The Metabolic Mechanism Of Arginine Amino Acids During The The Process Of Traditional Rice Wine Fermentation

Ethyl carbamate is a kind of trace carcinogens found in fermented foods in recent years,whoseprecursor substances has proved including urea, citrulline and arginine group. The current study onhow to reduce the content of ethyl carbamate in fermented foods has become a research hotspot andcaught several governments’ attention worldwide. The traditional Chinese rice wine, with long historyand rich cultural connotation, has delicious flavour, rich nutrition, which is the typical representative oforiental fermented drinks and one of the three famous ancient wine in the world.The detection of ethylcarbamate in traditional rice wine, and the limit standard of ethyl carbamate in fermented foods foreigncountrys developed, which make great influence on exports and domestic consumption of rice wine inChina. How to effectively reduce the content of ethyl carbamate in rice wine production is currently thescientific problems to be solved. This research mainly investigate the metabolic mechanism of arginineand its related amino acids such as citrulline and ornithine in fermentation mash during the process ofsaccharification and alcohol fermentation process of traditional rice wine, so as to provide scientificbasis for improving the safety of traditional rice wine fermentation.In this study, firstly the traditional rice wine fermentation process was simulated at laboratory leveljust as the rice wine industry required. The content change of ethyl carbamate precursor substances,citrulline and related amino acid arginine and ornithine in fermented mash was analized by the use ofspectrophotometric method, while the amount change of mold, yeast and lactic acid bacteria were alsocounted by the use of traditional microbial plate count. Together with arginine family amino acids andmicrobial flora change research during ricw wine fermentation, the metabolism mechanism of ethylcarbamate in rice wine fermentation was analized. The results are as follows.1In rice soaking stage, the citrulline was accumulated in rice wine, and up to2.26ug/L in Japonicarice fermentation,while citrulline concentrations in the control group was up to2.14ug/L in glutinousrice fermentation by the metabolism of lactic acid bacteria. So the citrulline can be introduced into ricewine fermentation process by using sour water instead of fresh water adding into main fermentationprocess. It was suggested that the rice leaching time should not be too long, if the rice was soaked atroom temperature,2days or less is prefered, and the acid slurry water should not be too much addedback to the next fermentation cycle.2. In the fermentation stage, yeast and microbial group in wheat koji was a competitive relationship.When the wheat koji and yeast strains were added simutaniously(1);or wheat koji firstly added,2dayslater yeast strains added (2); or yeast strains propagated firstly and then the wheat koji added3dayslater (3), of which the yeast maximum concerntration was1.2×10~7cfu/mL (1),1.4×10~9cfu/mL (2) and4.8×10~6cfu/mL (3, Japonica rice fermentation)，3.0×10~6cfu/mL (3, glutinous rice fermentation)separately.3. As to the fermentation process as (1) in2, the arginine concerntration was too low to be detectedat the beginning. Until60hours later, the arginine concentration was accumulated up to17.2ug/L(Japonica rice fermentation) and17.6ug/L (glutinous rice fermentation) separately. In the (2), the finalarginine concentation was7.6ug/L and17.3ug/L and all of them were not more than20ug/L. In the (3),the data was71ug/L and90ug/L, and the growth of microbes in wheat koji was greatly inhibited byyeast. So it can be concluded from above experiment results that the microbes in wheat koji woulddecrease the contents of arginine, produced by yeast strains, which would enlighten how to deal with thereduction of ethyl carbamate at the fermentation stage in the rice wine production. The concentration ofcitrulline and ornithine was also measured during the whole fermentation process of three methods (1,2,3). How the concentration of citrulline changed was not clear and the ornithine was accumulated andwas no clear difference between saccharification and alcoholic fermentation stage, which would beinvestigated deeply in the future. 4For the first time found in wheat saccharifying stage has citrulline piece of accumulation, in theprocess of fermentation, citrulline concentrations fluctuate in6~12ug/L，this should be considered inthe fermentation process to reduce the content of ethyl carbamate.