Sugarcane Syrup Improves Xylitol Bioproduction from Sugarcane Bagasse and Straw Hemicellulosic Hydrolysate

摘要

To evaluate the supplementation of the sugarcane bagasse and straw hemicellulosic hydrolysate with sugarcane syrup, which is a sucrose-rich co-product, for xylitol production by Candida guilliermondii FTI 20037. Recently, we demonstrated that sucrose supplementation to sugarcane straw hemicellulosic hydrolysate favoured this bioprocess. A mixture 1:1 of sugarcane bagasse and straw was submitted to dilute-acid hydrolysis with H_2SO_4 to obtain the hemicellulosic hydrolysate, which was concentrated, detoxified and autoclaved. Three sugarcane syrup concentrations (0.83, 2.50 and 3.33% v/v) were added to the hemicellulosic hydrolysate, which was also supplemented with rice bran extract, (NH_4)_2SO_4, CaCl_2·2H_2O. Next, a full factorial design was performed to assess the replacement of conventional nutrients by sugarcane syrup. Fermentations were performed in 125 mL Erlenmeyer flasks containing 50 mL of fermentation medium, for 48 h at 30 °C and 200 rpm. Improvements of 16.85% and 12.24% in xylose uptake rate (1.04 ± 0.01 g L~(-1) h~(-1)) and xylitol volumetric productivity (0.55 ± 0.02 g L~(-1) h~(-1)), respectively, were achieved with syrup supplementation (2.50% v/v), which led to a final xylitol titer of 26.19 ± 0.02 g L~(-1). Conventionally employed nutrients (rice bran extract, (NH_4)_2SO_4 and CaCl_2-2H_2O) did not have significant influence on xylitol production when sugarcane syrup was added to the fermentation medium. Sugarcane syrup as a nutritional supplement improved xylitol production from a mixture of bagasse and straw, becoming an alternative to reduce costs in the formulation of the fermentation medium and contributing to the integration of this bioprocess in a sugarcane biorefinery.