Reduction Of Ethyl Carbamate Precursors By Microbiological Methods In Chinese Liquor During Production Process

Ethyl carbamate,a byproduct that existed in fermented food,has the potential of genetic toxicity and carcinogenicity to the human body,can cause diseases such as liver cancer,lung cancer,non-hodgkin's lymphoma.Urea is one of the main precursors of ethyl carbamate in Chinese liquor fermentation process.By reducing urea in material is one of the effective measures to control and reduce EC in Chinese liquor.For liquor production involves the mixed bacteria in food fermentation system,and the urea content increased in fermentation process,so the research of microbial intervention method which ruduce urea content in material has great significance to ensure the security of fermented food.This study by screening of urease-production bacteria and characteristic comparing,then applies urease-production bacteria to liquor production process,which contains pretreatment of raw material,fermentation process and stackig,to investigate the removal effect of urea in material.The main results as follow:(1)Three urease-production bacteria were screened from Daqu,identified as s.saprophytic.Higher activity urease was pruduced from S.saprophyticus M39.The pure urease can tolerate 5% ethanol,optimum reaction pH 6.5,can degrade urea and EC.(2)Simulated wetting raw material process of liquor production technology,use bacteria liquid or crude urease liquid of L.reuteri and S.saprophyticus M39 instead of water wetting raw materials.Remove urease in raw materials before putting in fermentation,the effect is remarkable.The results showes that,the optimum condition for wetting raw material with S.saprophyticus M39 is 1×108 CFU·g-1 raw material,40?C and two hours;the optimum condition of its urease is 2×103 U·kg-1 raw material,40?C and two hours;the removal rate is 92.8% and 97.1% respectively.The optimum condition for wetting raw material with L.reuteri is 1×108 CFU·g-1 raw material,30?C and two hours;the optimum condition of its urease is 250 U·kg-1 raw material,35?C~40?C and two hours;the removal rate is 78.8% and 100% respectively.(3)L.reuteri and three S.saprophyticus strains were used in the solid-state fermentation of fermented grains.Simulating fermentation process to explore its urea removal effect in fermented grains.L.reuteri or its urease had remarkable removal effect better than S.saprophyticus to urea in fermented grains.Reducing urea in fermented grains with L.reuteri or its urease,the best cell concentration is 1×107 CFU·g-1,the best crude urease concentration is 50 U·kg-1.At the end of fermentation,the urea content in fermented grains adding L.reuteri or its urease,were reduced 92.4% and 100%,respectively,the EC production were reduced 50.3% and 69.9%.Furthermore,urea removal efficiency of L.reuteri and its urease were better than commodity urease.(4)Adding L.reuteri and its crude urease to fermented grains to decrease urea in stacking process,reduced urea content significantly.The optimum condition with L.reuteri is 1×108 CFU·g-1,10?C~30?C,4 h,the removal rate of urea is 79.8%~82.8%.The optimum condition with its urease is 100 U·kg-1,4 h,30?C,the removal rate of urea is 100%.Fermented grains out of cellar with different content of urea was simulated distillation,reducing the content of urea can effectively reduce the formation rate of EC,the highest reducing rate is 65.3%.