Geographical Tracing of the West Lake Longjing Tea Based on the Stable Isotope Ratios

The West Lake Longjing tea is a famous specialty with long history in Zhengjiang province and its price is higher than any other flatten-shaped tea. However, traders tend to sell counterfeit West Lake Longjing tea in the market to acquire higher economic values. Otherwise, plants from different geographical locations have distinct isotope ratio, which form the element fingerprints due to the variation of climate and soil properties. Thus, it is necessary to do the geographical tracing of the West Lake Longjing tea based on the stable isotope ratios. In this study, we collected the flatten-shaped tea samples from the Hangzhou, Shaoxing and Lishui of Zhejiang, Qingchuan of Sichuan, Liping of Guizhou and Rizhao of Shandong where the flatten-shaped tea were widely produced. And the stable isotope ratios (C, H, O, N, Cd, Pb, Sr ) in the flatten-shaped tea samples were also assayed. Differences of the stable isotope ratios in the flatten-shaped tea from different producing areas were obtained by the variance analysis. The comparision of the stable isotope ratio values of West Lake Longjing tea and other flatten-shaped tea producing from different areas were completed. Fisher linear discriminant analysis (FLDA), decision tree and back propagation artificial neural network (BP-ANN) were used to establish the origin recognition model. The stable isotope ratios in flatten-shaped tea produced from different areas showed the difference followed with the different producing areas. For the δD and δ¹⁸O in samples, maybe influenced by the land effect and the elevation effect; a positive correlation was found between δD and δ¹⁸O; The ratio of ⁸⁸Sr/⁸⁶Sr was increased following the latitude’s increasing of the four provinces. Compared the recognition ability among those models of FLDA, decision tree and BP-ANN, all the recognition ability were above 76%. As applied by external validation samples, decision tree model was suitable for geographical origin traceability of different regions, while the accuracy rate was 92%. So the decision tree model was more suitable for geographical tracing of West Lake Longjing tea.