Black Tea Polyphenols Research Articles

Exploration of the prebiotic potential of black tea infusion powder on the human gut microbiota in vitro

Black tea is well known for its health-promoting properties, which are mostly attributed to its polyphenol content. Black tea polyphenols are mostly non absorbable and thus readily reach the colon, where they come in contact with the gut microbiota. Several gut microbial species are able to metabolize these polyphenols, which results in bioactive metabolites on the one hand and alterations in microbial community composition on the other. To date, most studies regarding the impact of black tea on the gut microbiota have used a limited set of endpoints. In this study, a more detailed view on the potential prebiotic effects of black tea was generated. The impact of black tea infusion powder on the composition and activity of the human gut microbiota was compared to that of inulin, by applying both products in the Mucosal Simulator of the Human Intestinal Microbial Ecosystem (M-SHIME®). The results indicated that black tea infusion powder increased acetate and butyrate production, though less than inulin. The black tea infusion powder also increased microbial diversity in most colon regions and stimulated several butyrate- and propionate-producing species, next to the well-known probiotic Bifidobacterium, as identified through metagenomic sequencing. In addition, the metabolic fingerprint of the gut microbiota was beneficially altered, compared to the control, especially by the black tea product. Finally, both the black tea infusion powder and inulin increased the gut microbiota's barrier strengthening properties. Together these results indicate that black tea infusion powder has the potential to function as a prebiotic in humans.

Alkali‐induced aggregation behaviour of tea polyphenols and its gel strengthening mechanism to alkali‐induced egg white

SummaryThe effect of black and green tea extracts with different alkali induction degrees on gel properties of alkali‐induced egg white gels (EWGs) was evaluated. Results indicate that, with the increase in alkali induction time, the concentration of soluble polyphenols gradually decreases while their relative polymerisation degree increases, especially for black tea polyphenols. The addition of tea extracts, especially induced by alkaline treatment for 6, 12, and 24 h, can promote the coagulation and browning and inhibit the ‘alkali injury liquefaction’ of alkali‐induced EWGs. Additionally, under alkali‐induced conditions, polyphenols in tea, especially black tea, can enhance the textural properties and thermal stability of alkali‐induced EWGs, this enhancement reaches its peak at 12 h of alkali induction and is consistent with protein secondary structure and interaction forces results. This research provides theoretical support for selection and induction of tea in high‐gel‐strength preserved eggs and other alkali‐induced protein gel food processing.

Theaflavins mitigate diabetic symptoms in GK rats by modulating the INSR/PI3K-Akt/GSK-3 pathway and intestinal microbiota

Dietary management and interventions are crucial in the clinical management of diabetes. Numerous active dietary components in black tea have demonstrated positive effects on blood glucose levels and metabolic functions. However, limited research has explored the potential of theaflavins (TF), polyphenols in black tea, for diabetes management. In this study, high-purity TF was administered to Goto–Kakizaki (GK) diabetic model rats for four weeks to investigate its impact on diabetic pathology and analyze the underlying mechanisms through liver transcriptomics, hepatocyte metabolomics, and gut microbiome analysis. The findings indicated that continuous administration of TF (100 mg/kg) significantly suppressed blood glucose levels, reduced insulin resistance, and decreased the expression of oxidative stress indicators and inflammatory factors in GK rats. Further analysis revealed that TF might alleviate insulin resistance by improving hepatic glycogen conversion and reducing hepatic lipid deposition through modulation of key pathways, such as peroxisome proliferator-activated receptors and PI3K/AKT/GSK-3 pathways within the liver, thereby ameliorating diabetic symptoms. Additionally, TF intake facilitated the restoration of the intestinal microbial community structure by reducing the abundance of harmful bacteria and increasing the abundance of beneficial bacteria. It also reduced endotoxin lipopolysaccharide production, thereby lowering the chances of insulin resistance development and enhancing its efficacy in regulating blood glucose levels. These findings offer a novel perspective on the potential of black tea and its active constituents to prevent and treat diabetes and other metabolic disorders, providing valuable references for identifying and applying active dietary components from tea.

