Calorimetric determination of the inhibitory effect of C1-C4 n-alcohols on growth of some yeast species

The inhibitory action of methanol, ethanol, 1-propanol and 1-butanol on growth of nine yeast strains was quantitatively assayed using a calorimetric technique. Yeast cultures in the presence of alcohol at Various concentrations were incubated in a multiplex batch isothermal calorimeter, which allowed the recording of the heat evolved during microbial growth. Changes were visible in the pattern of the thermal profiles recorded when the alcohol concentration in the growth medium increased: the initial slope of the thermal profiles decreased significantly, and the peak time was retarded. By analyzing both these modifications, quantitative parameters could be obtained to characterize the inhibitory action of alcohols. The parameters determined were: K-mu, K-theta (the alcohol concentrations that inhibited 50% of the growth activity) and MICmu, MICtheta (minimum inhibitory concentrations), where the subscript 'mu' stands for determination based on the changes observed in the growth rate constant and the subscript 'theta' stands for determination based on the retardation of growth. Results showed that the alcohol tolerance of the yeasts decreases significantly with the increase in the number of carbon atoms in the alcohol molecule, although the linear relationship reported in other studies between the alcohol tolerance of yeasts and the number of carbon atoms in the alcohol molecule could not be confirmed for all species. (C) 1997 Elsevier Science B.V.