Citrulline Production and Ethyl Carbamate (Urethane) Precursor Formation From Arginine Degradation by Wine Lactic Acid Bacteria Leuconostoc oenos and Lactobacillus buchneri

Abstract

The catabolism of the amino acid arginine by Leuconostoc oenos MU2 and Lactobacillus buchneri CUC-3 was investigated to assess the potential for formation of ethyl carbamate precursors in model wine and wine. Both organisms catabolized arginine and excreted citrulline into the media; however, only Lb. buchneri CUC-3 reutilized this citrulline. Upon subsequent heating (71°C/48 hours), substantial amounts of ethyl carbamate were formed from precursors generated during fermentation. The formation of ethyl carbamate was correlated with arginine degradation and citrulline production in both media. Only insignificant amounts of ethyl carbamate were formed (<10 ppb) without heating. This is the first report demonstrating that certain wine lactic acid bacteria are capable of forming citrulline, a precursor of ethyl carbamate, from arginine and excretion of this precursor into the medium. A strain not able to degrade arginine, L. oenos ML34, was also used for comparison. Surprisingly, growth of this strain in a wine resulted in a small, but significant, increase in ethyl carbamate, suggesting that precursors other than those derived from arginine may be involved. The results indicate the need for caution in the selection of malolactic starter cultures for conducting malolactic fermentation in wine, since citrulline formation from arginine degradation could result in high amounts of ethyl carbamate, even at normal temperatures during prolonged storage. In addition, spontaneous malolactic fermentation by undefined strains should be avoided, as this may lead to formation of ethyl carbamate precursors.