UNDERSTANDING THE IMPACT OF UV RADIATION ON SKIN HEALTH: MECHANISMS, RISKS, AND PHOTOPROTECTION STRATEGIES

This comprehensive review examines the intricate relationship between UV radiation and skin health, delving into its mechanisms, associated risks, and potential photoprotection strategies. Drawing from centuries of herbal medicine and cosmetic practices, the efficacy of antioxidant-rich herbs in shielding against UV radiation-induced damage is highlighted. Studies showcasing the protective properties of plant extracts, such as green and black tea polyphenols and aloe vera formulations, underscore the potential of botanicals in skincare. The rise of herbal sunscreens in response to growing concerns over UV exposure reflects a paradigm shift in skincare practices. The review elucidates the diverse effects of UV radiation on the skin, encompassing sunburns, premature aging, and skin cancer development. Mechanisms underlying UVB-induced skin damage, including collagen breakdown, generation of free radicals, and interference with DNA repair mechanisms, underscore the imperative of implementing protective measures. The role of antioxidants in mitigating UV-induced damage and the development of innovative sunscreen formulations underscores ongoing efforts to enhance photoprotection strategies. Furthermore, the review underscores the multifaceted nature of UV radiation’s impact on skin health, emphasizing the importance of holistic approaches to photoprotection.Future research endeavors aimed at exploring novel photoprotective agents and assessing their efficacy in preserving skin health will be instrumental in mitigating the adverse effects of UV radiation and fostering overall skin well-being.

Role of tea polyphenols in enhancing the performance, sustainability, and catalytic cleaning capability of membrane separation for water-soluble pollutant removal

Tea polyphenols (TPs), like green tea polyphenol (GTP) and black tea polyphenol (BTP), with phenolic hydroxyl structures, form coordination and hydrogen bonds, making them effective for bridging inorganic catalysts and membranes. Here, TPs were employed as interface agents for the preparation of TPs-modified needle-clustered NiCo-layered double hydroxide/graphene oxide membranes (NiCo-LDH-TPs/GO). The incorporation of porous guest material, NiCo-LDH-TPs, facilitated water channel expansion, enhancing membrane permeability and resulting in the development of high-performance, sustainable catalytic cleaning membranes. The introduction of TPs through coordination weakened the surface electronegativity of NiCo-LDH, promoting a uniform mixed dispersion with GO and facilitating membrane self-assembly. NiCo-LDH-GTP/GO-5 and NiCo-LDH-BTP/GO-5 membranes demonstrated permeances of 85.98 and 90.76 L m−2 h−1 bar−1, respectively, with rejections of 98.73% and 99.54% for methylene blue (MB). Notably, the NiCo-LDH-BTP/GO-5 membrane maintained a high rejection of 97.11% even after 18 cycles in the catalytic cleaning process. Furthermore, the modification of GTP and BTP enhanced MB degradation through PMS activation, resulting in a 0.33% and 0.35% increase in the reaction rate constants of NiCo-LDH, respectively, while reducing metal ion spillover. These findings highlighted the potential of TPs in enhancing the efficiency and sustainability of catalytic cleaning GO membranes for water purification and separation processes.

Biopolyphenol stabilized CoFe2O4-rGO/GO catalytic cleaning membrane for fast and high-efficiency contaminants removal

Utilizing membrane materials for the purification of wastewater represents an effective approach to address water scarcity. Nonetheless, the issues of membrane fouling and stability hinder their widespread application. Herein, an effective biopolyphenols (PP) modification strategy was proposed to construct strongly stable cobalt ferrite-loaded graphene oxide (CoFe2O4-rGO-PP/GO) membranes with catalytic cleaning function. Compared with the membranes without PP modification, the incorporation of polymerized tannic acid (pTA), green tea polyphenol (GTP), and black tea polyphenol (BTP) significantly improved membrane separation efficiencies of methylene blue (MB), with high removal reaching 99.11, 98.92, and 99.20 %, respectively. Notably, the CoFe2O4-rGO-pTA/GO membrane demonstrated high rejection and outstanding permeability of 167.2 L m−2 h−1 bar−1. Introducing pTA, GTP, and BTP could enhance MB degradation rate constants by 61.54, 38.46, and 19.23 % via peroxymonosulfate (PMS) activation, respectively. Remarkably, CoFe2O4-rGO-pTA/GO membrane achieved near-complete MB degradation within 12 min. Moreover, CoFe2O4-rGO-PP/GO membranes maintained high MB rejection exceeding 97 % even after ten cycles, highlighting exceptional stability and catalytic cleaning performance. The separation mechanism of these membranes was dominantly governed by the nano-confined adsorption under pressure-driven flow-through process, which was greatly distinguished from a size-sieving mechanism of densely stacked 2D lamellar membranes replying on their in-plane pores or interlayer nano/subnano-channels. This PP modification strategy can be extended to design diversified 2D lamellar membranes with guest intercalation, to achieve high stability, superior separation and multi-function.

