Resumo

Despite the high ethanol yield productivities by the Brazilian fuel ethanol production process, wine with low ethanol concentration is obtained, inducing the generation of a large volume of residual vinasse (∼12L/L of ethanol), which demand increasing costs in energy consumption in distillation, beside environmental problems. In this study fermentations of sucrose, main carbohydrate in brazilian ethanol fuel must, were conducted at 30 and 35°C, under agitation, in very high gravity process by industrial yeasts strains. Brazilian Saccharomyces cerevisiae ethanol producing strains were used to ferment sucrose concentrations varying from 22 to 35% (w/v), in based sugar cane industrial must with or without nutritional supplementation. Fermentation performance was followed by biomass accumulation (turbidimetry and dry weigth), ethanol production (gas chromatography), sugar consumption (DNS method) and trehalose production. For the consecutive batch fermentation process, yeast cells were separated from fermentation broth and re-used repeatedly. Despite decreased fermentation performance, with cell reutilization, for all strains in very high gravity conditions, with high cell density, were observed efficient fermentation performance, obtaining wines with 16 to 17% (v/v) (sucrose 30% (p/v)) and 20 to 21% (v/v) (sucrose 35% (p/v)) ethanol. Higher levels of trehalose accumulation was observed in the fermentation conditions, when compared with cells in the stationary phase used as inoculum, suggesting industrial strains with the ability to adapt to stress conditions induced by ethanol. Nitrogen supplementation induced improved fermentation performance. The results shown in this work have industrial relevance since indicate that efficient sugar conversion, with high levels of ethanol production can be obtained from very high gravity sucrose fermentation, depending on finding of ideal fermentation conditions such as fermentation time, cell recycling and appropriate nutritional strains status. CAPES