Kinetics and equilibria of tea infusion: Theaflavin and caffeine concentrations and partition constants in several whole teas and sieved fractions

Concentrations of theaflavin and caffeine were determined in whole Kapchorua Pekoe Fannings and in six of its sieved fractions, as well as in Kapchorua Pekoe Dust, Betjan Flowery Broken Orange Pekoe and Rupai Flowery Orange Fannings and in one sieved fraction of each. The partition constants of theaflavin and caffeine between these leaves and water at 80°C were also determined. Neither property varied significantly with leaf size but did depend on leaf origin and manufacture. The concentration and partition constants for caffeine were greater than for theaflavin. As a corollary, the ratio of caffeine to theaflavin is larger in tea initially drawn from the teapot than in the beverage prepared after topping up with fresh hot water.     

Kinetics and equilibria of tea infusion—Part 6: The effects of salts and of pH on the concentrations and partition constants of theaflavins and caffeine in Kapchorua Pekoe fannings

The concentrations of theaflavins and of caffeine in sieved Kapchorua Pekoe Fannings (600–710 μm) have been determined at 80°C with a range of aqueous salt and buffer solutions of ionic strength 0·11 mol dm⁻³ and of pH 1·9 to 8·3. The caffeine concentration in the infusions and in the leaf, and its partition constant between swollen leaf and solution, was little affected by the presence of electrolytes or pH changes. The concentration of theaflavins in the infusions was not changed by the addition of salts but was considerably greater in acid media and also, temporarily, in borate buffers. The acid effect was corroborated by experiments with a Ceylon Broken Orange Pekoe blend. The most significant finding was that the concentration of theaflavins in the Kapchorua leaf rose markedly with falling pH while its partition constant decreased. These results show that hydrogen ions liberate extra theaflavin by breaking down the leaf structure and/or the bonding of some theaflavin within the leaf. The effect has significant commercial implications since the market price of tea leaf correlates with its theaflavin content.     

Kinetics and equilibria of tea infusion: Part 8—the effects of salts and of pH on the rate of extraction of theaflavins from black tea leaf

The rates of extraction of theaflavins from sieved Kapchorua Pekoe Fannings (600–710 μm) and from a Ceylon Broken Orange Pekoe Fine Leaf Blend have been measured at 80°C with a set of aqueous salt and buffer solutions spanning the pH range 3·1 to 8·1. There was little effect on adding 1:1 electrolytes but considerable decreases in rate occurred in the presence of calcium chloride. The rate constants in acid buffers were the same as in a normal unbuffered infusion but in alkaline buffers of pH 8 they were over 50% larger. This phenomenon was quantitatively accounted for by the partial dissociation of theaflavins at higher pH and the greater diffusion coefficient of the resulting ionic salt. The relevance of these findings to tea brewing and to industrial theaflavins extraction is discussed.     

Evaluation of Data Mining Strategies for Classification of Black Tea Based on Image-Based Features

In this study, a new procedure based on computer vision was developed for qualitative classification of black tea. Images of 240 samples from four different classes of black tea, including Orange Pekoe (OP), Flowery Orange Pekoe (FOP), Flowery Broken Orange Pekoe (FBOP), and Pekoe Dust One (PD-ONE), were acquired and processed using a computer vision system. Eighteen color features, 13 gray-image texture features, and 52 wavelet texture features were extracted and assessed. Two common heuristic feature selection methods: correlation-based feature selection (CFS) and principal component analysis (PCA), were used for selecting the most significant features. Seven of the primary features were selected by CFS as the most relevant ones, while PCA converted the original variables into 11 independent components. These final discriminatory vectors were evaluated by using four different classification methods including decision tree (DT), support vector machine (SVM), Bayesian network (BN), and artificial neural networks (ANN) to predict the qualitative category of tea samples. Among the studied classifiers, the ANN with 7–10–4 topology developed by CFS-selected features provided the best classifier with a classification rate of 96.25%. The other methods assayed provided slightly lower accuracies than ANN from 86.25% for BN till 87.50% for SVM and 88.75% for DT. In all the cases, the accuracy of the classifiers increased when using the CFS-selected features as input variables in front of PCA obtained ones. It can be concluded that image-based features are strong characterizing factors which can be effectively applied for tea quality evaluation.     

