Bioprocessing of bagasse hydrolysate for ethanol and xylitol production using thermotolerant yeast.

Fermentation of xylose-rich and glucose-rich bagasse hydrolysates, obtained from the two-stage acid hydrolysis was studied using the thermotolerant yeast Kluyveromyces sp. IIPE453. The yeast could grow on xylose-rich hydrolysate at 50 °C with the dry cell weight, cell mass yield and maximum specific growth rate of 5.35 g l(-1), 0.58 g g(-1) and 0.13 h(-1), respectively. The yeast was found to be very promising for ethanol as well as xylitol production from the sugars obtained from the lignocellulosic biomass. Batch fermentations of xylose-rich and glucose-rich hydrolysates yielded 0.61 g g(-1) xylitol and 0.43 g g(-1) ethanol in the broth, respectively based on the sugars present in the hydrolysate. Overall ethanol yield of 165 g (210 ml) and 183 g xylitol per kg of bagasse was obtained, when bagasse hydrolysate was used as a substrate. Utilization of both the glucose and xylose sugars makes the process most economical by producing both ethanol and xylitol based on biorefinery concept. On validating the experimental data of ethanol fermentation, the modified Luong kinetic model for product inhibition as well as inhibition due to inhibitory compounds present in hydrolysate, the model was found to be the best fit for ethanol formation from bagasse hydrolysate using Kluyveromyces sp. IIPE453.