Reduction Of Ethyl Carbamate And Its Precursor In Fermented Grains

Ethyl carbamate?EC?is a carcinogenic substance that can cause liver cancer,skin cancer and other diseases.It is widely detected in fermented foods and alcoholic beverages.The presence of EC is a potential hazard to food safety,so it is of great importance to study how to reduce the content of EC in fermented foods.Endogenous strains with capability of degrading EC and its precursors were obtained from fermented grains,these strains and urease were used for reduction of EC and its precursors during Chinese spirit production.Properties of enzyme that degrades EC and urea produced by B.amyloliquefaciens JP21 were preliminarily studied.The main research results are as follows:?1?Two strains that degrade EC were obtained from Luzhou-flavor spirit fermented grains by high-throughput screening.They were characterized as B.amyloliquefaciens JP21,which reduces urea and EC;and Bacillus licheniformis DX530,which reduces citrulline,urea and EC.?2?Four strains?B.amyloliquefaciens JP21,B.licheniformis DX530,citrulline degrading strain B.amyloliquefaciens JY06,EC degrading strain Lysinibacillus fusiformis LJJ4?were employed in the process of Luzhou-flavor spirit fermentation by mixing with grains and Daqu.The results showed that B.amyloliquefaciens JP21 had the best ability to reduce EC and its precursor in the fermentation process.It could reduce 12%of urea and 17%of EC.After distillation,the content of EC in fermented grains was 64?g·kg^-1,which was 28%less than that in the control.?3?A combination of B.amyloliquefaciens JP21(10⁸ CFU·g^-1)and urease(0.1 U·g^-1)was added in fermented grains during Luzhou-flaovor spirit fermentation to reduce EC and its precursors.EC and urea in fermented grains were reduced by 32%and 43%using this method,respectively.After distillation,EC content in base liquor decreased by 52%.The results also showed that addition of B.amyloliquefaciens JP21 and urease had no effect on the flavor and aroma.?4?Enzymes that degrade EC and urea from B.amyloliquefaciens JP21 was partial purified.Three main bands?61 kDa?15 kDa and14.5 kDa?were detected by SDS-PAGE analysis,which may correspond to UreC,UreA,UreB subunits of urease.Enzymatic properties analysis demonstrates that the optimal pH and temperature for this enzyme are 5.5 and 35?.This enzyme also showed tolerance to low concentration of ethanol and could catalyze both urea and ethyl carbamate.This results showed that urease produced by B.amyloliquefaciens JP21degrading both ethyl carbamate and urea.