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 o n growth of nine yeast strains was quantitatively assayed using a calo rimetric technique. Yeast cultures in the presence of alcohol at Vario us concentrations were incubated in a multiplex batch isothermal calor imeter, which allowed the recording of the heat evolved during microbi al growth. Changes were visible in the pattern of the thermal profiles recorded when the alcohol concentration in the growth medium increase d: 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 inhibit ory 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 su bscript 'mu' stands for determination based on the changes observed in the growth rate constant and the subscript 'theta' stands for determi nation based on the retardation of growth. Results showed that the alc ohol tolerance of the yeasts decreases significantly with the increase in the number of carbon atoms in the alcohol molecule, although the l inear relationship reported in other studies between the alcohol toler ance 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.