Bioactive components and antioxidant properties of γ-aminobutyric acid (GABA) tea leaves

Various ethanolic concentrations (0–95%, v/v) and temperatures (25–95 °C) were used to extract γ-aminobutyric acid (GABA) tea leaves. Extraction yields, and contents of total phenols, various catechins, GABA, theanine, and antioxidant properties of extracts were determined. The 50% (v/v) ethanol at 50–95 °C gave higher yields (32.05–32.56 g dried extract/100 g dried tea leaves). The bioactive components and antioxidant properties of extracts were affected by the ethanolic concentrations and temperatures. Among catechins, epigallocatechin gallate was the main catechin in all extracts, followed by epigallocatechin, epicatechin, epicatechin gallate, gallocatechin and gallocatechin gallate. The 50–75% (v/v) ethanol at 75–95 °C gave higher contents of ester type (102.92–104.54 mg/g extract) and non-ester type (61.75–63.55 mg/g extract) catechins. Water at 50–75 °C gave higher GABA and theanine contents and higher chelating ability of extracts. The 75% (v/v) ethanol at 25–75 °C gave higher scavenging ability and reducing power of extracts. Based on dried tea extracts or leaves results obtained, the optimal extraction conditions to maintain the total contents of various catechins, GABA and theanine in the maximum level were 50% ethanol (v/v) and 75–95 °C.     

Quantitative and Qualitative Portrait of Green Tea Catechins (Gtc) Through Hplc

Green tea (Camellia sinensis) is a prosperous source of polyphenols, especially catechins. In the current research, an effort was made to optimize the extraction conditions for maximum yield of catechins from the local green tea Qi-Men. For the purpose, three different solvents were used, i.e., aqueous ethanol (50%), aqueous methanol (50%), and water at different time intervals (20, 40, and 60 min). Green tea catechins were quantified through HPLC using a C18 column and UV detector. The antioxidant activity of green tea catechins was measured through in vitro tests including DPPH radical scavenging ability and antioxidant activity. Results showed that extraction through aqueous ethanol resulted in maximum yield of green tea catechins (17400 ± 0.19 mg/100 g green tea leaves. Moreover, epigallocatechin, epigallocatechin gallate, epicatechin gallate, and epicatechin ranged from 4.26 ± 0.09 to 6.4 ± 0.2, 12.1 ± 0.123 to 17.7 ± 0.3, 1.32 ± 0.03 to 1.81 ± 0.02, 5.48 ± 0.099 to 8.6 ± 0.2 g/100 g of dry-extract, respectively. Furthermore, highest antiradical (80.65 ± 3.69%) and antioxidant activity (67.12 ± 3.08%) were observed in catechins extracted through aqueous ethanol.     

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.     

Stability of tea polyphenols solution with different pH at different temperatures

Although tea polyphenols possess a variety of biological activities, the oxidative stability of tea polyphenols limits its application in the diet as preventive medicine. To enlarge biological activity of tea polyphenols, we investigated changes of tea polyphenols with different pH (3, 4, 5, 6, and 7) at different temperatures (4, 25, and 100°C). Changes in transmittance, deterioration, color values, and contents of catechins were evaluated. The results showed that tea polyphenols with a pH of 3–6 remained stable at 4 and 25°C. With increase of temperature, the tea polyphenol solutions became darker and less green, but deeper yellow in color. When the heating temperature was 100°C, a significant reduction in both total catechins and transmittance was observed. Individual catechins undergo epimerization in this process. Not only temperature and pH, but also heating time influenced the epimerization. Total contents of catechins incubated in pH 3, 4, 5, 6, and 7 citrate buffer solutions for 24 h declined by 15, 24, 41, 57, and 96% at 100°C, respectively. Therefore, tea polyphenols were pH-sensitive: the lower the pH, the more stable the tea polyphenols during storage. Storing at low temperature and acidic pH conditions did not significantly affect the characteristics of tea polyphenols.     