The Antiobesity Effects and Potential Mechanisms of Theaflavins.

Theaflavins are the characteristic polyphenols in black tea which can be enzymatically synthesized. In this review, the effects and molecular mechanisms of theaflavins on obesity and its comorbidities, including dyslipidemia, insulin resistance, hepatic steatosis, and atherosclerosis, were summarized. Theaflavins ameliorate obesity potentially via reducing food intake, inhibiting pancreatic lipase to reduce lipid absorption, activating the adenosine monophosphate-activated protein kinase (AMPK), and regulating the gut microbiota. As to the comorbidities, theaflavins ameliorate hypercholesterolemia by inhibiting micelle formation to reduce cholesterol absorption. Theaflavins improve insulin sensitivity by increasing the signaling of protein kinase B, eliminating glucose toxicity, and inhibiting inflammation. Theaflavins ameliorate hepatic steatosis via activating AMPK. Theaflavins reduce atherosclerosis by upregulating nuclear factor erythropoietin-2-related factor 2 signaling and inhibiting plasminogen activator inhibitor 1. In randomized controlled trails, black tea extracts containing theaflavins reduced body weight in overweight people and improved glucose tolerance in healthy adults. The amelioration on the hyperlipidemia and the prevention of coronary artery disease by black tea extracts were supported by meta-analysis.

Comparison of Si-GA-PLS and Si-CARS-PLS build algorithms for quantitation of total polyphenols in black tea using the spectral analytical system.

The objective of the current study was to compare two machine learning approaches for the quantification of total polyphenols by choosing the optimal spectral intervals utilizing the synergy interval partial least squares (Si-PLS) model. To increase the resilience of built models, the genetic algorithm (GA) and competitive adaptive reweighted sampling (CARS) were applied to a subset of variables. The collected spectral data were divided into 19 sub-interval selections totaling 246 variables, yielding the lowest root mean square error of cross-validation (RMSECV). The performance of the model was evaluated using the correlation coefficient for calibration (RC ), prediction (RP ), RMSECV, root mean square error of prediction (RMSEP) and residual predictive deviation (RPD) value. The Si-GA-PLS model produced the following results: PCs = 9; RC = 0.915; RMSECV = 1.39; RP = 0.8878; RMSEP = 1.62; and RPD = 2.32. The performance of the Si-CARS-PLS model was noted to be best at PCs = 10, while RC = 0.9723, RMSECV = 0.81, RP = 0.9114, RMSEP = 1.45 and RPD = 2.59. The build model's prediction ability was amended in the order PLS < Si-PLS < CARS-PLS when full spectroscopic data were used and Si-PLS < Si-GA-PLS < Si-CARS-PLS when interval selection was performed with the Si-PLS model. Finally, the developed method was successfully used to quantify total polyphenols in tea. © 2023 Society of Chemical Industry.

