The Research Of The Mechanism Of Carbon Isotope Fractionation During Microbial Fermentation And Application

Food authenticity is a live topic that attracts worldwide attention; Consumers increasingly demand reassurance of the (ingredients) origin and content of their food. Unscrupulous businessmen could produce high-profit foods which will be up to the state and enterprise standard of physicochemical quota with cheap materials.In this case,physical chemical methods will lost their function,but stable isotopic methods are suitable for food authenticity assessment of this type.we studied how the carbon isotope ratio813C values changing during the fermentation, and Developed a pretreatment of distillation unit for carbon isotope analysis of ethanol.The determination of13C/12C of alcohol beverage by GC-C-IRMS has been set up with the pretreatment of dilution by organic solvent.we had set up the carbon isotope ratio δ13equation model between sugar component and ethanol,the technique is applied to authenticity identification of traditional Chinese liquor.The summary as follows:(1) The determination of13C/12C of alcohol beverage by GC-C-IRMS has been set up with the pretreatment of dilution by organic solvent.With the optimization of the condition,the concentration of the ethanol diluted to8g/L and the ethanol was separated effectively by the wax chromatographic column,and then the values of the carbon isotope ratio of ethanol can be determined effectively.The results show that this method is easy to operate, and then has a good stability and high accuracy.This method will provides the technique for authenticity identification of alcoholic beverage by the difference of the carbon isotope ratio.(2) The carbon isotope ratio δ13C values of ethanol had been determined by GC-C-IRMS. The influence of the factors such as temperature,substrate concentration, original pH and yeast species to the carbon isotope ratio δ13C values had been analysed,and we studied how the carbon isotope ratio813C values changing during the fermentation through the orthogonal experimental design L9(43).The result indicates:The influence of the four factors to the carbon isotope ratio813C values is not significant.The reason that carbon isotope fractionation during the process of fermentation is the differential distribution of six carbon isotope ratio within sugar molecules and the production of carbon dioxide.(3) Base on the analysis of several reasons and technological improvement, ultimately,a distillation device has been developed,the device can distillate ethanol solution, and the ethanol concentration can come to89.2%.Although the result of distillate ethanol concentration hasn’t reached the level of advanced laboratory in Europe,the method of distillation only need a short time (1hour),and this rate of distillation is four times faster than that in European advanced laboratory. This method has a positive effect to the distillation of large capacity sample,and laid groundwork for the development work in this field.(4) we had set up the carbon isotope ratio δ13C equation model between sugar component and ethanol.The factors of fermentation:asaccharide/ethanol=1.001-1.002, asaccharide/CO2=0.995-0.997.The correlation of the813C values between sugar component and ethanol is perfect:δ13CEthanol=1.06×δ13Csugar-0.07,R2=0.997.This study will provide theoretical support for developing stable isotope technique in the area of Chinese spirit authenticity.(5) The δ13C values of several kinds of grain alcohol have been determined, the upper limit value of Chinese spirit and the95%confidence interval of Chinese spirit have been got. Through the δ3C of ethanol in Chinese spirit in the market,we get the result that25%of the goods may be false.This provides a new testing method for authenticity of Chinese spirit.