Polyphenols Extracted from Black Tea (Camellia sinensis) Residue by Hot‐Compressed Water and Their Inhibitory Effect on Pancreatic Lipase in vitro

Abstract: Polyphenols, retained in black tea wastes following the commercial production of tea beverages, represent an underutilized resource. The purpose of this study was to investigate the potential use of hot‐compressed water (HCW) for the extraction of pancreatic lipase‐inhibiting polyphenols from black tea residues. Black tea residues were treated with HCW at 10 °C intervals, from 100 to 200 °C. The resulting extracts were analyzed using high‐performance liquid chromatography‐mass spectrometry and assayed to determine their inhibitory effect on pancreatic lipase activity in vitro. Four theaflavins (TF), 5 catechins, 2 quercetin glycosides, quinic acid, gallic acid, and caffeine were identified. The total polyphenol content of extracts increased with increasing temperature but lipase inhibitors (TF, theaflavin 3‐O‐gallate, theaflavin 3′‐O‐gallate, theaflavin 3,3′‐O‐gallate, epigallocatechin gallate, and epicatechin gallate) decreased over 150 °C. All extracts inhibited pancreatic lipase but extracts obtained at 100 to 140 °C showed the greatest lipase inhibition (IC₅₀s of 0.9 to 1.3 μg/mL), consistent with the optimal extraction of TFs and catechins except catechin by HCW between 130 and 150 °C. HCW can be used to extract pancreatic lipase‐inhibiting polyphenols from black tea waste. These extracts have potential uses, as dietary supplements and medications, for the prevention and treatment of obesity. Practical Application: Active forms of lipase inhibitors can be recovered from black tea residues. They could be used as dietary supplements or medications.     

Effects of cosolvents on the decaffeination of green tea by supercritical carbon dioxide

Due to the adverse effects of the caffeine in a variety of plant products, many methods have been explored for decaffeination, in efforts to remove or reduce the caffeine contained in plant materials. In this study, in order to remove caffeine from green tea (Camellia sinensis) leaves, we have employed supercritical carbon dioxide (SC–CO₂), which is known to be an ideal solvent, coupled with a cosolvent, such as ethanol or water. By varying the extraction conditions, changes not only in the amount of caffeine, but also in the quantities of the principal bioactive components of green tea, including catechins, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC), were determined. The extraction conditions, including temperature, pressure and the cosolvent used, were determined to affect the efficacy of caffeine and catechin extraction. In particular, the type and concentration of a cosolvent used constituted critical factors for the caffeine removal, combined with minimal loss of catechins, especially EGCG. When the dry green tea leaves were extracted with SC–CO₂ modified with 95% (v/v) ethanol at 7.0 g per 100 g of CO₂ at 300 bar and 70 °C for 120 min, the caffeine content in the decaffeinated green tea leaves was reduced to 2.6% of the initial content. However, after the SC–CO₂ extraction, a substantial loss of EGCG, as much as 37.8% of original content, proved unavoidable.     

Antimicrobial activities of tea catechins and theaflavins and tea extracts against Bacillus cereus

We evaluated the antimicrobial activities of seven green tea catechins and four black tea theaflavins, generally referred to as flavonoids, as well as the aqueous extracts (infusions) of 36 commercial black, green, oolong, white, and herbal teas against Bacillus cereus (strain RM3190) incubated at 21 degrees C for 3, 15, 30, and 60 min. The results obtained demonstrate that (i) (-)-gallocatechin-3-gallate, (-)-epigallocatechin-3-gallate, (-)-catechin-3-gallate, (-)-epicatechin-3-gallate, theaflavin-3, 3'-digallate, theaflavin-3'-gallate, and theaflavin-3-gallate showed antimicrobial activities at nanomolar levels; (ii) most compounds were more active than were medicinal antibiotics, such as tetracycline or vancomycin, at comparable concentrations; (iii) the bactericidal activities of the teas could be accounted for by the levels of catechins and theaflavins as determined by high-pressure liquid chromatography; (iv) freshly prepared tea infusions were more active than day-old teas; and (v) tea catechins without gallate side chains, gallic acid and the alkaloids caffeine and theobromine also present in teas, and herbal (chamomile and peppermint) teas that contain no flavonoids are all inactive. These studies extend our knowledge about the antimicrobial effects of food ingredients.     

