白化和黄化茶树品种绿茶游离氨基酸、儿茶素类及咖啡碱差异分析

为探究以白化和黄化茶树品种鲜叶为原料制成的绿茶滋味品质和代谢物差异,对广德市6个白化品种绿茶(奶白茶)和14个黄化品种绿茶(黄金芽茶)进行感官审评和代谢物分析。结果表明,奶白茶滋味鲜爽而收敛性略弱;黄金芽茶滋味收敛性强而鲜度低于奶白茶。游离氨基酸总量以及呈现鲜味、甜味的游离氨基酸在奶白茶中的含量显著高于黄金芽茶,而贡献收敛性的儿茶素类化合物和没食子酸含量以及呈现苦味的咖啡碱含量在奶白茶中显著低于黄金芽茶。偏最小二乘法判别分析(PLS-DA)表明导致两种绿茶滋味差异的标志性化合物有7种,分别是茶氨酸、精氨酸、谷氨酸、天冬氨酸、表没食子儿茶素没食子酸酯(EGCG)、表儿茶素没食子酸酯和咖啡碱。味觉活性值(Dot)最高的EGCG在黄金芽茶中的呈味贡献显著高于奶白茶。因此,游离氨基酸、儿茶素类化合物、没食子酸和咖啡碱含量差异导致白化和黄化茶树品种绿茶滋味不同。     

人工接种冠突散囊菌对白茶主要呈味物质的影响

本文为了排除其他微生物的干扰,首次以人工接种的方式研究了冠突散囊菌Eurotium cristatum对白茶主要呈味物质的作用。采用高效液相色谱、分光光度计等方法,分析表明冠突散囊菌能够显著降低白茶中呈苦涩味的表没食子儿茶素没食子酸酯（EGCG）和表儿茶素没食子酸酯（ECG）,并提高表没食子儿茶素（EGC）、Asp、His、咖啡碱和山奈酚的含量;灭菌压制的过程中EGCG可能异构化成为更稳定的没食子儿茶素没食子酸酯（GCG）,且二者以相近的含量共存。冠突散囊菌可以降低人工发花白茶饼中呈苦涩味的化合物含量,从而达到减少白茶饼苦涩味的效果;灭菌压制过程也能够降低白茶饼的苦涩味物质的含量。“发花”处理为白茶带来了新的风味,可以丰富白茶产品种类,同时为促进粗老原料白茶的综合利用提供新思路。     

中压制备液相色谱快速分离制备儿茶素单体

以反相中压制备液相色谱为工具,甲醇-水作为洗脱溶剂,通过C18 (ODS-AQ)填料从茶多酚中一步分离出表没食子儿茶素(EGC)、表没食子儿茶素没食子酸酯(EGCG)、表儿茶素(EC)、表儿茶素没食子酸酯(ECG)等四种儿茶素单体.1.0g纯度为92.6％的茶多酚经过中压色谱,制备得到了90 mg EGC、355 mg EGCG、23 mgEC和92mg ECG,它们的纯度分别为91.8％、97.6％、97.7％、99.3％,纯品得率56.0％,四种单体总回收率达到68.2％.四种儿茶素单体的结构经核磁共振氢谱、碳谱以及高分辨质谱加以确证.     

绿茶、乌龙茶、红茶中的主要组分和酚类化合物抑制脂肪氧合酶活性和抗油脂自动氧化特性的研究

绿茶、乌龙茶和红茶中含有多种抑制脂肪氧合酶及抗油脂自动氧化的有效成分。实验结果表明,其中以表没食子儿茶素没食子酸酯(EGCG)的抗氧化活性最强,延缓猪油自动氧化诱导期为55.5小时,比无添加抗氧化成分的延长11倍,抑制脂肪氧合酶活性的IC_(50)值为10.0μmol/L。茶黄素单酯-2B(TFM-2B)和茶黄素双酯(TFD)比EGCG抑制脂肪氧合酶活性的效果更强,其IC_(60)值分别为0.57和0.23μmol/L。在三种茶叶的四种溶剂萃取物中,以乙酸乙酯萃取物的抗氧化活性最强。本文还研究了茶叶中主要生物活性物质的分离与纯化方法,以及抗氧化活性与结构的关系。     

