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Tea is cultivated in diverse environments causing yield and quality differences in its beverages. To maximise yields and quality, agronomic practices should be optimised. But agronomic recommendations are uniform in different environments in Kenya despite variations in the growth factors responsible for changes in yields and quality. Plucking is labour intensive and a costly agronomic input in tea production. Trials were conducted for ten years in five tea growing regions in Kenya to assess yields and quality responses of clone BBK 35 tea to location of production and harvesting intervals. There were different (P ⩽ 0.05) yields in the various locations, with significant (P ⩽ 0.05) interaction effects between locations and harvesting intervals. Yields declined in three out of five regions but increased in one location with longer plucking intervals. Yields in a geographical area of production can not be used to estimate its expected yields in other tea growing areas. Black tea theaflavins varied significantly (P ⩽ 0.05) with geographical area of production, but other plain tea quality parameters did not vary with location. It is therefore possible to make similar black teas with similar plain tea quality parameters except theaflavins from all tea growing regions of Kenya. Tea quality improved with short plucking rounds. One way to maximise tea quality is through shortening harvesting intervals. It is necessary to establish optimal harvesting rounds in the different tea growing regions in Kenya to maximise yields and quality.

Following the oxidation of epicatechin (EC), three novel compounds and two known compounds were isolated. The chemical structures of these oxidation products were determined by mass spectrometry (MS) and various nuclear magnetic resonance (NMR) experiments, and the A-ring-B-ring linkage that is characteristic of catechin was found in each molecule. Three compounds showed similar ultraviolet-visible (UV-Vis) spectra to EC, whereas two compounds showed different spectral absorption in the region between 300 and 500 nm. A similar spectrum was obtained for the thearubigin fraction prepared from a black tea infusion. This result suggests that the condensation reaction between the A-ring and B-ring is more important than reaction between B-rings for thearubigin formation.

Phenolic compounds constitute 50-70% of tea water extract and are the main quality parameters for teas. Theaflavins (TF), thearubigins (TR) and theabrownins (TB) are the major polyphenols that determine the quality of black tea. These compounds were measured in 56 leaf teas and teabags sampled from Australian supermarkets in Queensland. The various quantities of TF, ranging from 0.29% to 1.25%, indicate a quality difference that exists among the teas studied. Low TF content in black tea may be due to over-fermenting and/or long periods of storage. The solubility of TR and TB from teabags ranged from 82% to 92%, indicating that the permeability of teabags was variable. Variable quantities of TF in Australian teas show instability and a tendency of TF to oxidize during storage. Total polyphenols in green teas ranged from 14% to 34%, indicating a large variation, which was not reflected in price. The solubility of total polyphenols from teabags has been proposed as a useful quality index of the filtering paper used for the teabags. This chemical analysis of phenolic compounds in commercial teas may be a potential tool for the quality control of Australian manufactured and imported teas in Australian markets. (C) 2005 Elsevier Ltd. All rights reserved.

Increase in coarser plucking standards significantly (P

Separation factor is an important index for judging the eluotropic sequence of solutes in countercurrent chromatography (CCC). This paper has proven that the contribution of the common basic agglomerate can be eliminated when calculating the separation factor for analogues and introduced a computational equation based on UNIFAC. According to the equation, the estimation of separation factors needs only a few different groups of analogues. Eleven kinds of analogues, such as phytosterol, chlorinated s‐triazines, flavonoids, theaflavins, anthocyanins, sporaviridins, etc., have been tested with the method. Though the solvent systems used are different from each other, the estimated eluotropic sequences are all consisted well with the literatures except for two chlorinated s‐triazines.

Although most clones are selected for quality and yields, there are clones in production with superior yields but producing inferior black tea quality and vice versa . Some of these clones with superior yield give very poor black tea quality characteristics. Such clones are normally not progressed in selection programmes. Blending the clonal leaf prior to maceration results in the production of black teas with average quality relative to the amount of the clonal leaf in the mixture. There is no evidence of clonal incompatibility. Slow fermenting clones with superior yields may therefore be selected and planted, provided they are not planted in single stands. ©

In recent years, Turkish black tea has been manufactured by a combination of orthodox + rotorvane + orthodox systems, especially developed for the conditions of Turkey. The optimum fermentation time of black tea manufactured by this system was investigated at the factory level by measuring the theaflavin contents during the fermentation step, which starts with rolling and ends with drying processes. Optimum fermentation times from the start of rolling in the ORO system were determined to be 83 min and 80 min for coarse tea and sieved fine tea, respectively, by theaflavin analysis. Low levels of theaflavin in Turkish black tea were attributed to the very low quality of the fresh tea leaves and of the plucking standards.

