P. Okinda Owuor

Changes in the chemical and sensory quality parameters of black tea due to variations of fermentation time and temperature

Abstract The changes in theaflavins and residual catechin compositions, thearubigins TRSI and TRSII, sensory characteristics of total colour, brightness and briskness of black tea were investigated. It was demonstrated that the degradation of individual theaflavins varied during fermentation. Decline in the levels of individual theaflavins was influenced by both duration and temperature and coincided with decline in brightness and briskness. ECG and EGCG were the main residual catechins in black tea. The formation of thearubigins TRSI and TRSII, differed in their response to fermentation duration and temperature. The effects of processing parameters, fermentation temperature and duration, on chemical quality and tea liquor sensory characteristics are discussed.

Changes in thearubigin fractions and theaflavin levels due to variations in processing conditions and their influence on black tea liquor brightness and total colour

Increase in coarser plucking standards significantly (P<0.05) depressed levels of theaflavin (TF; μmol/g), total colour and brightness (spectrophotometer) of black tea. But total thearubigins (TR) TRSI, TRSII and brightness (taster) levels did not significantly (P<0.05) change with plucking standards. Increasing fermentation duration led to rise in TF (μmol/g), total TR, total colour, TRSI and TRSII, liquor brightness (taster) but not liquor brightness determined by spectrophotometer method (P<0.05). Correlation analysis showed that total TR and TRSII had negative correlations (r=−0.66 and −0.77, P<0.01), respectively, while total TF levels had positive correlation with taster brightness (r=0.57, P<0.01). Total TF level had highest correlation with spectrophotometer liquor brightness (r=0.87, P<0.01) for a single substance. TRSII and total TR gave an r of 0.86 indicating that the two groups of substances were strongly correlated to each other. Regression analysis showed that the direct linear model gave the best fit for the sample data studied. The coefficient of multiple determination (R2) was 0.606 in linear model I for the tasters’ liquor brightness. Thus, the independent variables TF and total TR explained 60.6% of the total variation in liquor brightness scores observed. When TRSI and TRSII were included in the linear model II instead of total TR, but with TF maintained, the coefficient of multiple determination improved to 78.9%. This confirmed that the brightness attribute of black tea, assessed by the taster, could best be explained by the combination of TF and TRSII and that TRSI had a lesser role in the tasters’ evaluation of liquor brightness. Indeed, the test statistic in linear model I showed that the coefficient of TF positively and significantly influenced liquor brightness at P<0.01 whereas the coefficient of total TR negatively and significantly influenced liquor brightness (P<0.0001). However, in linear model II the effect of total TR on the taster brightness was clearly unmasked and the influence of each individual component well elucidated. The coefficient of TRSII was negative and significantly explained liquor brightness at 0.01% level (P<0.0001). The coefficient of TRSI was negative but insignificant. Hence it has no discernible influence on the taster liquor brightness. The coefficient of TF was positive and significantly explained taster liquor brightness (P<0.01). Thus, TF and TRSII explain taster liquor brightness and the lower the level of TRSII the higher the score for brightness. The situation for spectrophotometer brightness was somewhat different. The coefficient of multiple determination was 0.896 in linear model I. Thus, TF and total TR explained 89.6% of the variation in spectrophotometer brightness. The coefficient of TF was positive whereas that of total TR was negative. Both coefficients were significant (P<0.0001). When TRSI and TRSII were included in the linear model II instead of total TR, R2 improved to 91%. Unlike for the tasters’ brightness, the coefficient of TRSI was now significant (P<0.05). The coefficient of TRSII was negative and significant (P<0.01) whereas the coefficient of TF was positive and significant (P<0.0001). The differences in the contributions of TRSI and TRSII to black tea liquor brightness and the observed discrepancy between the test methods, due to variations in plucking standards and fermentation duration, are discussed.

Clonal variation in the individual theaflavin levels and their impact on astringency and sensory evaluations

Abstract 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.

