Abstract
Tibetan tea (Kangzhuan) is an essential beverage of the Tibetan people. In this study, a lyophilized aqueous extract of Tibetan tea (LATT) was prepared and analyzed by HPLC. The results suggested that there were at least five phenolic components, including gallic acid, and four catechins (i.e., (+)-catechin, (−)-catechin gallate (CG), (−)-epicatechin gallate (ECG), and (−)-epigallocatechin gallate). Gallic acid, the four catechins, and LATT were then comparatively investigated by four antioxidant assays: ferric reducing antioxidant power, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO•) scavenging, 1,1-diphenyl-2-picryl-hydrazl radical scavenging, and 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) radical scavenging assays. In these assays, LATT, along with the five phenolic components, increased their antioxidant effects in a concentration-dependent manner; however, the half maximal scavenging concentrations of ECG were always lower than those of CG. Gallic acid and the four catechins were also suggested to chelate Fe2+ based on UV-visible spectral analysis. Ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC−ESI−Q−TOF−MS/MS) analysis suggested that, when mixed with PTIO•, the five phenolic components could yield two types of radical adduct formation (RAF) products (i.e., tea phenolic dimers and tea phenolic-PTIO• adducts). In a flow cytometry assay, (+)-catechin and LATT was observed to have a cytoprotective effect towards oxidative-stressed bone marrow-derived mesenchymal stem cells. Based on this evidence, we concluded that LATT possesses antioxidative or cytoprotective properties. These effects may mainly be attributed to the presence of phenolic components, including gallic acid and the four catechins. These phenolic components may undergo electron transfer, H+-transfer, and Fe2+-chelating pathways to exhibit antioxidative or cytoprotective effects. In these effects, two diastereoisomeric CG and ECG showed differences to which a steric effect from the 2-carbon may contribute. Phenolic component decay may cause RAF in the antioxidant process.
Highlights
Tibetan tea (“Zangcha” in Chinese, Figure S1), a member of the fully fermented tea family, has a history of approximately 1000 years in China
In the PubMed database, only three papers about Tibetan tea can be retrieved from 1991 to 2016 [3,6,7]. According to their working procedures and materials, Tibetan tea products are classified into three main types: Kangzhuan, Jinjian, and Kangjian
The prepared lyophilized aqueous extract of Tibetan tea (LATT) was analyzed by the HPLC method, and at least five phenolic components were found, including gallic acid (GA) and four catechins [(+)-catechin and its galloylated derivatives catechin gallate (CG), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG), Figure 1]
Summary
Tibetan tea (“Zangcha” in Chinese, Figure S1), a member of the fully fermented tea (dark tea) family, has a history of approximately 1000 years in China. It has become an essential beverage for millions of Tibetan people. Tibetan people eat various meat products, such as beef, milk, and butter tea These high-protein, high-lipid foods can effectively help them to resist the severe cold of high altitude. In the PubMed database, only three papers about Tibetan tea can be retrieved from 1991 to 2016 [3,6,7] According to their working procedures and materials, Tibetan tea products are classified into three main types: Kangzhuan, Jinjian, and Kangjian. The present study attempted to use Kangzhuan as a representative to estimate the antioxidant or cytoprotective effects of Tibetan tea and examined the possible mechanisms
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