Ethanol production from high-glucose industrial substrates using ethanol-tolerant Saccharomyces cerevisiae strains

Ethanol is well known as a toxic metabolite for yeast cells. Thus, strains that can grow well under high ethanol stress condition are highly desirable. This work aims to select and characterize Saccharomyces cerevisiae strains with improved ethanol tolerance. Moreover, it aims to evaluate the feasibility of industrial residues as fermentation media and to optimize the composition of such media. The ethanol production and tolerance of the yeast strains have been evaluated, carrying out batch alcoholic fermentations with high-glucose YP medium. The most ethanol-tolerant strain was able to ferment 300 g/L glucose producing up to 17.4 % (v/v) of ethanol in trials carried out in anaerobic shake-flasks. Aiming to develop a fermentation medium based in industrial substrates, corn steep liquor (CSL) has been tested as medium supplement, in order to replace nutrients that are needed to allow both cellular growth and fermentation. Supplementation of 300 g/L glucose medium with CSL concentrations around 90- 110 g/L has resulted in fermentation performance similar to that observed in YP medium with the same glucose concentration, thus confirming the feasibility of CSL as peptone and yeast extract substitute.