PURIFICATION OF BIO-XYLITOL PRODUCED BY Candida tropicalis FERMENTATION USING NANOFILTRATION

The world’s production of lignocellulosic biomasses reaches 181.5 billion tons annually. This biomass can be converted into valuable products as xylitol, a naturally occurring polyol. It has one third less calories than sucrose and is used as a sucrose substitute for diabetics patients and it has anticariogenic properties. For this biotechnological process to become technically viable, the purification steps remain as an obstacle. In this context, nanofiltration should be considered as an option since it has the capability of separating low molar mass molecules. This study aimed at producting xylitol from sugarcane bagasse and developing a strategy for xylitol purification by nanofiltration. For xylitol production, sugarcane bagasse was pre-treated, concentrated and detoxified. The fermentation was carried out in a rotary incubator, and xylitol conversion efficiencies of 63.0% and 60.4% were obtained for the fermentation in synthetic and hydrolyzed broth, respectively. The nanofiltration was carried out in a stirred dead-end cell. NF membrane was selected and was used to optimize the factors pH, temperature and pressure by response surface methodology. Optimum nanofiltration conditions were 40 bar, 40 °C, and pH 5.4. These conditions were used for the fermented hydrolysate nanofiltration. The xylitol purification was reached in the permeate fraction, with a xylitol-protein separation factor and purification factor of 8.4 and 3.3, respectively. Protein and color removal were 84.0% and 96.0% by the selected strategy. It facilitates the formation of homogeneous crystals in the next downstream steps. An integrated strategy of purification should be implemented in order to attain a high purity in xylitol. Certainly, nanofiltration can be used prior to crystallization as an alternative process to purify xylitol obtained by fermentation of sugarcane bagasse hemicellulose hydrolysate.