ETHANOL-PRODUCTION FROM GLUCOSE AND XYLOSE BY SEPARATED AND COCULTURE PROCESSES USING HIGH CELL-DENSITY SYSTEMS

Media containing xylose and/or glucose were tested utilizing Zymomonas mobilis or Saccharomyces diastaticus and Pichia stipitis. The best fermentation results were obtained in separated glucose (180 g/litre) and xylose (80 g/litre) fermentations utilizing Zymomonas mobilis and Pichia stipitis strains, respectively. In these conditions, the maximum ethanol concentrations achieved were 86.2 g/litre and 29 g/litre, respectively. The complete conversion of a glucose and xylose mixture (50 g/litre) was obtained using a respiratory deficient mutant of Saccharomyces diastaticus co-cultivated with Pichia stipitis in continuous culture. Using the co-culture process, the maximum ethanol concentration was 21.5 g/litre (Yp/s = 0.45 g/g) and the maximum volumetric ethanol productivity was 4.3 g/(litre x h).