Study On Ethyl Carbamate During The Production Of Chinese Rice Wine

Ethyl carbamate (EC) is a well-known carcinogen. The existence of EC in Chinese ricewine significantly restricts the development of Chinese rice wine industries and may bringsome food safety issues. Hence reducing EC content in Chinese rice wine is becomingincreasingly important. Urea used to be recognized as the major precursor of EC and previousresearches mostly focused on the control of urea content.Determination methods of EC by gas chromatography/mass spectrometry and urea byhigh performance liquid chromatography-fluorescence detector were set up in the presentstudy. The precision and recovery of the methods were tested and the feasibility of themethods was proved. According to the analysis of Chinese rice wines collected from the localmarkets, most Chinese rice wines contained high contents of EC (80~270μg L-1). Besides, thecontents of citrulline in Chinese rice wine were at the same level of urea.Reactions of urea and citrulline with ethanol were performed separately by heating ofmodel Chinese rice wine solution and Chinese rice wine. The resulting EC contents andreaction rates were compared then. The results showed that some components repressed thereaction of urea in Chinese rice wine and the reaction rate of urea was only2times higherthan that of citrulline. citrulline reacted intensely with ethanol and formed significant amountof EC. It show that citrulline was another important precursor of EC in Chinese rice wine.Studies of the metabolism of citrulline in Chinese rice wine showed that lactic acidbacterium could produce large content of citrulline. Nine strains of lactic acid bacteria wereisolated from Chinese rice wine, and most of which possessed the enzymes of the argininedeiminase (ADI) pathway and had the ability to catabolize arginine to citrulline.Urea and citrulline directly came from the raw materials of Chinese rice wine and thecontent of arginine in raw materials will affect the final content of urea and citrulline in wine.The precursors in raw materials were detected and helped to pick up high quality materials forproduction. Pretreatment such as washing or polishing could reduce the content of precursorsin raw materials. Urea content was reduced from12.15mg·kg-1to5.13mg·kg-1whenpolishing rate rose to60%, washing could reduce the urea content down by50.0%, arginineby13.4%and citrulline by58.2%.Since temperature significantly affected the formation of EC, thus optimization of thehigh temperature process could limit the formation of EC. Lowering the boiling temperaturefrom95℃to80℃in the lab scale would reduce the EC formation by60%. In the followingscale-up experiment, lowering the boiling temperature from92℃to80℃reduced the ECformation by55.6%, while adding a cooling process would reduce the EC formation by66.9%. Lowering the temperature from85℃to70℃in the sterilization of bottle winesreduced the EC formation by40.0%, with an EC content decrease from145.8μg·L-1to91.9μg·L-1. Besides, the change of temperature would not affect the biological stability andnon-biological stability of the Chinese rice wine.