Black Tea Theaflavins Research Articles

Chemopreventive and Therapeutic Potential of Tea Polyphenols in Hepatocellular Cancer

The prophylactic and therapeutic properties of tea have been attributed to green tea catechins and black tea theaflavins besides several other polyphenolic compounds. Tea polyphenols possess potent antioxidant and antiinflammatory properties and modulate several signaling pathways. These biochemical facets of tea polyphenols are responsible for its anticancer properties. Several lethal cancers, such as liver cancer, develop within a background of oxidative stress and inflammation. Liver cancer, also known as hepatocellular carcinoma (HCC), has been shown to occur throughout the world including Asia, Africa, Western Europe, and the United States. Phytochemicals, such as tea polyphenols, provide an effective and promising alternative for the chemoprevention and treatment of HCC. In this article, we systematically review, for the first time, the effects of tea polyphenols in the preclinical in vitro and in vivo HCC models. The review also examines, in critical detail, the biochemical mechanisms involved in the chemopreventive and antineoplastic effects of tea polyphenols in hepatic cancer. Finally, we highlight the role of synergy, bioavailability and pharmacokinetics of tea polyphenols, current status of clinical trials, discuss future directions, and comment on the future challenges involved in the effective use of tea polyphenols for the prevention and management of liver cancer.

Protective effect of theaflavin on erythrocytes subjected to in vitro oxidative stress.

Antioxidant and free radical scavenging effect of black tea theaflavins has been shown in many epidemiological studies. In the present work we report the protective mechanism of tea theaflavins on biomarkers of oxidative stress, which are elevated during stress conditions. We hereby report the in vitro effect of theaflavins on erythrocyte malondialdehyde (MDA), intracellular reduced glutathione (GSH), and plasma membrane redox system (PMRS) of rats. The effect of theaflavin on PMRS has also been validated through an in silico docking simulation study using Molegro Virtual Docker (MVD). We report that theaflavins show significant protection to erythrocyte against oxidative stress induced by tert-butyl hydroperoxide (t-BHP). The findings suggest a possible protective role of theaflavins as antioxidant.

Theaflavins, dimeric catechins, inhibit peptide transport across Caco-2 cell monolayers via down-regulation of AMP-activated protein kinase-mediated peptide transporter PEPT1

In the small intestine, peptide transporter 1 (PEPT1) plays a role in the transport of di- and tripeptides. In this study, we investigated whether theaflavins (TFs) affect the absorption of small peptides in human intestinal Caco-2 cells, since TFs do not penetrate through the cells and might be involved in intestinal transport systems. In transport experiments, the transport of glycyl-sarcosine (Gly-Sar, a model molecule for PEPT1 transport) and other dipeptides (Val-Tyr and Ile-Phe) were significantly reduced (P<0.05) in TFs-pretreated cells. In TF 3′-O-gallate-pretreated cells, Western blot analysis revealed attenuated expression of PEPT1 transporter and Gly-Sar transport was completely ameliorated by 10μM Compound C, an AMP-activated protein kinase (AMPK) inhibitor. In conclusion, the present study demonstrated that TFs inhibit peptide transport across Caco-2 cell monolayers, probably through suppression of AMPK-mediated PEPT1 expression, which should be considered a new bioactivity of TFs in black tea.

A RAPID HPLC-DAD METHOD FOR ANALYSIS OF THEAFLAVINS USING C12 AS STATIONARY PHASE*

Theaflavins are the major pharmacologically active antioxidant compounds present in the black tea. In this study we have developed a rapid, simple, and sensitive HPLC-DAD method for estimation and analysis of theaflavins using a RP-C12 (4.6 × 250 mm, 4 micron) column. The present study aims at rapid estimation and analysis of theaflavins in black tea and black tea based products (Ready to Drink Teas and Instant Teas) for their qualitative analysis. The use of RP-C12 as stationary phase with a simple gradient method enables the excellent separation of all the four major tea theaflavins: theaflavin (TF-1), theaflavin-3-gallate (TF-2), theaflavin-3, 3′-digallate (TF-3), and theaflavin-3′-gallate (TF-4) within 7 min. A linear calibration curve (r2 = 0.999) was plotted against standard theaflavin. The purification of theaflavins from black tea (CTC) was done by reverse phase solid phase extraction (RP-SPE) technique and quantification of individual theaflavins were carried out as theaflavin equivalent per mg of total purified theaflavins (TFS) from black tea. The results of present study clearly shows that use of C12 as a new stationary phase owes high sensitivity and faster analysis of theaflavins that otherwise are not easy to separate within 10 min.

