Research Database

Author: Jin-Ye Fu and Jing Gao and Zhi-Yuan Zhang and Jia-Wei Zheng and Jian-Feng Luo and Lai-Ping Zhong and Yong-Bing Xiang

Author: Yanlan Xie and Agnieszka Kosińska and Hairong Xu and Wilfried Andlauer

The effect of milk on the absorption of polyphenols is still controversial so far. In order to determine the impact of milk addition on green tea catechins bioaccessibility and intestinal absorption an in vitro digestion/Caco-2 cell model was applied. Green tea extract (GTE) was solubilized in distilled water at 23 °C and 100 °C, combined with skimmed milk (GTE + 10% milk and GTE + 25% milk) and subjected to simulated gastric and intestinal digestion, followed by transepithelial absorption in Caco-2 cells monolayers. In the mixture with milk, gallated catechins: ECG and EGCG showed binding to milk proteins while EC and EGC seemed to have weaker affinity. Catechins were stable during gastric incubation and very sensitive to intestinal digestion. Bioaccessibility of green tea catechins brewed at 100 °C was higher than brewed at 23 °C. Catechins from digested GTE with 10% and 25% milk exhibited enhanced intestinal permeability in Caco-2 model in comparison to non-digested GTE and digested GTE without milk. Apparent permeability coefficients (Papp) of EGCG and ECG in digested GTE with 25% milk were significantly higher compared to those in GTE with 10% milk, and amounted to 2.41 × 10− 6 cm/s and 1.39 × 10− 6 cm/s. The recoveries of all catechins in GTE with milk in Caco-2 cells after 2 h incubation were significantly higher than that without milk. To summarize, these data suggest that milk addition may increase catechin bioavailability by enhancing their transepithelial absorption and uptake from green tea extract.

 

 

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Author: Chung S. Yang and Guangxun Li and Zhihong Yang and Fei Guan and Amber Chen and Jihyeung Ju

Tocopherols (vitamin E) and tea polyphenols have been reported to have cancer preventive activities. Large-scale human trials with high doses of alpha-tocopherol, however, have produced disappointing results. This review presents data showing that - and -tocopherols inhibit colon, lung, mammary and prostate carcinogenesis in animal models, whereas -tocopherol is ineffective in animal and human studies. Possible mechanisms of action are discussed. A broad cancer preventive activity of green tea polyphenols has been demonstrated in animal models, and many mechanisms have been proposed. The cancer preventive activity of green tea in humans, however, has not been conclusively demonstrated and remains to be further investigated.

 

 

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Author: B. Giménez and S. Moreno and M.E. López-Caballero and P. Montero and M.C. Gómez-Guillén

A green tea aqueous extract was prepared and blended at different percentages (2, 4 and 8%) with a commercial fish-skin gelatin in order to provide gelatin films with antioxidant capacity. This green tea extract proved to be an efficient antioxidant at non-cytotoxic concentrations. Gelatin films with green tea extract were subjected to enzymatic digestion with pepsin (gastric digestion) and with pepsin, trypsin and chymotrypsin (gastrointestinal digestion). The gelatin matrix was efficiently hydrolysed during gastrointestinal digestion and protein hydrolysates composed of low molecular weight peptides, regardless the content of green tea extract, were obtained in all the formulations. High percentages of total polyphenols were recovered from the films with green tea extract after gastrointestinal digestion, although a significant degradation of the major catechins of the green tea (EGCG and EGC) was observed. The increase of the content of green tea extract in the film formulation gave an increase in the antioxidant activity released from the film samples after enzymatic digestion. 85–100% of the maximum expected antioxidant activity was recovered after both gastric and gastrointestinal digestion in spite of the degradation observed of EGCG and EGC.

 

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Author: Wenping Tang and Shiming Li and Yue Liu and Mou-Tuan Huang and Chi-Tang Ho

Tea is one of the most popular beverages worldwide. The variety of tea and tea extracts in the market has different polyphenol profiles, which are the bioactive chemical entities. In searching for efficacious molecules from tea against hyperglycaemia, we performed a direct comparison between green tea extracts (GTE) and black tea extracts (BTE), which have been chemically well-characterized by HPLC, in a type 2 diabetic mouse model combining low dose streptozotocin (STZ) with high fat (HF) diet. The results revealed that both GTE and BTE in drinking water substantially lowered blood glucose levels and ameliorated glucose intolerance, but GTE was more effective in anti-hyperglycaemic activity and in lowering body weight gain. GTE was also more effective than BTE in reversing histological deterioration of liver in the diabetic mice. Serum insulin levels significantly increased in BTE group but not in GTE group, suggesting that they might exert their hypoglycaemic effects through different pathways. We explored the possible mechanisms by homeostatic model assessment (HOMA), and results showed that the predominant mechanism for the anti-diabetic effect of GTE was through insulin resistance, while for BTE it was through insulin secretion.

 

 

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Author: Chia-Fang Tsai and Yu-Wen Hsu and Hung-Chih Ting and Chun-Fa Huang and Cheng-Chieh Yen

 

The in vivo antioxidant and antifibrotic properties of green tea (Camellia sinensis, Theaceae) were investigated with a study of carbon tetrachloride (CCl4)-induced oxidative stress and hepatic fibrosis in male ICR mice. Oral administration of green tea extract at doses of 125, 625 and 1250 mg/kg for 8 weeks significantly reduced (p < 0.05) the levels of thiobarbituric acid-reactive substances (TBARS) and protein carbonyls in the liver by at least 28% compared with that was induced by CCl4 (1 mL/kg) in mice. Moreover, green tea extract administration significantly increased (p < 0.05) the activities of catalase, glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Rd) in the liver. Our study found that oral administration of green tea extract prevented CCl4-induced hepatic fibrosis, as evidenced by a decreased hydroxyproline level in the liver and a reduced incidence of hepatic fibrosis by histological observations. These results indicate that green tea exhibits potent protective effects against CCl4-induced oxidative stress and hepatic fibrosis in mice by inhibiting oxidative damage and increasing antioxidant enzyme activities.