COMPARATIVE RESPONSES IN PLAIN BLACK TEA QUALITY PARAMETERS OF DIFFERENT TEA CLONES TO FERMENTATION TEMPERATURE AND DURATION

Abstract The amounts of black tea theaflavins, brightness, and sensory evaluations varied with clones in the order clone 6/8>SC12/28>S15/10, while thearubigins and total colour changed in the reverse order. The rates of change of these plain tea quality parameters varied in all clones causing significant (P⩽ 0.05) fermentation duration and clone interactions. Thus, the total amount and rate of development of each quality parameter is unique to a clone and a change in fermentation duration for optimal quality parameter achievement in one clone cannot be extrapolated to another clone. Although processing of black tea at low fermentation temperatures improved black tea quality, there was no significant difference between fermenting at 15 and 20°C. Long fermentation duration and high temperature favoured production of more intense coloured black teas with high thearubigin levels, which were less bright and had lower theaflavin levels. There were significant (P⩽ 0.05) interactions between fermentation duration and temperature in all the plain black tea parameters development indicating that their rates of formation and amounts formed varied with time at different temperatures. Clones 6/8 and SC12/28 plain tea quality parameters were more sensitive to temperature and duration changes than clone S15/10. Thus there are clones, which can withstand high temperature and long fermentation duration without drastic impairment of their plain black tea quality parameters.

The Impact of Withering Temperature on Black Tea Quality

High leaf temperatures during the withering process of black tea manufacture decrease the theaflavins, brightness, flavour index and sensory evaluation scores of black tea. Black teas manufactured with withering temperature above 30°C have high thearubigins and total colour levels but lack briskness. Results suggest a need to control temperatures below 30°C during withering.

Effects of Genotype, Environment and Management on Yields and Quality of Black Tea

The tea beverages processed from the young tender shoots of Camellia sinensis (L.) O. Kuntze, are claimed to be the most widely consumed fluids after water. The tea plant originates from the point of confluence of Northeast India, North Burma, Southwest China and Tibet. Its production has spread and economic production has been reported in between 49 ∘ N in Outer Carpathians to 33 ∘ S in Natal, South Africa, at altitudes ranging from sea level to 2,700 m above mean sea level. The adaptability of the plant to areas with large variations in geographical, climatic and environmental factors can cause changes in growth patterns in different genotypes leading to variations in yields and black tea quality. Tea producers usually import genotypes, management and production techniques suitable for optimal production in one region in the hope that beneficial attributes observed at source shall be maintained in the new areas. But the tea plant responses in new environments have not always yielded the desired results. Here we review the effects of genotypes, environment and management on the yields and quality of black tea. Previous investigations demonstrated that black tea yields and quality changes are due to environmental factors like soil type, altitude, seasons, weather factors, geographical areas of production, agronomic inputs, processing technologies and management. Black tea quality and yields of similar genotypes grown on different soils vary. The extent and patterns of the variations change with varieties. High altitude grown teas are more aromatic than low altitude grown black teas, implying that the low grown teas are plain in character. Thus producers at high altitudes should aim at producing aromatic black teas, although yields will be lower than same genotypes at lower altitudes. Producers growing teas at low altitudes should focus on high output and ensure optimal conditions for production of plain black teas. There are seasonal black tea quality and yield variations. Cold seasons lead to slow growth resulting in low yields, but high black tea quality. Provided soil moisture and temperatures are adequate, warm temperatures lead to fast growth, leading in turn to high yields, but low black tea quality. It is therefore not possible to have uniform production or to produce the same black tea quality throughout the year. The situation is adverse further away from the equator with no production in winter as the labour management can be critical during the long cold seasons, necessitating long labour layoffs. Many genotypes have been developed, some with very high yields and quality. As a result, producers continuously try to access the good varieties into new geographical areas in the hope the genotypes would retain their economic advantages. While some genotypes are stable to locational changes, most show wide variations due to planting in the new areas. Management policies induce yield and black tea quality differences. Imported management policies should be domesticated and modified to suit the new environments. Harvesting, by hand plucking, the young tender shoots is done when they are of the right size. Delayed harvesting leads to shoot overgrowth and crop loss. Whereas plucking two leaves and a bud is a compromise between yields and black tea quality, some growers practice coarser plucking standards. Black tea quality declines with coarse plucking standards. Short plucking rounds lead to high production and high quality black teas. When a plucking standard is preset, growers in a location need to establish the shortest harvesting interval for realization of good yields and quality. Fertilizers are essential for establishment and growth. Varying results have been recorded on yield and quality responses to NPK application. For potassium and phosphorus, evaluations are necessary in different regions because where there is no beneficial effects their application can be reduced to decrease costs. High rates of nitrogen reduce black tea quality and do not increase yields. Nitrogen fertilizers need to be applied at rates that are a compromise between yields and black tea quality. Such rates vary with regions and genotypes. To reach high production and quality, region- and genotype-specific fertilizer rates are needed. In regions producing relatively inferior black teas producers try to import processing technologies from other areas. These efforts may not improve quality due to variations of environmental conditions. Indeed, for the same genotype grown in different regions and processed under identical conditions, differences in quality and chemical composition have been reported. This was due to variations in the leaf biochemical constituents composition caused by the environment in which the plant was grown. Different regions must therefore optimize their processing conditions to realize high quality.