Black tea polyphenols induce human leukemic cell cycle arrest by inhibiting Akt signaling

Tea polyphenols have potent biological activities against human cancer cells. A major causative factor in malignancies is disregulation of cell-cycle kinetics. In this study, we observed that black tea polyphenols, theaflavins (TF) and thearubigins (TR) induced cell-cycle arrest at the G(0) /G(1) phase in human leukemic U937 and K562 cells. Our objective was to understand the underlying molecular mechanism of cell-cycle inhibition by TF and TR. During elucidation, we observed that both TF and TR treatment augmented expression of p19, p21 and p27, while ablating cylcin-dependent kinase (CDK)2, CDK4, CDK6 and cyclin D1 levels. Our experimental results further determined that Akt signaling suppression by TF and TR played a major role in this process. Moreover, suppression of glycogen synthase kinase-3β, β-catenin and amplification of forkhead transcription factor 1 (FOXO1) expression were associated with regulation of certain key components of the cell-cycle machinery. In addition, depletion of heat shock protein (Hsp) 90 by TF and TR also had a pivotal role in cell-cycle arrest. More specifically, inhibition of Akt signaling by TF and TR correlated with the depletion of its downstream targets like Wnt/β-catenin signaling, cyclin D1 and increase of FOXO1, p27 levels. Inhibition of upstream Hsp90 by TF and TR consequently attenuated Akt signaling and reduced the level of CDK2. These results suggest possible mechanisms for the chemopreventive effect of TF and TR on human leukemic cells. To our knowledge, this is the first report of such a detailed molecular mechanism for TF and the less-investigated polyphenol TR-mediated cell-cycle inhibition in human leukemic U937 and K562 cells.

Therapeutic Attenuation of Neuroinflammation and Apoptosis by Black Tea Theaflavin in Chronic MPTP/Probenecid Model of Parkinson’s Disease

Neuroinflammation and apoptosis in the dopaminergic neurons of substantia nigra play an important role in the pathogenesis of experimental and clinical Parkinson's disease (PD). This study focused on the possible anti-inflammatory and anti-apoptotic effects of theaflavin (TF), a black tea polyphenol against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in mice. C57BL/6 male mice were treated with 10 doses of MPTP (25mg/kg, s.c.) and probenecid (250mg/kg, i.p.) for 3.5days interval. TF (10mg/kg) was administered 1h prior to the administration of MPTP for 35days of experimental period. MPTP/p treatment upregulates the release of interleukin-1beta, IL-6, tumor necrosis factor-alpha, IL-10, glial fibrillary acidic protein and Bax, and downregulates anti-apoptotic marker Bcl-2. Oral treatment of black tea polyphenol TF significantly attenuates MPTP-induced neuroinflammation as well as apoptosis. Behavioral studies (catalepsy and akinesia) were carried out to confirm these molecular studies. The results demonstrate that TF mediated its neuroprotection against chronic MPTP-induced toxicity through the involvement of multiple molecular events. It was concluded that TF may provide a precious therapeutic strategy for the treatment of progressive neurodegenerative disease such as PD in future.

Metabolism of black tea theaflavins by gut microbiota

As a popular beverage, tea (Camellia sinensis, Theaceae) has been associated with many beneficial health effects, including the prevention of cancer and heart disease, a phenomenon mostly attributed to the presence of polyphenolic compounds. The main bioactive polyphenols in black tea are theaflavins, which are formed by the oxidation and polymerization of catechins in green tea leaves during fermentation. Theaflavins including theaflavin (TF), theaflavin‐3‐gallate (TF3G), theaflavin‐3′‐gallate (TF3′G), and theaflavin‐3,3′‐digallate (TFDG). We and others have found that theaflavins have poor systematic bioavailability. Therefore, it is still unclear how these compounds could exert their biological functions. It has been reported that higher molecular weight polyphenols are metabolized by the microbiota and their metabolites may play an important role in chronic disease prevention. In the present study, we investigated the microbial bioconversion of theaflavins in specific pathogen free (SPF) mice, germ free (GF) mice, and in human fecal microbiota in vitro. Microbial bioconversion was monitored using liquid chromatography/electrospray ionization tandem mass spectrometry by analyzing the MSn (n = 1–3) spectra. Our results indicated that TFDG, TF3G and TF3′G can be metabolized by gut microbiota to generate gallic acid, pyrogallol, and TF. Glucuronidated and sulfated, instead of methylated metabolites of TF3G, TF3′G and TFDG were detected and identified as the minor mouse fecal metabolites of TFDG. To our knowledge, this is the first report on the microbial metabolism of theaflavins.