茶槲寄生“螃蟹脚”中黄酮醇及黄烷醇类化合物的分析

随着古树普洱茶的流行,寄生在古茶树上的茶槲寄生"螃蟹脚"也成为一种饮料,但是相关研究甚少。本文应用三氯化铝比色法和酒石酸铁法分别测定了"螃蟹脚"中黄酮类化合物与茶多酚的总含量;应用HPLC法检测了黄酮醇及表没食子儿茶素(EGC)、表儿茶素(EC)、表没食子儿茶素没食子酸酯(EGCG)和表儿茶素没食子酸酯(ECG)4种茶叶中主要的黄烷醇类物质。结果表明:"螃蟹脚"中黄酮类化合物的总含量为7.65 mg/g,检测到了包括杨梅素(0.16 mg/g)、槲皮素(0.03 mg/g)、山柰酚(0.05 mg/g)和6个未知组分在内的9个黄酮醇组分;并检测到EGC、EGCG、ECG三种黄烷醇类物质,但其茶多酚总含量比茶叶低,仅为0.84%。     

表没食子儿茶素没食子酸酯及其不同氧化级分的抑菌活性研究

本文研究了表没食子儿茶素没食子酸酯(EGCG)及其氧化产物中性萃取级分(EOFA)、酸性萃取级分(EOFB)的抑菌活性.结果表明,EGCG及其氧化级分EOFA、EOFB对细菌有较强的抑菌活性,而对供试的酵母和霉菌抑制作用不明显.抑菌活性大小为:EGCG>EOFA>EOFB,且EGCG及其氧化级分随温度升高抑菌活性下降;在弱酸性条件下,EGCG、EOFA及EOFB抑菌活性较强,强酸或强碱条件下,抑菌活性均大幅下降;一定浓度的氯化钠可增强EGCG、EOFA及EOFB的抑菌活性.     

表没食子儿茶素没食子酸酯抗流感作用的研究进展

茶叶的饮用历史已有千年,其保健功效得到广泛关注。表没食子儿茶素没食子酸酯(EGCG)是茶叶提取物中含量最高、活性最强的单体,研究表明EGCG具有显著的抗流感病毒活性。因其来源丰富、价格低廉、且无耐药,是抗流感药物的有利候选。本文首次针对EGCG的抗流感机制进行综述,全面评价EGCG的抗流感价值,为后续进一步开发EGCG类抗流感药物提供参考。     

茶树表没食子儿茶素-3-O-(3-O-甲基)没食子酸酯研究进展

表没食子儿茶素-3-O-(3-O-甲基)没食子酸酯(EGCG3"Me)是茶叶中最常检测到的甲基化表没食子儿茶素没食子酸酯(EGCG"Me),具有较表没食子儿茶素没食子酸酯(EGCG)更好的保健功效。本文对EGCG3"Me的理化性质、制备方法、保健功效、茶树EGCG3"Me含量影响因素、EGCG3"Me体内合成路径等国内外研究现状进行了综述,展望EGCG3"Me的体内代谢途径及其深加工产品研发将成为研究热点。     

几种茶叶生化成分及其抗氧化活性分析

目的：比较白茶与绿茶、红茶生化成分的差异,探讨生化成分与抗氧化活性的关系。方法：以寿眉、安吉白茶及白琳工夫分别为白茶、绿茶、红茶代表,分析茶叶成分,测定茶汤抗氧化活性,并对二者进行相关性分析。结果：总黄酮含量与年份呈正相关关系,而咖啡碱则相对稳定;白茶茶多酚及儿茶素含量均低于绿茶,但其酯型儿茶素所占比重显著高于绿茶,且游离氨基酸、茶氨酸及总黄酮含量也显著高于其他两种茶类;EGC所占比重与酯型儿茶素均与茶汤抗氧化活性有较强的相关性。结论：白茶与其他茶在成分和抗氧化性上均有显著差异;EGCG与抗氧化活性相关性最强。     

一测多评法测定茶多酚中6种儿茶素类含量

采用HPLC法,以表没食子基儿茶素没食子酸酯(EGCG)为对照品,外标法测定其在茶多酚提取物中的量,并分别测定EGCG与表没食子儿茶素(EGC)、儿茶素(C)、表儿茶素(EC)、没食子基儿茶素没食子酸酯(GCG)和没食子酰表儿茶素(ECG)的相对校正因子,用获得的相对校正因子计算后5种成分的量,实现一测多评;同时,用外标法测茶多酚提取物中EGC、C、EC、GCG和ECG的量。向量夹角余弦法分析,表明外标法的测定值与采用相对校正因子的计算值之间无显著性差异,说明一测多评法可以应用于茶多酚提取物及其制剂的多指标质量评价。     

Evidence for alpha-tocopherol regeneration reaction of green tea polyphenols in SDS micelles

The synergistic antioxidant mechanism of alpha-tocopherol (vitamin E) with green tea polyphenols, i.e., (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG), and gallic acid (GA), was studied by assaying the kinetics of the reaction of alpha-tocopheroxyl radical with green tea polyphenols by stopped-flow electron paramagnetic resonance, the inhibition of linoleic acid peroxidation by these antioxidants, and the decay of alpha-tocopherol during the peroxidation. It was found that the green tea polyphenols could reduce alpha-tocopheroxyl radical to regenerate alpha-tocopherol with rate constants of 0.45, 1.11, 1.31, 1.91, and 0.43 x 10(2) M(-1) s(-1) for EC, EGC, ECG, EGCG, and GA, respectively, in sodium dodecyl sulfate micelles. In addition, these second-order rate constants exhibited a good linear correlation with their oxidation potentials, suggesting that electron transfer might play a role in the reaction.     