Chitosan-polypeptide nanocomplexes crosslinked by a natural crosslinker enhanced the intestinal permeability of black tea polyphenol

The discrepancy between in vitro and in vivo bioefficacies of hydrophilic polyphenols often stems from their low intestinal permeabilities. Chitosan (CS)-based polysaccharide-polypeptide nanocomplexes are promising delivery systems for enhancing the intestinal permeability of hydrophilic polyphenols. However, these nanocomplexes are intrinsically susceptible to pH changes, which limits their applications. In this study, the nanocomplexes self-assembled by CS and caseinophosphopeptides (CPPs) were crosslinked by a natural crosslinker genipin, aiming to improve their pH stabilities. The crosslinking reaction altered not only the size, surface charge, and morphology but also the microstructures of the CS-CPPs nanocomplexes (CCNs). Compared to the non-crosslinked counterparts, genipin-crosslinked CCNs (GCCNs) showed higher stability against pH change as they were more resistant to acid-induced dissociation at gastric pH. GCCNs were further used to encapsulate theaflavin-3,3′-digallate (TF-3), an important polyhydroxylated polyphenol in black tea that has low intestinal permeability. Encapsulation of TF-3 also influenced the physicochemical features of the nanocomplexes. Notably, loading in GCCNs significantly enhanced the in vitro intestinal permeability of TF-3. This study demonstrated that GCCNs not only had high pH stability but also had the capacity to enhance the in vitro intestinal permeability of TF-3.

Black Tea Extracts/Polyvinyl Alcohol Active Nanofibers Electrospun Mats with Sustained Release of Polyphenols for Food Packaging Applications

The efficiency in the capabilities to store and release antioxidants depends on the film morphology and its manufacturing process, as well as on the type and methodology used to obtain the polyphenol extracts. Here, hydroalcoholic extracts of black tea polyphenols (BT) were obtained and dropped onto different polyvinyl alcohol (PVA) aqueous solutions (water or BT aqueous extract with and without citric acid, CA) to obtain three unusual PVA electrospun mats containing polyphenol nanoparticles within their nanofibers. It was shown that the mat obtained through the nanoparticles precipitated in BT aqueous extract PVA solution presented the highest total polyphenol content and antioxidant activity, and that the addition of CA as an esterifier or PVA crosslinker interfered with the polyphenols. The release kinetics in different food simulants (hydrophilic, lipophilic and acidic) were fitted using Fick's diffusion law and Peppas' and Weibull's models, showing that polymer chain relaxation is the main mechanism in all food simulants except for the acidic, which presented an abrupt release by Fick's diffusion mechanism of about 60% before being controlled. This research provides a strategy for the development of promising controlled-release materials for active food packaging, mainly for hydrophilic and acidic food products.

Suppressive effect of black tea polyphenol theaflavins in a mouse model of ovalbumin-induced food allergy.

Food allergy is recognized as a global medical problem with increasing prevalence in recent years. Currently, the treatment of food allergy mainly involves avoidance of allergens and allergen-specific immunotherapy. Barring the spontaneous resolution of food allergy during the growth process, this disease is difficult to treat fundamentally. In recent years, the use of functional food ingredients derived from natural products has been attracting attention for their prophylactic use in food allergy. Theaflavins, i.e., black tea polyphenols, are potent antioxidants that have inhibitory effects on a variety of diseases. However, little is known about the preventive effect of theaflavins on food allergy. In this study, we designed a mouse model of food allergy and examined the effect of theaflavins using the severity of diarrhea, a symptom of food allergy, as an indicator. The administration of a black tea extract rich in theaflavins or theaflavin 1 (subgroup of theaflavins) to mice reduced the severity of diarrhea when compared with a normal diet. A reduction in malondialdehyde levels, a key marker of lipid peroxidation, was also observed. Overall, these data suggest that theaflavins may potentially inhibit food allergy by alleviating oxidative stress in the colon and can be a potential food material for prevention of food allergy.

