Analysis Of Ethyl Carbamate Formation During Luzhou-flavor Spirits Fermentation Process

Ethyl carbamate(EC) is a toxic contaminant, which has an indispensable potential carcinogenic risk to human. This compound has been widely detected in fermented foods and alcoholic beverages, including Chinese spirits. Clarifying mechanism of EC formation is of great importance and required for finding solutions in reducing EC level in Chinese liquor. The formation of ethyl carbamate during grains fermentation, distillation, and base liquor ageing procedures of Luzhou-flavor sprits production was analyzed and evaluated in this study. The main results are as follows:(1) Ethanol, ethyl carbamate and its precursors including urea, citrulline and cyanide were determined in Luzhou-flavor base liquors stored for 0-12 years. Cyanide was not detected in base liquor(less than 20 μg·L-1). In the first year of the aging process, concentration of EC in base liquor increased correlately with the reduction of urea and citrulline. An expedited reaction model for EC formation from urea-ethanol or citrulline-ethanol was constructed. The results showed that urea and citrulline were the major EC precusors in base liquor, while cyanide had little contribution to EC formation.(2) EC and its precusors urea and citrulline was confirmed to be present in fermented grains and materials used for base liquor distillation using quantitive analysis. Both urea and citrulline were detected in all five grains, the raw material. In order to evaluate the contribution of each kind of grain to EC formation during distillation, a distillation model containing individual grain and ethanol was setted up. It was shown that sorghum and wheat were the main contributors to EC formation during Luzhou-flavor Chinese liquor distillation process.(3) Fermented grains were collected at different time intervals of Luzhou-flavor Chinese liquor fermentation. EC and its precusors were detected in all fermented grains. During fermentation, citrulline and urea levels in fermented grains increased 63.9% and 16.9%, repectively. Strains with citrulline producing properties were then isolated from fermented grains using high-throughput screening techniques. These isloates were characterized belonging to genera of Bacillus, Lactococcus, Pediococcus and Staphylococcus. All of these strains were verified to contain intact arginine deiminase pathway(ADI pathway) and citrulline is produced by them from arginine utilization. Among these isolate, Pediococcus acidilactici PH7 and Bacillus amyloliquefaciens BG5 exhibited extraodinary citrulline accumulation capability.