Evaluation of the inhibitory effect of dimethyl dicarbonate (DMDC) against wine microorganisms

Several microbial species associated with wine were challenged against increasing concentrations of dimethyl dicarbonate (DMDC). The concentration inducing complete cell death upon addition to red wine was regarded as the minimum inhibitory concentration (MIC). In dry red wines with 12% (v/v) ethanol and pH 3.50, the inactivation depended on the initial cell concentration. For an initial inoculum of 500 CFU/ml, the MIC of the yeasts species Schizosaccharomyces pombe, Dekkera bruxellensis, Saccharomyces cerevisiae and Pichia guilliermondii was 100mg/l. The most sensitive strains belong to Zygosaccharomyces bailii, Zygoascus hellenicus and Lachancea thermotolerans, with MIC of 25mg/l DMDC. For inoculation rates of about 10(6)CFU/ml, the maximum dose of DMDC legally authorized (200mg/l) was not effective against the most resistant species. The addition of 100mg/l potassium metabisulphite (PMB), equivalent to 1mg/l molecular sulphur dioxide, increased the inactivation effect of 100mg/l DMDC over initial yeast populations of 10(6)CFU/ml but did not fully kill S. pombe and S. cerevisiae. Lactic acid and acetic acid bacteria were not killed by the addition of 300 mg/l of DMDC. Trials performed in wines before bottling showed that in most samples indigenous bacterial populations were not affected by 200mg/l DMDC. Therefore, under winery practice, DMDC at the maximum dose legally permitted may be regarded as an efficient preservative to control low contamination rates of yeasts but ineffective against lactic acid and acetic acid bacteria.