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Beneficial effects of green tea: A literature review
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Please enter the message. Please verify that you are not a robot. Would you also like to submit a review for this item? You already recently rated this item. Your rating has been recorded. Write a review Rate this item: Preview this item Preview this item. Food science and technology Marcel Dekker, Inc. Black tea is completely oxidized. The dark color of black tea is due to the phenolase catalyzed oxidation of catechins in green tea [ 3 ].
An enzyme, polyphenol oxidase, is activated during the rolling and chopping process of the tea leaves. People in China have heated the leaves of the Camellia sinensis plant to inactivate the polyphenol oxidase which has resulted in green tea.
Green tea : health benefits and applications
Oxidation of polyphenol oxidase for about 1 or 2 hours results in oolong tea. Tea is produced by processing shoots that include tender apical bud and subtending three leaves [ 4 ]. Processing procedures of the Chinese include roasting the tea shoots in a metal roaster and then using the unidirectional rotary roller for processing. The unidirectional roaster twists the leaves and compact the particles. The Japanese use steaming procedures to inactivate the shoots and then process by bi-directional rolling. Bi-directional rolling makes the shoot surface flat without any twists and by spreading the leaf juice over the entire surface.
The chemistry of tea is complex: But there are other compounds in green tea with interest for human health like fluoride, caffeine, minerals and trace elements like, chromium and manganese [ 7 - 9 ].
The aim of this review is to summarize the information related to beneficial properties of the green tea poly phenols and the application of green tea in food industry. Polyphenols are powerful antioxidants and free radical scavengers. They are strong scavengers of superoxide, hydrogen peroxide, hydroxy radicals, and Nitric Oxide NO produced by various chemicals. Flavonoids are polyphenolic compounds that include the subclasses of flavanones, flavones, isoflavones, flavanols flavans , flavonols and anthocyanins [ 10 ].
The pharmaceutical activities of the components have been studied [ 12 - 14 ]. Chemically, the beverage is characterized by the major polyphenolic catechins such as — —epigallocatechin- 3-gallate EGCG , — —epigallocatechin EGC , — —epicatechin gallate ECG , and — —epicatechin EC ; these are the most abundant water-soluble components of tea [ 11 , 15 ]. An infusion of green tea contains up to mg of catechins [ 16 ].
Green tea extracts have higher antioxidant capacity than black tea, and the total antioxidant potential correlates strongly with the total phenolic content of tea [ 17 , 18 ]. They can also chelate metal ions, often decreasing the metal ion pro-oxidant activity. Tea polyphenol scavenge the reactive oxygen species and chelate transition metal ions in a structure-dependent manner. The flavonoids are antioxidants by virtue of the number and arrangement of their phenolic hydroxyl groups [ 20 ]. The chemical structures contributing to the effective antioxidant activity of catechins include the vicinal dihydroxy or trihydroxy structure, which can chelate metal ions and prevent the generation of free radicals.
The structure also allows for electron delocalization, conferring high reactivity to quench free radicals [ 21 - 23 ]. The antioxidant effect of polyphenols depends on their structure and the position as well as number of hydroxyl groups. Vitamin C is an anti-scorbutic, prevents cataracts, and strengthens the immune system. Some of the essential health benefiting effects of these polyphenols is discussed below:. One benefit of consuming green tea is that carcinogenesis in the digestive tract is postulated to be inhibited by ECGC as demonstrated in cells [ 25 ]. EGCG was shown to prevent neuronal cell death caused by several neurotoxins [ 26 ].
Gastrointestinal tract cancer is mainly associated with an excess intake of protein and fat [ 27 ]. The polyphenols of green tea have been shown to exhibit inhibitory effects on cancer of the gastrointestinal tract and also have shown preventive effects against several other types of cancer. However, the evidence to support the preventive effects of green tea polyphenols on stomach and intestinal cancer is not clear.
Studies indicate that green tea has a protective effect on adenomatous polyps and chronic atrophic gastritis formations. The inhibitory effect of green tea polyphenols was studied on the human lung cancer cell line, PC-9 [ 28 ]. These studies shows the protective effects of green tea and health benefits associated with it on the cell line studied. Breast carcinoma is considered to be one of the most common cancers in women [ 29 ].