Monitoring the occurrence and distribution of selected organophosphates and carbamate pesticide residues in the ecosystem of Lake Naivasha, Kenya

Although use of pesticides is critical in agricultural production, their residues present a potential risk to non-target organisms and lower the quality of surface water. In Kenya for instance, widespread use of pesticides in the catchment of Lake Naivasha, has raised concern over the years due to possible pollution of the lake through discharge of runoff from agricultural fields. In this study, sediment, water, and fish samples were analyzed for selected pesticide residue contamination. Chlorpyrifos-ethyl (CPF) was detected in the range of 2.6–24.9 ng/ml and 6.8–35.8 ng/g dry weight (dw) in water and sediment, respectively. Meanwhile, diazinon was detected in the range of below detection limit (bdl) to 33.3 ng/ml and bdl to 9.3 ng/g dw in water and sediment, respectively. CPF was detected in fish tissues (Niloticus leucosticus) in the range of bdl to 8.9 ng/g dw with diazinon and carbofuran not detected in any fish sample. A significant difference was observed between different seasons with wet season recording higher levels. Concentrations detected varied seasonally and on average exceeded the maximum criterion set by European Union. Therefore, data generated in this study are useful in environmental risk assessment and as a baseline in formulation of mitigation measures to protect the lake from pesticides residues pollution.

Quality response of clonal black tea to nitrogen fertiliser, plucking interval and plucking standard

Variations in the black tea quality of high-yielding clone S15/10 in response to rates of NPKS 25:5:5:5 fertiliser of 200 and 400 kg Nha ˇ1 year ˇ1 , plucking intervals of 7, 14 and 21 days and a selective plucking standard of up to two leaves and a bud or an unselective plucking standard were studied. Generally, quality declined with longer plucking intervals and unselective plucking. Although there was a general decline in quality with increasing nitrogen rate, only the black tea total colour declined significantly on increasing the nitrogen rate from 200 to 400 kg Nha ˇ1 year ˇ1 . For each nitrogen rate and each plucking interval, unselective plucking reduced the black tea quality. No significant interactions between any two of the three (nitrogen rate, plucking interval and plucking standard) or all three factors were noted, indicating that the patterns of response were similar. The results demonstrate that black tea quality changes due to the factors studied occur in the same pattern with variations in treatments. Poor black tea quality due to any of the factors studied cannot therefore be corrected by varying the other factors. # 2000 Society of Chemical Industry

The effects of blending clonal leaf on black tea quality

Abstract 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. ©

VARIATIONS IN THE PRECURSORS OF PLAIN BLACK TEA QUALITY PARAMETERS DUE TO LOCATION OF PRODUCTION AND NITROGEN FERTILIZER RATES IN EASTERN AFRICAN CLONAL TEA LEAVES

Theaflavins contribute to astringency and brightness while thearubigins contribute to colour and mouth feel of black tea. Green leaf flavan-3-ols influence levels and distribution of theaflavins and thearubigins in black tea and are black tea quality precursor compounds. Caffeine also contributes to tea quality. Although location of production and nitrogenous fertilizer rates influence black tea quality, it is not known if the variations arise from the levels and distribution of the precursor compounds in green leaf or other factors. The variations and distribution of the flavan-3-ols and caffeine in young green leaves of clone TRFK 6/8 due to nitrogen fertiliser rates in seven locations within Eastern Africa were evaluated. Green leaf comprising two leaves and a bud were harvested from each plot, and subjected to HPLC analysis for caffeine, total polyphenol, dihydroxyflavan-3-ols, trihydroxyflavan-3-ols, ratios of trihydroxyflavan-3-ols to dihydroxyflavan-3-ols and total catechins levels. Results were subjected to statistical analysis using split plot design, with locations as main treatments and nitrogen rates as the sub-treatment. Caffeine and flavan-3-ols levels changed (p 0.05) with location of production, demonstrating that even with use of same cultivar and similar agronomic management quality of tea from one location cannot be replicated in another location. Caffeine levels increased (p 0.05) with rise in nitrogen fertilizer rate in all locations, but the extent depended on location. Total polyphenols and individual flavan-3-ols showed an inverse quadratic response, except EGCG that linearly decreased (p 0.05) in some locations, due to increasing rates of nitrogen fertilizer. Similar responses in the black tea quality parameters had been observed in previous studies. The black tea quality results were therefore directly influenced by the green leaf precursor compound patterns. Region specific nitrogenous fertilizer rates need development to ensure high tea quality.