绿茶多酚对自由基诱导的红细胞膜过氧化的抑制作用

采用水溶性偶氮引发剂2,2'-偶氮二(2-脒基丙烷)二盐酸盐(AAPH)在37引发入血红细胞膜的过氧化,通过测定氧气吸收及维生素E的消耗研究了过氧化过程的动力学,并对从绿茶中提取的主要多酚类化合物的抗氧化活性做了定量研究。使用的绿茶多酚有:(-)-表儿茶素(EC),(-)-表儿茶素(EGC),(-)-表儿茶素酸酯(ECG)和(-)-表儿茶素培酸酯(EGCG)。结果表明,这些绿茶多酚能够显著缩短过氧化反应的动力学链长,有效地抑制红细胞膜的过氧化。抗氧化活性顺序为:EC〉GCG〉EGCG〉EGC。     

茶中茶多酚的高效液相色谱法分离分析

用改进的Ａｇａｒｗａｌ方法萃取不同种类茶叶和茶饮料中的茶多酚,建立了用高效液相色谱（ＨＰＬＣ）法对茶多酚进行分离分析方法。ＨＰＬＣ可有效分离ＧＴＰｓ主要组成成分ＥＣ、ＥＧＣ、ＥＣＧ和ＥＧＣＧ并精确定量,相对标准偏差小于５％。茶叶加工过程对ＧＴＰｓ含量有很大影响,绿茶总ＧＴＰｓ含量在６￣１５ｇ／１００ｇ干茶叶、乌龙茶总ＧＴＰｓ含量在５￣７ｇ／１００ｇ干茶叶,红茶总ＧＴＰｓ含量低于２ｇ／１００ｇ干茶叶     

Electrochemical Characterization of Epigallocatechin Gallate Using Square‐Wave Voltammetry

Electrochemical oxidation of (?)‐epigallocatechin gallate (EGCG), the main monomer flavanol found in green tea, has been investigated over a wide pH range at a glassy‐carbon electrode using square‐wave voltammetry (SWV). Square‐wave voltammograms of (?)‐epigallocatechin (EGC) and gallic acid have been studied as well. The I–E profile of EGCG, i.e. the oxidation potentials and the current responses of the first and the second peak, is pH dependent. The oxidation of EGCG is a quasireversible process over the studied pH range, which was also confirmed by the non‐linear relationship between the peak currents and squre root of frequency. The best SWV responses for EGCG were obtained at pH 2.0, frequency of 100 Hz, step of 2 mV and amplitude of 50 mV. Under these conditions, linear responses for EGCG were obtained for concentrations from 1×10^?7 M to 1×10^?6 M, and calculated LOD and LOQ for the first oxidation peak were 6.59×10^?8 M and 2.19×10^?7 M, respectively. The proposed electroanalytical procedure was applied for the determination of EGCG content in green tea. Developed SWV methodology represents a potential analytical tool in determination of catechins in tea samples.     

Effect of Water Hardness on Catechin and Caffeine Content in Green Tea Infusions

The health benefits of green tea are associated with its high catechin content. In scientific studies, green tea is often prepared with deionized water. However, casual consumers will simply use their local tap water, which differs in alkalinity and mineral content depending on the region. To assess the effect of water hardness on catechin and caffeine content, green tea infusions were prepared with synthetic freshwater in five different hardness levels, a sodium bicarbonate solution, a mineral salt solution, and deionized water. HPLC analysis was performed with a superficially porous pentafluorophenyl column. As water hardness increased, total catechin yield decreased. This was mostly due to the autoxidation of epigallocatechin (EGC) and epigallocatechin gallate (EGCG). Epicatechin (EC), epicatechin gallate (ECG), and caffeine showed greater chemical stability. Autoxidation was promoted by alkaline conditions and resulted in the browning of the green tea infusions. High levels of alkaline sodium bicarbonate found in hard water can render some tap waters unsuitable for green tea preparation.     

