Antifungal activity of alkanols: inhibition of growth of spoilage yeasts

Primary aliphatic alkanols from C-6 to C-13 were tested for their antifungal activity against Saccharomyces cerevisiae using a broth dilution method. Undecanol (C-11) was found to be the most potent fungicide against this yeast with the minimum fungicidal concentration (MFC) of 25 mu g/ml (0.14 mM), followed by decanol (C-10) with the minimum inhibitory concentration (MIC) of 50 mu g/ml (0.31 mM). The time-kill curve study showed that undecanol was fungicidal against S. cerevisiae at any growth stages. This fungicidal activity was not influenced by pH values. Dodecanol (C-12) was the most effective fungistatic but did not show any fungicidal activity up to 1600 mu g/mL. Fungistatic dodecanol quickly reduced cell viability, but the cell viability recovered shortly after and then finally became no longer different from the control indicating that the effect of dodecanol on S. cerevisiae was classified as a sublethal damage. However, fungistatic dodecanol combined with sublethal amount of anethole showed a fungicidal activity against this yeast. Anethole completely restricted the recovery of cell viability. Therefore expression of the synergistic effect was probably due to the blockade of the recovering process from dodecanol induced-stress. The alkanols tested inhibited glucose-induced acidification by inhibiting the plasma membrane H+-ATPase. Octanol (C-8) increased plasma membrane fluidity in the spheroplast cells of S. cerevisiae. The same series of aliphatic primary alkanols was also tested against a food spoilage fungus Zygosaccharomyces bailii and compared with their effects against S. cerevisiae. Decanol was found to be the most potent fungicide against Z. bailii with an MFC of 50 mu g/ml (0.31 mM), whereas undecanol was found to be the most potent fungistatic with an MIC of 25 mu g/ml (0.14 mM). The time-kill curve study showed that decanol was fungicidal against Z. bailii at any growth stage. This antifungal activity was slightly enhanced in combination with anethole. The primary antifungal action of medium-chain (C-9-C-12) alkanols comes from their ability as nonionic surfactants to disrupt the native membrane-associated function of the integral proteins. Hence, the antifungal activity of alkanols is mediated by biophysical process, and the maximum activity can be obtained when balance between hydrophilic and hydrophobic portions becomes the most appropriate.