Alcohol tolerance in yeast : on factors influencing the inhibitory and toxic effects of alcohols on distilling yeast
An investigation of the factors influencing the inhibitory and toxic effects of ethanol and higher alcohols, byproducts of alcoholic fermentation, on yeast, is presented. The relative potency of alcohols was found to correlate strongly with the carbon chain-length or molecular size and the lipid solubility of the respective alcohols. Higher alcohols act synergistically with each other and with ethanol in causing cell death of suspensions of non-growing Saccharomyces cerevisiae. The presence of higher alcohols in fermented broth, even at low concentrations, and other by-products of alcoholic fermentation, could explain the higher potency of ethanol produced during fermentation compared to added ethanol. The kinetics of uptake of labelled ethanol supplied at different concentrations gave no evidence of enzymic involvement in the ethanol uptake process. The rate of release of labelled ethanol by cells fed labelled glucose paralled the rate of p14sC-C0b2s release. This does not support the view that ethanol accumulates within the cells to higher concentrations than occur in the medium. Supplementation of a basal synthetic medium with various nutrients did not confer additional survival capacity on yeast against the adverse effects of alcohol. Osmotic pressure did not influence alcohol toxicity below 10% (w/v) sorbitol equivalent of osmotic pressure. Alcohol toxicity is not influenced by hydrogen ion concentration (pH) over a range of pH 5.3 to 3.5.