Xylitol production from sugarcane bagasse hydrolysate

Sugarcane bagasse hydrolysate was used for batch xylitol production in stirred tank reactor with Candida guilliermondii cells entrapped in Ca-alginate beads. Experiments were carried out using five-fold concentrated hydrolysate, agitation speed of 300 rpm, air flowrate of 1.3 l min−1, initial cell concentration of 1.4 gDM l−1, and starting pH 6.0. Xylitol production reached 47.5 g l−1 within 120 h of fermentation, resulting in a bioconversion yield of 0.81 g g−1 and a productivity of 0.40 g l−1 h−1. The metabolic behaviour of C. guilliermondii was then investigated through material balances using the concentrations of consumed substrates and formed products and assuming that xylose was simultaneously assimilated by the yeast for anaerobic and semi-aerobic xylitol productions, complete oxidation by the TCA cycle and cell growth. Data collected at different times were finally used to estimate the overall ATP requirements for biomass growth and maintenance. The energy expenditure increased from 2.1 to 6.6molATPCmolDM−1 throughout the fermentation, highlighting a progressive difficulty of the microbial system in facing the energy needs of its semi-aerobic metabolism.