Fermentation of xylitol using immobilized Candida sp.ZU04 cells in three-phase fluidized-bed bioreactor

In order to develop an efficient continuous process for producing xylitol at high yield, batch xylitol production on corn cob hemicellulosic hydrolysates carried out in a three-phase fluidized-bed bioreactor using immobilized Candida sp.ZU04 cells was investigated. It was found that two phase aeration process was more effective than one-phase aeration process in xylitol production. In the first 24 h of aerobic phase, glucose was soon consumed and biomass in the Ca alginate beads increased quickly at high aeration rate of 1.00 wm. In the second fermentation phase, aeration rate was reduced to 0.30 wm and the xylitol yield increased remarkably. The immobilized cells could be reused successfully before 6 batch cycles with average xylitol yield of 0.73 g g-1 and average volumetric productivity of 0.84 g 1-lh-1 in the bioreactor for 501 h.