Free radical scavenging abilities in vitro and antioxidant activities in vivo of black tea and its main polyphenols

In the present study, in vitro free radical scavenging abilities and in vivo antioxidant activities of Assam black tea extract (ASTE) and theaflavins mixture (TFSM) were investigated. Our results showed that ASTE and TFSM had significant free radical scavenging activities in vitroin a dose-dependent manner, especially 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical. For antioxidant activities in vivo, the mice were fed with ASTE and TFSM everyday. The contents of malondialdehyde (MDA), and the activities of superoxide dismutase (SOD) and glutathione per- oxidase (GSH-Px) in the mice serum and liver were measured after 30 days. As a result, TFSM could obviously improve SOD and GSH-Px activities, and reduce MDA content in the serum and liver. Though ASTE also showed a certain antioxidant activity, it was slightly weaker than the antioxidant activity of TFSM in the mice. Moreover, ASTE did not change the activity of GSH-Px in the mice liver. In conclusion, our results showed that black tea and its main polyphenols were effective in scavenging DPPH, ABTS and OH free radicals in vitro, and increasing the SOD and GSH-Px activities, decreasing the MDA contents in the mice. These findings suggest the important significance of black tea consumption in prevention of diseases. Key words: Black tea, polyphenols, antioxidant, theaflavin.

A Genome-Wide Microarray Highlights the Antiinflammatory Genes Targeted by Oolong Tea Theasinensin A in Macrophages

Theasinensin A is one of the oolong tea theasinensins, which differ from green tea catechins and black tea theaflavins. In a previous study, we found that theasinesin A had a potential effect on antiinflammation since theasinensin A suppressed LPS-induced COX2 and PGE2 production. To clarify the molecular mechanisms, we investigated the gene expression profiling in macrophage-like cells treated with theasinensin A through a genome-wide DNA microarray in the present study. Among 22,050 oligonucleotides, the expression levels of 406 genes were increased by ≥3-fold in LPS-activated RAW264 cells, 259 gene signals of which were attenuated by theasinensin A treatment (≥2-fold). Expression levels of 717 genes were decreased by ≥3-fold in LPS-activated cells, of which 471 gene signals were restored by theasinensin A treatment (≥2-fold). These genes were further categorized as “defense, inflammatory response, cytokines activities, and receptor activities,” and some of them were confirmed by real-time polymerase chain reaction. Furthermore, pathways analysis revealed that theasinensin A regulated the relevant expression networks of chemokines, interleukins, and interferons to exert its antiinflammatory effects.

Molecular Binding of Black Tea Theaflavins to Biological Membranes: Relationship to Bioactivities

Molecular dynamics simulations were used to study the interactions of three theaflavin compounds with lipid bilayers. Experimental studies have linked theaflavins to beneficial health effects, some of which are related to interactions with the cell membrane. The molecular interaction of theaflavins with membranes was explored by simulating the interactions of three theaflavin molecules (theaflavin, theaflavin-3-gallate, and theaflavin-3,3'-digallate) with a mixed bilayer composed of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE). The simulations show that the theaflavins evaluated have an affinity for the lipid bilayer surface via hydrogen bonding. The molecular structure of theaflavins influenced their configuration when binding to the bilayer surface, as well as their ability to form hydrogen bonds with the lipid headgroups. The theaflavin-bilayer interactions studied here help to define structure-function relationships of the theaflavins and provide a better understanding of the role of theaflavins in biological processes. The significance of the results are discussed in the context of black tea composition and bioactivity.

