A CALORIMETRIC METHOD APPLIED TO THE STUDY OF YEAST GROWTH-INHIBITIONBY ALCOHOLS AND ORGANIC-ACIDS

Using a conduction-type isothermal batch calorimeter with 24 units, th e heat evolved during growth of four yeast strains from different spec ies in the presence of various concentrations of normal alcohols (C1-C 4) and saturated organic acids (C2, C4, C6, C8, C10) was recorded as g rowth thermograms. Changes in the growth thermograms were observed whe n the inhibitor concentration increased, and they were correlated to t he 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 ye ast strains in the presence of the studied alcohols and acids. The com bined inhibitory action of ethanol and some acids was also investigate d, 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 influenci ng factors are also discussed.