Quality standards of CTC black teas as influenced by sources of potassium fertiliser

The quality aspects of CTC (crush, tear and curl) black teas were examined against different sources of potassium fertiliser. Potassium supplied as muriate of potash (MOP) improved the liquor components such as theaflavin (TF), thearubigin (TR) and TF/TR ratio at higher levels. The same effect was noticed at lower level itself when the source of K was changed to sulfate of potash (SOP). Termination of K application reduced the TF/TR ratio drastically. The entity responsible for strength, body and colour of tea brew, namely highly polymerised substances, attained its optimum proportion at an NK ratio of 1:0.21 using SOP. Generally, there was a good response from SOP‐treated blocks to caffeine. The flavour index was a maximum at a 1:0.42 NK ratio, using SOP. A slight peak and trough were observed in the case of crude fibre content and water extract over control and MOP‐treated blocks. The leaf K content was negatively correlated with CFC content of made tea. An antagonism was observed between leaf K and Mg. Copyright © 2005 Society of Chemical Industry     

Black tea thearubigins—their HPLC separation and preparation during in-vitro oxidation

A reverse phase, gradient elution HPLC method has been developed to separate black tea thearubigin compounds. Using diode array spectroscopy, spectral data are provided for the major pigment peaks. The analytical method has been used to monitor the formation of the thearubigin compounds during black tea fermentation. In-vitro model fermentation systems using partially purified tea polyphenol oxidase and mixtures of six pure catechins have also been analysed. Data are presented to relate many of the thearubigins in black tea liquors to their catechin precursors. Manipulation of the in-vitro model system conditions will be used to prepare various thearubigins for further structural studies.     

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.     

Cocoa tea (Camellia ptilophylla Chang), a natural decaffeinated species of tea – Recommendations on the proper way of preparation for consumption

Cocoa tea is a new natural decaffeinated tea. Three types of cocoa tea (green, oolong and black) were produced and their sensory evaluation scores accessed. Main components and their dissolution rates in ten infusions of the three teas were analyzed by HPLC and spectrophotometry. The comprehensive score of sensory evaluations was 85.1, 86.8 and 94.4, respectively. Upon fermentation the contents of water extract (46.67%, 41.8% and 40%), tea polyphenols (38.58%, 30.41% and 23.6%) and total catechins (23.51%, 17.68% and 4.02%) in green, oolong and black teas decreased gradually, and theaflavins (0.11%, 0.11% and 0.17%), thearubigins (4.29%, 5.00% and 9.71%), theabrownins (2.75%, 4.90% and 13.52%), water-soluble carbohydrates, flavonoid glycoside and gallic acid in the three teas increased gradually. Theobromine (3.52%, 3.43% and 3.71%) was the alkaloid present in cocoa tea and its content did not change upon fermentation. In the three teas, 9–25% of the main components dissolved in the first 10 s-infusion, more than 80% of most components dissolved in five infusions. A recommendation for consuming cocoa tea is to infuse tea leaves (g) with 50 times boiling water (ml) for 3 min, the first infusion should not be discarded and five infusions were sufficient.     

Use of Porter's reagents for the characterisation of thearubigins and other non-proanthocyanidins

A previously published method for the HPLC analysis of the anthocyanidin pigments produced by the autoxidative depolymerization of proanthocyanidins by heating in a solution of n-butanol/HCl (95/5 v/v) and iron(III) salts (Porter's reagents) has been refined. The pigments are detected by monitoring at 530 nm, but by monitoring the eluate also at 280 nm and 380 nm a wider variety of products resulting from the same autoxidation and/or hydrolysis/transesterification reactions can be detected. Such products have been shown to include aglycones (particularly flavonols from flavonol glycosides) and n-butyl gallate (from galloyl esters). The advantages of monitoring the wider range of transformation products are illustrated by applying the method to the characterisation of two heterogeneous thearubigin fractions isolated from black tea liquor. The caffeine-precipitatable thearubigin fraction contained 181 g proanthocyanidins kg^?1 (as procyanidin dimer equivalents), a trace (～2 g kg^?1) of flavonols (as aglycones), 74 g kg^?1 galloyl ester and 5·6 g kg^?1 elemental N (determined by microanalysis): caffeine was not detectable and some 74% of the fraction remains uncharacterised. The theafulvin fraction contained 105 g proanthocyanidins kg^?1 (as procyanidin dimer equivalents), < 1 g kg^?1 quercetin and 71 g kg^?1 galloyl ester, but neither caffeine nor elemental N was detectable; some 82% of the fraction remains uncharacterised. The proanthocyanidins of both hump fractions contained not only prodelphinidins and procyanidins but also propelargonidins which have not previously been reported in tea.     