The Effectiveness of Titanium Dioxide Sunscreen in Combination with Skin Defensil Plus® as an Anti-inflammatory Agent against Ultraviolet Radiation

BACKGROUND: Ultraviolet (UV) radiation can cause tanning and sunburn in the short-term; nevertheless, continued exposure to UV on unprotected skin will promote premature aging and gene mutation that leads to malignancy. Photoaging caused by sun exposure can happen through inflammation and reactive oxygen species pathway. Defensil plus® consists of natural plant ingredients that have an anti-inflammatory and anti-oxidant activity to protect the skin from UV exposure. Sunscreen with anti-oxidant and anti-inflammatory properties will reduce the unwanted effect of UV radiation, such as tanning and sunburn. AIM: The aim of the study was to determine the effectiveness of the combination of titanium dioxide (TiO2) sunscreen with defensil plus® against UV radiation. METHODS: This was an experimental research design with pre- and post-test design approaches. Twenty subjects consisting of ten males and ten females with an average age of 23 years old, participated in this study. We conducted an experimental study with two groups. Group A was the TiO2+ defensil plus® group; Group B was the TiO2 group. The skin protection effect was compared by examining the erythema and melanin indexes using Mexameter® on day 0, post-radiation days 1, 2, 3, 4, and 7. Data Analysis using an independent t-test if the data distribution is expected, while the Mann–Whitney test is used if it does not meet the normality assumption. Data were considered significant with p &lt; 0.05. RESULTS: Melanin index decreased significantly from day 1 to 7 in the group that was given TiO2 + defensil plus® compared to the group that was only given TiO2 (p = 0.003). The erythema index gradually decreased and significantly different in the group given TiO2 application (p = 0.036). + defensi plus® compared to the group given TiO2 after 3rd day of application (p = 0.036). CONCLUSION: Application of sunscreen with TiO2 + defensil plus® is effective in response to UV radiation, as demonstrated by lower erythema and melanin indexes than those treated with TiO2 sunscreen alone, thus could protect the skin from UV radiation. Many studies showed that green and black tea (polyphenols) ameliorate adverse skin reactions following UV exposure.

THE CHANGES IN SALIVARY PH BY CHEWING BLACK TEA (Camellia sinensis) CANDY CONTAINING THE SORBITOL

Background: Tea contains beneficial chemical compounds, one of which is polyphenols. The polyphenols in black tea can inhibit the growth of bacteria and prevent oral infections. Black tea extract has been proven to increase salivary pH, but children do not like it because of its bitter taste. Therefore, innovation is needed by incorporating black tea extract into candy containing sorbitol. Objective: To determine the effectiveness of chewing black tea candy containing sorbitol on salivary pH compared to non-black tea candy in children aged 7-8. Methods: This research is an experimental field study using a single-blind randomized controlled trial with a pretest-posttest control group design. The research subjects were of 42 children aged 7-8 years divided into two groups, the treatment group, and the placebo group, using a simple random sampling technique. A sampling of saliva was carried out before and after chewing hard candy. Monitoring was carried out for approximately 23 days, and pH was measured three times. Measurement of pH using a digital pH meter®. Results: After conducting the research, it can be seen that there is a significant difference between chewing hard candy made from black tea and sorbitol on the changes in salivary pH (p-value = 0.0001). Conclusion: Chewing hard candy made from black tea and sorbitol is likely to help increase salivary pH, and it could be a solution to prevent dental caries in the future. Keywords : Black tea; Dental caries; Hard candy; Salivary pH ; Sorbitol.

Prevention of carcinogen-induced oral cancers by polymeric black tea polyphenols via modulation of EGFR-Akt-mTOR pathway

The overexpression of Epidermal Growth Factor Receptor (EGFR) and dysregulation of its downstream effector pathways are important molecular hallmarks of oral cancers. Present study investigates the chemopreventive potential of polymeric black tea polyphenols (PBPs)/thearubigins (TRs) in the hamster model of oral carcinogenesis as well as determine the effect of PBPs on EGFR and the molecular players in the EGFR pathway. In dose-dependent manner, pre and concurrent treatment with PBPs (1.5%, 5%, 10%) decreased the number and volume of macroscopic tumors as well as the number and area of microscopic lesions. Interestingly, at 10% dose of PBPs, no macroscopic or microscopic tumors were observed. We observed PBPs mediated dose-dependent decrease in oxidative DNA damage (8OHdG); inflammation (COX-2); proliferation (PCNA, Cyclin D1); expression of EGFR, and its downstream signaling kinases (pAkt, Akt, and mTOR); hypoxia (HIF1α) and angiogenesis (VEGF). There was also a PBPs mediated dose-dependent increase in apoptosis (Bax). Thus, our data clearly indicate that the observed chemopreventive potential of PBPs was due to modulation in the EGFR pathway associated with cell proliferation, hypoxia, and angiogenesis. Taken together, our results demonstrate preclinical chemopreventive efficacy of PBPs and give an insight into its mechanistic role in the chemoprevention of experimental oral cancer.

