Separation and classification of the brown pigments of aqueous infusions of black tea

Rapid thin-film counter-current dialysis of a typical infusion of black tea indicates that 10–12% of the soluble solids are non-dialysable. the major components of this fraction are polysaccharides and a complex mixture which could not be separated into its protein and polyphenolic constituents. This latter complex accounts for 30–40% of the colour (E₄₅₀) of the infusion. Solvent extraction of the infusion followed by dialysis of the various extracts reveals that the polyphenol-protein complex may be approximately equated with ‘S_II thearubigins’. Chromatography of infusions and various extracts thereof on alkylated Sephadex allows a partial separation of the coloured components largely owing to differences in molecular size. At least 7 distinct zones can be recognised.     

The roles of catechins and caffeine in cream formation in a semi-fermented tea

The mechanism of cream formation in a semi-fermented tea was investigated by adding caffeine or catechins to the de-creamed tea infusions. The addition of catechins to the clarified infusion could not re-induce cream formation. However, creaming occurred again after replenishing the de-creamed tea infusion with caffeine. It was thought that the ester-form catechins which possessed a galloyl group and a hydroxylphenyl B ring acted like a claw. They could thus entrap and interact with caffeine more effectively through hydrogen bonding and hydrophobic interaction to form a large complex, resulting in creaming. © 1999 Society of Chemical Industry     

Effect of extraction temperature on cream and extractability of black tea [Camellia sinensis (L.) O. Kuntze]

Summary Tea cream and haze in black tea infusions increased with the rise in the tea extraction temperature. The temperature at which substances involved in cream and haze formation began to be extensively extracted into the tea infusion was between 50 and 60 °C. The tea cream particle volume concentration in infusions extracted at 50 °C or below formed less tea cream particles, and their particle sizes were larger and more heterogeneous than those extracted at 60 °C and second infusions extracted at 90 °C from the residual leaves that were previously extracted at 40–50 °C. High‐performance liquid chromatography confirmed that constituents with pyrogallol groups are involved in tea creaming, and the effect of caffeine on tea cream and haze depends on whether these constituents are sufficiently present. The extractability of tea increased with the rise in extraction temperature. Two‐stage extraction of tea in ready‐to‐drink tea processing and its effects on colorimetric indicators were also examined.     

The effect of withering on fermentation of tea leaf and development of liquor characters of black teas

Depression in polyphenol oxidase (PPO) activity during the withering of tea leaf (Camellia sinensis) in black tea manufacture affected the oxidative-condensation of tea flavanols in forming theaflavins (TF) and thearubigins (TR), which are associated with brightness, briskness and ‘body’ of tea liquors. In contrast to conventionally manufactured CTC teas, unwithered fresh leaf CTC produces a higher proportion of TF and lower TR, resulting in bright, brisk and thin liquors. Hardness of wither was accompanied by a further depression in PPO activity, and formation of TF also declined with a concomitant loss in brightness and briskness. The TR content increased up to a certain degree of wither and thereby improved the ‘body’ of the liquor. Very hard wither, accompanied by a large reduction in moisture content, restricts PPO activity. It appears that in the fresh leaf, high moisture levels together with dissolved oxygen accelerate the enzymic oxidation and produce large amounts of TF. Senescence of the leaf seems to facilitate the production of TR.     

Cream formation in a semifermented tea

The formation of cream in Paochung tea, a popular semifermented tea, which undergoes a lesser degree of enzymic oxidation during manufacture, was investigated at various extraction temperatures, extraction times, pHs and leaf/water ratios. The primary components of Paochung tea cream were catechins (30%), caffeine (20%) and protein (16%). (−)-Epigallocatechin gallate and (−)-epicatechin gallate were the major catechins precipitated during creaming, constituting 19% and 5% of the tea cream respectively. The amount of tea cream produced and its composition were influenced by extraction temperature and pH. The tea leaf/water ratio determined the amount of tea cream formed but did not affect the cream composition. Catechins were considered to be the key component in tea cream. They interacted with caffeine and protein to induce tea cream formation. © 1999 Society of Chemical Industry     

