PHYSIOLOGICAL EFFECTS OF INHIBITORS FROM THE SECOND GENERATION ETHANOL IN DIFFERENT STRAINS OF SACCHAROMYCES CEREVISIAE

In fuel ethanol production, yeast strains encounter a variety of stressful conditions, which includes high ethanol and salt titers, and high temperatures. Additional obstacles arise in the production of second-generation ethanol, in which lignocellulosic sugars will be the substrate for fermentation. The pre-treatment step generates different yeast growth inhibitors which reduce the efficiency of fermentation. In this work, we identified differences in physiological parameters in the presence of three inhibitors (glycolic acid, levulinic acid, and furfural) of four strains of the yeast Saccharomyces cerevisiae: CEN.PK113-7D , SA-1, PE-2, and NS. Maximum specific growth rate was evaluated in three different concentrations for each inhibitor. The presence of furfural inhibited growth in concentrations higher than 30 mM, and at this concentration, NS strain had the best performance presenting only 12% reduction while the other strains average were 30%. PE-2 strain had the best performance in the presence of aliphatic acids (glycolic and levulinc acids) at a concentration of 150 mM, displaying a areduction of only 12%. Conversion to biomass was assessed in shake flasks in the presence of aliphatic acids and decreased in bothCPK and PE-2 strains. Detoxification effects were observed in the presence of the inhibitor furfural, which concentration decreased linearly.