The analysis by HPLC of green,black and Pu'er teas produced in Yunnan

Samples of tea (Quingmao, steamed, black and Pu'er) produced in Yunnan Province, People's Republic of China, from the locally characteristic large-leaved Camellia sinensis, have been brewed and the brews analysed for their contents of flavonol glycosides, flavan-3-ols and their oxidation products. Several samples of Pu'er tea manufactured in the 1920s, 1930s and 1940s were also examined. The brews prepared from Quingmao tea and steamed green tea leaf were very similar containing primarily flavan-3-ols accompanied by flavonol glycosides, theogallin and gallic acid. The profile of flavanols was unusual, being dominated by (?)-epicatechingallate (rather than (?)-epigallocatechingallate) and by an unusually large (+)-catechin content. The brew of the equivalent black tea retained significant amounts of residual flavanols (particularly (?)-epicatechingallate and (+)-catechin), and contained significant amounts of thearubigins, theaflavic acids and theaflavins (including the less common analogues probably derived from the oxidation of (+)-catechin). The brews prepared from the Puer teas were distinguishable from the black tea brew by the absence of theaflavins and theaflavic acids, and by much smaller residues of flavanois and flavonol glycosides. The contents of thearubigins varied considerably whereas those of gallic acid were similar.     

The chemical oxidation of catechins and other phenolics: A study of the formation of black tea pigments

The chemical oxidation of polyphenols has been used to produce black tea pigments. (+)-Catechin, (?)-epicatechin, (?)-epicatechin gallate and (?)-epigallocatechin gallate were isolated from convenient sources, their identity being confirmed by mass spectrometry and HPLC. The oxidation of a mixture of (?)-epicatechin gallate and gallic acid gave an oxidation product of (?)-epicatechin gallate in addition to epitheaflavic acid 3-gallate. The catechins were oxidised chemically and the products analysed by HPLC, the chromatograms being compared with a black tea chromatogram. The reactions gave both resolved and unresolved pigments, and many of the resolved pigments had HPLC retention times close to black tea pigments. Each catechin behaved differently, the chromatograms of the oxidation products from each starting material being clearly distinguishable. Resolved pigments were obtained by the chemical oxidation of other phenolic compounds. This work provides a convenient method for studying the formation of resolved and unresolved black tea pigments.     

The formation of thearubigin-like substances by in-vitro polyphenol oxidase-mediated fermentation of individual flavan-3-ols

An enzymic in-vitro model tea fermentation system has been used in combination with gradient elution reversed-phase high-performance liquid chromatography to study the formation from individual fiavan-3-ols of resolvable and unresolvable thearubigin-like substances. It has been found that in 30 min at pH 5.6 tea polyphenol oxidase (EC 1.14.18.1) produces a distinctive range of resolvable thearubigin-like products from each flavan-3-ot substrate examined ((+)-catechin, (?)-epicatechin, (?)-epigallocatechin, (?)-epicatechin gallate and (?)-epigallocatechin gallate). However, (?)-epicatechin, and to a much lesser extent (+ )-catechin, were the only flavan-3-ols converted to an unresolvable thearubigin-like hump under these conditions. In addition, it was demonstrated that varying the pH of incubation in the range 5.0–6.0 had little effect on the profile of products obtained from the simple catechins, but a pronounced effect in the case of the gallocatechins. It is concluded that the combination of (?)-epicatechin and polyphenol oxidase is the simplest model of tea fermentation that can be used to generate in quantity thearubigin-like materials for structure elucidation.     

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.