Analysis of black tea theaflavins by non-aqueous capillary electrophoresis.

In this study a new capillary electrophoresis (CE) method was developed to quantify the four major theaflavins occurring in black tea. Where aqueous based CE methods showed poor selectivity and considerable band broadening, non-aqueous CE achieved baseline separation of the theaflavins within 10 min. The effects of the organic solvent composition and background electrolyte concentration on the separation selectivity and electrophoretic mobilities were investigated. Our optimized separation solution consisted of acetonitrile-methanol-acetic acid (71:25:4, v/v) and 90 mM ammonium acetate. This method was used to analyze three black tea samples.     

Comparative analysis of tea catechins and theaflavins by high-performance liquid chromatography and capillary electrophoresis

This paper describes the simultaneous determination of catechins and theaflavins in green and black teas, using reversed-phase high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The tea polyphenols analyzed included (+)-catechin, catechin gallate, (-)-epicatechin, epicatechin-3-gallate, epigallocatechin, epigallocatechin-3-gallate, theaflavin, theaflavin-3-monogallate, theaflavin-3'-monogallate and theaflavin-3,3'-gallate. These polyphenols together with six other tea ingredients such as caffeine, adenine, theophylline, quercetin, gallic acid and caffeic acid were separated within 27 min by HPLC and in less than 10 min by CE. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE were found to be reliable and compatible. The reproducibility of the within-day assay using both methods was generally >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <2%. The analysis time of CE was three-times faster, however it is five-times less sensitive than HPLC, which has detection limits of 0.05 microg/ml and 0.5 microg/ml for catechins and theaflavins, respectively.     

Counter-current chromatography of black tea infusions

Counter-current chromatography using a multilayer coil planet centrifuge, with solvent system ethyl acetate-butanol-water, permits the separation of black tea infusions into fractions which include pure SII and a mixture of SI and SIa thearubigins. Good resolution of several components of the infusion may be achieved in elution times of 1 to 2 h. The appearance of chromatograms is altered on decaffeinating the infusion. The effect of stationary phase composition is considered. Resolution of the peaks improves with butanol content.     

Determination of methyl salicylate in black tea

Summary Methyl salicylate is a naturally occurring compound in black tea. A method has been developed for the determination of the methyl salicylate in tea samples. The method consists of hot extraction of the teas withn-hexane, distilling off the solvent and steam distillation of the resinous mass to obtain the volatile oil. This oil was analysed gas chromatographically using suitable standards. The effect of methyl salicylate on the overall flavour quality is also reported.

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Zusammenfassung Methylsalicylat ist ein natürlicher Bestandteil in schwarzem Tee; für dessen Bestimmung wurde eine Methode ausgearbeitet. Sie beruht auf der Extraktion der Teeblätter mit heißemn-Hexan; das Lösungsmittel wird dann abdestilliert und der harzartige Rückstand einer Wasserdampfdestillation unterzogen, um das flüchtige Öl zu gewinnen. Dieses wird gaschromatographisch unter Verwendung geeigneter Standardproben analysiert. Der Einfluß von Methylsalicylat auf das Aroma wurde besprochen.

     

红茶、绿茶和乌龙茶多糖及多酚对DNA的保护作用研究

用溴化乙锭(EB)作为荧光探针研究了各种茶叶多糖、多酚类化合物对DNA的保护作用.测定了龙井、普耳茶、乌龙茶等8种茶叶中多糖和多酚类提取物存在下DNA与EB混合液的荧光积分强度,并把不同茶叶与DNA相互作用的常数定义为结合常数D,根据D的大小讨论了多糖及多酚类化合物的存在DNA保护作用的影响.结果表明,8种茶叶与DNA...     

不同提取方法对红茶提取物抗氧化活性影响的研究

采取沸水浴法、回流法、微波法及超声波法探讨信阳红茶和印度红茶的抗氧化性,通过测定吸光度利用Fenton反应表征提取物对羟自由基的清除率.不同的提取方法对红茶抗氧化活性有一定的影响,羟自由基的清除率与红茶的抗氧化活性成正比.结果表明:信阳红茶沸水浴法提取率较高,印度红茶超声波法提取率较高.     

