| Popis: |
Co-cultures for simultaneous production of ethanol and xylitol were studied under different operation bioreactor modes using Candida tropicalis IEC5-ITV and Saccharomyces cerevisiae ITV01-RD in a simulated medium of sugarcane bagasse hydrolyzates. Xylitol and ethanol tolerance by S. cerevisiae and C. tropicalis, respectively, was evaluated. The results showed that C. tropicalis was sensitive to ethanol concentrations up to 30 g/L, while xylitol had no effect on S. cerevisiae viability and metabolism. The best condition found for simultaneous culture was S. cerevisiae co-culture and C. tropicalis sequential cultivation at 24 h. Under these conditions, productivity and yield for ethanol were QEtOH = 0.72 g L−1 h−1 and YEtOH/s = 0.37 g/g, and for xylitol, QXylOH = 0.10 g L−1 h−1 and YXylOH/S = 0.31 g/g, respectively; using fed-batch culture, the results were QEtOH = 0.87 g L−1 h−1 and YEtOH/s = 0.44 g L−1 h−1, and QEtOH = 0.27 g L−1 h−1 and YEtOH/s = 0.57 g/g, respectively. Maximum volumetric productivity in continuous multistep cultures of ethanol and xylitol was at dilution rates of 0.131 and 0.074 h−1, respectively. Continuous multistep production, QEtOH increased up to 50% more than in fed-batch culture, even though xylitol yield remained unchanged. |
