Identification of the age of white tea using proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-MS) coupled with multivariate analysis.

RATIONALE In recent years, white tea has become increasingly popular. Some merchants confuse the age of white tea and sell poor-quality products for profit. Therefore, it is necessary to provide technical support for product authentication and valorization in white tea of different marked ages. METHODS Volatile organic compounds (VOCs) were detected by proton transfer reaction time of flight-mass spectrometry (PTR-TOF-MS) and identified as volatile fingerprints. PTR-TOF-MS combined with multivariate analysis was found to identify white tea of four different marked ages (1, 3, 5, and 8 years) for authentication. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used as classification models to identify key volatile metabolites. RESULTS The OPLS-DA model achieved the best result (96.67%, 96.67%,96.67%, and 96.67% in the training set and 96.00%,96.00%, 100% and 100% in the prediction set for 1-year, 3-year, 5-year and 8-year tea samples, respectively), showing that PTR-TOF-MS with the OPLS-DA model could successfully be used in the identification of white tea with different marked ages. Out of the 60 identified volatile organic compounds, 26 volatile materials were closely correlated with tea age and were used as markers to discriminate white tea of different ages. CONCLUSIONS PTR-TOF-MS coupled with multivariate analysis could be applied for quality evaluation of tea products of different ages and provided a feasible technical support for product authentication and valorization in white tea of different marked ages.