Tea polyphenols

Table 4. Enzymes Involved With Biosynthesis of Tea Polyphenols ...

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

Tea extracts and tea polyphenols inhibit copper- and peroxide-induced oxidation of LDL in vitro (116,123,124). The inhibitory concentration for 50% reduction (IC q) values for inhibition of copper-induced oxidation of LDL by some phenoHc antioxidants are Hsted in Table 7. The IC q for epigaHocatechin gaHate was found to be 0.075 p.mM, which was the most potent of all the phenoHc antioxidants tested (123,124). Similar results have been reported elsewhere (115,116,125,126). 

Animal studies have shown that teas are effective in blocking or slowing carcinogenesis (121,131,133). Administration of teas or tea polyphenols to mice or rats have also been shown to decrease oxidative biomarkers, suggesting that tea polyphenols act as antioxidants (125,134). 

Retinoids, isothiocyanates and tea polyphenols have been identified as possible chemopreventive agents for cancers of the lung and oral cavity. While a number of trials have been conducted with retinoids or (3-carotene, the results were ambiguous and the causes are still being debated. 

The effectiveness of tea polyphenols as antioxidants in elastomeric mixes was evaluated and comparison was made with standard styrenated phenol-based antioxidant [45]. The data showed that thermal and oxidative aging resistance was comparable for both natural and synthetic antioxidants. 

Vayalil PK, Mittal A, Kara Y, Elmets CA, Katiyar SK (2004) Green tea polyphenols prevent ultraviolet light-induced oxidative damage and matrix metal-loproteinases expression in mouse skin. J Invest Dermatol 122 1480-1487... 

KATiYAR s K and MUKHTAR H (1997) Inhibition of phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate-caused inflammatory responses in SENCAR mouse skin by black tea polyphenols . Carcinogenesis, 18 1911-16. 

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

ELMETS C A, SINGH D, TUBESING K, MATSUI M, KATIYAR S and MUKHTAR H (2001) CutaneOUS photoprotection from ultraviolet injury by green tea polyphenols , JA mAcad Dermatol, 44, 425-32. 

ISHIGAMI T (1991) Antibacterial activity of tea polyphenols against foodbome, cariogenic and phytopathogenic bacteria , in Proc of Intern Symp on Tea Sci, 26-29 August, 1991, Shizuoka, Japan, 248-52. 

JAVED s, MEHROTRA N K and SHUKLA Y (1998) Chemopreventive effects of black tea polyphenols in mouse skin model of carcinogenesis , Biomed Environ Sci, 11 (4), 307-13. 

KATIYAR s K, ELMETS c A, AGARWAL R and MUKHTAR H (1995) Protection against ultraviolet-B radiation-induced local and systemic suppression of contact hypersensitivity and edema responses in C3H/HeN mice by green tea polyphenols , Photochem Photobiol, 62, 855-61. 

KATIYAR s K, PEREZ A and MUKHTAR H (2000b) Green tea polyphenol treatment to hiunan skin prevents formation of ultraviolet light B-induced pyrimidine dimers in DNA , Clin Cancer Res, 6 (10), 3864-9. 

KLEIN R D and FISCHER s M (2002) Black tea polyphenols inhibit IGF-I-induced signaling through Akt in normal prostate epithelial cells and Dul45 prostate carcinoma cells , Carcinogenesis, 23 (1), 217-21. 

LEE M J, WANG Z Y, LI H, CHEN L, SUN Y, GOGGO S, BALENTINE D A and YANG C S (1995) Analysis of plasma and urinary tea polyphenols in human subjects , Cancer Epidem Biomed Prev, 4, 393-9. 

OKABE s, SUGANUMA M, HAYASHi M, SUEOKA E, KOMORI A and FUJIKI H (1997) Mechanisms of growth inhibition of hmnan lung cancer cell line, PC-9, by tea polyphenols , Jpn J Cancer Res, 88 (7), 639-43. 

SAKANAKA s, SATO T, KIM M and YAMAMOTO T (1990) Inhibitory effects of green tea polyphenols on glucan synthesis and cellular adherence of cariogenic streptococci , Agric Biol... 

SAKANAKA s (1995) Anti-caries and anti-periodontal disease effects of green tea polyphenols , in Proc of Intern Symp on Tea-Quality-Human Health, 7-10 December, 1995, Shanghai, China, 97-106. 

UNTEN L, KOKETSU M and KIM M (1997) Antidiscoloring activity of green tea polyphenols on beta-carotene , JAgric Food Chem, 45, 2009-12. 

J (2001) Green tea polyphenol extract attenuates inflammation in interleukin-2-deficient mice, a model of autoimmunity , J Nutr, 131 (7), 2034-9. 

WANG s M and zhao j f (1997) Antioxidant activities of tea polyphenol on edible oils . Western Cereal and Oil Technology, 11, 44-6. 

WEISBURGER J H, VELIATH E, LARIOS E, PITTMAN B, ZANG E and KARA Y (2002) Tea polyphenols inhibit the formation of mutagens during the cooking of meat , MutatRes, 516 (1-2), 19-22. 

YANG X Q, WANG Y F and XU F (1995) Natural antioxidant tea polyphenols application on oil and food Study on inhibiting the deterioration of salad oil and instant noodles , J UnivAgric Zhejiang, 21 (5), 513-18. 

Historically, the absorption of lipid-soluble nutrients has been considered to be carrier-independent, with solutes diffusing into enterocytes down concentration gradients. This is true for some lipid-soluble components of plants (e.g. the hydroxytyrosol in olive oil Manna et al., 2000). However, transporters have been reported for several lipid-soluble nutrients. For example, absorption of cholesterol is partly dependent on a carrier-mediated process that is inhibited by tea polyphenols (Dawson and Rudel, 1999) and other phytochemicals (Park et al., 2002). A portion of the decreased absorption caused by tea polyphenols may be due to precipitation of the cholesterol associated with micelles (Ikeda et al., 1992). Alternatively, plant stanols and other phytochemicals may compete with cholesterol for transporter sites (Plat and Mensink, 2002). It is likely that transporters for other lipid-soluble nutrients are also affected by phytochemicals, although this has not been adequately investigated. 

KOBAYASHI Y, SUZUKI M, SATSU H, ARAI S, KARA Y, SUZUKI K, MIYAMOTO Y, SHIMIZU M (2000) Green tea polyphenols inhibit the sodiiun-dependent glucose transporter of intestinal epithelial cells by a competitive mechanism. JAgric Food Chem. 48 5618-23. 

JiAZ s,ZHOU B, YANG L, wu L M and LIN z L (1998) Autioxidant synergism of tea polyphenols and a-tocopherol against free radical induced peroxidation of linoleic acid in solution, J Chem Soc Perkin Trans, II, 911-15. 

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Sava, V.M. et al., Isolation and characterization of melanic pigments derived from tea and tea polyphenols, Food Chem., 73, 177, 2001. 

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