Study On The High Productivity Fermentation Technology Of An Extracellular Microbial Polysaccharide-Curdlan

Curdlan is an extra-polysaccharide produced by Alcaligenes faecalis. Enhancement of biomass during the cell growth phase is important to realize curdlan high production.Due to the high resistance of oxygen transfer in the process of high cell density cultivation, curdlan biosynthesis is weaken in the production phase. In this work, a two-stage fermentation strategy for curdlan producing was proposed according to changing demands for nutrition and oxygen in different stages of curdlan fermentation. Firstly, high cells density cultivation was carried on in the first fermenter. Secondly, inoculant cultures were diluted into the next larger fermenter for curdlan production, in which oxygen was enough and glucose was fed as sole carbon source. The effect of biomass on the productivity of curdlan was investigated. This work was available for commercialization of curdlan. The main research conclusions were as follows:Based on the previous work,fed-batch fermentation process of cell culitivation was investigated in the first fermenter. An optimal feeding method was applied: The pH was controlled at 7.0 by ammonia water(5%) with initial glucose and NH4Cl concentration at 15g/L and 0.5g/L in the favor of cell growth, the glucose feeding solution(400 g/L) was fed as carbon source at the rate of 5.5g/L/h from 12h to22h. At the end of cell cultivation (22h), the final biomass reached 27g/L, which was 4.5 times lager than that of batch fermentation (initial NH4Cl was 3.6g/L), besides, the dissolved oxygen(DO) was dropped to zero although the agitation was maintain at 1000r/min. The oxygen transfer became the limitation of getting a higher biomass.On the foundation of high cell density cultivation of cells, inoculant cultures were diluted into the second lager fermenter for curdlan production. The effect of biomass on curdlan production was investgated. The highest production of curdlan 66g/L with productivity of 673.5mg/L?h was achieved with the biomass of 11g/L,showing an increase of 106% and 131.4% as compared with that of batch fermentation.