Research Database

Author: E.J. Okello and G.J. McDougall and S. Kumar and C.J. Seal

There is mounting evidence that the deposition and aggregation of β-amyloid peptides (Aβ) in the brain play a significant role in the development and pathogenesis of Alzheimer's disease. There is further evidence that free radical species such as hydrogen peroxide (H2O2) mediate Aβ induced toxicity. Previous studies have demonstrated that green tea polyphenols possess neuroprotective properties through their ability to ameliorate oxidative stress induced by free radical species. Green tea polyphenols have also been shown to enhance cognition in various animal models of induced cognitive impairment. Upon ingestion, green tea polyphenols are metabolised and undergo bio-transformation which affects their bioavailability and therefore efficacy. In this study, a green tea extract was subjected to a simulated gastrointestinal digestion and a ‘colon-available’ extract (CAGTE) prepared and assessed for its potential protective effects against H2O2 and Aβ(1–42) induced cytotoxicity using differentiated PC12 cells (dPC12) as a model for neuronal cells. CAGTE represents green tea phytochemicals potentially available after upper gastrointestinal digestion. CAGTE which was depleted in flavan-3-ols, as shown by LC–MS analysis, protected dPC12 cells at concentration ranges of 0.3–10 μg/ml and 0.03–0.125 μg/ml for H2O2 and Aβ(1–42), induced cytotoxicity, respectively. At high concentrations, CAGTE exhibited direct anti-proliferative effects, in line with the reputed anti-cancer properties of green tea polyphenols. These results demonstrate that potentially bioavailable green tea metabolites are able to ameliorate both H2O2 and Aβ(1–42) induced cytotoxicity.

 

 

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Author: Chung S. Yang and Hong Wang and Guang Xun Li and Zhihong Yang and Fei Guan and Huanyu Jin

The cancer preventive activities of tea (Camellia sinensis Theaceae) have been studied extensively. Inhibition of tumorigenesis by green tea extracts and tea polyphenols has been demonstrated in different animal models, including those for cancers of the skin, lung, oral cavity, esophagus, stomach, small intestine, colon, bladder, liver, pancreas, prostate, and mammary glands. Many studies in cell lines have demonstrated the modulation of signal transduction and metabolic pathways by (−)-epigallocatechin-3-gallate (EGCG), the most abundant and active polyphenol in green tea. These molecular events can result in cellular changes, such as enhancement of apoptosis, suppression of cell proliferation, and inhibition of angiogenesis. Nevertheless, the molecular mechanisms of inhibition of carcinogenesis in animals and humans remain to be further investigated. Future research directions in this area are discussed.

 

 

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Author: Jian-Min Yuan and Canlan Sun and Lesley M. Butler

Experimental studies have consistently shown the inhibitory activities of tea extracts on tumorigenesis in multiple model systems. Epidemiological studies, however, have produced inconclusive results in humans. A comprehensive review was conducted to assess the current knowledge on tea consumption and risk of cancers in humans. In general, consumption of black tea was not associated with lower risk of cancer. High intake of green tea was consistently associated with reduced risk of upper gastrointestinal tract cancers after sufficient control for confounders. Limited data support a protective effect of green tea on lung and hepatocellular carcinogenesis. Although observational studies do not support a beneficial role of tea intake on prostate cancer risk, phase II clinical trials have demonstrated an inhibitory effect of green tea extract against the progression of prostate pre-malignant lesions. Green tea may exert beneficial effects against mammary carcinogenesis in premenopausal women and recurrence of breast cancer. There is no sufficient evidence that supports a protective role of tea intake on the development of cancers of the colorectum, pancreas, urinary tract, glioma, lymphoma, and leukemia. Future prospective observational studies with biomarkers of exposure and phase III clinical trials are required to provide definitive evidence for the hypothesized beneficial effect of tea consumption on cancer formation in humans.

 

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Author: Jonathan W. Betts and Stuart P. Kitney and Yiton Fu and Wei-Min Peng and Stephen M. Kelly and Stephen J. Haswell

Green tea catechins have been reported to have multiple health benefits. To understand their metabolic and toxicological interactions in the human body studies need to be undertaken using stable isotope labelled compounds, but they can be time consuming and expensive. Using microreactor technology labelling catechins could be produced more quickly and at a reduced cost. This research reports on a 2-step synthesis of deuterium labelled epicatechin developed using microreactor technology for the production.

 

 

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Author: Yang Zhao and Pei Chen and Longze Lin and J.M. Harnly and Liangli (Lucy) Yu and Zhangwan Li

Tea (Camellia sinensis L.), an important drink and a natural medicine for thousands of years, contains many health beneficial compounds. Growing season, geographical region, and fermentation methods create many variations in tea compositions, which contribute to each tea’s uniqueness. In this study, a simple, rapid, and efficient ultra-performance liquid chromatography (UPLC) method combined with diode array detector (DAD) and mass spectroscopic (MS) detection and chemometrics analysis was used to analyse three different types of teas (green pu-erh, green tea, white tea). Using the developed method, 68 compounds were identified and 54 were quantified based on retention times, UV spectra, and MS spectra by referencing to available standards and data in the literatures. The results showed the chemical differences between the tested teas. Principal component analysis (PCA) was applied to classify and distinguish between tea samples.