Cholesterol-Lowering Effect of Black Tea Polyphenols, Theaflavins, Theasinensin A and Thearubigins, in Rats Fed High Fat Diet

Rats were fed a high fat diet containing 0.2% black tea polyphenols, theaflavins, theasinensin A or thearubigins for 4 weeks. The hepatic cholesterol concentration was significantly lower in rats fed the theaflavins, theasinensin A or thearubigins diet than in those fed the control diet without black tea polyphenols. Theasinensin A and thearubigins significantly accelerated fecal neutral and acidic steroid excretion, respectively. These results suggest that theasinensin A and thearubigins might induce the hepatic cholesterol-lowering activity through the promotion of fecal steroid excretion.

Oolong Tea Theasinensins Attenuate Cyclooxygenase-2 Expression in Lipopolysaccharide (LPS)-Activated Mouse Macrophages: Structure−Activity Relationship and Molecular Mechanisms

Oolong tea theasinensins are a group of tea polyphenols different from green tea catechins and black tea theaflavins. The present study reports the inhibitory effects of oolong tea theasinensins on the expression of cyclooxygenase-2 (COX-2) and underlying molecular mechanisms in lipopolysaccharide (LPS)-activated murine macrophage RAW264 cells. The structure-activity data revealed that the galloyl moiety of theasinensins played an important role in the inhibitory actions. Theasinensin A, a more potent inhibitor, caused a dose-dependent inhibition of mRNA, protein, and promoter activity of COX-2. An electrophoretic mobility shift assay (EMSA) revealed that theasinensin A reduced the complex of NF-κB- and AP-1-DNA in the promoter of COX-2. Signaling analysis demonstrated that theasinensin A attenuated IκB-α degradation, nuclear p65 accumulation, and c-Jun phosphorylation. Furthermore, theasinensin A suppressed the phosphorylation of MAPKs, IκB kinase α/β (IKKα/β), and TGF-β activated kinase (TAK1). These data demonstrated that the down-regulation of TAK1-mediated MAPKs and NF-κB signaling pathways might be involved in the inhibition of COX-2 expression by theasinensin A. These findings provide the first molecular basis for the anti-inflammatory properties of oolong tea theasinensins.

Preventive effects of black tea theaflavins against mouse type IV allergy

Tea (Camellia sinensis L.), one of the most popular beverages, contains various beneficial constituents. We investigated the preventive effects of black tea theaflavins, theaflavin-3-gallate (3-TF) and theaflavin-3,3'-digallate (TFDG), on oxazolone-induced type IV allergy in male ICR mice. Percutaneous administration of both 3-TF and TFDG at 0.2 mg ear(-1) showed significant preventive effects against mouse type IV allergy. Oral administration of these agents at 50 mg kg(-1) body weight also showed significant preventive effects against mouse type IV allergy. Oral administration of 3-TF and TFDG at a dose of 50 mg kg(-1) body weight prevented the increases in levels of some proinflammatory cytokines, interleukin-12 (IL-12), interferon-gamma (IFN-gamma), and tumour necrosis factor-alpha (TNF-alpha), in the sera and/or ears of mice with type IV allergy. Lowering of serum antioxidant activity in mice with allergic symptoms was also prevented by oral administration of these theaflavins at a dose of 50 mg kg(-1) body weight. The anti-allergic mechanisms of action of theaflavins involve inhibition of the fluctuations of cytokines and maintenance of antioxidant status in allergic mice. These results suggest that the theaflavins as well as catechins contribute to the anti-allergic effects of black tea.

Simultaneous determination of theanine, gallic acid, purine alkaloids, catechins, and theaflavins in black tea using HPLC

SummaryIn the present study, we employed high performance liquid chromatography with an amide‐C16 column to determine the eighteen major active ingredients in black tea, including theanine, gallic acid, four purine alkaloids, eight catechins and four theaflavins. The method was successfully used to analyse two new kinds of black teas from the leaves of Camellia ptilophylla and Camellia kucha in China and several other world‐ famous black teas. Forty percentage ethanol was chosen as the extraction solvent for preparing tea extracts. All of the eighteen compounds could be separated within 86 min with a gradient elution system. Excellent linearity was observed for all the standard calibration curves, and correlation coefficients were above 0.9991. The developed method is accurate and sensitive enough for the determination of active components in black tea.