Development of rapid and simultaneous quantitative method for green tea catechins on the bioanalytical study using UPLC/ESI‐MS

A rapid and quantitative analytical method for the simultaneous determination of green tea catechins using ultra‐performance liquid chromatography/electrospray ionization–mass spectrometry was developed. Total analytical run time was 3.5 min for the detection of (?)‐epicatechin (EC), (?)‐epicatechin‐3‐O‐gallate (ECG), (?)‐epigallocatechin (EGC), (?)‐epigallocatechin‐3‐O‐gallate (EGCG) and myricetin as the internal standard (IS) in rat plasma. The calibration curves were linear over the range of 10–5000 ng/mL for all the catechins. The inter‐ and intra‐day precision (relative standard deviation) and accuracy (percentage deviation) of the method were both lower than 10%. The average extraction recoveries in plasma ranged from 68.5 to 86.5%, and the lower limits of quantification of EC, EGC, ECG and EGCG were 10 ng/mL with a signal‐to‐noise ratio of >10. The assay developed was successfully applied to a pharmacokinetic study of catechins following intravenous and intragastric administrations of green tea extract in rats. Plasma concentrations of four catechins were detected up to 5–24 h after administration, and the pharmacokinetic parameters of catechins were in agreement with previous studies. From these findings, taken together with the high productivity and precision, the developed method could be a reliable and reproducible tool for the evaluation of pharmacokinetic properties of catechins. Copyright © 2012 John Wiley & Sons, Ltd.     

高效液相色谱-质谱法及模式识别法用于鉴别普洱生茶与熟茶

采用高效液相色谱-质谱联用技术及高效液相色谱法对生熟普洱茶中的主要成分进行定性和定量分析。鉴定出普洱茶水溶液中8种主要成分,分别为没食子酸(GA)、没食子酸儿茶素(GC)、表没食子酸儿茶素(EGC)、儿茶素(C)、咖啡因(CAF)、表儿茶素(EC)、表没食子酸儿茶素没食子酸酯(EGCG)和表儿茶素没食子酸酯(ECG)。以这8种成分的含量为指标,对普洱生茶和熟茶各20批进行主成分分析、聚类分析和判别分析,能准确地区分普洱生茶与熟茶。     

Electroanalytical Sensing of Green Tea Anticarcinogenic Catechin Compounds: Epigallocatechin Gallate and Epigallocatechin

A novel electroanalytical methodology for the sensing of anticarcinogenic catechin compounds epigallocatechin gallate (EGCG) and epigallocatechin (EGC) is presented. The protocol is based on the electrochemical oxidation of aminophenol in aqueous solutions, where the quinoneimine oxidation product chemically reacts with the EGCG or EGC compounds resulting in consumption of quinoneimine and consequently results in a reduction in the magnitude of the quinoneimine reduction wave, which is found to provide an analytical signal from which to indirectly detect EGCG and/or EGC.     

Reactions of tea polyphenol four constituents with hydroxyl radical: A pulse radiolytic study

Ｆｒｅｅｒａｄｉｃａｌｂｉｏｌｏｇｙａｎｄｍｅｄｉｃｉｎｅｈａｖｅｄｅｍｏｎｓｔｒａｔｅｄｔｈａｔｆｒｅｅｒａｄｉｃａｌｄｉｒｅｃｔｌｙｒｅｌａｔｅｓｔｏｔｈｅｐａｔｈｏｇｅｎｅｓｉｓｏｆｖａｒｉｏｕｓｂｉｏｌｏｇｉｃａｌｄｉｓｏｒｄｅｒ,ｅ.ｇ.ｃａｒｃｉｎｏｇｅｎｅｓｉｓ,ｃａｒｄｉｏｖａｓｃｕｌａｒｄｉｓｅａｓｅｓ,ｒａｄｉａｔｉｏｎｉｎｄｕｃｅｄｂｉｏｌｏｇｉｃａｌｄａｍａｇｅｓａｎｄａｇｉｎｇ[1],ｔｈｅｓｅｒａｄｉｃａｌｓ,ｉｎｃｌｕｄｉｎｇＯＨ·,Ｏ·-2,ｅｔｃ.,ｃａｎｂｅｐｒｏｄｕｃｅｄｂ…     