Kinetics and equilibria of tea infusion: Kinetics of extraction of theaflavins,thearubigins and caffeine from Koonsong broken pekoe

The rates of infusion of theaflavins, thearubigins, and caffeine from Koonsong Broken Pekoe into water were measured at 79.5 and 94.0°C. The kinetic data have been interpreted in terms of a simple two-phase model, and the rate constants of infusion and of re-absorption were calculated. At low infusion times thearubigins were extracted faster than theaflavins, with the caffeine rate intermediate. However, the rate constants for the overall infusion process were quite similar for the three constituents. The corresponding activation energies are small as are those calculated from Long's data on the rate of extraction of all soluble material.     

Kinetics of tea infusion. Part 3: the effect of tea bag size and shape on the rate of caffeine extraction from Ceylon orange pekoe tea

The rate of infusion of caffeine from Ceylon Orange Pekoe tea of leaf size 1.4–2 mm in loose form and inside a tea bag membrane was determined at 80°C. The tea bags were varied in size and shape. It was found that the rate constant increased significantly with an increase in tea bag size until the ratio of tea leaf to tea bag size was 1:10. The results also indicate that the shape of a tea bag had no influence on the rate of infusion, and that the tea bag membrane offered some hindrance to the infusion of caffeine.     

不同类型沱茶品质与特征性成分分析

目的 探明不同类型沱茶的品质和特征性成分。方法 本文采用高效液相色谱、感官审评、Lab颜色模型等方法,比较分析供试沱茶的主要品质成分、干茶色泽和感官品质,结合多元统计学方法明确不同沱茶的特征化学物质组成。结果 云岭沱茶的感官审评综合得分高于其他沱茶,其汤色亮度和叶底嫩度优于其他沱茶,下关沱茶以儿茶素、表儿茶素、表儿茶素没食子酸酯含量较高,而茶黄素含量较低为特征,山城沱茶以茶红素含量较高,而水浸出物、咖啡碱、没食子酸含量较低为特征,云岭沱茶以茶黄素、茶多酚、表没食子儿茶素没食子酸酯、表没食子儿茶素、没食子酸、咖啡碱含量较高,而茶红素、茶褐素、儿茶素含量较低为特征,与沱茶感官审评得分呈显著正相关的生化成分有茶多酚、咖啡碱、没食子酸、茶黄素、表没食子儿茶素、表没食子儿茶素没食子酸酯。结论 不同类型沱茶生化成分的含量与组成特征差异较大。     

Kinetics and equilibria of tea infusion. Analysis and partition constants of theaflavins,thearubigins, and caffeine in koonsong broken pekoe

Koonsong Broken Pekoe tea leaf was equilibrated with water at 79.5 and 94.0°C using water: leaf ratios from 25:1 to 100:1. The concentrations of theaflavins, thearubigins, and caffeine were measured in the aqueous extracts. Analysis of the results by a simple two-phase model gave the concentrations of the three constituents in the original leaf without the necessity for the usual assumption of complete extraction. The theory also yielded the partition constants (distribution coefficients) of the three constituents between swollen leaf and aqueous solution, and the enthalpy changes for their extraction.     

Distribution of Catechins, Theaflavins, Caffeine, and Theobromine in 77 Teas Consumed in the United States

ABSTRACT: To help define the composition of commercial teas consumed in the United States, we have developed and validated an high-performance liquid chromatography (HPLC) method to analyze levels of catechins, theaflavins, and alkaloids in 77 commercial black, green, specialty (brown rice, white, oolong), and herbal teas extracted with hot water to simulate home use. The following 13 compounds were separated in a single analysis on an Inertsil ODS-3v column with acetonitrile/potassium dihydrogen phosphate as the mobile phase: (−)-epigallocatechin, (+)-catechin, (−)-epicatechin, (−)-epigallocatechin-3-gallate, (−)-gallocatechin-3-gallate, (−)-epicatechin-3-gallate, (−)-catechin-3-gallate, theaflavin, theaflavin-3-gallate, theaflavin-3'-gallate, theaflavin-3, 3'-digallate, caffeine, and theobromine. The data show that (1) extraction time from 3 min to 20 min did not significantly affect measured levels of tea compounds and (2) there was a wide variation in the composition of the tea compounds both within each tea category and among categories: black teas contained both theaflavins and catechins, green and white teas contained catechins and trace amounts of theaflavins, herbal teas contained very low amounts of all tea compounds. A statistical profile of the distribution of catechins, theaflavins, caffeine, and theobromine in the evaluated teas offers consumers a choice of teas containing high levels of health-promoting compounds.     

