Advantage of LC-MS metabolomics to identify marker compounds in two types of Chinese dark tea after different post-fermentation processes

Chinese dark tea (CDT) was investigated for chemical characteristics using liquid chromatography coupled with tandem mass spectrometry (LC-MS) metabolomics analysis. The LC-MSn method was used for detection of secondary metabolites in 10 CDT varieties. Pattern recognition methods, including principal component analysis (PCA) and orthogonal projection on latent structure-discriminant analysis (OPLS-DA), revealed clear differences and classified the CDT varieties into 2 categories. One category is fermented with Aspergillus niger while the other (fu teas) is fermented with Eurotium cristatum. Chemical analyses identified 25 marker compounds that contribute to the classification of the 2 CDT types. Flavonoid triglycosides and catechin derivatives were the distinctive compounds of fu teas, based on MS/MS fragmentation analysis. Although both fu teas and dark teas are commonly called CDTs, differences between these two CDT types are significant in the chemical classification.