Development of a “Stress Model” Fermentation System for Fuel Ethanol Yeast Strains

Abstract

During industrial scale fuel ethanol fermentations, yeast encounters a multitude of stress factors that impose constraints on growth and fermentative metabolism. These stresses include high sugar concentration, elevated temperature, high ethanol concentrations, low external pH and the weak organic acids lactic and acetic. Yeast strains which are tolerant to these stresses and able to synthesize high ethanol concentrations in their presence would be most desirable for use in industrial scale fuel ethanol production. In this study, a “stress model” fermentation system was developed as a tool to screen candidate yeast strains for relative stress resistance. The stress model was designed on the basis that the degree of ethanol produced by a particular strain would be indicative of the stress resistance of that particular strain. Eight strains of Saccharomyces cerevisiae, each with different backgrounds and fermentative capabilities, were screened for relative stress resistance using the stress model. The results obtained indicate that the sum of the stress factors in the stress model exceeded the tolerance level of most of the strains screened (approximately 40%). Two strains in particular, J006 and A007, displayed superior fermentative performance and produced significantly (P > 0.01) higher final ethanol concentrations when compared to the other strains.