Batch xylitol production by Candida guilliermondii FTI 20037 from sugarcane bagasse hemicellulosic hydrolyzate at controlled pH values

Batch fermentation of sugarcane bagasse hemicellulosic hydrolyzate by the yeast Candida guilliermondii FTI 20037 was performed using controlled pH values (3.5, 5.5, 7.5). The maximum values of xylitol volumetric productivity (Q(p)=0.76 g/l h) and xylose volumetric consumption (Q(s)=1.19 g/l h) were attained at pH 5.5. At pH 3.5 and 7.5 the Q(p) value decreased by 66 and 72%, respectively. Independently of the pH value, Y-x/s decreased with the increase in Y-p/s suggesting that the xylitol bioconversion improves when the cellular growth is limited. At the highest pH value (7.5), the maximum specific xylitol production value was the lowest (q(pmax)=0.085 g/l h.), indicating that the xylose metabolism of the yeast was diverted from xylitol formation to cell growth.