Evaluation of Oolong Teas Using 1H and 13C Solid-state NMR, Sensory Analysis, and Multivariate Statistics

The classification of Wuyi rock tea (Oolong type) is performed by solid-state nuclear magnetic resonance (NMR) for the first time. Quality differences of eight Oolong teas grown in Wuyi Mountains in southeastern China are analyzed by a combination of solid-state H-1 and H-1- C-13 CP-MAS (cross-polarization magic angle spinning) NMR, partial least-squares discriminate analysis (PLS-DA), and quantitative descriptive analysis (QDA). The contents of caffeine, carbohydrate, polyphenol, and terpenoid were distinguished, and quantification of the metabolites was made based on the H-1 and C-13 MAS spectra. PLS-DA shows a separation of high- and low-quality Oolong teas, in good agreement with the result of QDA. These results indicate that NMR metabolomic approach enables us to differentiate the analyzed teas based on their chemical composition.