Correlation of theaflavins content and valuations of kenyan black teas

Correlation between theaflavins content and tasters' valuations of Kenyan black teas generally give positive but statistically non-significant correlation coefficients. In 105 correlations using 12 samples each, only eight analyses gave statistically significant (P?0.05) correlations. Theaflavins contributed positively towards valuations but Kenyan black plain teas have high and possibly above optimum theaflavins content. Consequently other factors appear to play major roles in tea pricing, for example the generally higher prices realised by Kenyan black plain teas compared to Malawi black plain teas can only be partly attributed to the higher theaflavins content of the Kenyan teas.     

Seasonal variations in theaflavins,thearubigins, total colour and brightness of Kangra orthodox tea (Camellia sinensis (L) O Kuntze) in Himachal Pradesh

Variations in theaflavins, thearubigins, total colour and brightness of orthodox black tea were studied for four consecutive years (1993–1996) with a view to evaluating the effects of changing weather conditions on the quality of Kangra tea. A degree of withering of 600–650 mg g⁻¹ during the first, second and fourth seasons was optimal for the development of significantly higher brightness and total colour characteristics. The quality of rainy season teas suffered owing to high chlorophyll content and low degree of withering. Hot air circulation through the withering troughs to assist evaporation of leaf moisture increased the brightness and total colour of rainy season teas. High atmospheric demand during the dry season assisted loss of green leaf moisture, but withering and brightness exhibited significant negative correlations with high relative humidity and rainfall. Summer season teas were superior in their total colour and brightness. © 2000 Society of Chemical Industry     

The Stability of Theaflavins During HPLC Analysis of a Decaffeinated Aqueous Tea Extract

It has been shown that the theaflavins and thearubigin hump of decaffeinated aqueous extracts of black tea remain virtually stable for up to 850 min, thus permitting their automated overnight analysis. Within-run coefficients of variation for the total chromatogram area and peak area for each of the major theaflavins, following repeated (up to 10 times) injections of a single extract, did not exceed 2·5 and 6·0%, respectively. The corresponding values obtained by pooling data obtained on three separate occasions were 3·0 and 7·3%, respectively. Trend-line analysis indicated that there was a tendency for each of the areas studied to decline by factors in the range 0·11–0·53% of the original value per injection. This factor was not statistically significant for theaflavin-3,3′-digallate but reached 5% significance for theaflavin and total chromatogram area and 1% for both theaflavin monogallates. The magnitude of these changes is too small to warrant an avoidance of automated sample handling in routine screening or quality assurance programmes where the increased throughput allowed is advantageous. It was also noted that the use of citric acid to acidify the chromatographic solvents was not superior to acetic acid. © 1997 SCI.     

Variations in the leaf standard,chemical composition and quality of black tea (Camellia sinensis) due to plucking intervals

Green leaf standard, chemical composition and quality of black tea (Camellia sinensis (L) O Kuntze) change with plucking intervals. Long plucking intervals lead to poor leaf standard with a lot of mature leaves and lower theaflavins, the sum of volatile flavour compounds imparting a sweet flowery aroma (group II volatile flavour compounds), caffeine contents and tasters' evaluations of black tea. The sum of volatile flavour compounds imparting inferior, grassy, green flavour (group I volatile flavour compounds) to tea, however, increases with long plucking intervals.     

Changes in the quality parameters of seedling tea due to height and frequency of mechanical harvesting

Quality parameters of black tea change due to the use of a mechanical harvester, varying plucking round lengths and plucking heights. Compared with hand plucking, mechanically harvested teas have inferior quality as measured by volatile flavour compounds, theaflavins and caffeine. Similarly, longer plucking rounds produced inferior teas compared with shorter rounds. Raising mechanical plucking height by 2 cm from the previous plucking height caused less quality deterioration than increasing the height by 1 cm irrespective of plucking rounds.     

小叶种红茶发酵外观色差及其主要品质成分相关性

目的依据形成红茶优良品质的理化变化原理,借助现代科学仪器无损检测手段判断小叶种红茶发酵程度。方法在小叶种红茶发酵过程中,对发酵叶色差及不同发酵程度茶样的儿茶素、茶黄素等成分进行跟踪检测。结果发酵叶色差"L,a,b"值逐步上升或下降,其值在180~240 min均有"稳态"的存在,结合不同发酵程度茶样感官审评结果,得出"稳态"即是小叶种红茶发酵的最佳品质状态,尤以210 min最佳。儿茶素含量呈现逐渐下降趋势,茶黄素含量呈现的先增长再下降的变化趋势,茶红素与茶黄素比值的变化情况,均与发酵叶色外观差值存在显著性相关。结论采用统计方法分析色差值与审评结果之间的相关性,探讨小叶种红茶发酵适度的判别指标,提出适度发酵相关判别式ΔL≤0.10,Δa≤0.16,Δb≤0.16和品质的线性回归方程。     

Impact of shoot maturity on chlorophyll content,composition of volatile flavour compounds and plain black tea chemical quality parameters of clonal leaf

Chlorophyll content in black teas increased with a rise in shoot maturity, while the theaflavin content, brightness, total colour and tasters' evaluation declined. The increase in chlorophyll content in black teas of clone S15/10 was in a parallel with the greenness of the black tea infusions as described by tea tasters. These relationships were less pronounced in clone 6/8. The thearubigins content and the individual volatile flavour compounds composition in black tea remained the same or declined with increased shoot maturity, respectively. The results suggest that the impact of chlorophyll content on black tea quality is clonal dependent and becomes more significant as tea shoots mature and when the other plain black tea chemical quality parameters are low.     

A comparison of the hplc,mass spectra,and acid degradation of theafulvins from black tea and proanthocyanidin polymers from wine and cider

The HPLC chromatograms, mass spectra, and acid degradation of a theafulvin fraction (a fraction of polymeric thearubigins) and proanthocyanidin polymers from cider and wine were compared. The cider, wine, and theafulvin fractions ran as broad bands on a Hamilton PRP-1 column. The cider and wine polymers gave positive-ion FAB spectra characteristic of proanthocyanidin polymers, but the theafulvins gave low-molecular-mass flavanol fragments only. The cider and wine polymers gave cyanidin on acid degradation, the reaction products being analysed by HPLC on a Hamilton PRP-1 column. The theafulvins gave mainly material that ran close to the void volume of the HPLC column. These experiments provided support for previous conclusions, that the theafulvins are flavanol polymers with different intermonomer linkages to the proanthocyanidin polymers.     

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