Abstract
Most previous studies have been focused on the variation of tea chemical composition by fermentative processes as well as different cultivars and regions. The detailed changes of flavonoid profiles were described for the first time by each processing step of green and black tea leaves in this study. A total of 24 flavonoid derivatives including catechins, theaflavins, and flavonols were separated and identified from the tea samples based on UPLC-DAD-QToF/MS data and constructed library. Among these, the fragmentation pathway of theaflavins was proposed specifically in positive ionization mode for structural interpretation. During leaf processing, the individual flavonols were changed as diverse patterns according to their aglycone types and glycosylated forms, but their total content showed a slight difference. EGCG and ECG were increased after roasting approximately twofold higher than that of fresh leaves (EGCG, 2709.5 →6085.6; ECG, 1548.0 →2318.2 mg/100 g dry weight, respectively) in green tea while considerably decreased their contents due to oxidation and conversion to theaflavins after fermentation during black tea processing. Especially, the drying steps also found to be factor to influence positively to increase the flavonoid contents in both tea processing. Therefore, this result indicated that detailed conditions of each processing step played important roles in changing the flavonoid profiles from tea leaves.Graphical abstract
Highlights
Green tea (Camellia sinensis) is one of the most widely consumed beverages in mainly Asia and Europe
From leaves of green and black teas, the mass fragmentations of flavonoid derivatives were summarized and presented in the constructed liquid chromatography–mass spectrometric (LC–MS) library for identification based on the literatures (Table S1)
This study described the changes of individual flavonoids according to each processing step of green and black tea leaves
Summary
Green tea (Camellia sinensis) is one of the most widely consumed beverages in mainly Asia and Europe. Healthpromoting compounds such as catechins, theaflavins, thearubigins, flavonols, caffeine, and other phenolic compounds are predominantly distributed in the leaves of green and black (fermented) tea [1,2,3,4]. Catechin derivatives are belonging to flavan-3-ols and known to be abundant in tea products [5]. Theaflavins are the responsible compounds to determine the color and taste of black tea infusions as conjugates of epicatechin (EC), epigallocatechin (EGC), and gallic acid by enzymatic oxidation reaction in fermentations [6]. Dietary polyphenols played an important role in the preventive aspects of human diseases such as Alzheimer’s, cardiovascular disease, diabetes mellitus, and obesity [9,10,11,12], and revealed remarkable activity as anti-carcinogenic agent [13,14,15]
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