Breast cancer is more prevalent in western countries compared to Japan because of their daily intake of green tea as part of the diet.
Green tea : health benefits and applications (eBook, ) [xecykisypife.tk]
Consumption of green tea prior to the clinical cancer onset is believed to have decreased the risk of stage I and II breast cancer in women. Drinking green tea is believed to inhibit certain cancers, such as lung, skin, esophagus, liver, and stomach [ 30 ]. Tea catechins are mainly absorbed by the small intestines and are metabolized by enzymatic reactions. Epidemiological studies on the consumption of green tea and risks associated with cancer are still not clear.
The reasons for the inconclusive studies might be due to poorly designed studies, differences in lifestyle and metabolic systems of individuals.
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Oxidative stress plays a major role in several liver diseases. Green tea has an antiproliferative activity on hepatoma cells, suppresses hepatoma-induced hyperlipidemia hypercholesterolemia and hypertriglyceridemia , and also prevents hepatotoxicity [ 31 ]. Green tea may be a chemopreventive agent for hepatocarcinogenesis in the absence of chronic hepatocyte damage.
It suppresses D-galactosamine induced liver injury in rats, which could be through inhibition of tumor necrosis factor-induced apoptosis [ 32 ]. Daily ingestion of green tea prevented hepatotoxicity increase in serum glutamic-oxaloacetic transaminase and glutamicpyruvic transaminase; decrease in hepatic glycogen, serum triglyceride, and lactate dehydrogenase and cell proliferation in the liver of rats on administration of 2-nitropropane [ 33 ]. Most pro-carcinogens require metabolic activation by metabolite enzymes such as phase I and II enzymes in order to convert to electrophiles before they can exert any carcinogenic effects [ 34 ].
In limiting the formation of carcinogens, green tea and its catechins promote the elimination of procarcinogens such as polycyclic hydrocarbons and heterocyclic amines from the body by inducing phase I cytochromes P 1A1, 1A2, and 2B1 enzymes and phase II detoxification enzymes, for example, GT [ 35 ]. The procarcinogen-activating enzyme cytochrome P 3A4 is also suppressed [ 36 , 37 ].
Exposure of experimental animals to dioxins causes adverse effects such as body weight loss, immunosuppression, endocrine disruption, cancer promotion, teratogenesis, and lethality. Dioxins bind to the cytosolic aryl hydrocarbon receptor AhR , commonly called the dioxin receptor, resulting in its transformation.
Since AhR transformation is the initial step in the expression of dioxin toxicity, inhibition of transformation would protect humans from toxic effects. Tea extracts can inhibit the cytochrome Pmediated metabolism of 2-aminomethylimidazo, [4,5-f] quinoline IQ into its ultimate mutagenic metabolite forms, and interact with both the promutagens and their metabolites in a way that can reduce their mutagenic potential [ 39 ]. Benzopyrene BaP - and cyclophosphamide CP -induced genotoxicity in microbial and mammalian test systems are inhibited in a dose-dependent manner by theaflavins [ 40 ].
The polyphenols of black tea are more potent inhibitors of mutagenicity than those of green tea caused by the food mutagen PhIP [ 41 , 42 ]. Cigarette smoking is a known cause of lung cancer and other respiratory diseases. Cigarette smoke contains numerous compounds that generate reactive oxygen species which can damage DNA directly or indirectly via inflammatory processes [ 21 , 22 , 43 ]. Regular drinking of green tea might protect smokers from oxidative damages and reduce cancer risk or other diseases caused by free radicals associated with smoking [ 44 ].
A tea infusion fed to rats in drinking water during an N-nitroso-methylbenzylamine NMBA adminisration period inhibited esophageal tumorigenesis [ 45 , 46 ]. Along with the antioxidative activity, green tea is shown to exhibit tumor suppressing activity in a cell [ 47 ]. Evidence has accumulated to show that the ingestion of green tea and tea catechins leads to a reduction in body fat as described in recent reviews [ 48 - 50 ].