Formation of damascenone derived from glycosidically bound precursors in green tea infusions

Damascenone is well-known for its potent flavour with an extremely low odour threshold. Several glycosidically bound precursors of damascenone have been isolated from several plants, but little is known about their occurrences in green tea infusions. In this work, three major glycosidic precursors of damascenone, 9-O-β-d-glucopyranosyl-megastigma-6,7-dien-3,5,9-triol (1a), 9-O-β-d-glucopyranosyl-3-hydroxy-7,8-didehydro-β-ionol (2a), and 3-O-β-d-glucopyranosyl-3-hydroxy-7,8-didehydro-β-ionol (2b) were isolated and identified in green tea infusions, and the stereochemistries at C-3 and C-9 positions of aglycone parts of the three glycosidic precursors were determined as (3S, 9R)-1a, (3R, 9R)-2a, and (3R, 9R)-2b, respectively. Compounds 1a, 2a, and 2b as well as 3-O-β-d-glucopyranosyl-megastigma-6,7-dien-3,5,9-triol (1b) were hydrolysed to form damascenone in a model system with strong acidic conditions (pH 2.0) and at high temperature (90 °C). In contrast to hydrolysis of 2a and 2b, more damascenone was transformed from 1a and 1b. Furthermore, the β-d-glucosyl moiety at the C-3 position gave a higher dehydration rate from megastigma-6,7-dien-3,5,9-triol to 3-hydroxy-7,8-didehydro-β-ionol than compound 1a carrying the sugar residue at C-9 position. Interestingly, the four glycosidic precursors of damascenone were not hydrolysed to give damascenone under slightly acidic conditions (pH 5.4 and 120 °C for 10 min), but they could be transformed to damascenone in the presence of green tea infusions even under the equal conditions.     

Selenium-containing green tea has higher antioxidant and prebiotic activities than regular green tea

The effects of selenium-containing green tea (SGT; 1.4 mg selenium/kg) and China green tea (CGT; 0.13 mg selenium/kg) on the in vitro growth of lactobacilli and bifidobacteria were investigated using pure and mixed cultures. SGT had significantly higher phenolic contents (TPC), higher reducing activity, higher DPPH free-radical scavenging activity, and higher ferrous-ion chelating activity (P < 0.05–0.0001) than CGT. The addition of aqueous extracts from CGT to Mann-Rogosa-Sharpe (MRS) broth at 10% and 25% (v/v) resulted in small but nonsignificant (P > 0.05) increases in the numbers of Lactobacillus rhamnosus and Bifidobacterium breve over the control incubations (without tea). Addition of 10% and 25% of SGT extract resulted in a significant increase (P < 0.05–0.0001) in the number of lactobacilli and bifidobacteria recovered from batch fermentation while CGT did not increase the number of bifidobacteria. The higher prebiotic activity of SGT over CGT may be related to the higher TPC or minerals, notably selenium or a combination of these factors. To test whether selenium itself has an effect on bacterial growth, Na-selenite and Na-selenate were added alone or in combination with CGT to the MRS broth containing pure culture of L. rhamnosus. Growth of this bacterium was enhanced relative to the control incubation of MRS only. When added in combination with CGT, Na-selenate was more effective at enhancing the growth of L. rhamnosus than Na-selenite. The prebiotic effect of SGT could be largely explained by its selenium content.     

Comparison of bioactive components in GABA tea and green tea produced in Taiwan

The aim of this study is to investigate the bioactive components of GABA (γ-aminobutyric acid) tea as compared with green tea produced in Taiwan. Using in total 56 tea samples (28 green tea and 28 GABA tea), moisture content, Hunter L, a and b values, phenolic compounds, amino acids including GABA, fatty acids and ascorbic acid were determined. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea.     