HPLC analysis of Kenya clonal black tea liquors revealed the presence of four major theaflavins in the following order: theaflavin > theaflavin-3-gallate > theaflavin-3,3′-digallate > theaflavin-3′gallate. The total amounts and the ratios of the individual theaflavins varied with clones resulting in variations in the astringency of the teas as measured by theaflavin digallate equivalent. Theaflavin digallate and theaflavin digallate equivalent showed a better relationship with sensory evaluation than did total (Flavognost) theaflavins.

Both theaflavins and sensory evaluations vary in a quadratic manner with fermentation duration in the process of black tea manufacture. The rate of formation of total (Flavognost) theaflavins varies with clones, and within a clone the individual theaflavins form at different rates with resultant changes in the theaflavin ratios as fermentation progresses. The astringency of black tea also varies with composition and total amounts of the theaflavins, as individual theaflavins have different astringencies. The measurement of total theaflavins may therefore not correctly predict total astringency and hence value of tea.

Thearubigins are the most abundant group of phenolic pigments found in black tea accounting for an estimated 60% of the solids in a typical black tea infusion. Fifty years ago the term thearubigins was first introduced and up to now the chemical nature of the thearubigins remains largely unresolved if not mysterious despite many efforts clarifying their structure. This paper summarizes some of our attempts to clarify and elucidate the chemical nature of the thearubigins, presenting for 15 commercially representative teas data obtained using combustion analysis, IR spectroscopy, NMR spectroscopy, Diffusion NMR spectroscopy, UV–vis spectroscopy, Circular Dichroism spectroscopy and atomic force microscopy, MALDI-TOF-MS and ESI-FT-ICR-MS. The thearubigin fractions from these 15 teas are remarkably similar with respect to their spectroscopic fingerprint. The data obtained are consistent with the thearubigins being structures of not more than 2000 Da with more than 5000 individual chemical entities detected that are susceptible to concentration-driven aggregation in aqueous solution, and that retain the chiral properties of the flavanols and theaflavins. By applying petrolomics-style data interpretation strategies and by developing novel data interpretation strategies a structural model for the thearubigins was developed.

Modern chromatographic techniques such as high-performance liquid chromatography are currently the most helpful approach to the routine analysis of and research of non-volatile tea constituents. Using these techniques some errors in the more classical analytical techniques could be detected. Unfortunately, some of these methods of analysis are still in widespread use, even as official methods. However, knowledge of especially the polyphenols in tea is still lacking, and for many of the minor polyphenols no chromatographic methods for the determination exist.

There are several critical stages in the Flavognost method for theaflavin analysis in black tea. These have been identified and their significance determined experimentally. During sample preparation, the particle size of the ground material, and the type of grinder used to produce it, directly influence the level of extracted theaflavin. The temperature of the water used and the time over which infusion is carried out are also very significant as is the method of shaking. Failure to control conditions at these critical stages can give rise to a fourfold variation in results. Recommendations are given for possible incorporation into standard protocols.

Black tea clones have different contents of theaflavins, thearubigins and caffeine. The amounts vary with localities and the patterns of variations change from clone to clone. There was no significant relationship between altitude and theaflavins (except in clones 6/8, 31/8 and 31/11), or thearubigins or caffeine. Tea breeding programmes for high quality need to evaluate the clones in areas of intended release, as chemical composition—and hence quality—vary with localities.

The Flavognost assay for measurement of theaflavin in black tea is discussed, and experimental evidence presented to explain why some parts of the assay can cause within and between laboratory variation. The major problems raised are concerned with the temperature of the infusion, and with the proportion of the total theaflavin present in the tea leaf that is actually extracted. The role of the leaf's endogenous aluminium in theaflavin analysis is discussed, and it is shown that it might be possible to replace the expensive Flavognost reagent with aluminium chloride, which is less than 1% of the price.

A comparative study using in-line theaflavins analysis (ILTF), theaflavins of made-tea analysis (TFMT) and tasters' evaluations, to optimise fermentation during tea manufacture, was carried out. All methods obeyed a quadratic relationship with time. On average, the optimum fermentation times were 107.7, 135.3, 136.2 and 147.4 min for ILTF, TFMT, taster D and taster E, respectively. Linear relationships between different methods had good correlation coefficients but TFMT and tasters' evaluations related best. In the absence of a taster, TFMT can be used to optimise fermentation time in tea processing.