A study on chemical estimation of pu‐erh tea quality

Chemical compositions and infusion colour differences of seven pu‐erh tea samples and their correlation to sensory quality were investigated. The results showed that the pu‐erh tea contained 37.1 mg g^?1 caffeine, 15.7 mg g^?1 amino acids, 67.0 mg g^?1 polyphenols and 8.41 mg g^?1 total catechins, on average. Among the 17 tested volatile compounds, n‐valeraldehyde was not detected. The most abundant volatile was β‐ionone and the next was linalool oxide II. Infusion colour analysis showed that the pu‐erh tea had deep hue with ΔE ranging from 66.8 to 79.2. Spearman's linear correlation analysis showed that total quality score (TQS) of the pu‐erh tea was significantly correlated to concentration of amino acids, linalool oxide II and infusion colour indicator ΔE. Five components were extracted from the 34 tested indicators by principal component analysis and were regressed on the TQS to produce six Pearson's linear regression equations for estimating sensory quality of pu‐erh tea, among which two were statistically significant, ie TQS = 57.47 ? 0.18geraniol + 0.33polyphenols ? 1.14n‐caproaldehyde ? 1.38linalool oxide I + 0.21caffeine (p < 0.01) and TQS = 57.42‐0.03Citral + 0.33polyphenols ? 1.14n ? caproaldehyde ? 1.40linalool oxide I + 0.20caffeine (p < 0.01). Copyright © 2004 Society of Chemical Industry     

The solubility of tea cream

The heterogeneous nature of tea cream, with regard to solubility, is shown. A simple three-component system enables some of the observed cream characteristics to be explained. Suggestions are made concerning the compositions of these components and a model for the formation of cream particles, from a hot infusion, is proposed. Extraction of leaf tea with cold water gives an infusion incapable of creaming.     

Some molecular and colloidal aspects of tea cream formation

The formation of tea cream for a range of black tea materials was studied by turbidity measurements, time-resolved light scattering, gravimetric measurements and High Performance Liquid Chromatography (HPLC). These techniques demonstrate that, in the absence of caffeine and/or gallate esters the solubility of tea solids in black tea infusions is enhanced compared with the ‘standard’ black tea material. All the tea system show an increase in cream-point, amount of tea cream and particle size with increasing tea solids concentration. Decaffeination has a larger impact on enhancing the solubility of tea colloids than degallation. HPLC studies indicate that theaflavins have a preference for the cream phase, whereas ie. catechin C is preferentially partitioned into the aqueous supernatant phase. Caffeine is preferentially partitioned into the cream phase, albeit less favourably than theaflavins and other relatively high-molecular mass polyphenols. Comparison between ‘standard’ and decaffeinated black tea shows that in the absence of caffeine, epigallocatechin gallate (EGCG) is preferentially partitioned into the cream phase.     

Seasonal Variations in Quality of Kangra Tea ( Camellia sinensis(L) O Kuntze) in Himachal Pradesh

Periodic seasonal variations in infusion quality of orthodox Kangra tea over various growth flushes are reported. Theaflavins, thearubigins and caffeine recorded maximum content during early flush and gradual decline with progress in season, showing a minimum during main flush and slight improvement through backend flush. Flavour profile analysis also revealed qualitative and quantitative seasonal variations in aroma complex. High proportions of provisionally identified flavour components, linalool, geraniol, β-ionone, methyl salicylate, phenyl acetaldehyde, trans -2-hexenal, and several unidentified components with typical Kangra notes recorded during early flush exhibited comparatively lower contents or even total loss through main flush. Flavour quality also registered slight improvement in backend flush over main flush. Results suggest increasing crop productivity during early and backend flushes could enhance profitability.     