Withering timings affect the total free amino acids and mineral contents of tea leaves during black tea manufacturing

The aim of the present study was to investigate the effect of withering timings (i.e. 0, 21, 22, 23 and 24 h) on the moisture, total free amino acids, ash, essential and toxic mineral element contents of tea (Camellia sinensis L.) leaves during black tea manufacturing. Moisture, ash, Na, P, Mg, Cu, Zn, Mn, Al, Ni and Pb contents were significantly (P < 0.05) affected by withering, whereas non-significant (P > 0.05) results were noted for total free amino acids, K, Fe and Cd contents. The highest moisture content (76.4%) was examined in fresh leaves that progressively decreased to 63.8% in 24 h withering. Total free amino acid contents gradually increased up to 23 h and then decreased. Ash, P, Cu, Zn and Mn contents showed an increasing trend with withering time. Conversely, significantly lowered amounts of Na (162.5 mg/kg) and Mg (803 mg/kg) were recorded in tea leaves after 24 h withering. Among the toxic elements, Al, Ni and Pb contents were progressively increased over withering time. It was concluded that tea is a potential source of essential chemical constituents and during processing proper care should be taken to produce high quality black tea.     

Polymer-like polyphenols of black tea and their lipase and amylase inhibitory activities

Lipase and amylase inhibitory activities of black tea were examined. After solvent partitioning of a black tea extract with the ethyl acetate and n-butanol, the two soluble fractions showed comparable inhibitory activities. Activity in the ethyl acetate fraction was mainly attributable to polyphenols with low-molecular weights, such as theaflavin gallates. On the other hand, the active substance in the n-butanol layer was ascertained to be a polymer-like substance. 1H- and 13C-NMR spectra showed signals arising from the flavan A-ring and galloyl groups, although signals due to flavan B-rings were not detected, suggesting that the polymer-like substances were generated by oxidative condensation of flavan B-rings, a result which was previously deduced from our results of in vitro catechin oxidation experiments. Enzymatic oxidation of epicatechin 3-O-gallate produced a similar polymer-like substance and suggested that condensation between a B-ring and galloyl groups was involved in the polymerization reaction.     

Transition metal ions in black tea: an electron paramagnetic resonance study

Tea (Camellia Sinensis) is the most widely consumed beverage in the world and is known to have therapeutic, antioxidant and nutritional effects. It contains dimeric flavanols and polyphenols which are known as the most important organic compounds in tea infusions, and can make strong and stable complexes with metal ions. In this study, we carried out a series of electron paramagnetic resonance experiments on well-known paramagnetic transition metal ions, namely Mn²⁺, Fe³⁺, Cu²⁺, VO²⁺, and Cr³⁺ doped in black tea cultivated along the shore of Black Sea, Turkey, to see the effects and structures formed.     

解吸电喷雾质谱法协同主成分分析快速鉴定红茶茶水

茶叶的快速鉴定对于茶叶的高效生产和品质控制十分重要.目前茶叶品质主要依赖于专业评茶师主观鉴定,亟待建立快速、准确的仪器方法进行客观评价.解吸电喷雾(DESI)质谱法是一种新型快速的质谱分析方法,在农产品和日用品的快速检测上有着很强的应用优势.本文采用解吸电喷雾质谱法和主成分分析方法对外观相近的三个品牌红茶产品进行了分析.结果表明,该方法能够快速清晰地分辨不同品牌的红茶产品,有着良好的应用前景.     

Evaluation of black tea polyphenol extract against the retrogradation of starches from various plant sources

The effects of black tea polyphenol extract (BTPE) on the retrogradation of starches from different plant sources were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). DSC analysis shows that the gelatinization temperature of maize starch and starches from different rice varieties increased with increasing BTPE level. After storage at 4 °C, BTPE at a concentration of 15% markedly retarded the retrogradation of maize starch and starches from different rice varieties. Native maize starch and starches from different rice varieties showed typical A-type X-ray diffraction patterns, while native potato starch showed a typical B-type X-ray diffraction pattern. Adding BTPE significantly affected the crystalline region and intensities of X-ray diffraction peaks of maize and rice starch granules. It is concluded that adding BTPE markedly inhibits the retrogradation of maize starch and starches from different rice varieties, but has no significant influence on the gelatinization and retrogradation characteristics of potato starch.     

A qualitative study of the essential oil of manufactured black tea by thin layer chromatography

Summary Using two-dimensional thin layer chromatography more than 30 constituents in the volatile oil of black tea are separated and many of these compounds are tentatively identified by co-chromatography with authentic samples and by the characteristic colours given with the vanillin-sulphuric acid colour reagent.

