Research Of Ethyl Carbamate Formation In Chinese Liquor From The Cyanide Way

Ethyl carbamate（EC）, which commonly found in fermented foods and alcoholic beverage, is a group 2A carcinogen. Domestic researches of EC in Chinese liquor were mostly focused on the detection methods, but few studies have been conducted on its formation mechanism. High performance liquid chromatography-mass spectrometry（HPLC-MS） and gas chromatography-mass spectrometry（GC-MS） were applied to quantify EC, cyanogenic glycoside, cyanohydrin and cyanide in sorghum, fermented grains and Chinese liquor, respectively, as well as changes of urea and citrulline, in order to identify the main precursor of EC during fermentation, distillation and storage of Chinese liquor, respectively. Radiochemcal studies were conducted to study the mechanism of EC formation in free state matrix of Chinese liquor, as well as factors influencing the reaction between cyanide and ethanol to form EC, in order to clarify EC formation in Chinese liquor from the cyanide way.The details are as follows:（1） Qualitative analysis of cyanogenic glycoside（dhurrin） in sorghum was performed with HPLC-MS-MS. The results showed that dhurrin was ubiquitous in sorghum, which provided an explanation for the source of cyanide in Chinese liquor, and dhurrin content varies in different species(4.52¹9.28 mg×kg^-1). Qualitative analysis of cyanohydrin（DL-4-hydroxymandelonitrile） was performed with HPLC-MS-MS. Qualitative analysis of cyanide was performed with GC-MS-MS, avoiding color interference using the spectrophotometric colorimetry method.（2） Changes of EC and its possible precursors in fermented grains during stacking and fermentation process were studied. The results showed that EC increased from 15.13 μg×kg^-1 to 217.08 μg×kg^-1 during stacking and fermentation process, and dhurrin gradually decomposed during stacking process. However, no DL-4-hydroxymandelonitrile was detected in fermented grains. Cyanide and urea showed a decline trend after an initial increase, while citrulline content increased all the time. To analyze from the content and degradation rate, urea, whose increase was 324.65 mg×kg^-1, was most likely to be the main precursor of EC during stacking and fermentation process with degradation rate of 0.39 mg×kg^-1×h-1.（3） The variability of EC and its precursors in distillate fractions were analyzed, mostly focused on the correlation between EC, cyanide and urea content. The results showed that the trend of EC was similar to that of cyanide. The linear fit found that R2 was 0.5972, and there was a good linear relation between EC and cyanide at confidence level of 0.01.（4） Content of EC, cyanide and urea were analyzed in different aroma type Chinese based liquor. The linear fit bewteen EC, cyanide and urea content in the same aroma type Chinese based liquor of different vintage revealed that EC formation was related with cyanide rather than urea.（5） Isotope tracing method was adopted to find the main EC precursor during fermentation and storage process. The results showed that urea was the main EC precursor during fermentation, while cyanide during storage. Urea and cyanide degradation showed a logarithmic decline（first-order kinetics characteristics）, which meaned that the initial degradation rate was high, while slowed with time.（6） Effects of metal ions, temperature and p H on the reaction between cyanide and ethanol were investigated. The results showed that metal ions could catalyze the formation of EC from cyanide. A hot acid condition could also significantly promote EC formation.