Inhibitory Effect of Copper and Dichlofluanid on Oenococcus oeni and Malolactic Fermentation

¹ Department of Biochemistry and Biotechnology, Unitat d’Enologia del CeRTA, Rovira i Virgili University, Plaça Imperial Tàrraco, 1, Tarragona, Catalonia, Spain.

email: abpd{at}astor.urv.es

The inhibitory effect of pesticides, mainly copper and dichlofluanid, on Oenococcus oeni and malolactic fermentation was studied in simulated wine. The minimal inhibitory concentrations that affected malolactic fermentation were just under 5 mg/L, which was enhanced by ethanol. In control conditions, malolactic fermentation lasted 2 days, but in the presence of 7% ethanol and 5 mg/L copper it lasted 16 days. Inhibition was due mainly to a decrease in cell number but not to lower specific malolactic activity. Other wine compounds or conditions, such as lower pH or sulfur dioxide, increased the inhibitory effect of copper. Copper uptake by Oe. oeni was also studied, and it was found that very small quantities of Cu⁺⁺ (about 0.02 per 1000) were retained by resting cells at pH 6 but that this amount decreased significantly at pH 3.5 or when substrates such as glucose, fructose, or L-malic acid were available for cells. Inhibition of malolactic fermentation by copper and dichlofluanid was studied in several strains and species of lactic acid bacteria of wine. Their sensitivity to these pesticides varied, even within the same species.

Note:
Acknowledgments: M.T. Vidal was the recipient of a PhD fellowship from the Catalan Government. This work was supported by the Spanish research commission CICYT, projects n. ALI95-0887-C04-01 and ALI97-1077-C02-02.

Key words: Oenococcus oeni, malolactic fermentation, pesticides, copper, dichlofluanid

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