Preparation of an Alcoholic Beverage from Tea Leaves

The preparation of a fermented tea beverage from a Sri Lankan Broken Orange Pekoe (BOP) tea type is reported. The tea beverage was produced using 1–2.5% (w/v) Broken Orange Pekoe and was brewed using boiling sucrose sweetened (5–25°Brix) water (100°C for 3 min), followed by fermentation at 25°C, utilizing an 8.5% (v/v) inoculum of Saccharomyces cerevisiae G. A maximum ethanol of 14.91% (v/v) was obtained from an initial 25°Brix substrate with a 2.67°Brix drop per day. The tea beverage with an initial 15°Brix and 1.5% (w/v) tea yielded the best sensory score and was stable over a test period of 6 weeks at 15°C.     

Using Defatted Rice Bran as a Bioadsorbent for Carrying Tea Catechins

The potential of rice bran as a bioabsorbent for tea catechins was examined. Defatted rice bran had the highest adsorption capacity for tea catechins and the best selectivity for (‐)‐epigallocatechin gallate over total catechins among water‐washed rice bran and untreated rice bran. The adsorption characteristics of tea catechins onto defatted rice bran were determined over a range of concentration (0.5 to 2.5 g/L) and temperatures (10, 25, and 45 °C). The adsorption of tea catechins onto defatted rice bran showed excellent fitness with the pseudo‐second‐order model at different temperature. Both the Langmuir and Freundlich models adequately describe the isothermal adsorption of tea catechins onto defatted rice bran. The adsorption of total catechins on rice bran decreased from 10 to 25 °C, whereas was greatly enhanced at 45 °C. The adsorption system of bioadsorbent with multiconstituents may not be as simple as the single‐force‐driving adsorption system. Protein and cellulose are the main contributors to the adsorption of tea catechins on defatted rice bran.     

Comparison of the main compounds in Fuding white tea infusions from various tea types

The purpose of this study was to compare the main components, and particularly catechins, caffeine, theanine, free amino acids, and water extracts, in Bai Hao Yin Zhen, Bai Mu Dan, and Shou Mei Fuding white tea infusions brewed at different temperatures, and their contributions to taste were estimated by dose-over-threshold value. Infusion temperature had a distinct effect on the main components extracted, and 100 °C was found to be optimal for extracting catechins and caffeine. However, the effect of temperature on theanine, free amino acids, and water extracts varied with tea type. Bai Mu Dan and Shou Mei yielded a higher content of the major compounds than did Bai Hao Yin Zhen. Thus, infusion temperature had a large effect on extracting the main compounds, and the differences in content between the three white teas presumably reflected differences in the harvest time, processing method or leaf shape.     

The development of a suitable manufacturing process for ‘Benifuuki’ green tea beverage with anti‐allergic effects