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Zusammenfassung Durch zweidimensionale Dünnschichtchromatographie wurden mehr als 30 Bestandteile des flüchtigen, aus schwarzen Teeblättern destillierbaren Öls getrennt. Viele dieser Verbindungen wurden durch Vergleiche mit Testsubstanzen und mit Hilfe der Farbreaktion mit Vanillin-Schwefelsäure zu identifizieren versucht.

     

亚临界水萃取及气相色谱-串联质谱法检测红茶中多种农药残留

建立了亚临界水萃取及气相色谱-串联质谱(GC-MS/MS)检测红茶中21种有机氯和拟除虫菊酯农药残留的方法。在萃取压力为5 MPa条件下,样品经150 ℃的亚临界水提取15 min后,将目标物转移至丙酮-正己烷(1:1, v/v)中,经ENVI-Carb固相萃取净化小柱净化,DB-5毛细管气相色谱柱分离,在多反应监测(MRM)模式下进行MS/MS检测,基质匹配溶液内标法定量。各目标物在5.0～320.0 μg/L范围内线性关系良好,相关系数均大于0.99,其定量限(信噪比(S/N)＞10)为50 ng/g,检出限(S/N＞3)为10 ng/g。茶叶基质中添加50、100和200 ng/g的标准品时,21种农药的回收率为70.18%～119.98%,相对标准偏差(RSD)为5.01%～11.76%。该方法的灵敏度、准确度和精密度均符合农药残留测定的技术要求,适用于红茶中有机氯和拟除虫菊酯农药残留的检测。     

An Investigation of the Tea Aroma. Part I. New volatile black tea constituents

A total of 68 constitutents, mainly aldehydes, ketones and esters, have been identified for the first time in a black tea aroma concentrate using coupled gas-chromatography/mass spectrometry.     

The inhibition of the mammalian DNA methyltransferase 3a (Dnmt3a) by dietary black tea and coffee polyphenols

Background  

Black tea is, second only to water, the most consumed beverage globally. Previously, the inhibition of DNA methyltransferase 1 was shown by dietary polyphenols and epi-gallocatechin gallate (EGCG), the main polyphenolic constituent of green tea, and 5-caffeoyl quinic acid, the main phenolic constituent of the green coffee bean.     

Mass spectrometric characterization of black tea thearubigins leading to an oxidative cascade hypothesis for thearubigin formation

Thearubigins are the most abundant group of phenolic pigments found in black tea, accounting for an estimated 60-70% of the solids in a typical black tea infusion. Fifty years ago the term thearubigins was first introduced and to date the chemical nature of the thearubigins remains largely unresolved, if not mysterious, despite numerous attempts made to clarify their structure. Thearubigins isolated from 15 commercial black teas have been analyzed using a strategy combining standard chemical characterization along with a series of modern complementary mass spectrometry techniques, including MALDI-TOF-MS, FTICR-MS, LC/TOF-MS and LC/MS/MS. Fifteen molecular formulas have been matched to constituents of fresh tea leaf that have survived processing and 21 to dimeric transformation products such as theasinensins, theaflavins, theaflavates, theanaphthoquinones, theacitrins and oolongtheanins, which were further confirmed by ESI MS/MS. MALDI-TOF-MS data revealed an average of 5000 additional thearubigin components in the mass range between m/z 1000 to 2100 clearly defining the molecular weight range of the thearubigin fraction. Six selected samples have for the first time been analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). FT-ICR-MS data revealed the presence of a maximum of 9428 peaks in the mass range 300 to 1000 m/z and molecular formulas were assigned to 1517 of them. Data interpretation strategies developed for petrolomics studies (van Krevelen and Kendrick analyses) have for the first time been applied to black tea thearubigins and a novel interpretation protocol has been developed to refine these procedures for the investigation of complex mixtures, leading to a novel hypothesis for the formation and structure of the black tea thearubigins named oxidative cascade hypothesis.     

Comparison of multivariate preprocessing techniques as applied to electronic tongue based pattern classification for black tea

In an electronic tongue, preprocessing on raw data precedes pattern analysis and choice of the appropriate preprocessing technique is crucial for the performance of the pattern classifier. While attempting to classify different grades of black tea using a voltammetric electronic tongue, different preprocessing techniques have been explored and a comparison of their performances is presented in this paper. The preprocessing techniques are compared first by a quantitative measurement of separability followed by principle component analysis; and then two different supervised pattern recognition models based on neural networks are used to evaluate the performance of the preprocessing techniques.