Selective elution of tea catechins and caffeine from polyvinylpolypyrrolidone

Desorption of catechins and caffeine from polyvinylpolypyrrolidone (PVPP) was comprehensively investigated. The result showed that caffeine could easily be desorbed from PVPP by the tested solvents except n‐hexane, while catechins could only be thoroughly done by dimethyl sulphoxide (DMSO) and N, N‐dimethylformamide (DMF). Excellent desorption efficiency of DMSO and DMF might be attributed to their high dipole moments and H‐bond potentials. Addition of ethanol was recommended considering the elution efficiency and fluidity, but ethanol volume should be <40% (v/v) for DMSO or 20% (v/v) for DMF. Desorption would get to equilibrium within 1 h and followed the pseudo‐second‐order model. Caffeine and catechins could be separately desorbed through two‐stage elution procedure, that is, water or 20% aqueous ethanol for desorbing caffeine and part of nongalloylated catechins and DMSO/ethanol (8/2, v/v) for eluting the remaining catechins. Highly purified catechins (~95%) with high level (~70%) galloylated catechins would be achieved when the desorption procedure was applied in column chromatograph.     

5种多酚类化合物提高紫甘蓝花色苷热稳定性及辅色机理初探

该研究选取儿茶素、没食子酸、香兰素、槲皮素、山奈酚五种多酚化合物作为辅色剂对紫甘蓝花色苷进行辅色,结果表明随着浓度增加,儿茶素和没食子酸的辅色作用不断加强,当浓度达到0.01 mol/L时,辅色作用增长缓慢;香兰素浓度达到0.004 mol/L时,辅色作用最强,浓度继续增加辅色作用反而减弱;槲皮素和山奈酚对紫甘蓝花色苷...     

Polyphenolic composition and in vitro antioxidant activities of native‐ and tannase‐treated green tea extracts

The antioxidant activities of native‐ and tannase‐treated green tea extracts along with their major polyphenol components were investigated. The polyphenolic content and composition of the tea before and after tannase treatment were determined by liquid chromatography coupled with mass spectrometry (LC‐MS). Approximately 99% of the (?)‐epigallocatechin gallate (EGCG) and (?)‐epicatechin gallate (ECG) in green tea extract were converted by tannase to (?)‐epigallocatechin (EGC) and (?)‐epicatechin (EC), respectively, after 30 min. Biotransformed green tea exhibited a significantly higher DPPH˙ radical scavenging activities than native green tea (EC₅₀ value of 0.024 ± 0.001 and 0.044 ± 0.001 mg mL^?1, respectively). Kinetic parameters such as scavenging rate and stoichiometry were calculated. The rate of DPPH˙ radical scavenging activities for tannase‐treated green tea extract was shown to be higher than native green tea extract.     

Cognitive enhancement and neuroprotection by catechin‐rich oil palm leaf extract supplement

BACKGROUND: Catechin‐rich oil palm (Elaeis guineensis) leaf extract (OPLE) has good cardiovascular and phytoestrogenic properties. The OPLE (0.5 g day^?1) was supplemented to young, healthy, adult human volunteers, and their cognitive learning abilities were compared to placebo‐controlled groups (N = 15). Their short‐term memories, spatial visualisations, processing speeds, and language skills, were assessed over 2 months by cognitive tests computer programs. RESULTS: Relative to the controls, volunteers taking OPLE had improved (P < 0.05) short‐term memory, after 1 month of intervention which became highly significant (P < 0.005) after 2 months. The spatial visualisation ability and processing speed improved (P < 0.05) after 2 months consumption. The dietary OPLE showed neuroprotection in nitric oxide‐deficient rats. The mechanisms involved systemic and cellular modulations that eventually enhance neuron survival. The longer the duration of OPLE consumption, the more significant was the enhancement, as shown for short‐term memory. CONCLUSION: This is the first report on the cognitive‐enhancing effects of dietary OPLE in humans. The computer‐assisted cognitive tests were simple, low in cost, errors and man hours, and hence are better than conventional cognitive test methods. In rats, the equivalent OPLE dose showed brain antioxidant enzymes modulating properties and neuroprotection under nitric oxide deficiency, with possibly neurogenesis in normal rats. This supported the effects in humans. © 2012 Society of Chemical Industry     

Antioxidant activity of tea theaflavins and methylated catechins in canola oil

The present study examined the antioxidant activity of black tea theaflavins and catechin derivatives in canola oil. Oxidation was conducted at 95°C by monitoring the oxygen consumption and decreases in the linoleic and α-linolenic acids of canola oil. All were tested at a concentration of 0.5 mM. Catechins, including (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, and (−)-epigallocatechin gallate (EGCG), were more effective than theaflavins, namely, theaflavin-1, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3,3′-digallate (TF₃), against the lipid oxidation of canola oil. Among the four theaflavins, TF₃ was the most effective, whereas among the four catechins, FGCG was the most potent. Under the same conditions, all theaflavins and catechins were more powerful than BHT as an antioxidant in heated canola.oil. Little or no difference in antioxidant activity was observed between each catechin and epimer pair. Methylation of the 3′-OH led to a significant loss of antioxidant activity of the catechins.     

