Abstract:Curdlan is a water-insoluble extracellular polysaccharide produced by Agrobacterium sp. under nitrogen-limited condition. A strategy was established to maintain a constant dissolved oxygen(DO) level by real-time control of the air ventilation volume. The DO levels kept stable at 5%, 25%,50% and 75%,respectively,during curdlan-producing period. Afterwards,the effects of DO level on the fermentation of A. sp. ATCC 31749 and curdlan rheological properties were investigated. The results indicated that curdlan productivity decreased remarkably at DO 5%, whereas the curdlan specific production rate kept constant when DO level was more than 25%. Furthermore,the pseudoplastic fluid pattern was observed in curdlan-alkali solution. The viscosity of curdlan solution increased rapidly along with the fermentation time,and the non-Newtonian fluid behavior turned more obvious. At the same fermentation time,the curdlan solution reached the highest viscosity at DO 25%,while the viscosity decreased both at DO 5% and 75%. It was concluded that curdlan products with different rheological properties can be prepared by controlling of the dissolved oxygen level.
