Resumo

The species Dekkera bruxellensis is a multifaceted yeast because it has been regarded as spoiling yeast of wine production, fermenting yeasts in both first and second-generation ethanol fermentation and as contaminant yeasts in sugar cane juice-based fermentations for fuel production. In Brazil the peculiarity of re-pitching the yeast into the tanks during a 250- day season should be examined in view of the yeast growth and alcohol production in such conditions. This work evaluated the performance of D. bruxellensis (CCA059, isolated from a alcohol-producing unit) in batch system with and without cell recycle using sugar cane juice (140 g/L of total reducing sugars - TRS). Analysis of TRS, ethanol, number of cells and parameters like yield and productivity were determined in both experiments either for D. bruxellensis or Saccharomyces cerevisiae (PE-02). In batch system without cell recycle, the former consumed approximately 40% of TRS in 72 hours producing 20 g/L ethanol. The cell number increased six times during this period of fermentation. By the other hand, S. cerevisiae exhausted the TRS within 32 hours producing 50 g/L ethanol. The cell number increased three times along the course of the fermentation. The yields (g alcohol/g TRS) did not differ significantly between the strains but the productivity (g alcohol/L.h) was fourfold higher with S. cerevisiae. In batch system with 14 12-hour fermentative cycles, D. bruxellensis consumed 80% of TRS but only from the 11th cycle, producing 25 g/L ethanol. The yeast number increased 6 log cycles along 14 fermentative cycles. For S. cerevisiae, TRS were near zero by the 5th cycle, 50 g/L ethanol produced and cell number increased by 3-4 log cycles along the fermentations. The yield and productivity for D. bruxellensis were the half the ones of S. cerevisiae. In brief, in Brazilian conditions of alcoholic fermentations, in which the yeast cells are recycled along the sugar cane season, D. bruxellensis is considered a contaminant yeast because it shows expressive growth in fermentation conditions, with low alcohol productivity. Even though the yield may be comparable to the S. cerevisiae strain, a parameter considered by many authors as an attribute of this yeast for the alcoholic fermentation, productivity would be the best one to evaluate the performance of D. bruxellensis in batch process. Support: Fapesp (2009/14617-4 and 2011/17928-0).