The Past and Future of Studies on Tea and Cancer Prevention

Tea (Camellia sinensis, Theaceae) is the most popular beverage in the world. Tea preparations are classified into four types: green, black, oolong and pu-erh teas. The cancer-preventive effects of tea extracts and tea polyphenols have been demonstrated in various experimental systems of mutagenesis and carcinogenesis. Anticarcinogenic effects of tea polyphenols have been reported in the tissues/organs of skin, esophagus, stomach, colon, bladder, lung, liver, pancreas, prostate, and mammary glands of various animal models. These effects are believed to be based on green tea catechins and black tea theaflavins. Polyphenols play potential roles in reducing oxidative stress, modifying carcinogen metabolism, enhancing DNA damage repair, inhibiting tumor promotion and metastasis, and/or modulating cell-cycle arrest, apoptotic death of pre-cancerous/cancerous cells, and oncogenic signal transduction. Indeed, much evidence on the cancer preventive effects of tea polyphenols has been reported in in vitro and animal experiments. However there is insufficient and inconsistent evidence for the association between tea consumption and cancer incidence or mortality in humans. This review includes perspective on: 1) antimutagenic and anticarcinogenic effects in in vitro systems; 2) anticarcinogenic effects in animal models; 3) molecular mechanisms of anticarcinogenesis; 4) biotransformation and pharmacokinetics of tea catechin; 5) epidemiological studies; and 6) possibilities of human cancer prevention by tea polyphenols and future problems for clarification.

Nutritional supplements and serum lipids: Does anything work?

Hyperlipidemia is a risk factor for the development of coronary heart disease. Many patients decline prescription lipid-lowering agents and opt instead for supplements. Before any supplement can be routinely recommended it is crucial to examine the types of clinical trials that have been performed, the mechanism by which a supplement is felt to alter lipids, the population studied, potential adverse effects, and the possibility that investigators might be biased. Clinical trial evidence strongly supports the notion that both red yeast rice and plant stanols and sterols effectively lower low-density lipoprotein (LDL) cholesterol. Preliminary evidence supports the possibility that green tea catechins and black tea theaflavins may lower LDL. Data do not support an LDL-lowering claim for guggulipid, policosanol, or cinnamon. Finally, there is strong clinical trial evidence suggesting that marine omega-3 fatty acids lower triglycerides.

Black tea theaflavins extend the lifespan of fruit flies

Black tea extract (BTE) is a mixture of epicatechins and theaflavins. The present study investigated the effect of BTE on the lifespan of Drosophila melanogaster. Results showed the mean lifespan was significantly extended from 51 to 56 days upon BTE treatment. Gene expression of superoxide dismutase (SOD1 and SOD2), catalase (CAT), and methuselah (MTH) was characterized by an increase in young and then a decrease in aged fruit flies. Higher gene expression of SOD1 and CAT was observed in the BTE-treated group than the control flies. However, BTE exerted a minimal effect on the expression of SOD2 and MTH genes. Dietary fat could induce oxidative stress and shorten the maximum lifespan to 15 days, while addition of 10 mg/ml BTE into diet extended it to 28 days. Paraquat and H 2O 2 challenge tests demonstrated that BTE prolonged the survival time only for Oregon-R wild type flies but not for SOD n108 or Cat n1 mutants. This suggests that the lifespan-prolonging activity of BTE is mediated at least in part through SOD and CAT.

Purified black tea theaflavins and theaflavins/catechin supplements did not affect serum lipids in healthy individuals with mildly to moderately elevated cholesterol concentrations