茶叶及茶多酚中儿茶素的高效液相色谱分析方法研究

 筛选出HypersilBDSC18和ZorbaxSBC18两种适合同时分离茶叶和茶多酚中 7种儿茶素和咖啡因的反相柱。采用甲醇 水 醋酸 (或三氟醋酸 )作流动相 ,分别以等强度洗脱和梯度洗脱 (均在 30min内 )分离测定了我国 6种不同产地茶叶样品和 3种茶多酚样品中 7种儿茶素的含量。考察了 7种儿茶素和咖啡因的保留值与流动相组成及柱温的关系 ,优化了色谱条件及样品前处理方法。用电喷雾电离质谱 (ESI MS)定性确认没食子儿茶素没食子酸酯(GCG)和儿茶素没食子酸酯 (CG)两组分 ,并用高效液相色谱制备两对照品用于定量分析。     

Protective role of tea catechins on erythrocytes subjected to oxidative stress during human aging

Antioxidant effect of tea catechins has been shown in many epidemiological studies. In the present study we report the protective mechanism of tea catechins (EGCG, ECG, EGC, EC) on various oxidative stress parameters, which are elevated during aging in humans. We hereby report the in vitro effect of tea catechins on erythrocyte malondialdehyde (MDA), reduced glutathione (GSH), and on membrane sulphydryl (-SH) group in humans. Results show an age-dependent increase in erythrocyte MDA level and a decrease in GSH and membrane-SH group concentration. We report that tea catechins show significant protection to erythrocyte against oxidative stress induced by tert-butyl hydroperoxide (t-BHP). The effect was more pronounced in older age group compared to lower age group. The findings suggest a possible role of tea catechins as anti-aging compounds.     

Camellia sinensis: Insights on its molecular mechanisms of action towards nutraceutical,anticancer potential and other therapeutic applications

The Camellia sinensis plant provides a wide diversity of black, green, oolong, yellow, brick dark, and white tea. Tea is one of the majorly used beverages across the globe, succeeds only in the water for fitness and pleasure. Generally, green tea has been preferred more as compared to other teas due to its main constituent e.g. polyphenols which contribute to various health benefits. The aim of this updated and comprehensive review is to bring together the latest data on the phytochemistry and pharmacological properties of Camellia sinensis and to highlight the therapeutic prospects of the bioactive compounds in this plant so that the full medicinal potential of Camellia sinensis can be realised. A review of published studies on this topic was performed by searching PubMed/MedLine, Scopus, Google scholar, and Web of Science databases from 1999 to 2022. The results of the analysed studies showed that the main polyphenols of tea are the four prime flavonoids catechins: epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC), and epicatechin (EC) along with the beneficial biological properties of tea for a broad heterogeneity of disorders, including anticancer, neuroprotective, antibacterial, antiviral, antifungal, antiobesity, antidiabetes and antiglaucoma activities. Poor absorption and low bioavailability of bioactive compounds from Camellia sinensis are limiting aspects of their therapeutic use. More human clinical studies and approaching the latest nanoformulation techniques in nanoparticles to transport the target phytochemical compounds to increase therapeutic efficacy are needed in the future.     

Solid-state NMR analysis of the orientation and dynamics of epigallocatechin gallate, a green tea polyphenol, incorporated into lipid bilayers

Catechins are the principle polyphenolic compounds in green tea; the four major compounds identified are epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECg) and epigallocatechin gallate (EGCg). Tea catechins tend to attach externally to their targets, such as viral envelopes, cell membranes, or the surface of low-density lipoproteins. In order to further our understanding of the molecular mobility of these compounds in cells, we examined the interaction of tea catechins with lipid membranes using solid-state NMR techniques. Our previous work indicated that the EGCg molecule is incorporated into lipid bilayers in a unique orientation. However, the detailed configuration, orientation, and dynamics of EGCg in lipid bilayers have not been well-characterized. Here, we investigated the orientation and dynamics of EGCg incorporated into multi-lamellar vesicles (MLVs) and bicelles using solid-state NMR spectroscopy.     

