pH-control modes in a 5-L stirred-tank bioreactor for cell biomass and exopolysaccharide production by Tremella fuciformis spore

The effect of pH-control modes on cell growth and exopolysaccharide production by Tremella fuciformis was evaluated in a 5-L bioreactor. The results show that the maximal dry cell weight (DCW) and exopolysaccharide production were 23.57 and 4.48 g L(-1) in pH-stat fermentation, where the maximal specific growth rate (mu(max)) and specific production rate of exopolysaccharide (P(P/X)) were 1.03 and 0.24 d(-1). respectively; under pH-shift cultivation, the maximal DCW and exopolysaccharide production were 30.57 and 3.90 g L(-1), where the mu(max) and P(P/X) were 1.21 and 0.06 d(-1). Unlike batch fermentation, maximal DCW and exopolysaccharide production merely reached 15.04 and 2.0 g L(-1), where the mu(max) and P(P/X) were 0.86 and 0.05 d(-1), respectively. These results suggest that a pH-stat strategy is a more efficient way of performing the fermentation process to increase exopolysaccharide production. Furthermore, this research has also proved that the three-stage pH-control mode is effective for cell growth. (C) 2011 Elsevier Ltd. All rights reserved.