Stable isotope signatures versus gas chromatography-ion mobility spectrometry to determine the geographical origin of Fujian Oolong tea (Camellia sinensis) samples

Identifying the geographical origin of tea has become imperative due to increased consumer awareness and turbulence in the tea market. In this study, the potential of stable isotope tracer technique and gas chromatography-ion mobility spectrometry (GC-IMS) for the differentiation of Tieguanyin (TGY) and Dahongpao (DHP) oolong tea, as well as DHP samples from three smaller parcels, was explored and compared. Both the methods are based on stable isotope signatures and GC-IMS clearly differentiated the TGY and DHP oolong tea, then the k-NN model was cross validated with an accuracy of 95.2% and 97.8%, respectively. GC-IMS was sensitive enough to distinguish different DHP samples with an acceptable accuracy of 86.7%, whereas stable isotope signatures showed an ineffective separation. In addition, we identify putative markers specific for the different areas. Finally, we revealed a significant correlation between stable isotope ratio and volatile compounds, although the underlying mechanism is still unclear.