Ethyl Carbamate Formation by Malolactic Bacteria

Arginine is one of the major amino acids found in grapes and wine. Certain strains of malolactic wine lactic acid bacteria can degrade this amino acid with the formation of ornithine, carbon dioxide and ammonia. The degradation of arginine by two strains of malolactic bacteria, Leuconostoc oenos MU2 and Lactobacillus buchneri CUC-3, was investigated to assess the potential formation of ethyl carbamate precursors in wine. Both strains degraded arginine and surprisingly, excreted citrulline, a known precursor of ethyl carbamate. The excreted citrulhne reacts with alcohol to form substantial amounts of ethyl carbamate with heat treatment (71°C/48 hours). The formation of ethyl carbamate correlated well with arginine degradation and citrulline production. From a winemaking point of view, the production of citrulhne is a problem, since it can react with alcohol over time to form ethyl carbamate even at low storage temperatures. However, only very small amounts of ethyl carbamate were formed without heat treatment (<10 ng/g or ppb). 7-1 Our results show that malolactic bacteria can indeed be a potential source of ethyl carbamate precursor (at least citrulline). Thus, care must be exercised in selection of starters to conduct malolactic fermentation in wine. Ideally, those strains unable to degrade arginine should be chosen in order to minimize precursor formation. In addition, spontaneous malolactic fermentation by undefined indigenous strains should be discouraged, as this may result in formation of ethyl carbamate precursors.