长江中下游产区红茶品质分析

针对长江中下游不同产茶区的红茶进行感官品质评价,结合理化成分和香气成分分析,提取滋味和香气品质相关特征信息。结果表明:长江中下游区域红茶在感官品质上呈现甜香、薯甜香、甜醇等香气、滋味等特征。品质成分中水浸出物、咖啡碱、萜烯醇含量均较高,大部分产区茶红素与茶黄素的比例为1:10~1:13之间,是长江中下游区域红茶汤色红亮、滋味醇厚、甜香持久的物质基础。其中湖北茶区红茶的可溶性糖、茶红素等含量较高,是茶汤红亮、滋味甜醇的物质基础,湖南茶区红茶的水浸出物、茶多酚、咖啡碱、黄酮、儿茶素总量、茶黄素及茶红素含量较高,是其茶汤深红、滋味浓厚的物质基础;浙江、安徽茶区红茶的氨基酸和可溶性糖含量较高,是其茶汤甜醇的物质基础。醇类和醛类是主要的香气化合物,芳樟醇、氧化芳樟醇、香叶醇、苯甲醛、苯乙醛、2-甲基丁醛、2-己烯醛、β-环柠檬醛、水杨酸甲酯和β-紫罗酮等共同构成了红茶甜香、糖香及花香的物质基础,另外2-正戊基呋喃、2-乙基呋喃和1-乙基-2-甲酰吡咯呈现坚果、焦香等风味,对红茶的焦糖香形成有着直接影响。     

传统滇红工夫红茶与野生滇红工夫红茶的品质分析

为了解传统滇红工夫红茶与野生滇红工夫红茶品质特点的差异，本文收集了5个传统滇红工夫红茶和5个野生滇红工夫红茶，对其感官品质和生化品质成分进行了分析。感官审评表明，供试样品的外形、汤色、叶底均符合滇红工夫红茶的特征，即干茶色泽乌黑油润，茶汤红艳或橙红明亮，叶底嫩匀，但传统滇红滋味浓强，而野生滇红滋味醇和鲜爽。传统滇红工夫红茶的水浸出物、总儿茶素、咖啡碱含量分别为41.07%、18.53和14.60 mg/g，明显高于野生滇红的38.42%、10.58和9.54 mg/g；而游离氨基酸平均含量（3.92%）低于野生滇红（5.01%）；二者茶多酚平均含量分别为16.61%、16.56%，无明显差异；茶黄素、茶红素和茶褐素的平均含量分别为0.64%、6.75%、10.93%和0.61%、2.70%、11.80%，其中茶红素含量差异明显；槲皮素、芦丁、山柰酚、杨梅素的平均含量分别为0.09、0.67、0.01、0.07 mg/g和0.14、0.27、0.16、0.15 mg/g，差异明显。以19个生化成分含量为指标，进行了主成分分析（Principal component analysis，PCA）和聚类分析（Clustering analysis，CA），均能将传统滇红工夫红茶和野生滇红工夫红茶明显地分为两类，说明二者的生化成分含量具有明显差异。综合来看，传统滇红的水浸出物、儿茶素类、咖啡碱及黄酮醇类含量高，导致其滋味浓强；而野生滇红的游离氨基酸含量高，是其滋味鲜醇的原因。     

THE FOULING AND CLEANING OF ULTRAFILTRATION MEMBRANES DURING THE FILTRATION OF MODEL TEA COMPONENT SOLUTIONS

Proteins and polyphenols are the principal fouling constituents in the ultrafiltration (UF) of black tea liquor. The aim of this study was to determine the relative importance of individual components in the fouling process, to investigate any synergetic interactions that were occurring and to compare the cleaning characteristics of different fouled membranes. A 30‐kD molecular weight cutoff polysulfone UF membrane in dead‐end mode was challenged with model solutions of tea components. Model solutions consisted of tea proteins, theaflavins (TFs), thearubigins and caffeine. Sodium hydroxide was used as a cleaning reagent. Permeate flux decline curves were presented for single components and mixtures. Individual component transfer fluxes and rejections were also presented. An unexpected finding was that protein in a mixture with TFs could permeate the membrane to a degree, while a protein solution in the absence of the polyphenol was completely rejected. The inspection of membranes fouled by different solutions revealed different foulant morphologies. Membrane cleaning with 0.2 wt % sodium hydroxide was generally found to be effective.     

