Quantitative study of yeast growth in the presence of added ethanol and methanol using a calorimetric approach

Using a calorimeter with 24 sample units the heat evolved during incubation of yeast cultures at 30 degrees C was detected in the form of growth thermograms. Ethanol and methanol added to the culture medium produced changes in the growth thermograms that could be analyzed to calculate the 50% inhibitory concentration (K-i) and minimum inhibitory concentration (MIC). Correlation of the heat evolution curves with the number of cells and the turbidity of the culture was found to be very good. It was found that addition of ethanol and methanol up to 7.65% had clear effects of inhibition on growth of all yeast strains studied, reducing the growth rate constant and delaying growth. However, the amounts of ethanol produced from the nutrients available in the culture vial was only little affected by the initial addition of up to 7.65% (v/v) of ethanol or methanol in the medium.