Tuesday, April 30, 2013
Exhibit Hall
The biotechnological production of ethanol from lignocellulose hydrolyzate requires microorganisms that can ferment hexoses and pentoses, and provide sufficient tolerance to the inhibitors existing in this hydrolyzate. However, currently there are few microorganisms (Saccharomyces cerevisiae 424A (LNH-ST), Zymomonas mobilis AX101, Scheffersomyces stipitis (formerly Pichia stipitis) and Escherichia coli KO11 ATCC 55124) capable of fermenting pentoses (mainly xylose) to ethanol. These microorganisms have low ethanol yields when compared to microorganisms that ferment hexoses and sucrose. In this sense, an investigation is necessary to increase the ethanol yield. With regard to Bioprocess Engineering, oxygen transfer to culture broth can be cited as the most important operating condition for the alcoholic fermentation, as it determines the division of flow between carbon growth and product formation. Therefore, the oxygen transfer volumetric coefficient (kLa) was studied to access Scheffersomyces stipitis NRRL-Y-7124 kinetic parameters maximum specific growth rate (μmax), yield of xylose to ethanol (YP/S), yield of xylose in cells (YX/S), and ethanol volumetric productivity (QP) from xylose. Bioreactor experiments were performed in microaerophilic (kLa values of 4.9, 6.7 and 18.9 h-1) conditions. The results obtained with lower kLa value (4.9 h-1) showed the highest ethanol production, yield of xylose to ethanol (0.42 g g-1) and ethanol volumetric productivity (0.5 g L-1 h-1). Therefore, it is possible to conclude that S. stipitis has potential for ethanol second generation technology.