Fermentation of sugar cane bagasse hemicellulosic hydrolysate for xylitol production: Effect of pH

Candida guilliermondii FTI 20037 was grown in sugar cane bagasse hydrolysate supplemented with (NH4)2SO4 2.0 g l−1, CaCl2 0.1 g l−1 and rice bran 20.0 g l−1, through 45-h batch tests (agitation of 200 min−1 and temperature of 30°C) with initial pH varying from 2.5 to 7.5. Under pH < 4.5 the consumption of glucose, xylose and arabinose as well as the production of xylitol and cells were inhibited. Nevertheless, at pH values ≥ 5.5 the yeast produced xylitol with a yield of 0.75 g g−1 and productivity of 0.57 g l−1 h−1. Moreover, the yeast was also capable of metabolizing the acetic acid, which is always present in media made from hydrolysates of plant material. The inhibition of xylose/xylitol bioconversion could be related to the effects of low pH and undissociated acetic acid concentration over 5.0 g l−1.