PROCEDURE PROPOSED FOR ETHANOL PRODUCTION IN A SYNTHETIC MEDIUM IN A SUCESSION OF FERMENTATION CYCLES WITH CELL REUSE

Meline Rezende Morais (IQ-UNESP); Karen Fernanda de Oliveira (IQ-UNESP); Reinaldo Marchetto (IQ-UNESP); Cecília Laluce (IQ-UNESP)

In the Brazilian distilleries, rapid fermentations are successfully carried out due to the use of high cell densities while the cell reuse is one important factor that contributes to reduce the costs of ethanol production processes. In the ethanol production process, part of the sugar has to be used for cell propagation in order to guarantee the formation of young and robust cells in each fermentation cycle. Although synthetic media are not used at industrial scale for ethanol production, this type of medium exhibits favorable characteristics over the traditional complex or natural media, since it is composed of pure chemicals in precisely known proportions. A procedure for carrying out a succession of fermentation cycles with cell reuse at high cell densities using a synthetic medium was established in the present  work. The yeast propagation was initially carried out in an agitated batch culture at 30¡ãC while the fermentations were carried out in mini-reactors fed by pulses of concentrated sucrose solutions added to the synthetic medium, which was maintained at 34¡ãC or 37¡ãC during the fermentation. Yeast strains constructed in our laboratory and commercial yeast were used and compared in the present work. This work also shows that it is possible to carry out a succession of fermentation cycles in a defined medium at high cell densities by reducing the amount of sugar added to the reactors (¡Ü20 %, ART) and by applying a revitalization treatment to the yeast cream before its reuse from one fermentation cycle to the next. Viability was restored and increases in biomass were obtained during the revitalization treatment. The synthetic medium is nutritionally poor to maintain a high viability and cell growth during ethanol production at high cell densities. Losses in viability and biomass are usually observed during a succession of fermentation cycles due to the intracellular accumulation of ethanol and toxic by-products.