Effect of pH on cream particle formation and solids extraction yield of black tea

Effect of pH on tea solids extraction yield was significant in increasing instant tea yield. Solids extraction yield was doubled when tea was extracted at pH 1.2 compared with that extracted in boiling distilled water with pH 6.8. H⁺ encouraged black tea cream particle formation by either releasing more solids into the infusion or stimulating polyphenols to interact with polysaccharides and nucleophilic groups on protein in tea infusions. HPLC results revealed that theaflavins and tea catechins were leading substances affecting the formation of cream particles and infusion colour. Theaflavins and some tea catechins, such as EGCG, ECG and EGC, were dissociated or degraded under alkaline conditions and thus tea cream particles tended to dissolve and tea infusion became dark in colour. Feasibility of stepwise extraction of instant teas used for iced tea and normal drinking tea, by controlling temperature and pH, is also considered in the present paper.     

不同品种红茶及茶膏的Fisher判别分析

为探究Fisher判别分析法对不同品种红茶及茶膏种类品质区分的可行性,针对不同品种红茶及滇红碎茶茶膏,以蛋白质、总糖、茶红素、茶黄素、茶褐素及9 种矿物质元素为变量进行判别分析。结果表明：采用Fisher判别分析法评定不同品种红茶及不同加工工艺滇红碎茶茶膏的真实归属及品质是可靠的。红茶茶叶及茶膏品质评定中采用Fisher判别分析有利于降低传统感官评定过程中人为主观因素的干扰,避免模糊性和不确定性,保证评审的稳定和可靠性。     

Application of chemical composition and infusion colour difference analysis to quality estimation of jasmine-scented tea

Infusion chemical composition, colour difference indicators and volatile constituents of seventeen jasmine‐scented tea samples and their correlation with sensory total quality score given by tea‐tasting panel were studied by techniques of HPLC, colour difference metre and gas chromatograph. Spearman's linear correlation analysis showed that concentration of nitrogen, caffeine, catechin, epicatechin, catechin gallate, total catechins, terpineol, nerol and infusion light‐black indicator ΔL, yellow‐blue indicator Δb, total colour difference indicator ΔE were significantly correlated with sensory total quality score, respectively. Regression of the total quality score upon twelve components extracted from thirty‐six tested indicators by principal component analysis could properly estimate total quality score of two jasmine‐scented tea samples which were not included in the seventeen samples used to construct the regression model.     

Analysis of characteristic aroma of fungal fermented Fuzhuan brick‐tea by gas chromatography/mass spectrophotometry

Fuzhuan brick‐tea is a popular fermented Chinese dark tea because of its typical fungal aroma. Fungal growth during the production process is the key step in achieving the unique colour, aroma and taste of Fuzhuan brick‐tea. To further understand the generation of the characteristic aroma, changes in the main volatile compounds of Fuzhuan brick‐tea during the fungal growth stage were studied by gas chromatography/mass spectrophotometry. The results showed that the content of volatile compounds, especially aldehyde compounds with stale aroma such as (E)‐2‐pentenal, (E)‐2‐hexenal, 1‐penten‐3‐ol, (E, E)‐2,4‐heptadienal and (E, Z)‐2,4‐heptadienal, increased significantly in fermented tea samples. The concentration of terpene alcohols with flower aroma also increased notably during the fermentation process. The compounds with stale and flower aromas in combination with some volatile components of the raw material contributed to the characteristic ‘fungal/flower’ aroma of Fuzhuan brick‐tea. Microbial metabolism during the fermentation process probably played the key role in the generation of characteristic aromatic compounds of Fuzhuan brick‐tea. Copyright © 2007 Society of Chemical Industry     