Significant Inactivation of SARS-CoV-2 In Vitro by a Green Tea Catechin,a Catechin-Derivative,and Black Tea Galloylated Theaflavins

Potential effects of tea and its constituents on SARS-CoV-2 infection were assessed in vitro. Infectivity of SARS-CoV-2 was decreased to 1/100 to undetectable levels after a treatment with black tea, green tea, roasted green tea, or oolong tea for 1 min. An addition of (−) epigallocatechin gallate (EGCG) significantly inactivated SARS-CoV-2, while the same concentration of theasinensin A (TSA) and galloylated theaflavins including theaflavin 3,3′-di-O-gallate (TFDG) had more remarkable anti-viral activities. EGCG, TSA, and TFDG at 1 mM, 40 µM, and 60 µM, respectively, which are comparable to the concentrations of these compounds in tea beverages, significantly reduced infectivity of the virus, viral RNA replication in cells, and secondary virus production from the cells. EGCG, TSA, and TFDG significantly inhibited interaction between recombinant ACE2 and RBD of S protein. These results suggest potential usefulness of tea in prevention of person-to-person transmission of the novel coronavirus.     

The Dual Action of Epigallocatechin Gallate (EGCG), the Main Constituent of Green Tea, against the Deleterious Effects of Visible Light and Singlet Oxygen-Generating Conditions as Seen in Yeast Cells

Green tea extracts (GTEs) as well as their main component, the polyphenol epigallocatechin gallate (EGCG), are known for their versatile antioxidant, antimicrobial, antitumoral or anti-inflammatory effects. In spite of the huge beneficial action, there is increasing evidence that under certain conditions green tea and its components can be detrimental to living organisms. Using Saccharomyces cerevisiae strains with various defects in the response to oxidative stress, we found that GTEs or EGCG act in synergy with visible light, exhibiting either deleterious or protective effects depending on the solvent employed. Similar synergistic effects could be observed under singlet oxygen-generating conditions, such as light exposure in the presence of photosensitizers or UV-A irradiation, therefore solvent variance may represent a powerful tool to modulate the preparation of green tea extracts, depending on the intended target.     

Simultaneous determination of twelve tea catechins by high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic method with electrochemical detection was developed for the determination of twelve tea catechins including four major catechins: epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG); four of their epimers at the C-2 position, C, GC, CG and GCG; and four methylated catechin derivatives, epigallocatechin-3-O-(3-O-methyl)gallate, gallocatechin-3-O-(3-O-methyl)gallate, epigallocatechin-3-O-(4-O-methyl)gallate and epicatechin-3-O-(3-O-methyl)gallate. These catechins were separated on an ODS C18 reversed-phase column by isocratic elution with 0.1 M NaH2PO4 buffer (pH 2.5)-acetonitrile (87:13) containing 0.1 mM EDTA.2Na. The detection limits (S/N = 3) of these catechins were approximately 10-40 pmol ml-1 at an applied voltage of 600 mV. Extracting these catechins from tea leaf powder with H2O-acetonitrile (1:1) at 30 degrees C for 40 min inhibited the epimerization at C-2 significantly from these epicatechins compared to extraction with hot water at 90 degrees C. This analytical method is sensitive to and appropriate for the simultaneous determination of various biologically active catechins in green tea.     

半制备型液相色谱法分离纯化茶叶鲜叶中7种儿茶素类化合物

建立了从茶叶鲜叶中分离纯化7种儿茶素类化合物(没食子儿茶素(GC)、表没食子儿茶素(EGC)、儿茶素(C)、表没食子儿茶素没食子酸酯(EGCG)、表儿茶素(EC)、表没食子儿茶素3-O-(3-O-甲基)没食子酸酯(EGCG3"Me)和表儿茶素没食子酸酯(ECG))的半制备色谱法。铁观音鲜叶经甲醇超声浸提、浓缩、氯仿萃取后,向水相中加入碱式醋酸铅沉淀,得到茶多酚粗品。分别以甲醇-水、乙腈-水作为流动相,采用半制备色谱法纯化7种儿茶素类化合物,纯度均达到90%。此外,利用同样的方法分离纯化另外两种茶叶鲜叶中的7种儿茶素类化合物,得到相似的结果。该方法以溶剂提取、离子沉淀结合半制备色谱,适于简单、高效地同时分离制备多种儿茶素类化合物。     