Characterization and Analysis of Polyphenols in Green and Black Tea Brands Available in Commercial Market of Pakistan

In present study, the quality of commercial brands of green and black tea available in Pakistan was analyzed on the basis of phenolic contents. Total phenolic content was analyzed through spectrophotometric measurement using the ferrous Tartrate method. Individual catechins along with gallic acid and caffeine were determined using HPLC-UV. TPC of green tea was found to be higher than black tea. Among green tea brands, Lipton Clear Green showed higher TPC than Tapal Gulbahar. Both green and black tea polyphenols showed higher solubility in the aqueous acetone (50%, v/v) compared towater. (-)-EGCG was detected as the most abundant catechins in all green and black tea samples. Theaflavin content of Lipton Yellow Label and Vital was significantly higher than Tapal Family Mixture and Tetley. Based on catechins and theaflavins content, Lipton Clear Green, Lipton Yellow Label, and Vital Tea were considered to be of higher quality than other brands.

Gut Microbiota as a Novel Tool to Dissect the Complex Structures of Black Tea Polymers.

Thearubigins, polymers of tea catechins, account for more than 20% of the black tea polyphenols and have been reported to be the active components in black tea. However, the chemical structures and underlying mechanisms regarding how the thearubigins, being poorly bioavailable, generate in vivo health benefits are still largely unknown. Using germ-free and specific pathogen-free husbandry conditions combined with LC/MS-based nontargeted and targeted metabolomic analyses, we investigated the role of intestinal bacteria in thearubigin metabolism. Theaflavins and theasinensins were identified as the major microbial metabolites of thearubigins, suggesting that these molecules are the building units for the complex thearubigins. To further confirm this, thearubigin depolymerization was done using menthofuran in an acidic condition. Menthofuran-conjugated theaflavins, theasinensins, and catechins as well as their free forms were detected as the major degradation products of thearubigins. This indicated that theaflavins and theasinensins could be further polymerized through B-type proanthocyanidin linkages. Furthermore, four microbial degradation products were able to be detected in urine samples, suggesting that they can be absorbed into the circulatory system. Using the combination of microbial degradation, metabolomics, and chemical degradation, our results demonstrate that thearubigins are the complex polymers of theaflavins, theasinensins, and catechins and can be metabolized by gut microbiota to their corresponding bioactive and bioavailable smaller molecular metabolites.

Innovative Green Chemistry Approach to Synthesis of Sn2+-Metal Complex and Design of Polymer Composites with Small Optical Band Gaps.

In this work, the green method was used to synthesize Sn2+-metal complex by polyphenols (PPHs) of black tea (BT). The formation of Sn2+-PPHs metal complex was confirmed through UV-Vis and FTIR methods. The FTIR method shows that BT contains NH and OH functional groups, conjugated double bonds, and PPHs which are important to create the Sn2+-metal complexes. The synthesized Sn2+-PPHs metal complex was used successfully to decrease the optical energy band gap of PVA polymer. XRD method showed that the amorphous phase increased with increasing the metal complexes. The FTIR and XRD analysis show the complex formation between Sn2+-PPHs metal complex and PVA polymer. The enhancement in the optical properties of PVA was evidenced via UV-visible spectroscopy method. When Sn2+-PPHs metal complex was loaded to PVA, the refractive index and dielectric constant were improved. In addition, the absorption edge was also decreased to lower photon. The optical energy band gap decreases from 6.4 to 1.8 eV for PVAloaded with 30% (v/v) Sn2+-PPHs metal complex. The variations of dielectric constant versus wavelength of photon are examined to measure localized charge density (N/m*) and high frequency dielectric constant. By increasing Sn2+-PPHs metal complex, the N/m* are improved from 3.65 × 1055 to 13.38 × 1055 m−3 Kg−1. The oscillator dispersion energy (Ed) and average oscillator energy (Eo) are measured. The electronic transition natures in composite films are determined based on the Tauc’s method, whereas close examinations of the dielectric loss parameter are also held to measure the energy band gap.

