The production of ethyl carbamate (EC) and its precursor citrulline by two strains of Oenococcus oeni and one of Lactobacillus plantarum during malolactic fermentation (MLF) was studied in different conditions of pH, temperature, and ethanol and l-malic acid concentrations. The potential EC, defined as the concentration of EC after wine is heated at 80°C for 48 h, was also investigated. The O. oeni strains were able to degrade arginine in the conditions studied and to excrete some citrulline. In these strains, the conditions that led to a slight increase in EC were a high ethanol concentration, low pH and a high l-malic acid concentration. However, the potential EC increased with higher pH. In the case of L. plantarum, arginine was not degraded and citrulline was not produced, although the potential EC was comparable with that of the O. oeni strains studied.

Ethyl carbamate (EC) is a carcinogenic compound found in fermented food and beverages such as wine. Although its carcinogenic potential in animals is known, information regarding its effects in humans remains insufficient, thus there is increasing interest in its research. EC content is higher in products with high alcohol content and in aged products. The main precursor involved in EC production in wine is urea, which is produced by metabolism of arginine by yeast, but there is also evidence that EC levels can increase after malolactic fermentation (MLF). Some lactic acid bacteria (LAB) can degrade the arginine present in must and wine via the arginine deiminase pathway, producing citrulline and carbamyl phosphate. Both compounds can react with ethanol in acidic conditions and produce EC. Our research group is studying the influence of MLF induced at different points of wine-making on the quality of the resulting wine. Among other parameters, the content of toxic compounds such as EC was evaluated. Results so far indicate that EC levels at the end of MLF were quite low (less than 3 μg/l) in all cases, i.e. below the existing legal limit (e.g. 30 μg/l in Canada). In almost all wines, EC concentrations increased after 8 months of storage as has been described by other authors. In some of the wines in which MLF was carried out by selected LAB, the increase in EC concentration was lower.

Eighty-seven strains of lactic acid bacteria were isolated from musts and corresponding fresh wines from southern Catalonia, Spain. They were selected for their ability to degrade malic acid in a semisynthetic medium with 10% ethanol at pH 3.5. Ten selected strains were tested in seven filtered wines. Three of the strains finished the malolactic fermentation in five wines in less than 14 days. In addition, the isolated strains were identified, 40 being Leuconostoc cenos and 20 Lactobacillus sp. that exhibited many characteristics ofhn. oenos.