Matrix metalloproteinase inhibition by green tea catechins

We have investigated the effects of different biologically active components from natural products, including green tea polyphenols (GTP), resveratrol, genistein and organosulfur compounds from garlic, on matrix metalloproteinase (MMP)-2, MMP-9 and MMP-12 activities. GTP caused the strongest inhibition of the three enzymes, as measured by fluorescence assays using gelatin or elastin as substrates. The inhibition of MMP-2 and MMP-9 caused by GTP was confirmed by gelatin zymography and was observed for MMPs associated with both various rat tissues and human brain tumors (glioblastoma and pituitary tumors). The activities of MMPs were also measured in the presence of various catechins isolated from green tea including (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate(ECG), (-)-epigallocatechin (EGC), (-)-epicatechin (EC) and (+)-catechin (C). The most potent inhibitors of these activities, as measured by fluorescence and by gelatin or casein zymography, were EGCG and ECG. GTP and the different catechins had no effect on pancreatic elastase, suggesting that the effects of these molecules on MMP activities are specific. Furthermore, in vitro activation of proMMP-2 secreted from the glioblastomas cell line U-87 by the lectin concanavalin A was completely inhibited by GTP and specifically by EGCG. These results indicate that catechins from green tea inhibit MMP activities and proMMP-2 activation.     

Green tea compounds inhibit tyrosine phosphorylation of PDGF beta-receptor and transformation of A172 human glioblastoma

The effect of the green tea compounds 2-(3,4-dihydroxyphenyl)-3, 4-dihydro-2H-1-benzopyran-3,5,7-triol (catechin), epicathechin (EC), epigallocathechin-3 gallate (EGCG), epicathechin-3 gallate (ECG) and catechin-3 gallate (CG) on the tyrosine phosphorylation of PDGF beta-receptor (PDGF-Rbeta) and on the anchorage-independent growth of A172 glioblastoma cells in semisolid agar has been investigated. Treatment of A172 glioblastoma with 50 microM CG, ECG, EGCG and 25 microM Tyrphostin 1296 resulted in an 82+/-17%, 77+/-21%, 75+/-8% and 55+/-11%, respectively (mean+/-S.D., n=3) inhibition of the PDGF-BB-induced tyrosine phosphorylation of PDGF-Rbeta. The PDGF-Rbeta downstream intracellular transduction pathway including tyrosine phosphorylation of phospholipase C-gamma1 (PLC-gamma1) and phosphatidylinositol 3'-kinase (PI 3'-K) was also inhibited. Spheroid formation was completely inhibited by 50 microM ECG, CG, EGCG and by 25 microM Tyrphostin 1296. We conclude that catechins of the green tea possessing the gallate group in their chemical structure act as anticancer agents probably partly via their ability to suppress the tyrosine kinase activity of the PDGF-Rbeta.     

Enhancement of phagocytic activity of macrophage-like cells by pyrogallol-type green tea polyphenols through caspase signaling pathways

We investigated the phagocytosis-enhancing activity of green tea polyphenols, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC) catechin (+C) and strictinin, using VD3-differentiated HL60 cells. EGCG, EGC, ECG and strictinin, but not EC and +C, increased the phagocytic activity of macrophage-like cells, and a caspase inhibitor significantly inhibited phagocytic activities. These results suggest that the pyrogallol-type structure in green tea polyphenols may be important for enhancement of the phagocytic activity through caspase signaling pathways.     

Kinetics of the inhibition of bovine liver dihydrofolate reductase by tea catechins: origin of slow-binding inhibition and pH studies