 

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Author: Lucie Trnková and Daniela Ricci and Caterina Grillo and Gianni Colotti and Fabio Altieri

Background Green tea is a rich source of polyphenols, mainly catechins (flavanols), which significantly contribute to the beneficial health effects of green tea in the prevention and treatment of various diseases. In this study the effects of four green tea catechins on protein ERp57, also known as protein disulfide isomerase isoform A3 (PDIA3), have been investigated in an in vitro model. Methods The interaction of catechins with ERp57 was explored by fluorescence quenching and surface plasmon resonance techniques and their effect on ERp57 activities was investigated. Results A higher affinity was observed for galloylated cathechins, which bind close to the thioredoxin-like redox-sensitive active sites of the protein, with a preference for the oxidized form. The effects of these catechins on ERp57 properties were also investigated and a moderate inhibition of the reductase activity of ERp57 was observed as well as a strong inhibition of ERp57 DNA binding activity. Conclusions Considering the high affinity of galloylated catechins for ERp57 and their capability to inhibit ERp57 binding to other macromolecular ligands, some effects of catechins interaction with this protein on eukaryotic cells may be expected. General significance This study provides information to better understand the molecular mechanisms underlying the biological activities of catechins and to design new polyphenol-based ERp57-specific inhibitors.

 

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Author: S.P.J. Namal Senanayake

Green tea is one of the most popular and extensively used dietary supplement in the United States. Diverse health claims have made for green tea as a trendy ingredient in the growing market for nutraceuticals and functional foods. Green tea extract contains several polyphenolic components with antioxidant properties, but the predominant active components are the flavanol monomers known as catechins, where epigallocatechin-3-gallate and epicatechin-3-gallate are the most effective antioxidant compounds. Additional active components of green tea extract include the other catechins such as epicatechin and epigallocatechin. Among these, epigallocatechin-3-gallate is the most bioactive and the most scrutinized one. Green tea polyphenols are also responsible for distinctive aroma, color and taste. Green tea extract can also be used in lipid-bearing foods to delay lipid oxidation and to enhance the shelf-life of various food products. This review outlines the chemistry, flavour components, antioxidant mechanism, regulatory status, food applications, and stability of green tea extract in food.

 

 

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Author: Arpita Basu and Nancy M. Betts and Afework Mulugeta and Capella Tong and Emily Newman and Timothy J. Lyons

Green tea, a popular polyphenol-containing beverage, has been shown to alleviate clinical features of the metabolic syndrome. However, its effects in endogenous antioxidant biomarkers are not clearly understood. Thus, we tested the hypothesis that green tea supplementation will upregulate antioxidant parameters (enzymatic and nonenzymatic) in adults with the metabolic syndrome. Thirty-five obese participants with the metabolic syndrome were randomly assigned to receive one of the following for 8 weeks: green tea (4 cups per day), control (4 cups water per day), or green tea extract (2 capsules and 4 cups water per day). Blood samples and dietary information were collected at baseline (0 week) and 8 weeks of the study. Circulating carotenoids (α-carotene, β-carotene, lycopene) and tocopherols (α-tocopherol, γ-tocopherol) and trace elements were measured using high-performance liquid chromatography and inductively coupled plasma mass spectroscopy, respectively. Serum antioxidant enzymes (glutathione peroxidase, glutathione, catalase) and plasma antioxidant capacity were measured spectrophotometrically. Green tea beverage and green tea extract significantly increased plasma antioxidant capacity (1.5 to 2.3 μmol/L and 1.2 to 2.5 μmol/L, respectively; P < .05) and whole blood glutathione (1783 to 2395 μg/g hemoglobin and 1905 to 2751 μg/g hemoglobin, respectively; P < .05) vs controls at 8 weeks. No effects were noted in serum levels of carotenoids and tocopherols and glutathione peroxidase and catalase activities. Green tea extract significantly reduced plasma iron vs baseline (128 to 92μg/dL, P < .02), whereas copper, zinc, and selenium were not affected. These results support the hypothesis that green tea may provide antioxidant protection in the metabolic syndrome.

 

 

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Author: Marcia da Silva Pinto

Although among the five main types of teas (white, green, oolong, black and pu-erh), black tea is the most consumed worldwide, an impressive number of scientific publications have been focused on green tea and its major compounds, flavan-3-ols (“catechins”). However, besides flavan-3-ols, there are other compounds present in tea that could be accounted as potential bioactive compounds. Therefore, the objective of the present review is to provide a new perspective on the health benefits associated with tea consumption by critically analyzing the available literature on the potential tea bioactive compounds and the current level of scientific evidence for these health benefits. Until now the exact mechanisms of action or compounds responsible for the health benefits associated with tea consumption have only been poorly investigated. It is important to consider that tea compounds will be extensively metabolized to different metabolites that will, most likely, be the compounds circulating in blood and potentially reaching the different sites of action.

 

 

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