茶叶儿茶素组分HPLC测定中的提取方法研究

以蒸青绿茶为材料,利用单因素试验和正交实验研究了不同提取时间、不同提取温度以及不同提取料液比例等对茶叶中儿茶素组分的影响。结果表明:当提取料液比例为1:125(g:mL)、提取温度为70℃、提取时间为30 min时,蒸馏水一次提取可以达到相对理想的提取效果,适用于常规分析实验。     

Presence of two forms of methylated (–)‐epigallocatechin‐3‐gallate in green tea

Crude catechins extract from Chinese green tea were fractionated using Sephadex LH‐20 column chromatography. The fraction containing (–)‐epigallocatechin‐3‐gallate (EGCG) was then subjected to a semipreparative high‐performance liquid chromatography (HPLC). Using a mobile phase of water : dimethyl formamide : methanol : acetic acid (157 : 49 : 2 : 1 v/v/v/v( the mixture of two methylated catechins was separated and isolated. According to mass spectrometry (MS) and nuclear magnetic resonance (¹H‐NMR) date, these compounds were identified as (–)‐epigallocatechin‐3‐(3‐O‐methylgallate) and (–)‐epigallocatechin‐3‐(4‐O‐methylgallate).     

不同类型白茶儿茶素、香气成分与感官品质比较

白茶是我国特有的一种微发酵茶,为探明不同类型白茶的品质差异,本研究选取了白毫银针、白牡丹、贡眉、寿眉、新工艺白茶共10个白茶样品,分别进行了高效液相色谱(HPLC)检测儿茶素、气相色谱-质谱(GC-MS)检测香气成分以及感官评价,并结合方差分析和OPLS-DA等多元统计学分析。结果表明,不同类型白茶中儿茶素含量差异较大,贡眉的总儿茶素含量最高,寿眉最低,分别为66.84和32.66 mg/g,并且所有白茶共检测到50种香气物质,主要香气组分有正己醛、(E)-2-己烯醛、苯甲醛、芳樟醇及其氧化物(I、II)等。白毫银针、白牡丹、贡眉、寿眉等4种传统工艺白茶的香气组成和含量与新工艺白茶有明显差异,其中,(E)-2-戊烯醛、2-庚酮等8种香气成分在4种传统工艺白茶中大量存在,而在新工艺白茶中未检测出。通过多组分化学计量学分析发现,白毫银针、白牡丹、贡眉与新工艺白茶的儿茶素和香气代谢物存在显著差异,而寿眉与新工艺白茶相差不大。本研究初步探明了不同类型白茶的品质差异,为白茶风味品质调控提供理论依据。     

Analysis of the theaflavin composition in black tea (Camellia sinensis) for predicting the quality of tea produced in Central and Southern Africa

A parameter of black tea that correlates with quality is highly desired. Twenty good and 20 poor quality tea clones were selected from the breeding programme at the Tea Research Foundation (Central Africa) (TRF(CA)). The theaflavin (TF) composition of the black tea manufactured from each clone was analysed by capillary electrophoresis and correlated with total scores and valuation from two tea tasters with regression analysis. The significance of the differences between the 20 good and 20 poor quality tea clones was determined with the Student t‐test and the distribution‐free Kruskal–Wallis test. The sum of the TFs of the black tea correlated well (r = 0.785, P = 0.0002) with the value of the tea. Of the individual TFs determined in the black tea, the highest correlation was obtained with TF‐3′‐monogallate (TF‐B) (r = 0.788, P = 0.0016), TF‐3‐monogallate (TF‐A) (r = 0.741, P = 0.0004) and free TF (TF‐f) (r = 0.705, P = 0.0002). TF‐B (m = 24.90) followed by TF‐A (m = 12.48) showed the steepest slopes against value, making them good indicators for value. The TF‐digallate (TF‐dg) content did not show significant correlation with value (r = 0.316, P = 0.358). The individual TF content thus can be used for optimising the black tea manufacturing process in Central and Southern Africa. © 2002 Society of Chemical Industry     

单宁酶对酯型儿茶素作用研究

通过对单宁酶分解酯型儿茶素的研究，找出在恒定的pH与温度条件下，底物浓度与分解时间及单宁酶的添加量的变化关系，并指出用单宁酶解决茶汤浑浊过程中需注意的问题。