The kinetics and mechanism of caffeine infusion from coffee: The effect of particle size

Measurements have been made of the rate of infusion of caffeine into distilled water from medium roast Kenyan Arabica coffee beans and from eight sieved fractions of the ground beans at 25.8°C. The first-order rate constants increased dramatically as the particle size decreased. For one of the size fractions the rate constants were then measured at various temperatures up to 84.1°C and were found to rise eight-fold over this temperature interval. The partition coefficients of caffeine between ground beans and water were also determined. These results, interpreted by a new steady-state theory of extraction, show that the rate-determining step in the infusion is diffusion of caffeine through the swollen coffee particles. The low magnitude of the diffusion coefficient and its high activation energy demonstrate that caffeine diffusion within the bean particles is a hindered process.     

Kinetics and equilibria of tea infusion: Part 7—The effects of salts and of pH on the rate of extraction of caffeine from Kapchorua Pekoe Fannings

The rates of extraction of caffeine from sieved Kapchorua PF (600–710 μm) have been measured at 80°C with a range of aqueous salt and buffer solutions of ionic strength 0·11 mol dm⁻³. The first-order rate constants and the half-times of infusion showed no trend with pH when buffers from pH 3·0 to pH 8·3 were employed. The rate constants decreased on the addition of common salts like NaCl, KCl and CaCl₂ but increased in the presence of electrolytes such as Bu₄NCl that contain large ions. The results cannot be interpreted by changes in osmotic pressure although Donnan effects may be involved. Close parallels were found between the rate constants and the solubilities of caffeine in electrolyte solutions at 25°C. In particular, the values of both properties rise appreciably in the presence of species containing aromatic or other organic rings with which caffeine molecules associate.     

Biochemical quality characteristics of CTC black teas of south India and their relation to organoleptic evaluation

A study was conducted over a period of 5 years to quantify the quality characteristics of CTC (crush, tear and curl) black teas produced in Wayanad, Central Travancore, Anamallais, High Range, Nilgiris and Chikmagalur areas of south India and their correlation with organoleptic evaluation. Quality characteristics such as theaflavins (TF), thearubigins (TR), highly polymerised substances (HPS), total liquor colour (TLC), TR/TF ratio and colour index (CI) were estimated. Teas from Karnataka, Nilgiris and Anamallais had the highest theaflavin content and better TR/TF ratio than the teas from Travancore, High Range and Wayanad regions. A significant positive correlation of theaflavin content with the values of thearubigins, total liquor colour, colour index, infused leaf appearance (ILA) and taste (TAS) was observed.     

Response of some black tea quality parameters to nitrogen fertiliser rates and plucking frequencies

The effects of the rate of application of nitrogenous fertiliser and frequency of plucking (harvesting) on various black tea quality parameters and yields were compared on done 6/8. High rates of nitrogen application and long plucking intervals reduced the theaflavin content and brightness of black tea liquor. The caffeine content of the black tea increased with increasing rates of nitrogen application but decreased with increase in the plucking interval. The Group I volatile flavour compounds increased with nitrogen application rate and long plucking intervals while the Group II volatile flavour compounds and the flavour index decreased. Tasters preferred teas from shorter plucking intervals and low rates of nitrogen application. Yields increased with increasing rates of nitrogen but were lowered by long harvesting intervals. The rate of nitrogen application did not change the distribution of leaf into different standards.     

The kinetics and mechanism of caffeine infusion from coffee: The hindrance factor in intra-bean diffusion

Green and medium-roast Kenyan arabica coffees were ground and sieved, and the 0·85–1·8 mm size fractions partially converted into two water-swollen forms by an appropriate series of treatments. The first form still contained a mix of coffee solubles, the second only caffeine. The rates of caffeine infusion into water at 80°C were then measured for the dry coffee and for the two water-swollen preparations. The caffeine was extracted two to three times faster from the solute-free water-swollen preparation than from the dry material Analysis of the results showed that counterflow of water the swelling of coffee particles, caffeine association with other solubes and physical restraints within the bean matrix all contribute to the low diffusion coefficient of caffeine inside the coffee particles. The behaviour of the green and the medium roast coffees was surprisingly similar.     

HPLC Analysis of Catechins, Theaflavins, and Alkaloids in Commercial Teas and Green Tea Dietary Supplements: Comparison of Water and 80% Ethanol/Water Extracts

