Qingzhuan
tea (QZT) is a unique type of dark tea exclusively produced
in Hubei Province of China. In the current study, liquid chromatography–mass
spectrometry (LC-MS) coupled with multivariate analysis was applied
to characterize the chemical composition of QZT and investigate the
effect of QZT processing on its metabolic profile and sensory quality.
The contents of polyphenols and flavonoids decreased significantly
while the polysaccharides content remained stable, while the theabrownin
content inversely increased during QZT processing. LC-MS-based metabolomics
analyses revealed that the tea sample after microbial fermentation
(MFT) was dramatically different from the sample before microbial
fermentation (UFT), while MFT was very similar to QZT. A total of
102 compounds were identified as critical metabolites responsible
for metabolic changes caused by QZT processing, with the contents
of catechins and flavonoids significantly decreased, and some novel
phenolic acids and catechin derivatives were formed. The sensory quality
of QZT was mainly formed during microbial fermentation, which greatly
reduced the astringency and bitterness of raw tea leaves and produced
its characteristic woody and stale aroma as well as mellow taste.
These results suggested that microbial fermentation is the critical
process in changing the metabolic profile of raw tea leaves and forming
the sensory quality of QZT.
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