial technical problems in production of high-quality curdlan.