Utilization of the hemicellulosic fraction of sugarcane straw for biotechnological production of xylitol

The sugarcane non-burning harvest is being introduced in Brazil to increase the crop sustainability; consequently, the sugarcane straw is becoming an available lignocellulosic biomass. Besides its agronomic benefits, it can be used as feedstock in thermochemical or biochemical conversion processes. This makes feasible its incorporation in a sugarcane biorefinery, whose economical profitability could be supported by integrated production of low value biofuels, e.g. ethanol, and high value chemicals, e.g. xylitol, which has important industrial applications. This work aims to present an alternative to use the hemicellulosic fraction of sugarcane straw through biotechnological production of xylitol. It was found that 27% (dry basis) of the biomass corresponded to hemicellulose, from which it was obtained a dilute-acid hydrolysate constituted by (gL^-1): xylose (18,6), glucose (3,7), arabinose (3,9), and toxic compounds as acetic acid (2,2) and phenolic compounds (4,1). The hydrolysate was concentrated (3X), and detoxified by pH adjustment and activated charcoal adsorption. Candida guilliermondii FTI 20037 was employed for batch fermentation (pH 5,5, 30^oC, 200rpm, 48h, 125mL Erlenmeyer flasks containing 25mL of medium) in different nutritional supplementation conditions. Interestingly, the yeast was able to grow and uptake glucose and partially xylose (28,9%) without any supplementation. In the hydrolysate supplemented with (NH₄)SO₂, the yeast consumed 60,6% of the xylose and produced xylitol (0,16g g^-1). The additional supplementation of rice bran extract led to an increase in xylose consumption (79,2%) and xylitol yield (0,47g g^-1). Furthermore, reduction of oxygen availability (medium volume 50mL) slightly improved the xylitol production (0,54 g g^-1).