Green tea flavanols

Csala M, Margittai E, Senesi S, Gamberucci A, Banhegyi G, Mandl J, Benedetti A. 2007. Inhibition of hepatic glucose 6-phosphatase system by the green tea flavanol epigallocatechin gallate. FEBS Lett 581 1693-1698. 

Garbisa, S., Sartor, L., Biggin, S., Salvato, B., Benelli, R., and Albini, A. 2001. Tumor gelatinases and invasion inhibited by the green tea flavanol epigallocatechin-3-gallate. Cancer 91 822-32. 

Tannins, theaflavins, and thearubigens Tannins and theaflavins are pigmented products in black tea formed after oxidation and condensation of green tea flavanols during the fermentation process. These compounds are analyzed by spectrophotometric, colorimetric, and chromatographic methods, using LC and GC. 

Flavanols are one of the most abundant classes of flavonoids, often referred to as flavan-3-ols or catechins. They are present as monomers, oligomers, and polymers and are often esterified with gallic acid [1]. The focus of this chapter are bioavailability and metabohsm of the flavanol monomers, catechin, epica-techin, and the green tea flavanols epigallocatechin gallate, epigallocatechin, and epicatechin gallate (Fig. 1). 

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. 

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. 

PRICE w E and spitzer j c (1993) Variations in the amounts of individual flavanols in a range of green teas . Food Chem, 47, 271-6. 

Aside from China, Japan, North Africa, and the Middle East, most tea is consumed as black tea, which is produced by promoting the enzymic oxidation of tea flavanols. For the production of green tea, inactivation of the tea enzyme system by rapid firing is carried out to prevent flavanol... 

The detailed processing that must be carried out to produce tea suitable for shipment and beverages will be described after consideration of the chemical changes that occur when green-leaf flavanols are oxidized. 

Green tea processing is designed to achieve a dry product exhibiting the desirable twisted leaf appearance, but without flavanol oxidation. This is accomplished by carrying out rapid enzyme inactivation either with steam in a rotating cylinder as practiced in Japan or with dry heat as practiced in the People s Republic of China. The inactivated tea is cooled, rolled partially dried, rerolled, and then completely dried. 

Catechins are widely distributed in plants however, they are rich only in tea leaves, where catechins may constitute up to 25% of dry leaf weight. Catechins of green tea include the flavanols epicatechin, epigallocatechin, and their gallate esters (Table 14). 

Wang, L.-F., Kim, D.-M., and Lee, C.Y. 2000b. Effects of heat processing and storage on flavanols and sensory qualities of green tea beverage. J. Agric. Food Chem. 48 4227-4232. 

A Bu-Abbas, E Copeland, MN Clifford, R Walker, C Ioannides. Fractionation of green tea extracts correlation of antimutagenic effect with flavanol content. J Sci Food Agric 75 453-462, 1997. 

Monomeric flavanols Catechin Chocolate, beans, apricot, green tea,... 

Green tea is made by steaming or frying fresh tea leaves at elevated temperatures to prevent polyphenol oxidation. The chemical composition of green tea is similar to that of the fresh leaves regarding the major components. It contains polyphenols, which include flavanols, flavandiols, flavonoids, and phenolic acids. Flavanols are the most abundant constituents and are commonly known as catechins. The major catechins present in green tea are (-)-epicatechin (EC), (-)-epicatechin-3-gallate... 

Figure 6.1 Chemical structures of flavanoids including catechins and theaflavins. These tiavanoids consisted of two major groups flavanones, including naringenin, taxifolin, and fustin, and flavanols including green tea polyphenols (EC, ECG, EGC, EGCG), black tea polyphenols (TF-1, TF-2a, TF-2b, TF-3), and oolong tea polyphenol (TSA).

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