Dihydrofolate reductase (DHFR) is the subject of intensive investigation since it appears to be the primary target enzyme for "antifolate" drugs, such as methotrexate and trimethoprim. Fluorescence quenching and stopped-flow fluorimetry show that the ester bond-containing tea polyphenols (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) are potent and specific inhibitors of DHFR with inhibition constants (K(I)) of 120 and 82 nM, respectively. Both tea compounds showed the characteristics of slow-binding inhibitors of bovine liver DHFR. In this work, we have determined a complete kinetic scheme to explain the slow-binding inhibition and the pH effects observed during the inhibition of bovine liver DHFR by these tea polyphenols. Experimental data, based on fluorimetric titrations, and transient phase and steady-state kinetic studies confirm that EGCG and ECG are competitive inhibitors with respect to 7,8-dihydrofolate, which bind preferentially to the free form of the enzyme. The origin of their slow-binding inhibition is proposed to be the formation of a slow dissociation ternary complex by the reaction of NADPH with the enzyme-inhibitor complex. The pH controls both the ionization of critical catalytic residues of the enzyme and the protonation state of the inhibitors. At acidic pH, EGCG and ECG are mainly present as protonated species, whereas near neutrality, they evolve toward deprotonated species due to ionization of the ester-bonded gallate moiety (pK = 7.8). Although DHFR exhibits different affinities for the protonated and deprotonated forms of EGCG and ECG, it appears that the ionization state of Glu-30 in DHFR is critical for its inhibition. The physiological implications of these pH dependencies are also discussed.     

Antioxidative effects of green tea polyphenols on free radical initiated and photosensitized peroxidation of human low density lipoprotein

Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.     

Inhibition of fucosyltransferase VII by gallic acid and its derivatives

Gallic acid (GA) and several gallate derivatives were identified as inhibitors of fucosyltransferase VII (FucT VII). The inhibition by GA and (-)-epigallocatechin gallate (EGCG) is time-dependent and irreversible. GA and EGCG showed inhibition with IC(50) of 60 and 700 nM, respectively, after pre-incubation with FucT VII in the presence of MnCl(2). Absence of MnCl(2) results in significantly weaker inhibition. Complexation of Mn(2+) with GA, EGCG, and gallate esters was observed. Such complexation, however, is not rate-limiting for the inhibition of FucT VII. Therefore, time-dependent inhibition of fucosyltransferases by GA and EGCG is likely due to the slow inactivation by the inhibitors or Mn-inhibitor complex. Although Mg(2+) or Ca(2+) can replace Mn(2+) for FucT VII activation, none forms a complex with GA or EGCG and hence results in weaker inhibition of FucT VII. GA and EGCG also inhibit FucT IV and alpha2,3-(N)-sialyltransferase in the low micromolar range. The structure-function divergence could be observed, as EGCG, but not GA or gallate esters, inhibits Zn(2+) containing metalloproteases such as TNFalpha convertase, matrix metalloproteases 2 and 7.     

In vitro chemopreventive activity of Camellia sinensis, Ilex paraguariensis and Ardisia compressa tea extracts and selected polyphenols

Several herbal teas contain bioactive compounds that have been associated with a lower risk of chronic diseases including cancer. The aim of this study was to evaluate the chemopreventive activity of tea aqueous extracts and selected constituent pure polyphenols using a battery of in vitro marker systems relevant for the prevention of cancer. The effects of (-) epigallocatechin gallate (EGCG), quercetin (Q), gallic acid (GA), green tea (GT, Camellia sinensis), ardisia tea (AT, Ardisia compressa) and mate tea (MT, Ilex paraguariensis) extracts were tested. Cytotoxicity, TPA-induced ornithine decarboxylase (ODC) and quinone reductase (QR) activities were evaluated in vitro using HepG2 cells. The topoisomerase inhibitory activity was also tested, using the Saccharomyces cerevisiae yeast system. Results suggest that MT, AT and GT are cytotoxic to the HepG2 cells, with MT demonstrating dominant cytotoxicity. EGCG showed greater cytotoxicity than Q and GA against HepG2 cells. The greatest inhibition (82%) of TPA-induced ODC activity was shown by Q, with 25 microM (IC50 = 11.90 microM). Topoisomerase II, but not topoisomerase I, was the cellular target of MT, AT, EGCG, Q and GA, which acted mainly as true catalytic inhibitors. The cytotoxic activity and the inhibition of topoisomerase II may contribute to the overall chemopreventive activity of AT and MT extracts. Ardisia and mate teas may thus share a public health potential as chemopreventive agents.     

Antioxidant effects of green tea polyphenols on free radical initiated peroxidation of rat liver microsomes

Antioxidative effects of the principal polyphenolic components extracted from green tea leaves, i.e. (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin gallate (EGCG), (−)-epigallocatechin (EGC), and gallic acid (GA), against free radical initiated peroxidation of rat liver microsomes were studied. The peroxidation was initiated by a water-soluble azo compound 2,2′-azobis(2-amidinopropane hydrochloride (AAPH). The reaction kinetics was monitored by oxygen uptake and formation of malondialdehyde (MDA). Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols (GOHs), especially EC and ECG which bear ortho-dihydroxyl functionality, are good antioxidants for microsomal peroxidation. The antioxidant synergism of these GOHs with the endogenous -tocopherol (TOH) (vitamin E) is also discussed.