Rapid method for measuring thearubigins and theaflavins in black tea using C18 sorbent cartridges

This communication describes the routine use of small inexpensive C₁₈ cartridges for rapid separation and accurate measurement of both thearubigins (TR) and theaflavins (TF) in a liquor brewed from black tea. The slow, traditional method overestimates TR content because of interference from flavonol glycosides. Comparison is also made favourably with other methods available for estimating total TF and sometimes TR in tea.     

Flavanol Composition and Caffeine Content of Green Leaf as Quality Potential Indicators of Kenyan Black Teas

The flavanol composition and caffeine content of green tea leaf, black tea quality parameters of theaflavins, thearubigins, liquor brightness and total colour varied more among clones than with time of the year. In green leaf, either (-)epicatechin gallate or (-)epigallocatechin gallate was the dominant flavanol present. Regression analysis of tasters' preferences for black teas against green leaf chemical components showed positive and significant correlations for (-)epicatechin gallate (r = 0·498, P ⩽ 0·05 for taster A; r = 0·665, P ⩽ 0·01 for taster B, and r = 0·678, P ⩽ 0·01 for both tasters' overall ranking), (-)epigallocatechin gallate (r = 0·513, P ⩽ 0·05 for taster B; r = 0·532, P ⩽ 0·05 for both tasters' overall ranking and caffeine (r = 0·523, P ⩽ 0·05 for taster A; r = 0·657, P ⩽ 0·01 for taster B; and r = 0·686, P ⩽ 0·01 for both tasters' overall ranking). Similar regressions against black tea theaflavins, thearubigin content, liquor brightness and total colour were not significant. The results suggest that the green leaf chemical components, (-)epicatechin gallate, (-)epigallocatechin gallate and caffeine could be used as quality potential indicators during clonal selection and propagation. © 1997 SCI.     

A New Type of Tea Pigment—From the Chemical Oxidation of Epicatechin Gallate and Isolated from Tea

( - )-Epicatechin-3-O-gallate (ECG), one of the major green tea poly-phenols, was oxidised chemically using potassium ferricyanide. The major oxidation product, termed theaflavate A, which gave a sharp peak on HPLC analysis, was separated and purified by a combination of chromatography on Sephadex LH-20 and a semi-preparative HPLC method. This compound was characterised by NMR spectroscopy (¹H, ¹³C, HMQC, HMBC and ROESY) and mass spectrometry (Electrospray method) and was found to have a novel benzotropolone skeleton formed between the B-ring of one ECG molecule and the galloyl ester group of another. Compounds containing this type of benzotropolone link were also found to be present in black tea. This benzotropolone link is of great interest, since it shows that the galloyl ester groups of flavan-3-ols participate in oxidative condensation reactions. This illustrates the complexity of theaflavin-type compounds in black tea and provides an additional reaction pathway for the formation of thearubigins which has not been previously considered. © 1997 SCI     

Quality evaluation of black CTC teas based upon seasonal variations

Effects of seasonal variations on the colour and chemical constituents of Indian black tea were investigated. The experimentation involved collection of different black tea samples that were cultivated at the same tea garden but harvested in three different seasons. Measurement of moisture content was done along with theaflavins (TFs), thearubigins (TRs) and colour (CIE La*b* values) of the brewed tea liquor using spectrophotometric approach. The correlation analysis between chemical constituents, that is, TFs and TRs, moisture content, colour and quality grading was done by using principal component analysis (PCA). The results suggest that quality of tea is dependent upon seasonal variations in terms of chemical changes such as TFs, TRs and moisture content, which also correlate well with colour. The efficacy of the colour of brewed tea liquor in explaining the changes in tea quality due to seasonal variations can be beneficial for scientific fixation of prices at tea auction centres.