The inhibitory effect of 1, 3-butanediol and 1, 2-pentanediol against the growth activity of six microbial species in liquid media was quantitatively studied by using a 24-unit isothermal calorimeter. The addition of increasing amounts of any of the two alcohols into the growth medium produced distinct changes in the heat evolution curves observed with the calorimeter. These changes were analyzed by means of two parameters derived from the calorimetric curves: the value of the growth rate constant m and the retardation time
tα (the time required for the cultures to reach a certain level of heat production). Analysis of the observed values of the growth rate constant μ led to the determination of the concentration of alcohol which inhibits the growth of the microbes by 50% (
Kμ), as well as the concentration which completely prevents the growth (MIC
μ). Two parameters with similar meanings (
Kθ and MIC
θ) were derived by analyzing the values of the retardation time
tα. It was concluded that the two alcohols, although used in cosmetics mainly for their properties as solvents, exert a significant antimicrobial activity. Also, 1, 2-pentanediol was more inhibitory (values of MICm between 1.72 and 3.81% w/v) than 1, 3-butanediol (MIC
μ between 4.34 and 13.04% w/v, depending on the microbial species).
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