Effects of geographical origin, processing and their interaction on stable isotopes in Pu-erh tea for traceability

To establish a robust traceability model for Pu-erh tea, this study systematically investigated the effects of geographical origin, processing, and their interaction on the stable isotope ratios (δ¹³C, δ¹⁵N, δ²H, and δ¹⁸O) in both tea and its caffeine monomer. Results revealed that the stable isotopic compositions in Pu-erh tea and caffeine significantly differed among regions, δ²H_tea, δ¹³C_caffeine, δ²H_caffeine and δ¹⁸O_caffeine were significantly influenced by processing, all the stable isotopes were significantly influenced by region-processing interaction, and region contributed most to the variation of each stable isotope. Among them, δ¹³C_caffeine, δ¹³C_tea, δ¹⁵N_tea, and δ²H_caffeine were identified as the key indicators for geographical discrimination. Furthermore, 97.2 % correct discrimination rate and good validation (Q² = 0.775) were achieved by linear discriminant analysis and orthogonal partial least squares-discriminant analysis, respectively. Ultimately, this study confirms that tea and caffeine stable isotope signatures are capable for classifying the Pu-erh tea geographical origin even mixed with different processed samples.