Ingestion of tea flavonoids found in both green and black tea is linked to cardiovascular health benefits such as lowering serum lipids. Evidence for a cholesterol-lowering benefit of green or black tea consumption from human intervention studies is, however, conflicting and active components responsible for the effect have not yet been clearly identified. In a randomized, double-blind, placebo-controlled, parallel design study the effects of ingesting a purified black tea theaflavins (TFs) powder alone or in combination with catechin (TFs/catechins) on lowering serum total (TC) and LDL-cholesterol (LDL-c) were assessed. In total, 102 mildly to moderately hypercholesterolemic (TC and LDL-c: 5.70 +/- 0.74 and 3.97 +/- 0.61 mmol/L, respectively) subjects (67 men and 35 women) were randomly assigned to consume once daily one capsule of one of the 3 treatments: TFs (providing 77.5 mg), TFs/catechins (providing 75.0 mg TFs plus 150.0 mg catechins and 195.0 mg of other polyphenols), or placebo (cellulose). Serum TC and LDL-c concentrations did not differ significantly among the 3 treatments as assessed at 4, 8, and 11 weeks using analysis of covariance (p = 0.1187 and p = 0.1063, respectively). Although changes over time from baseline to week 11 were significant for TC and LDL-c (p = 0.0311 and p = 0.0269, respectively), this decrease over time was seen in the TFs and placebo groups. In this human intervention study, no statistically significant LDL-c lowering effect was seen with either TFs alone or the TFs/catechins combination as compared to placebo. Based on these findings it cannot be concluded that tea flavonoids such as theaflavins and catechins are responsible for a putative cholesterol-lowering effect of black tea, at least not with the daily dose applied in the present study.

Antifungal Activity of Black Tea Polyphenols (Catechins and Theaflavins) against Candida Species

Background/Aims: The polyphenols catechins and theaflavins in black tea have been shown to possess many medicinal properties, including anticancer activity and some antifungal characteristics, but there have been few studies of their anti-Candida activity. In this paper we report the results of our study of the anti-Candida activity of tea polyphenols. Methods: The effects of 4 different concentrations of catechins and theaflavins were evaluated on 5 isolates each of 5 Candida species employing an agar diffusion growth inhibition assay. The minimum inhibitory concentration (MIC) of the polyphenols against C. albicans was determined. The post-antifungal effect (PAFE) of the polyphenols for C. albicans was investigated. C. albicans cells exposed to polyphenols were studied using a scanning electron microscope (SEM). Results: Both polyphenols showed anti-Candida activity against all tested Candida species and demonstrated a MIC of 6.25 mg/ml for C. albicans. C. glabrata was found to be the most sensitive species followed by C. parapsilosis, C. albicans, C. krusei and C. tropicalis (p < 0.05 for all). Significant intraspecies variations in sensitivity were noted among C. parapsilosis and C. tropicalis (p < 0.001) for both polyphenols. Theaflavins displayed standard PAFE while catechins showed a paradoxical PAFE with all isolates of C. albicans. SEM revealed considerable cell wall damage of C. albicans cells exposed to the polyphenols. Conclusion: The study reveals for the first time the anti-Candida properties of black tea polyphenols that may find therapeutic applications in future.

Green and black tea are equally potent stimuli of NO production and vasodilation: new insights into tea ingredients involved

Epidemiological studies suggest that consumption of tea is associated with beneficial cardiovascular effects. Since different types of tea are consumed throughout the world, a question of much interest is whether green tea is superior to black tea in terms of cardiovascular protection. We therefore compared the effects of green and black tea on nitric oxide (NO) production and vasodilation and elucidated the tea compounds involved. We chose a highly fermented black tea and determined concentrations of individual tea compounds in both green and black tea of the same type (Assam). The fermented black tea was almost devoid of catechins. However, both teas stimulated eNOS activity and phosphorylation in bovine aortic endothelial cells (BAEC) as well as vasorelaxation in rat aortic rings to a similar extent. In green tea, only epigallocatechin-3-gallate (EGCG) resulted in pronounced NO production and NO-dependent vasorelaxation in aortic rings. During tea processing to produce black tea, the catechins are converted to theaflavins and thearubigins. Individual black tea theaflavins showed a higher potency than EGCG in NO production and vasorelaxation. The thearubigins in black tea are highly efficient stimulators of vasodilation and NO production. Green and black tea compounds induced comparable phosphorylation of eNOS and upstream signalling kinases. Whereas stimulation of eNOS activity by EGCG was only slightly affected by pretreatment of cells with various ROS scavengers, TF3(theaflavin-3',3-digallate)-induced eNOS activity was partially inhibited by PEG-catalase. These results implicate that highly fermented black tea is equally potent as green tea in promoting beneficial endothelial effects. Theaflavins and thearubigins predominantly counterbalance the lack of catechins in black tea. The findings may underline the contribution of black tea consumption in prevention of cardiovascular diseases.