Calorimetric Study of Yeast Growth and Its Inhibition by Added Ethanol at Various pHs and Temperatures

Abstract

Using a multiplex isothermal calorimeter with 24 sample units the heat evolved during incubation of yeast cultures on glucose-peptone broth was detected under the form of growth thermograms, based on which the values of the growth rate constant μ were calculated. The effect of the initial pH of the yeast cultures was investigated for single strains of four yeast species. Judging from the calculated values of μ, the yeasts studied presented stable growth for pH values ranging approximately from 4 to 8. From growth experiments performed at various temperatures, the effect of the incubation temperature could be observed in the growth thermograms recorded. Using Arrhenius-type plots of the growth rate versus temperature the apparent activation energy of growth was calculated for the four yeasts studied. Furthermore, when ethanol was added in various concentrations to the yeast cultures, changes occurred in the growth thermograms which could be analyzed for the determination of the 50% inhibitory concentration (K_μ) and the minimum inhibitory concentration (MIC_μ) of ethanol. The variation of parameters K_μ and MIC_μ with the initial pH and the incubation temperature is also reported for a strain of Saccharomyces cerevisiae.