Enhanced Production of Curdlan by Alcaligenes faecalis by Selective Feeding with Ammonia Water during the Cell Growth Phase of Fermentation

A strategy of increasing nitrogen source to improve biomass production was adopted for curdlan production by Alcaligenes faecalis (ATCC 31749). In the batch fermentation of curdlan, a relatively higher NH4Cl level of 3.6 g/L, with continuous glucose feeding, increased the cell density, and curdlan production was improved. In addition, the feeding of ammonia water at an initial phase replaced NaOH solution to control pH at 7.0 and then NaOH solution was resumed to control pH at 5.6 for curdlan production after ammonium was consumed. As a result, biomass production and curdlan yield were both enhanced remarkably. However, excessive ammonium and high cell density also led to the decline of curdlan production and gel strength of the resulting product.