Probing the Antioxidant Activity of Polyphenols by CIDNP: From Model Compounds to Green Tea and Red Wine

Polyphenols occur naturally in a vast variety of plants. One of their predominant properties is their antioxidant activity. To provide a deeper understanding of the antioxidant mechanism, ¹H CIDNP spectroscopy (CIDNP=chemically induced dynamic nuclear polarization) is used to study model hydrogen abstraction reactions with four catechin‐based polyphenols: catechin (CA), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). The experiments involve photoinduced hydrogen‐atom transfer to a hydrogen abstractor (e.g., excited isopropylthioxanthone) followed under steady‐state conditions and in a time‐resolved fashion (resolution 500 ns–1 ms). It is found that hydrogen abstraction is an essentially stochastic process with a slight preference for the B rings in the catechin‐based polyphenols. Remarkably, analogous reactivity patterns could be followed in the “real systems”, green tea and red wine. We also show that CIDNP can be used as a semiquantitative tool to assess chemical reactivity.     

Health Benefits and Chemical Composition of Matcha Green Tea: A Review

Japanese matcha is a type of powdered green tea, grown in a traditional way. Shading of the plants during the growth period enhances the processes of synthesis and accumulation of biologically active compounds, including theanine, caffeine, chlorophyll and various types of catechins. Green tea contains four main catechins, i.e., (−)-epicatechin (EC), (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin-3-gallate (EGCG), of which the latter is the most active and abundant and matcha is their best condensed source. Due to its unique chemical composition and prized flavour, which sets it apart from other tea beverages, it is considered the highest quality tea. Its health-promoting properties are attributed to the high content of antioxidant and anti-inflammatory substances. Studies confirming the high antioxidant potential of tea beverages claim that it originates from the considerable content of catechins, a type of phenolic compound with beneficial effects on human health. Due to its potential for preventing many diseases and supporting cognitive function, regular consumption of matcha may have a positive effect on both physical and mental health. The aim of this review was to compile the health benefits of matcha tea. It is the first such review to be undertaken, and presents its main bioactive compounds in a systematic manner.     

Redifferentiation of human hepatoma cells induced by green tea polyphenols

A novel approach for the treatment of cancer is the differentiation therapy in which cancer cells are induced to attain a mature phenotype when exposed to differentiation inducers. To examine the effects of polyphenols extracted from green tea, i.e. ( – )-epicatechin (EC), ( – )-epigallocatechin (EGC), ( – )-epicatechin gallate (ECG) and ( – )-epigallocatechin gallate (EGCG), on the proliferation and redifferentiation of human hepatoma cell line SMMC-7721, we measured the changes of cell growth, cell surface charge and cell morphography after treament with green tea polyphenols. It was found that the growth curve of treated cells was decreased remarkably, cell surface charge of treated cells was decreased and the microvilli on the surface of treated cells were reduced obviously. It confirmed that green tea polyphenols could reverse malignant phenotypic characteristics and induced redifferentiation of SMMC-7721 cells. The ability of green tea polyphenols to inhibit reactive oxygen species (ROS)-mediated oxidative damage of DNA was also assessedin vitro by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular and linear forms. It was found that green tea polyphenols could significantly inhibit the oxidative damage of DNA induced by a water-soluble azo initiator 2,2-azobis(2-amidinopropane hydrochloride) (AAPH). However, they could promote the oxidative damage of DNA induced by H₂O₂ and Fe²⁺ at high concentrations. The relationship between the anti-cancer activity and antioxidation-prooxidation activity of green tea polyphenols is discussed.