发酵型绿茶黄瓜酸乳的研制

以绿茶、黄瓜、全脂奶粉、蔗糖为主要原料,通过保加利亚乳酸杆菌和嗜热链球菌发酵,研制出一种新型的绿茶黄瓜酸乳。确定了黄瓜护色的最佳条件为Zn(COOH)2浓度0.2g/L,护色温度90℃,时间2min。采用正交实验法筛选出最佳工艺条件黄瓜汁10%、蔗糖量6%、茶叶量0.3%、接种量2.5%,发酵时间5h,发酵温度43℃。实验结果表明产品各项理化指标都符合国家卫生标准。     

绿茶饮料的制备及品质控制

研究了影响绿茶色香味因素，探讨了绿茶饮料沉淀形成了变色的机理，得出茶水比1：100，浸提温度85℃，浸提时间10in为最佳萃取工艺条件，同时采用茶汁pH值为5．5，木瓜蛋白酶添加量为0.05g/100ml茶汁，β－CD添加量1.0g/500ml,Vc0.1g/500ml,D-葡萄糖酸－δ－内脂0.1g/500ml，可有效防止沉淀的产生和色泽的变化，得到满意的产品质量。     

胡萝卜绿茶酸乳工艺研究

以胡萝卜、绿茶、牛乳、蔗糖为主要原料，进行发酵工艺实验，通过正交实验确定了酸乳原料的最佳配方：茶叶0．5％、胡萝卜汁15％、蔗糖7％，菌种选用保加利亚乳杆菌和嗜热链球菌（1：1），接种量3％。     

不同温湿度与包装条件对茶叶干品贮藏的影响

通过短时间的模拟实验，研究了不同温度、湿度条件及包装材料对茶叶贮藏的影响。茶叶的考察指标为维生素C、茶多酚及色差和主要感官变化。结果表明，茶叶在环境湿度下冷藏就可以达到较高的贮藏要求，包装材料以玻璃瓶为宜。     

Survival and metabolic activity of probiotic bacteria in green tea

The aim of this study was to determine the enzymatic activity and survival of three probiotic strains (Lactobacillus paracasei LAFTI-L26, Lactobacillus acidophilus LAFTI-L10 and Bifidobacterium animalis ssp. lactis LAFTI-B94) during incubation in six different varieties of green tea extracts. The polyphenol content, antioxidant, antimicrobial and antihypertensive properties in green tea (variety Wu Lu Mountain) and in two standards (epigallocatechin-3-gallate and rutin) were also investigated before and after incubation with B. animalis B94. The green tea extracts permitted the survival of the selected probiotic strains better than the saline solution, with B. animalis B94 maintaining the highest levels of viable cells. These selected probiotic bacteria exhibited β-glucosidase, β-galactosidase and α-rhamnosidase activity. The antioxidant and antihypertensive properties of standard solutions of epigallocatechin-3-gallate and rutin increased after incubation with B. animalis B94, caused by polyphenol content reduction and the formation of other more highly biologically active metabolites. However, during the incubation of green tea with B. animalis B94, changes in the concentration of the most abundant green tea polyphenols did not enhance the biological activity.     

Quality and antioxidant property of green tea sponge cake

Green tea powder was used to substitute 0%, 10%, 20%, and 30% of wheat flour to make sponge cakes, called the control, GT10, GT20, and GT30, respectively. The viscosity and specific gravity in cake batter, and hardness, gumminess, chewiness, crumb a value, protein, total dietary fibre, ash, and various catechin content of baked cakes increased with increasing green tea levels whereas the volume, cohesiveness, adhesiveness, springiness, resilience, crust L, a, b and crumb L, b values of samples showed a reverse trend. No differences were found in all hedonic sensory results for control, GT10, and GT20 whereas GT30 were rated lower in all sensory results. Green tea cake contained a greater variety of catechins, and had good antioxidant activity, reducing power, scavenging ability on 1,1-diphenyl-2-picrylhydrazyl radicals and chelating ability on ferrous ions. Overall, green tea cake could be developed as a food with more effective antioxidant properties.     

复合酶对绿茶饮料质量影响的研究

在初步确立绿茶饮料生产工艺的基础上,对几种酶进行复合后应用于绿茶饮料的最佳作用参数、作用效果及对绿茶饮料的感观、理化品质的影响进行了探讨.     

