Dark
teas are prepared by a microbial fermentation process. Flavan-3-ol
B-ring fission analogues (FBRFAs) are some of the key bioactive constituents
that characterize dark teas. The precursors and the synthetic mechanism
involved in the formation of FBRFAs are not known. Using a unique
solid-state fermentation system with β-cyclodextrin inclusion
complexation as well as targeted chromatographic isolation, spectroscopic
identification, and Feature-based Molecular Networking on the Global
Natural Products Social Molecular Networking web platform, we reveal
that dihydromyricetin and the FBRFAs, including teadenol A and fuzhuanin
A, are derived from epigallocatechin gallate upon exposure to fungal
strains isolated from Fuzhuan brick tea. In particular, the strains
from subphylum Pezizomycotina were key drivers for these B-/C-ring
oxidation transformations. These are the same transformations seen
during the fermentation process of dark teas. These discoveries set
the stage to enrich dark teas and other food products for these health-promoting
constituents.
Polyphenols, the most abundant components in tea, determine the quality and health function of tea. The analysis of polyphenols in tea is a topic of increasing interest. However, the complexity of the tea matrix, the wide variety of teas, and the difference in determination purposes puts forward higher requirements for the detection of tea polyphenols. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterization of tea polyphenols. In order to provide new insight for the further development of polyphenols in tea, in the present review we summarize the recent literature for the detection of tea polyphenols from the perspectives of determining total polyphenols and individual polyphenols in tea. There are a variety of methods for the analysis of total tea polyphenols, which range from the traditional titration method, to the widely used spectrophotometry based on the color reaction of Folin–Ciocalteu, and then to the current electrochemical sensor for rapid on-site detection. Additionally, the application of improved liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) were emphasized for the simultaneous determination of multiple polyphenols and the identification of novel polyphenols. Finally, a brief outline of future development trends are discussed.
Understanding the microbial and chemical
diversities, as well as
what affects these diversities, is important for modern manufacturing
of traditional fermented foods. In this work, Chinese dark teas (CDTs)
that are traditional microbial fermented beverages with relatively
high sample diversity were collected. Microbial DNA amplicon sequencing
and mass spectrometry-based untargeted metabolomics show that the
CDT microbial β diversity, as well as the nonvolatile chemical
α and β diversities, is determined by the primary impact
factors of geography and manufacturing procedures, in particular,
latitude and pile fermentation after blending. A large number of metabolites
sharing between CDTs and fungi were discovered by Feature-based Molecular
Networking (FBMN) on the Global Natural Products Social Molecular
Networking (GNPS) web platform. These molecules, such as prenylated
cyclic dipeptides and B-vitamins, are functionally important for nutrition,
biofunctions, and flavor. Molecular networking has revealed patterns
in metabolite profiles on a chemical family level in addition to individual
structures.
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