Assessment of the viability of Saccharomyces cerevisiae in response to synergetic inhibition during bioethanol production

Second-generation biofuels, fuels produced from lignocellulosic materials, including wood, agricultural residues and biomass waste include bioethanol, bio-diesel and biogas. These fuel sources have great potential as useful substitutes to conventional fossil fuels. Biomass sources are also non-toxic and biodegradable energy sources that can be produced from a wide range of organic materials resulting in economic and renewable energy source. Pretreatment of lingo-cellulosic biomass is required to reduce physicochemical restrictions that hinder the accessibility of sugars necessary for hydrolysis and fermentation. Various pretreatment processes exist, but all of them produce inhibitory compounds that ultimately reduce ethanol production and cell viability of the fermenting microorganism, Saccharomyces cerevisiae. In this study different combinations of inhibitors (acetic acid, formic acid and vanillin) were considered to mimic realistic fermentation conditions during bioethanol production; ethanol yield and cell viability were then concurrently measured over a period of 48 h. The combination of acetic acid and formic acid exhibited ethanol reduction up to 11 +/- 3.74%, while cell viability decreased by 23 +/- 6.61%. Acetic acid and vanillin reduced ethanol production by 25 +/- 1.77% and cell viability by 4 +/- 4.38%. Formic acid and vanillin inhibited ethanol production by 31 +/- 3.14% and cell viability 16 +/- 7.54%. Finally, the synergistic effect of all three inhibitors reduced the final ethanol production by 58 +/- 5.09% and cell viability by 27 +/- 5.44%, indicating the toxic effect of the synergistic combination.