ABSTRACT:  To help meet the needs of consumers, producers of dietary tea supplements, and researchers for information on health-promoting tea compounds, we compared the following conditions for the extraction of tea leaves and green tea-containing dietary supplements: 80% ethanol/water at 60 °C for 15 min and boiled water for 5 min. The following 7 catechins, 4 theaflavins, and 3 alkaloids were separated in a 70-min single HPLC analysis: (−)-epigallocatechin, (−)-catechin, (+)-epicatechin, (−)-epigallocatechin-3-gallate, (−)–gallocatechin-3-gallate, (−)-epicatechin-3-gallate, (−)-catechin-3-gallate, theaflavin, theaflavin-3-gallate, theaflavin-3'-gallate, theaflavin-3,3'-digallate, caffeine, theobromine, and theophylline. The following ranges of concentrations of flavonoids (catechins plus theaflavins) in the tea leaves extracted with 80% ethanol were observed (in mg/g): in 32 black teas, 19.8 to 115.1; in 24 green teas, 12.3 to 136.3; in 14 specialty teas, 4.9 to 118.5; in 7 herbal teas, 0 to 46.0. Total alkaloids in all teas ranged from 0 to 32.6 mg/g. Significantly greater amounts of flavonoids were extracted from the tea leaves with aqueous ethanol than with boiled water. Levels of tea catechins in 10 capsules sold as dietary supplements were about 50 to 75% lower than the amounts listed on the labels. Catechin content of 4 commercial green tea extracts ranged from 96 to 696 mg/g. The results make it possible to maximize the extraction of tea compounds to better relate the flavonoid and alkaloid content of teas and dietary tea supplements to their health-promoting effects.     

Extractability of tea catechins as a function of manufacture procedure and temperature of infusion

Green teas were made by different inactivation procedures ranging from steaming, thermal inactivation by heating in an oven or microwave-mediated inactivation, followed by either unidirectional or bi-directional rolling and drying. Teas were infused at different temperatures (80 and 100 °C) and the tea ceremony way of infusing, and analyzed for tea catechins and xanthine alkaloids by HPLC. Teas manufactured following microwave inactivation, bi-directional rolling and drying showed higher catechins and methyl xanthines by HPLC, and extracted higher catechins and caffeine in infusions. Catechins, especially EGCG, EGC, and EC, showed marked differences when extracted at different temperatures. Considerable amounts of catechins and caffeine can be extracted each time when the same leaf is infused repeatedly 4–5 times, as done in Japan for making ceremonial teas.     

The response of quality and yield of black tea of twocamellia sinensis varieties to methods and intervals of harvesting

The sensory evaluation and chemical quality parameters of black teas changed with variety, plucking round length and method of plucking. Hand plucked teas had higher theaflavins (TF), caffeine, brightness, flavour index. Group II volatile flavour compounds (VFC) and sensory evaluations, but lower Group I VFC than shear plucked teas irrespective of variety. Black teas plucked from short plucking rounds were superior to those from long plucking rounds as assessed by TF, caffeine, brightness, the chemical aroma quality parameters and sensory evaluation. Long plucking intervals and shear plucking reduced tea yields and produced coarser leaf than short plucking intervals and hand plucking respectively.     

Kinetic study of mineral ion extraction from Kenyan Arabica coffee

The rate of infusion into distilled water of caffeine and of Mg, Mn, K and P have been measured. The coffee used was roasted Kenyan Arabica coffee, ground, and sieved to a size range of 1.70–2.00 mm. The analytical techniques employed were HPLC for the analysis of caffeine and ICP‐AES for analysing mineral ions. The kinetic data have been interpreted in terms of a steady‐state theory, and the rate constants of infusion have been calculated. The diffusion coefficients of the various species within the bean were calculated from the resultant rate constants. These values have been compared with the corresponding diffusion coefficients in pure water at 80°C and the hindrance factors in the bean have been determined. © 1999 Society of Chemical Industry     

Study on the increase mechanism of the caffeine content during the fermentation of tea with microorganisms

The tea caffeine content had previously been shown to increase reasonably after being treated with mixed microorganisms for a period of time. In this study, single microorganisms were used in the fermentation of black and green teas in order to find which microorganism has the best effect on increasing the caffeine content. The results demonstrated that molds fermentation increased the caffeine content, but yeasts fermentation decreased the caffeine content. Among the three molds in this study, Aspergillus niger van Tieghem has the most remarkable effect, and the caffeine content in dry green tea increased from an initial 3.47% to 9.63%. The increase rate was 177.5% on the 16th day. Furthermore, the changes of caffeine and theophylline were of a similar trend. Possibly theophylline instead of theobromine is the precursor of caffeine in the living microorganisms. The new biosynthetic route is different from that in tea plants.     

The effect of pH modification during fermentation on the quality parameters of central African black teas

Adjusting the pH of fermenting tea from the physiological value to within the range 4.5–4.8 resulted in an increase in theaflavin content, a reduction in thearubigin levels, and an increase in the organoleptic evaluation of the product. Industrial-scale acidification of commercial leaf was practicable and the market price realised on the London auction floors for treated teas was considerably higher than that for control consignments.