Morphological, physiological and genetic characterization of contaminant yeasts from the alcoholic fermentation and evaluation of their competitive potentiality based on the resistance to stress during fermentation

Abstract

The main concern in the sugar/alcohol industry lays on the contaminant microorganisms, bacteria and yeasts that come from the sugar cane juice. These yeasts are called wild yeasts and the main genera found in healthy sugar cane are Saccharomyces, Torula and Pichia. Saccharomyces cerevisiae that present pseudohyphae (buds that not separate from the mother cell) are very frequent into the fermentation tanks, and may cause troubles for the process with decrease in the fermentation yield. A little is known about the genetic, morphological and physiological characteristics as well as the resistance to stress showed by this yeast biotype. Besides, more recently, the presence of the genera Dekkera and Brettanomyces have been also related to troubles in the fermentation process for ethanol production. In this respect, this work aims the characterization of Saccharomyces cerevisiae yeasts that show cell clusters (pseudohyphae) and wrinkled colonies and the evaluation of their competitivity when comparing to the yeast strains that show mucous colonies, with dispersed cells. Regarding the yeast D. bruxellensis, it is aimed to study the stress tolerance to ethanol, sugar, pH and temperature, detecting conditions in which the growth of these yeasts is minimal, for an easier management of these contaminants in the process. To verify the competitive performance of S. cerevisiae strains with wrinkled biotype may help the understanding and management of the fermentation process to minimize the prospective harmful effects. (AU)