Tea, brewed from leaves of Camellia sinensis, is the most popular beverage worldwide. Congou black tea is the orthodox Chinese black tea known for its elaborate manufacturing procedures, from plucking of fresh leaves, to the processing (withering, rolling, fermentation, firing, refinement), and to the brewing. Thus it is of significance to investigate biochemical conversion and flavor chemistry of congou black tea at different stages. This report will summarize our recent efforts in this context, from fresh leaves to the processing and tea infusions. To explore the features of tea cultivars suited for black tea processing, nontargeted metabolomics, combined with comprehensive pathway mapping, were performed on fresh leaves of different tea cultivars. Cultivars suited for black tea manufacturing had significantly higher catechins, condensed products and phenolic acids, and lower contents of flavone C-glycosides, free sugars, and amino acids. Unique glycosylation patterns of flavonol glycosides were also identified. Further, a novel method for wide-scale tea lipids profiling was established, enabling simultaneous analysis of 200-300 tea lipids. This method was used to study the dynamic changes of tea lipids during black tea processing. The significantly differential lipids and related metabolic pathways have been identified, involved with chlorophylls degradation, glycoglycerolipids degradation, and other extraplastidial membrane lipids' metabolic pathways. Particularly, the glycolipids enriched with acyl chain 18:3, e.g., monogalactosyldiacylglycerol (MGDG) (18:3/18:3), showed the most significant decrease during the rolling phase, which may contribute to aroma formation during black tea manufacture. In addition, we investigated the key compounds that influence the sweet-mellow taste of congou black tea infusions, employing an integrated approach consisting of quantitative analysis of taste-active compounds, taste contribution analysis, taste supplementation experiments and human sensory evaluation. It was found that caffeine, γ-aminobutyric acid, rutin, succinic acid, citric acid, and gallic acid negatively affect the sweet-mellow taste. In contrast, glucose, sucrose, and ornithine positively contribute to the sweet-mellow taste. Particularly, rutin, γ-aminobutyric acid, gallic acid, and caffeine, which impart a significant inhibitory effect to the manifestation of the sweet-mellow taste, were identified as the key impact components.

Biochemical conversion and flavor chemistry of Congou black tea: From fresh leaves to tea infusions

ACS Spring Meeting 2021

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