A Calorimetric Method Applied to the Study of Yeast Growth Inhibition by Alcohols and Organic Acids

Abstract

Using a conduction-type isothermal batch calorimeter with 24 units, the heat evolved during growth of four yeast strains from different species in the presence of various concentrations of normal alcohols (C1-C4) and saturated organic acids (C2, C4, C6, C8, C10) was recorded as growth thermograms. Changes in the growth thermograms were observed when the inhibitor concentration increased, and they were correlated to the determined values of the growth rate constant. Subsequent analysis allowed precise determination of the 50% inhibitory concentration (K_i) and the 100% inhibitory concentration (MIC) for the growth of the yeast strains in the presence of the studied alcohols and acids. The combined inhibitory action of ethanol and some acids was also investigated, and it was found that ethanol presence leads to a decrease in the K_i and MIC values of the acids, suggesting an additive or synergistic activity mechanism. The advantages of the method, as well as influencing factors are also discussed.