Epigallocatechin‐3‐O‐(3‐O‐methyl) gallate (EGCG3″Me) has been reported to inhibit type I allergy better than epigallocatechin gallate (EGCG), a major catechin in tea leaves (Camellia sinensis L). We examined the effects of extraction and sterilization on the catechin content and histamine release from mast cells, as a representative reaction of early phase allergy, in the manufacture of ‘Benifuuki’ green tea beverage. Among various varieties of tea, the cultivar ‘Benifuuki’ contains approximately 2% of EGCG3″Me. Ester‐type catechins and their epimers increased with the increased extraction temperature of the tea. A tea infusion, extracted at 90 °C, strongly inhibited histamine release from mast cells. Furthermore, sterilization affected the catechin content in the manufactured green tea beverage. Sterilization at high temperature promoted the isomerization of catechins and the sterilized green tea beverage had a strong inhibitory effect. When EGCG3″Me, EGCG, epicatechin‐3‐O‐gallate (ECG) and their epimers, GCG3″Me (gallocatechin‐3‐O‐(3‐O‐methyl) gallate), GCG (gallocatechin‐3‐O‐gallate) and CG (catechin‐3‐O‐gallate) were compared, the anti‐allergic effect of GCG3″Me was strongest, and the order of activity was GCG3″Me > EGCG3″Me > GCG > EGCG. We consequently suggest that it was necessary to extract components from tea at the highest temperature possible, and to pasteurize under retort conditions (118.1 °C, 20 min), to manufacture functional green tea beverage with an anti‐allergic action. Copyright © 2005 Society of Chemical Industry     

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 effect of instant green tea on the foaming and rheological properties of egg albumen proteins

The effects of three varieties of instant green tea (from China, Japan and Kenya) on the foaming and thermal properties of 1% (w/v) egg albumen and the gelation properties of 5 and 15% (w/v) egg albumen were investigated. All varieties produced similar effects on the foaming and gelation properties of egg albumen, but to different extents depending on the tea constituents. Mixtures of 1% (w/v) egg albumen and 0.25–0.4% (w/v) instant green teas in distilled water showed the greatest foam expansion (800–1140%) and foam stability (97–100%) at 10 min after whipping compared with 1% (w/v) egg albumen alone (226% for foam expansion and 34% for foam stability). Addition of instant green teas at levels above 0.5% (w/v) decreased foam expansion and stability. Small‐deformation rheology of mixtures of 5% (w/v) egg albumen and 1 or 2% (w/v) instant green teas showed an initial increase in elastic modulus (G′) and viscous modulus (G″) followed by a small, broad peak, indicating that the binding of tea constituents (polyphenols) with proteins may be reversible between 20 and 54 °C; this peak was not seen for 5% (w/v) egg albumen on its own. Large‐deformation rheological tests also indicated increased strength of mixed egg albumen/green tea gels with increasing levels of instant green teas. Differential scanning calorimetry thermograms showed that for the same instant green tea a higher concentration decreased the onset and peak (T_m) temperatures and enthalpy change values of all egg albumen protein peaks. Copyright © 2007 Society of Chemical Industry     

不同采制季节信阳白茶品质成分的比较分析

该研究采用高效液相色谱法（HPLC）等方法对春季、夏季和秋季茶树鲜叶加工而成的18款信阳白茶茶样中的8种儿茶素、6种黄酮类、2种酚酸、3种嘌呤碱等品质成分进行测定,对不同采制季节的信阳白茶进行品质成分进行对比分析。主成分分析（PCA）和聚类分析（HCA）技术均能将信阳白茶茶样按照采制季节不同进行归类,分为春季、夏季和秋季白茶。通过独立样本t-检验和单因素方差分析,探究了不同采制季节信阳白茶中儿茶素、黄酮类、嘌呤碱等品质成分差异。结果显示：不同采制季节信阳白茶中的品质成分均存在显著性（p<0.01）或极显著性（p<0.001）差异;春季白茶中(-)-表没食子酸儿茶素（EGC）、(-)-表没食子儿茶素没食子酸酯（EGCG）和鞣花酸含量极显著性（p<0.001）高于夏季或秋季白茶,含量分别为33.26、59.30、2.81 mg/g左右;夏季白茶中(-)-儿茶素没食子酸酯（CG）、(-)-没食子儿茶素没食子酸酯（GCG）、花旗松素、芦丁、杨梅素、山奈酚、槲皮素、木犀草素含量极显著性（p<0.001）高于秋季白茶,含量分别高达0.72、4.40、0.84、2.40、0.97、0.21、0.25、0.11 mg/g;秋季白茶中(+)-儿茶素（C）、(-)-表儿茶素（EC）、(-)-表儿茶素没食子酸酯（ECG）、没食子酸、咖啡碱和可可碱极显著性（p<0.001）高于夏季或春季白茶,含量分别为4.98、14.35、27.02、10.10、36.85、1.53 mg/g。该研究揭示了信阳白茶的品质特征和不同采制季节信阳白茶品质成分差异,为白茶等茶叶采制季节的识别提供了科学依据。     