Non-Targeted Metabolomic Analysis of the Kombucha Production Process.

Kombucha is a traditional fermented beverage obtained from the transformation of sugared black tea by a community of yeasts and bacteria. Kombucha production recently became industrialized, but its quality standards remain poorly defined. Metabolomic analyses were applied using FT-ICR-MS to characterize the impacts of production phases and the type of tea on the non-volatile chemical composition of kombucha. Independently from tea type, the first phase of acidification in open vessel was characterized by the release of gluconate and gallate from acetic acid bacteria metabolism and probably from polymeric polyphenols, respectively. The second phase of carbonation in closed vessel induced a consumption or transformation of oleic acid that could be consecutive of oxygen limitation. The first phase had the most impact on molecular diversity, but tea type mainly influenced the global composition in polyphenol profile. Black tea polyphenols were more impacted by microbial activity compared to green tea polyphenols.

Mechanistic studies on polyphenol rich fractions of Kangra tea by HPTLC and NMR for their antioxidant activities.

The antioxidant activity in tea is largely driven by its polyphenolic content, however, the antioxidant reaction mechanism and the compounds involved are not well characterized. Therefore, in this study, we performed in-depth profiling ofthe antioxidant reaction mechanism of Green Tea (GT), Black Tea (BT), and their polyphenolic fractions with free radical using state-of-the-art analytical techniques. The polyphenol enriched fractions from GT and BT were isolated using column chromatography. Catechins were isolated and characterized by diverse spectroscopic techniques. Samples were screened for their antioxidant activity by HPTLC and further evaluated using a spectrophotometer. The free radical reactions with GT, BT, enriched fractions viz, GT Polyphenols (GTP), BT Polyphenols (BTP), and isolated catechins were studied using the13C NMR technique. The highest polyphenol content was found in GTP (795.4 ± 0.012mg/g) whereas GT (321.0 ± 0.028mg/g) showed maximum flavonoids content. Individual catechins isolated from GTP were EGCG, ECG, EGC, EC and C. Antioxidant activity followed the order EGCG > ECG > EGC > EC > GTP > C > BTP > GT > BT. In GT, the antioxidant reaction mechanism showed single electron and H-transfer in all catechins, which involved the transformation of the hydroxyl group to the carbonyl group. Whereas in BT theaflavins, conversion of the benzotropolone ring to the six-membered ring was observed. The online version contains supplementary material available at 10.1007/s13197-021-05297-w.

Effect of fermentation time and temperature on the of polyphenol compounds change of different Congou black tea

This study evaluated the effects of fermentation time and temperature on the content of high molecular weight polyphenol mitochondrial activation factors (MAFs) and other polyphenols in Congou black tea using high-performance liquid chromatography (HPLC). There were two broad chromatographic peaks in the HPLC spectra of MAFs: MAFs-1 (16.163 min) and MAFs-2 (34.31 min); MAFs-2 was satisfactorily analyzed by HPLC, with separation by paper chromatography. The MAFs-2 contents increased gradually in different varieties of Congou black tea as the fermentation time and temperature increased; the maximum MAFs-2 content was 5.11% in Xiaoxianghong 21-3 after 8 hr of fermentation. The total polyphenols and catechins contents decreased, whereas the theabrownins contents increased as the fermentation time and temperature increased; the theaflavins and thearubigins contents in different Congou black teas showed different variation tendencies. Therefore, studies regarding changes in polyphenols during fermentation will help improve the quality of Congou black tea and enhance its health benefits. Novelty impact statement A new method for the determination of MAFs-2 by high-performance liquid chromatography combined with paper chromatography was established. The content of MAFs-2 increased initially and then stabilized as fermentation was continued from 2 to 8 hr, it increased gradually as the fermentation temperature was increased from 23 to 37°C. These results provide a new analytical method for MAFs in black tea and a theoretical basis and technical guidance for improving the quality of Congou black tea.