The effect of ethanol on the plasma membrane permeability of spoilage yeasts

The effect of ethanol on the passive proton influx and on leakage of compou nds absorbing at 260 nm, as representatives of intracellular content, was s tudied on food spoilage yeasts such as Saccharomyces cerevisiae, Zygosaccha romyces bailii, Pichia sp. and Debaryomyces hansenii. For volume fraction b elow 10 %, the effect of ethanol on the proton influx was in general weak, but above a certain treshold of ethanol high values were observed. In Z. ba ilii ethanol had no effect up to 20 % (volume fraction). Previous growth of the cells in the presence of benzoic acid or ethanol did not affect the in flux of protons in the presence of ethanol. Leakage of compounds absorbing at 260 nm was not observed at 25 degrees C and occurred at 30 degrees C onl y after a rather long incubation in high concentrations of ethanol, which i nduced cell death. This suggests that in the yeasts this process does not c ontrol the leakage of compounds in the presence of ethanol.