-Xylitol has sweetening, anticariogenic and clinical properties that have attracted the attention of the food and pharmaceutical industries. The conversion of sugars from lignocellulosic biomass into xylitol by D-xylose-fermenting yeast represents an alternative to the chemical process for producing this polyol. A good source of D-xylose is sugarcane bagasse, which can be hydrolyzed with dilute acid. However, acetic acid, which is toxic to the yeast, also appears in the hydrolysate, inhibiting microbe metabolism. Xylitol production depends on the initial D-xylose concentration, which can be increased by concentrating the hydrolysate by vacuum evaporation. However, with this procedure the amount of acetic acid is also increased, aggravating the problem of cell inhibition. Hydrolysate treatment with powdered activated charcoal is used to remove or decrease the concentration of this inhibitor, improving xylitol productivity as a consequence. Our work was an attempt to improve the fermentation of Candida guilliermondii yeast in sugarcane bagasse hydrolysate by treating the medium with seven types of commercial powdered activated charcoals (Synth, Carbon Delta A, Carbon Delta G, Carbon 117, Carbon 118L, Carbon 147 and Carvorite), each with its own unique physicochemical properties. Various adsorption conditions were established for the variables temperature, contact time, shaking, pH and charcoal concentration. The experiments were based on multivariate statistical concepts, with the application of fractional factorial design techniques to identify the variables that are important in the process. Subsequently, the levels of these variables were quantified by overlaying the level curves, which permitted the establishment of the best adsorption conditions for attaining high levels of xylitol volumetric productivity and D-xylose-to-xylitol conversion. This procedure consisted in increasing the original pH of the hydrolysate to 7.0 with CaO and reducing it to 5.5 with H 3 PO 4 . Next, the hydrolysate was treated under adsorption conditions employing CDA powdered activated charcoal (1%) for 30 min at 60ºC, 100 rpm and pH 2.5. The optimized xylitol volumetric productivity (0.50 g/L h) corresponded to a D-xyloseto-xylitol conversion of 0.66 g/g.

A continuous system of combined columns of ion exchange resins and activated charcoal was proposed as a new approach for the removal of toxics from sugar cane bagasse hemicellulosic hydrolysate. A factorial design was carried out to evaluate the influence of temperature and feed flow rate in the performance of the detoxification procedure. By using a temperature of 30 °C and a flow rate of 2.5 VB/h, the total removal of furfural and 5-(hydroxymethyl) furfural was observed, as well as a large reduction in the color and concentration of phenolic compounds. Removal of metals was also observed, with 50, 63, and 23% reduction in the concentration of copper, chromium, and nickel, respectively. The product of the detoxification process was a hydrolysate with a reduced concentration of inhibitors that can be used as a raw material for a number of processes to obtain products of economic and social interest.