| Wine is a kind of alcoholic beverage which is beneficial to one's health.Nowadays,China's wine industry has developed rapidly and its consumption ranked the fifth in the world.Meanwhile,the phenomenon of adulteration of wine is endless,which has caused problems for regulators and consumers.Taking the hydrogen isotope of ethanol in wine as the research object,in view of the problem of wine authenticity detection and identification,an ethanol distillation system was developed.Ethanol Isotope Measurement-Isotope Ratio Mass Spectrometry(EIM-IRMS)method and Site-specific Natural Isotope Fractionation-Nuclear Magnetic Resonance(SNIF-NMR)method was used to determine the hydrogen isotopes of ethanol in wine to explore the ability of identify the authenticity of wine,which could lay the foundation for the establishment of wine authenticity testing standards in China.Development of ethanol distillation system: an ethanol distillation system was developed based on two indexes: ethanol recovery rate and ethanol concentration in distillation fraction,and the ethanol distillation system was determined whether the ethanol isotopic fractionation occurred.An ordinary distillation system was used to distill ethanol-water solution,the quality of ethanol in the solution before and after distillation is measured,the ethanol recovery rates were 84.44% ~ 98.88%,the average value is 94.14%,and the ethanol concentrations in fraction were 48.64% ~ 69.28%(w/w),the average value is 53.08%(w/w);the ethanol recovery rates for the rapid distillation apparatus combined with the method of dewatering reagent were 97.31% ~ 98.03%,the average value is97.56%,the ethanol concentration after distillation was 10.10% ~ 10.25%(w/w),the average value is 10.19%(w/w),the change of the ethanol concentration of the distillate by the water removal reagents were not obvious,both the two distillation methods can not obtain high concentration ethanol while obtaining high recovery rate.After extending the path of steam to the condenser pipe in the ordinary distillation system and adjusting the heating intensity by the temperature probe,an improved ethanol distillation system was obtained with 89.85% ~ 91.12% for the ethanol recovery rate and 83.33% ~ 97.71%(w/w)for ethanol concentration,while the average value were 90.59% and 85.38%(w/w).Compared with ordinary distillation method and fast distillation method,the improved ethanol distillation system ensured higher ethanol recovery rate and improved the ethanol concentration of fraction.The results of determination of total hydrogen isotope of ethanolbefore and after distillation showed that the improved distillation system has no isotopic fractionation of ethanol.Detection of non-exchangeable hydrogen isotope of wine ethanol: ethanol-water solutions from different sources of water were prepared to determine the total hydrogen isotope of ethanol.It was founded that the hydrogen of ethanol hydroxyl site exchanged with hydrogen in water,which affected the hydrogen isotope value of ethanol and proved that the ethanol hydroxyl site can not be used to identify the authenticity of wine.The grape juice was mixed with sugar to simulate real wine samples and adulterated wine samples.After fermentation,the samples were distilled using the improved distillation system.EIM-IRMS was used to determine the non-exchangeable hydrogen isotope of ethanol in the distillate.The samples were measured 5 times on the same day,and the RSD were 0.30% to 0.81%,with an average of 0.43%;continuous measurement for 5 days,the RSD were 0.08% to 0.59%,with an average of 0.38%,indicating that the method has good precision.The results of non-exchangeable hydrogen isotopes of ethanol in samples showed that the ethanol hydrogen isotope value of grape juice with exogenous sugar fermentation samples was lower than that of real grape juice fermentation samples,and the average difference was 6.17 ‰,proving that this method can identify the phenomenon of chaptalization in wine.EIM-IRMS measurements were performed on the same distilled samples in laboratories in three different countries.The intra-day precision of the method were 0.24% ~ 0.47%,the inter-day precision were 0.32% ~ 0.39%,the method precision was good;the results of not exchangeable hydrogen isotope detection showed that the average difference value of the non-exchangeable hydrogen isotope of ethanol in the grape juice with exogenous sugar samples and the real grape juice samples was 6.26‰,which further proves that determination of ethanol non-exchangeable hydrogen isotope by the EIM-IRMS has reached the purpose of the identification of wine authenticity.Detection of hydrogen isotopes at methyl and methylene sites of wine ethanol: The results of SNIF-NMR showed that the ethanol solution with higher water content consuming more detection time.Therefore,it was necessary to prepare high concentration ethanol samples for the detection of alcohol hydrogen isotopes in wine.SNIF-NMR method was used for the determination of hydrogen isotopes at methyl and methylene sites of ethanol of the distilled wine samples.The results showed that the hydrogen isotopes difference of 1.98 ppm at the ethanol-methyl site between the real samples and the sugar-doped samples can be distinguished.The method can identify the phenomenon ofadding sugar in wine.Compared with SNIF-NMR,EIM-IRMS has the advantages of strong identification of adulteration,low equipment cost,short detection time,simple sample preparation and low sample consumption.Therefore,EIM-IRMS is more suitable for wine authenticity identification.This paper improved a wine ethanol distillation system with high recovery and high ethanol concentration,The results of EIM-IRMS and SNIF-NMR showed that the hydrogen isotopes of alcohol specific sites can identify the authenticity of wine,and EIM-IRMS can identify the authenticity of wine better,which provides methods and data support for the improvement of the wine authenticity detection system in China. |
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