EFFECT OF ETHANOL AND FATTY-ACIDS ON MALOLACTIC ACTIVITY OF LEUCONOSTOC-OENOS

Medium-chain fatty acids (C-6 to C-12), produced by yeast metabolism d uring alcoholic fermentation, are known to be inhibitory to lactic aci d bacteria. The purpose of this work was to clarify the effect of both ethanol and decanoic and dodecanoic acids on the growth and malolacti c activity of a Leuconostoc oenos strain isolated from Portuguese red wine. Ethanol in concentrations up to 12% had no significant effect on malolactic activity but strongly inhibited cell growth. The fatty aci ds decanoic acid, in concentrations up to 12.5 mgl(-1), and, dodecanoi c acid up to 2.5 mgl(-1) seemed to act as growth factors stimulating a lso malolactic activity; at higher concentrations they exerted an inhi bitory effect. We found clear pH dependence between pH 3.0 and pH 6.0, between decanoic acid concentration and its effect on malolactic acti vity, indicating that the undissociated molecule is the active form. A t pH 3.0 the results can be explained by considering that fatty acids enter the cell as protonated molecules and dissociate in the cytoplasm due to the higher internal pH, leading to increased intracellular hyd rogenous concentration. This may be the basis of two different effects that contribute to the observed inhibition: decrease in the intracell ular pH and dissipation of the transmembrane proton gradient, thus inh ibiting intracellular enzymes and Delta pH-dependent transport systems .