Tea extracts

Concentration. Tea extracts are generally concentrated under vacuum to the soHds content desired for drying. Ereeze concentration has been described (99), as has reverse osmosis (qv) (100). Preserved aroma and the solubiHzed cream fraction may be added before drying. 

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). 

DETERMINATION OF POLYPHENOLIC ENANTIOMERS IN GREEN TEA EXTRACT BY CAPILLARY ZONE ELECTROPHORESIS... 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

Tea extracts have been demonstrated to inhibit a wide range of inflammatory responses and may be useful in treating chronic inflammatory states. For example, rheumatoid arthritis is an inflammatory disease that causes pain, swelling, stiffness and loss of function in the joints. The antioxidants in green tea may prevent or reduce the severity of these symptoms by reducing inflammation and slowing cartilage breakdown (Adcocks et al, 2002 Haqqi et al, 1999). 

Many solid dosage forms made with green tea extracts can be seen in the market, and several are standardised to a content of polyphenols or catechins. 

Tea flavonoids, or tea extracts, have been linked to benefits in reducing the risk of certain cancers and cardiovascular diseases in experimental animals. However, epidemiological studies have produced inconsistent evidence in the relationship between tea drinking and cancer (Blot et a/., 1997 Goldbohm etal, 1996 Hertog eta/., 1997 Yang eta/., 1996). Therefore, further research is needed before definitive conclusions on the impact of tea consumption upon the cancer risk in humans can be reached. The metabolites of catechins and flavonols after consumption of tea infusions have scarcely been investigated, and thus more research is needed as to the role of those compounds in the reported health benefits of tea consumption. 

Tea flavonoids, or tea extracts, are increasingly being added to foods. However, interactions with food and drink components remain unclear, and thus need to be carefully assessed in order that the full potential benefits from consuming tea, in whatever form, can be achieved. Meanwhile, tea catechins themselves undergo extensive O-methylation, glucuronidation, sulphation and ring fission... 

J (1999) Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in hiunans , AmJ Clin Nutr, 70, 1040-45. 

LIN z c and lin z s (2000) The application of tea extracts in the fresh-preserving of fish flesh , in Proc Tea Sci Symp Across the Taiwan Straits, 26-29 April, 2000, Fuzhou, China, 97-8. 

SAKANAKA s, KIM M, TANiGUCHi M and YAMAMOTO T (1989) Antibacterial substances in Japanese green tea extract against Streptococcus mutans, a cariogenic bacterium , Agric Biol Chem, 53, 2307-11. 

WORTH c c, wiESSLER M and SCHMITZ o J (2000) Analysis of catechins and caffeine in tea extracts by micellar electrokinetic chromatography . Electrophoresis, 21 (17), 3634-... 

YAYABE F (2001) Industrial application of tea extracts , in Proc as Intern Symp on Tea Sci, 6-8 October, 2001, Shizuoka, Japan, 30-33. 

YEN G c and CHEN H Y (1995) Antioxidant activity of various tea extracts in relation to their antimutagenicity , JAgric Food Chem, 43, 27-32. 

HU M and SKIBSTED L H (2002b) Kinetics of reduction of ferryhnyoglohin by (-)-epigallocatetechin gallate and green tea extract, J Agric Food Chem, 50, 2998-3003. 

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