Analysis of vitamin K in green tea leafs and infusions by SPME–GC-FID

The usual methods for determination vitamin K are laborious. With the aim of replace them by a simpler method that requires fewer solvents, lower analytical levels and allows reporting of results in a smaller period of time, a procedure based on solid-phase microextraction (SPME) and gas chromatography with flame ionization detector (GC-FID) was developed. This method was used to analyse vitamin K in green tea leafs and infusions from nine brands of green tea commercialised in Portugal.     

Persistence of acetamiprid in tea and its transfer from made tea to infusion

Acetamiprid, a new-generation, highly active neonicotinoid insecticide has been used to control mites and insect pests. In the present study, the disappearance trend of acetamiprid residue in tea under field conditions was studied at two dosages for two seasons (dry and wet), and transfer of residues from made tea to infusion was also determined. Acetamiprid dissipation rate was found to be faster in the wet season. Half-life of acetamprid was found to be 1.82–2.33 days in green tea shoots and 1.84–2.25 days in made tea for both dry and wet seasons. The percent transfer of acetamiprid residues from made tea to infusion was 36.84–50.00%; however, 31.11–44.40% of the residues remained stuck to the spent leaves during both the dry and wet seasons. On the basis of transfer of residues from made tea to infusion, a waiting period of 15 days for tea plucking after pesticide application at recommended dose may be suggested.     

Dissipation of imidacloprid in Orthodox tea and its transfer from made tea to infusion

Imidacloprid is a systemic insecticide used widely in controlling mites, mealy bugs and other related pests in fruits, vegetables and tea. The dissipation behaviour of imidacloprid residues in green tea shoots, made tea and its transfer potential from made tea to infusion in hot water was studied. Analysis in tea matrices of imidacloprid was carried out using high-performance liquid chromatography with diode array detection. Under field conditions, imidacloprid dissipation rate was found to be faster in the wet season than the dry season. Half lives in green shoots were in the range 1.14–1.23 and 1.03–1.09 days, and 1.14–1.25, 1.04–1.07 days in made tea, for the dry and wet season, respectively. The percent transfer of imidacloprid residue from made tea to infusion was in the range of 29.2–42.0% during the dry and wet season; however, 38.2% and 57.9% of the residues remained stuck to the spent leaves during the dry and wet seasons, respectively. On the basis of transfer of residues from made tea to hot water infusion, a waiting period of 7 days after pesticide application at a recommended dose for tea plucking is suggested.     

Analysis of some selected catechins and caffeine in green tea by high performance liquid chromatography

Green tea seems to have a positive impact on health due to the catechins-found as flavanols. Thus, the present study was aimed to develop a low cost reversed phase high performance liquid chromatographic (HPLC) method for simultaneous determination of flavanol contents, namely catechin (C), epicatechin (EC), epigallocatechin (EGC), epicatechin 3-gallate (ECG) and epigallocatechin 3-gallate (EGCG) and caffeine in 29 commercial green tea samples available in a Saudi Arabian local market. A C-18 reversed-phase column, acetonitrile–trifluoroacetic acid as a mobile phase, coupled with UV detector at 205 nm, was successfully used for precise analysis of the tested analytes in boiled water of digested tea leaves. The average values of N (No. of theoretical plates), HETP (height equivalent of theoretical plates) and R_s (separation factor) (at 10 μg ml⁻¹ of the catechins EC, EGC, EGCG and ECG) were 2.6 × 10³ ± 1.2 × 10³, 1.7 × 10⁻³ ± 4.7 × 10⁻⁴ cm and 1.7 ± 5.53 × 10⁻², respectively. The developed HPLC method demonstrated excellent performance, with low limits of detection (LOD) and quantification (LOQ) of the tested catechins of 0.004–0.05 μg ml⁻¹ and 0.01–0.17 μg ml⁻¹, respectively, and recovery percentages of 96–101%. The influence of infusion time (5–30 min) and temperature on the content of the flavanols was investigated by HPLC. After a 5 min infusion of the tea leaves, the average concentrations of caffeine, catechin, EC, EGC, ECG and EGCG were found to be in the ranges 0.086–2.23, 0.113–2.94, 0.58–10.22, 0.19–24.9, 0.22–13.9 and 1.01–43.3 mg g⁻¹, respectively. The contents of caffeine and catechins followed the sequence: EGCG > EGC > ECG > EC > C > caffeine. The method was applied satisfactorily for the analysis of (+)-catechin, even at trace and ultra trace concentrations of catechins. The method was rapid, accurate, reproducible and ideal for routine analysis.     