Extraction of active ingredients from green tea (Camellia sinensis): Extraction efficiency of major catechins and caffeine

The effect of different extraction set-ups that influence the extraction efficiency of catechins and caffeine from green tea leaves (variety Fanning Belas, China) were studied using different aqueous and pure solvents (acetone, ethanol, methanol, acetonitrile, water), different temperatures (60, 80, 95 and 100 °C) and times (5–240 min). Raw extracts were analysed for contents of major catechins (EC, EGC, ECG, EGCG), caffeine, proanthocyanidins and flavonols (myricetin, caempherol, quercetin). Starting material was found to contain 191 g major catechins/kg material, 36 g caffeine/kg material and 5.2 g flavonols/kg material on a dry mass basis. The content of major catechins in green tea extracts varied from approximately 280–580 g/kg dry extract, with extraction efficiencies of major catechins varying from 61% to almost 100%. Content of caffeine in extract was in the range of 75 g/kg, where its extraction efficiency varied from 62% to 76%. Average extraction yield was 30% with exceptions when using pure acetone and acetonitrile, where extraction yield was about 3%. Contents of flavonols and proanthocyanidins were in the ranges 6–20 and 12–19 g/kg, respectively. Different extraction procedures with water were also investigated and optimal conditions determined: maximum achieved extraction efficiency of catechins with water was obtained at 80 °C after 20 min (97%) and at 95 °C after 10 min of extraction (90%). Degradation of catechins was observed at higher extraction temperatures and with prolonged extraction times. Using a lower ratio of solvent to material, extraction efficiencies were increased by applying a multi-step extraction procedure. Optimal extraction procedure was then performed using decaffeinated green tea leaves, which were obtained by high-pressure extraction with CO₂, when 98% of caffeine was selectively isolated without significant impact on valuable catechins.     

White and Green Teas (Camellia sinensis var. sinensis): Variation in Phenolic,Methylxanthine, and Antioxidant Profiles

Abstract: Recent investigations have associated white teas with anti-carcinogenic, immune-boosting, and antioxidative properties that may impact human health in a manner comparable to green teas. An in-depth chemical analysis of white tea types was conducted to quantify polyphenols and antioxidant potential of 8 commercially available white teas, and compare them to green tea. Extraction and HPLC protocols were optimized and validated for the quantification of 9 phenolic and 3 methylxanthine compounds to examine inter- and intra-variation in white and green tea types and subtypes. A sampling strategy was devised to assess various subtypes procured from different commercial sources. Variation in antioxidant activity and total phenolic content (TPC) of both tea types was further assessed by the 1-1-diphenyl-2-picrylhydrazyl (DPPH) and Folin–Ciocalteau (F–C) assays, respectively. Total catechin content (TCC) for white teas ranged widely from 14.40 to 369.60 mg/g of dry plant material for water extracts and 47.16 to 163.94 mg/g for methanol extracts. TCC for green teas also ranged more than 10-fold, from 21.38 to 228.20 mg/g of dry plant material for water extracts and 32.23 to 141.24 mg/g for methanol extracts. These findings indicate that statements suggesting a hierarchical order of catechin content among tea types are inconclusive and should be made with attention to a sampling strategy that specifies the tea subtype and its source. Certain white teas have comparable quantities of total catechins to some green teas, but lesser antioxidant capacity, suggesting that white teas have fewer non-catechin antioxidants present. Practical Application: In this investigation white and green teas were extracted in ways that mimic common tea preparation practices, and their chemical profiles were determined using validated analytical chemistry methods. The results suggest certain green and white tea types have comparable levels of catechins with potential health promoting qualities. Specifically, the polyphenolic content of green teas was found to be similar to certain white tea varieties, which makes the latter tea type a potential substitute for people interested in consuming polyphenols for health reasons. Moreover, this study is among the first to demonstrate the effect subtype sampling, source of procurement, cultivation, and processing practices have on the final white tea product, as such analysis has previously been mostly carried out on green teas.     

