Research Of Ethyl Carbamate During The Distillation And Storage Of Chinese Liquors

Ethyl carbamate (EC) occurs naturally in many fermented foods, baked foods, andalcoholic beverages. It has been classified as a group2A carcinogen, probably carcinogenicto humans. So far many countries and organizations have established the maximum values ofEC in alcoholic beverages, and the formation and control strategy of EC in alcoholicbeverages were also studied. Whereas, most researches about EC in Chinese liquors werefocused on detection methods, and little study has been conducted on the formation andcontrol strategy of EC. The distillate fractions sampled every two minutes during distillation,Chinese final liquors and base liquors with different aroma types were analyzed for EC,cyanide,18kinds of free amino acids, and urea concentrations. To study the formation of ECduring distillation and storage of Chinese liquors, the correlations between concentrations ofEC and its possible precursors were analyzed by linear regression analysis and bivariatecorrelation analysis. At the same time, the main precursors of EC during storage were verifiedby a heat treatment with various additives.The details are as follows:(1) The quantitative methods of EC, cyanide, and urea were optimized. Analysis of EC inChinese liquors were performed by headspace solid-phase microextraction (HS-SPME)combined with gas chromatograph-mass spectrometry(GC-MS). Liquor samples werepreprocessed by diluting directly with water to decrease the liquor alcoholicity. This methodwas simple and rapid, accurate and reliable, and out of EC wastages. The content of cyanidein Chinese liquors was detected by spectrophotometry with modified K nig reaction. Standardcurves of cyanide at different alcoholic strength (0,30, and46%vol) were carried out, sincethe chromogenic reaction could be suppressed by ethanol and Chinese liquors are normallyranged from40to55%vol by ethanol volume. The analysis of urea in Chinese liquors wasperformed by high performance liquid chromatography with fluorescence detector. Thismethod was for the first time applied for urea determination in Chinese liquors. Thedetermination limit of this method was low and the analytical precision was high. Thesemethods met the analysis requirement.(2) The distillate fractions were analyzed for concentrations of EC and its possibleprecursors. The results showed that changes of EC and cyanide levels during distillation weresimilar and EC concentrations was correlated positively with cyanide contents at confidencelevel of0.01. It was concluded that EC in distillate fractions mainly came from fermentedgrains in the early stage of distillation. While in the late stage, EC was mainly from thereaction between EC precursors with ethanol and cyanide was the main precursor during thisstage.(3) The Chinese final liquors with different aroma types were analyzed forconcentrations of EC and its possible precursors. EC, cyanide, and amino acids were found inall the Chinese liquors studied, while urea was only detected in strong aroma, light aroma, andfeng-xiang aroma type final liquors. Levels of EC and its possible precursors were different invarious aroma type final liquors. (4) The soy sauce aroma, strong aroma, and light aroma type base liquors were analyzedfor contents of EC, cyanide, amino acids, and urea. The levels of EC and possible precursorsin Chinese liquors could be affected by storage time. Better relationships were demonstratedbetween cyanide and EC concentrations in these three aroma type liquors studied andcitrulline contents were also significantly related to the concentrations of EC in light aromatype liquors. The results of bivariate correlation analysis showed that cyanide was most likelyto be the main source of EC and citrulline might also made contribution to its formation,while the other17kinds of free amino acids and urea were not the predominant factors.(5) The main precursors of EC during storage were verified by a heat treatment withvarious additives. The results showed that cyanide was the main source of EC and citrullinemade some contribution to its formation, while arginine and urea were not the predominantfactors during the storage of Chinese liquor.