Chemopreventive potential of the tannase-mediated biotransformation of green tea

Green tea (Camellia sinensis) is one of the most widely consumed beverages in the world. The cancer chemopreventive qualities of green tea have been well documented. Epigallocatechin gallate (EGCG) is often described as the most potently chemopreventive green tea catechin; however, the low bioavailability of EGCG is a limiting factor for its biological effect. Thus, the aim of this work was to test the chemopreventive potential of green tea extract and EGCG after tannase-mediated hydrolysis. The results showed that the biotransformed compounds retained most of the beneficial properties of the original compounds, and some beneficial properties were improved in the biotransformed compounds. Biotransformation of EGCG decreased its toxicity without affecting its antiproliferative effects. Furthermore, human cells gene expression profiling showed that the biotransformed compounds modulated the expression of several genes related to carcinogenesis. These results demonstrate the benefits of the biotechnological modification of natural food molecules, allowing the improvement of the nutraceutical potential of a beverage as green tea.     

Intestinal transport of pure theanine and theanine in green tea extract: Green tea components inhibit theanine absorption and promote theanine excretion

Theanine, an amino acid contained in green tea, is known to possess many pharmacological functions. In this paper, we investigated the absorption of theanine in the human intestinal epithelium, using a Caco-2 monolayer model. Different concentrations of either pure theanine or green tea extracts were administered to Caco-2 cells. The theanine content in the samples was analysed by high-performance liquid chromatography, coupled with fluorescence detection. Cell permeation was also measured. The data revealed that the transport of pure theanine occurred in a manner consistent with passive diffusion. Surprisingly, pure theanine showed good absorption, whereas theanine in the green tea extract was poorly absorbed in the Caco-2 cell model. Furthermore, the transport of theanine in green tea extract in the basolateral (BL) to apical (AP) direction was much greater than that in the AP–BL direction, suggesting that green tea components profoundly affect the trans-epithelial transport of theanine in this Caco-2 cell model.     

In vitro antioxidative and anticancer activities of tea glycoprotein in green tea

In this paper, the antioxidative and anticancer activities of tea glycoprotein (TGP) in green tea were studied. TGP was extracted from coarse old green tea and purified by Sephadex G-100 gel filtration, and its purity was determined by high performance gel permeation chromatography (HPGPC). The antioxidative activity of the TGP was evaluated by determining the change of the values of the heat-induced oxidation in a linoleic acid system with β-carotene, the decoloration of the 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the superoxide generated from autoxidation of pyrogallol. The results show that the TGP possesses distinctive antioxidative activity. Furthermore, the anticancer activity of the TGP at different concentrations was evaluated by the MTT assay using two kinds of colon cancer cell lines (HCT-15, Caco-2). Dose-dependently TGP exhibited good antiproliferation activity to HCT-15, whereas exhibited very weak antiproliferation activity to Caco-2. Only at a very high concentration (409.6 μmol L⁻¹), the TGP obviously inhibited the proliferation of Caco-2. Whether there is a correlation between the antioxidative and the anticancer activity of the TGP, should be studied further.     

A minireview of effects of green tea on energy expenditure

In recent years, individuals have begun to tend more frequently to some natural and herbal products to be used alone or as a combination with diet and exercise for ensuring the weight loss. Green tea is the leading one of these products. In some studies, it is reported that the green tea causes an increase in thermogenesis and substrate with fat oxidation by affecting on the sympathetic nervous system. It is reported that green tea has two main components that are associated with energy expenditure. One of them is caffeine and the other is catechin content. Each of these two components has an impact on energy mechanism separately. In this minireview article, mechanisms of action and effects of caffeine and catechin, which are found in green tea composition, on energy expenditure are assessed.