Comparative Flavonoids Contents of Selected Herbs and Associations of Their Radical Scavenging Activity with Antiproliferative Actions in V79-4 Cells

ABSTRACT:  To elucidate the health benefit of herbal teas on the cytotoxicity induced by H₂O₂ in V79-4 cells, herbal extracts and its flavonoids were tested using lactate dehydrogenase release and determining intracellular reactive oxygen species generation and antioxidant activity with superoxide radical scavenging assay. Significant decrease in cell viability was observed on V79-4 cells treated with H₂O₂ (1 mM), while herbal extracts and its flavonoids including catechin and epigallocatechin gallate prevented the LDH release from H₂O₂ cytotoxicity. Total catechin contents of green tea (65.6 mg/g of dry matter) were significantly higher than other herbal teas (35.8 to 1.2 mg/g of DM). The relative concentration of the 4 major tea catechins ranked EGCG > EGC > EC > C. Green tea exhibited the lowest IC₅₀ values (2 g fresh herb/100 mL) of superoxide radical scavenging activity among the tested herbal tea, which indicates powerful antioxidant activity in O₂^·− radicals scavenging, followed by black tea, dandelion, hawthorn, rose hip, chamomile.     

Electron spin resonance spectroscopic assessment of the antioxidant potential of teas in aqueous and organic media

Electron spin resonance methodology has been used to assess the hydrogen-donating (antioxidant) ability of catechins and extracts of green and black tea to Fremy's radical and galvinoxyl radical in aqueous and organic solutions, respectively. Catechin flavanols accounted for 77–82% of the total antioxidant activity of green tea but only 47–58% of that of black tea. The radical quenching ability of the green tea was 21–24% more effective than that of the black tea in both aqueous and lipophilic systems. Epigallocatechin gallate was the most effective at reducing the two radical species, whereas epigallocatechin was least effective in the galvinoxyl/ethanol system, and catechin least effective in the Fremy's radical/water system. In a model system comprising a mixture of the flavanols in ethanolic or aqueous solution, in the same concentrations as they were present in the tea extracts, the antioxidant potential was a simple summation of the activity of the individual components indicating no synergistic or antagonistic side reactions. Results demonstrate that flavanol components of teas exhibit potent antioxidant activity in both aqueous and organic media. This will be of physiological relevance if such compounds partition into both the aqueous and lipid compartment of cells. © 1998 SCI.     

Decaffeination of fresh green tea leaf (Camellia sinensis) by hot water treatment

Hot water treatment was used to decaffeinate fresh tea leaf in the present study. Water temperature, extraction time and ratio of leaf to water had a statistically significant effect on the decaffeination. When fresh tea leaf was decaffeinated with a ratio of tea leaf to water of 1:20 (w/v) at 100 °C for 3 min, caffeine concentration was decreased from 23.7 to 4.0 mg g⁻¹, while total tea catechins decreased from 134.5 to 127.6 mg g⁻¹; 83% of caffeine was removed and 95% of total catechins was retained in the decaffeinated leaf. It is considered that the hot water treatment is a safe and inexpensive method for decaffeinating green tea. However, a large percentage of tea catechins was lost if rolled leaf and dry tea were decaffeinated by the hot water treatment and so the process is not suitable for processing black tea.