 

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Author: H.-H. Sherry Chow and Iman A. Hakim

Green tea and its major polyphenols constituents, tea catechins, have been shown to have many health benefits including cancer prevention. Tea catechins and tea catechin metabolites/catabolites are bioavailable in the systemic circulation after oral intake of green tea or green tea catechins. The metabolites/catabolites identified in humans include glucuronide/sulfate conjugates, methylated tea catechin conjugates, and microflora-mediated ring fission products and phenolic acid catabolites. Plasma levels of unchanged tea catechins in humans are mostly in the sub-μM or nM concentration range, which is much lower than the effective concentrations determined in most in vitro studies. However, some of the catechin metabolites/catabolites are present in the systemic circulation at levels much higher than those of the parent catechins. The contribution of catechin derived metabolites/catabolites to the biological effects associated with green tea is yet to be defined. A limited number of chemoprevention trials of green tea or green tea catechins have been conducted to date and have observed potential preventive activity for oral, prostate, and colorectal cancer. Emerging data from multiple ongoing intervention trials will further contribute to defining the cancer preventive activity of green tea or green tea catechins.

 

 

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Author: Yukihiko Hara

Author: Ling Rao and Khizar Hayat and Yi Lv and Eric Karangwa and Shuqin Xia and Chengsheng Jia and Fang Zhong and Xiaoming Zhang

Ultrafiltration, silica gel and chitosan treatment methods were investigated to study the clarification effect on the green tea infusion. The results showed that ultrafiltration reduced the protein and polyphenol content, as well as color of the tea infusion. The silica gel and chitosan treatment were effective methods to clarify green tea infusion; they decreased the haze-active protein significantly, without much effect on the polyphenol. The silica gel and chitosan treatment also reduced the proline content by 18.65% and 23.79%, and histidine amino acid by 90.97%, and 90.31%, respectively. After the silica and chitosan treatment, the protein did not decrease significantly compared to the raw (untreated) infusion, while ultrafiltration treatment reduced the protein content significantly from 11.36 to 5.85 mg/100 mL with the 10 kDa membrane. Transmittance of silica gel and chitosan treated infusion was above 95.0% and 99.0%, respectively; and decreased slowly under prolonged storage time. The chitosan and silica treatment decreased the greenness and yellowness of the green tea infusion.

 

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Author: Kouass Sahbani Saloua and Kouass Salah and Benbettaieb Nasreddine and Ayari Samia and Saidi Mouldi and Landoulsi Ahmed

Sterilization of milk protein without heating is of great interest. Gamma irradiation is a very powerful method to decontaminated casein. Gamma-irradiation of proteins in aqueous media at doses higher than 5 kGy is known to induce their aggregation (without oxygen) or degradation (in presence of oxygen). Camellia sinensis green tea extract addition before irradiation of caseins cow milk proteins was examined. It was found that the presence of C. sinensis green tea extract during irradiation in the presence of oxygen conditions prevented the protein aggregation even at doses higher than 10 kGy, probably by scavenging oxygen radicals produced by irradiation. The protective role of C. sinensis green tea extract allowing the gamma-irradiation treatment of caseins cow milk proteins in solution, was asserted by sodium dodecyl-sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and by high performance liquid chromatography inverse phase (RP-HPLC). The total viable microorganisms content evaluated by Plate Count Agar (PCA) incubation for 12 h at 37 °C, showed that caseins protein preparations gamma-irradiated remained sterile at a dose 2 kGy in absence of C. sinensis green tea extract and at a dose lower than 2 kGy in the presence of C. sinensis green tea extract.

 

 

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Author: Li Guo and Qin Liang and Xianfeng Du

Tea polysaccharide (TPS) is attracting more attention gradually in many fields due to its particular biological properties. To further elucidate the functions of TPS to starch-based foods, experiments were carried out using mixed amylose/amylopectin/TPS system as a model. The effects of TPS in green tea on the glass transition temperatures (Tgs) of the mixtures with different amylose/amylopectin ratios at low water contents were investigated using high-speed differential scanning calorimetry (Hyper-DSC). The results showed that the Tgs of amylose, amylopectin and their mixtures decrease with increasing concentration of TPS. It is suggested that the addition of TPS has plasticizing effects on the structures of amylose and amylopectin on the molecular level. Based on the molecular characteristics of TPS, the results in this study indicated that TPS is a homogeneous and spherical polymer with branch in solution, which can increase free volume and molecular movement of amylose and amylopectin chains. TPS can also produce greater electrostatic repulsion and decrease association among macromolecules, thereby resulting in the decrease of the Tgs of amylose, amylopectin and their mixtures.

 

 

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