Widely targeted metabolomics using UPLC-QTRAP-MS/MS reveals chemical changes during the processing of black tea from the cultivar Camellia sinensis (L.) O. Kuntze cv. Huangjinya

Huangjinya is a light-sensitive mutant tea cultivar that produces fresh leaves with a yellow phenotype, and the leaves also be used to produce black tea with special sensory characteristics. To thoroughly explore the chemical changes that occur during the processing of Huangjinya black tea, tea samples were collected from each processing step to perform quantitative and qualitative analyses by high-performance liquid chromatography and ultra-performance liquid chromatography coupled with high-resolution mass spectrometry (UPLC-HRMS). Compared to fresh tea leaves, only approximately 20% of the catechins remained at the end of processing, while theaflavins levels peaked at the rolling step and were slightly reduced in the fermentation and drying processes. The levels of amino acids derived from protein hydrolysis increased significantly in the withering and rolling processes. Altogether, 620 differential metabolites were identified from 11 subclasses using widely targeted metabolomics based on UPLC-HRMS for the four steps used to process Huangjinya black tea. Flavonoids, phenolic acids, and lipids were the three major classes of differential metabolites, accounting for 52.4% of the differential compounds. The greatest changes in the metabolite profile occurred during the rolling step, with 292 metabolites showing increases or decreases. Two glycoconjugates of the amino acid were first identified in tea, which was sharply increased in the drying stage. The present study provides comprehensive information on the chemical changes during the processing of Huangjinya black tea, and this information is valuable for optimizing manufacturing process and utilization of the Huangjinya tea plant.