The Characteristics Of Carbon And Nitrogen Stable Isotope Ratios Of Geographic Point-of-Origin Of Keemun Black Tea

Tea is considered regional products with region-specific qualities.Keemun black tea is a premium black tea with the reputation of "the queen of black tea" and is highly praised for its unique aroma and low astringency.In history,Keemun black tea was produced in Anhui Province,mainly in Qimen county,Dongzhi county,Guichi county.In 2004,Keemun black tea association of Qimen county submitted an application for registration of the GI trademark of "Keemun black tea" to the State Administration of Industry and Commerce,which limited the origin of "Keemun black tea" to only the territory in Qimen county,caused controversy.Consumers expect more information on the authenticity,geographical origin,growth conditions,and processing of their foods.Authentication of Keemun black tea origin is necessary for food safety and quality control In the present study,the origin identification of Keemun black tea was analyzed for variations in the values of δ13C andδ15N usingIRMS in core production areas in Qimen,traditional production areas in Guichi and Dongzh,and black tea in other production areas(Lapssang souchong and Zhenghe Gongfu from Fujian,Yunnan black tea,Darjeeling from India and Sri Lankablack tea).The possible influence factors on the δ13C and δ15N values were analyzed.Furthermore,the fractionation mechanism of 15N in Keemun black tea was studied from two aspects:nitrogen metabolite-tea protein and caffeine.The research contents mainly include the following:(1)The effects of 25 tea cultivars with the same tenderness,different tea leaves maturity and different grades of Keemun black tea on δ13C and δ15N values of Keemun black tea were analyzed.The results showed that tea cultivars have remarkable impact on δ13C andδ15N values.δ15N values showed negative correlated with tea leaves maturity,i.e.the higher the Iaturity,the smaller the δ15N values.During manufacture of Keemun black tea has no significant effect on δ15N values(p>0.05),indicating that Keemunblack tea produced by different enterpriseshasno effect on the identification of production sites.Different grades effect on δ15N of Keemun black tea was not obvious.(2)δ13C and δ15N values of black tea,and the origin identification of Keemun black tea were studied.Keemun black tea from Qimen county could be easily discriminated from samples from Dongzhi and Guichi counties based on δl5N signatures.The k-NN model was cross-validated with an accuracy of 91.6%.Environmental factors and/or genotype seem to be the major reasons for δ15N differences in Keemun black tea from the selected regions.(3)The 15N fractionation mechanism of 15N in Keemun black tea was investigated.Protein and caffeine with different leaves maturity has the same trend as fresh leaves,i.e.the higher the maturity,the smaller the δ15N values.15N fractionation mechanism of Keemun black tea may be tea protein enriched-15N and caffeine depleted-15N.The cross-validation accuracy of k-NN analysis based on the δ15N values of Keemun black tea protein and caffeine was 93.3%,which was better than the result of tea.