产胶期溶氧水平对土壤杆菌ATCC 31749发酵产热凝胶流变性质的影响

Effect of Dissolved Oxygen Level on the Rheological Properties of Curdlan Fermented by Agrobacterium sp. ATCC 31749

摘要:

热凝胶是由土壤杆菌在氮源限制条件下生产的水不溶性胞外多糖。通过在线实时调节通气量建立了恒定溶氧控制策略,并将产胶期溶氧分别恒定控制在饱和溶氧浓度DO 5%、25%、50%和75%水平。然后,考察了产胶期溶氧浓度对土壤杆菌(Agrobacterium.sp.ATCC 31749)发酵过程及热凝胶流变性质的影响。结果表明,低溶氧(DO 5%)造成热凝胶生产强度显著下降,而溶氧水平高于DO 25%后,热凝胶比生成速率基本恒定。同时,热凝胶-碱溶液的流变行为符合假塑性流体特征,随着产胶期发酵时间增加,热凝胶溶液粘度迅速升高,且非牛顿流体特征逐渐显著。相同发酵时间时,适度溶氧(DO 25%)热凝胶溶液具有最大粘度,而溶氧限制(DO 5%)和高溶氧时(DO 75%)粘度均较低。控制发酵溶氧水平可以获得具有不同流变性质的热凝胶产品。

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.