Tuesday, April 30, 2013
Exhibit Hall
Saccharomyces cerevisae is the most commonly used microorganism for production of ethanol in industry. The use of GMOs in biorefineries, on the other hand, has important constraints imposed by the regulatory legislation in countries like Brazil. However, natural S. cerevisae is able to metabolize xilulose. This was the basis of a technology, put forth in the early 80’s, to produce bioethanol from the C5-fraction of lignocellulosic biomass: the Simultaneous Isomerization and Fermentation (SIF) of xylose. This work revisits this technology, presenting results of SIFs for six different yeast strains: BG-1, CAT-1, PE-2, CEN.PK117-7D, Fleishmanm® and Itaiquara® (the last two are commercial baker yeast brands). Glucose isomerase (GI) from Genencor® was immobilized on chytosan and wrapped with alginate, together with the yeast cells. The resulting gel pellets were used in batch SIFs, spanning the following conditions: initial xylose concentration 65-120 g.L-1, 35-40oC, microaeration versus “semi-anaerobiosis”. The variables used to assess the performance of the systems were xylose conversion, ethanol productivity, selectivity with respect to other byproducts (the main one was xylitol) and cell viability at the end of the run. Itaiquara® strain, followed by BG-1, had the best scores.