New sources and methods to isolate vinasse-tolerant wild yeasts efficient in ethanol production

Abstract

In most Colombian distilleries, fuel alcohol is produced by a continuous operation mode, recycling vinasse to dilute B molasses, which is the main byproduct of the sugar refining process and, more recently, the main feedstock for ethanol production. Commercial yeasts are used as catalysts during the fermentation stage; however, their yield is significantly affected by hyperosmolarity-induced stress and high organic acid concentration, both of which gradually reduce the performance of these microorganisms after a 3-month period of vinasse recycling. In this study, a methodology for isolating wild yeasts obtained from molasses storage tanks and sugarcane buds and leaves was standardized. These yeasts exhibited natural tolerance to vinasse and 85 % of the isolates were characterized as Saccharomyces cerevisiae by biochemical testing. Based on intraspecific characterization by interdelta markers 12–21 and subsequent confirmation by the AFLP method, isolates were classified into five groups of strains with genetic distances ranging between 15 and 30 %. A culture medium containing 50 % vinasse and around 16 % (w/v) reducing sugars was used to determine their fermentation capacity; ethanol yield (Yp/s) ranged from 5.69 to 6.82 % (w/v), volumetric productivity (Qp) from 2.37 to 2.84 g L−1 h−1, and efficiency was 71.22–85.09 % after 24 h.