Robust Yeasts for the Conversion of Steam-Exploded Sugarcane Bagasse into Ethanol

Processing lignocellulose into ethanol results in the release of inhibitory compounds affecting the following fermentation phase. Ethanol production from lignocellulosic hydrolysates has been widely reported in literature, but only limited research focused on selecting yeasts able to both tolerate inhibitors and ferment sugars with high yield.One hundred and twenty yeast strains, mainly newly isolates belonging to Saccharomyces cerevisiae, were screened for their fermentative abilities in minimal media supplemented with high glucose and/or xylose concentrations. The yeasts were then evaluated for inhibitor tolerance in the presence of increasing concentrations of weak acids and furans. A number of S. cerevisiae strains showed ethanol yields from glucose much higher than those exhibited by benchmark yeasts previously utilised for bioethanol production. Few yeasts were able to grow well once exposed to high inhibitors levels. The newly isolated S. cerevisiae F17 and S. cerevisiae MEL2 were further studied for their fermentative abilities in a defined medium supplemented with increasing concentrations of inhibitors, as well as, in steam-exploded sugarcane bagasse. Although the sugarcane pre-hydrolysate was rich in inhibitors, S. cerevisiae F17 and MEL2 confirmed their high ethanol yields proving their great potential to be used as industrial strains for the conversion of lignocellulosic hydrolysates into ethanol.