Control of Ethyl Carbamate Formation in Wine from Arginine Degradation by
We have investigated factors influencing the excretion of citrulline (a precursor of carcinogenic ethyl carbamate) from arginine degradation by malolactic bacteria in laboratory-fermented wine. One strain of Lactobacillus buchneri (CUC-3) and two strains of Oenococcus oeni (MCW and Lolll) have been examined for differences in citrulline excretion during growth in wine at several initial pH-values (pH 3.3, 3.6 and 3.9), at several initial arginine concentrations (0, 500, 1000, 1500 mg/1 arginine) and in wine fermented with different yeast strains (Montrachet, Premiere Cuvee). It was shown for both Lactobacillus buchneri CUC-3 and Oenococcus oeni MCW that the citrulline excretion rate was proportional to the arginine degradation rate. Factors that increase the arginine degradation rate will lead to an increase in the excretion rate of citrulline and finally to an increase in the total amount of citrulline excreted into the wine, given that the reutilization of citrulline is small. In accordance with these findings, citrulline excretion was more significant at higher pH values, where arginine degradation proceeds at a faster rate for all three bacteria examined. However, lactobacilli and oenococci varied in their metabolic rates at several initial arginine concentrations. The arginine degradation rate of Lactobacillus buchneri CUC-3 increased during incubation and therefore, the highest citrulline concentration was produced at the highest initial arginine concentration. In the case of both oenococci, the arginine degradation rates were significantly lower than those for Lactobacillus buchneri CUC-3 and varied only slightly at different initial arginine concentrations. This resulted in similar amounts of citrulline being excreted during fermentation. Additionally, high arginine concentrations inhibit arginine degradation. Differences in the excretion of citrulline upon realization of malolactic fermentation in wines fermented with different yeast strains were found for Oenococcus oeni MCW. Wines previously fermented with strain Premiere Cuvee (previously Prise de Mousee) led to better growth, higher arginine degradation rates and thus, higher citrulline levels. Malic acid degradation was completed for both oenococci at least 12 days earlier than arginine degradation.