3-flavanols

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. 

Glycosides, particularly of phenoHc compounds, are widely distributed in plant tissues (2,10). Glycosides of anthocyanidins, flavones, flavanols, flavanones, flavanonols, stilbenes and saponins, gaUic acid derivatives, and condensed tannins are all common. 

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. 

In 1908, while working at University of Heidelberg, Auwers and Muller described the transformation of 4-methyl-2-cumaranone (3) to flavanol 6. Thus aldol condensation of 3 with benzaldehyde gave benzylidene derivative 4, which was brominated to give dibromide 5. Subsequent treatment of 5 with alcoholic KOH then furnished 2-methylflavonol 6. In the following years, Auwers published more extensively on the scope and limitations of this reaction. ... 

The cell-to-cell interaction following the expression of adhesion molecules (ICAM-1, VCAM-1 and selectin) in endothelial cells induced by cytokines treatment has been reported to be blocked by hydroflavones and flavanols. Apigenin, the most potent flavone tested in this study, inhibited the expression... 

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. 

SALAH N, MILLER N, PAGANGA G, TIJBURG L, BOLWELL G P and RICH-EVANS 0 (1 995) Polyphenlic flavanols as scavengers of aqueous phase radicals and as chain-breaking antioxidants , Arch Biochem Biophys, 322, 339-46. 

The chemical formulae for a variety of plant phenols are given in Fig. 16.2, including examples of simpler phenols, such as cinnamic acid derivative, and of tocopherols, flavonoids, flavonoid glycosides and anthocyanidins. The flavonoids include the following subclasses flavanones (taxifolin), flavones (luteolin), flavonols (quercetin) and flavanols (catechin/epicatechin). The... 

Wine and by-products Cinnamic acid derivatives, anthocyanins and flavanols dominate (10 to 20 J,M gallic acid equivalents) Oil-in-water emulsion (dressing model) Red wine yields better protection, but phenols in white and rose wine seem more efficient on a molar basis Sanchez-Moreno et al., 2000... 

McDougall, G.J. et al., Anthocyanin-flavanol condensation products from black currant (Ribes nigrum L.), J. Agric. Food Chem., 53, 7878, 2005. 

Salas, E. et ah. Demonstration of the occurrence of flavanol-anthocyanin adducts in wine and in model solutions. Anal. Chim. Acta, 513, 325, 2004. 

Duenas, M., Fulcrand, H., and Cheynier, V., Formation of anthocyanin-flavanol adducts in model solutions. Anal. Chem. Acta, 563, 15, 2006. 

Salas, E. et al.. Isolation of flavanol-anthocyanin adducts by countercurrent chromatography, J. Chrom. ScL, 43, 488, 2005. 

Each plant tissue tends to have an obviously distinctive profile of flavonoids. The flavonoid content can reach about 0.5% in pollen, 10% in propolis, and about 6 mg/kg in honey. Havonoid aglycones appear to be present only in propolis and honey, while pollen contains flavanols in herosidic forms. The flavonoids in honey and propolis have been identified as flavanones and flavanones/flavanols (Campos et ah, 1990). The antimi-crobially active flavanone pinocembrine was foimd to be a major flavonoid in honey (Bogdanov, 1989). Amiot et ah (1989) studied two blossom and two honeydew Swiss honey samples and foimd that pinocembrine was the main flavonoid. Pinocembrine concentration varied between 2 and 3 mg/kg (Bogdanov, 1989). Berahia et ah (1993) analyzed sunflower honey samples and detected six flavone/flavols, four flavanone/ flavols, and pinocembrin, of which pinocembrin is the main flavonoid. The flavonoids in sunflower honey and propolis were characterized and assessed for their effects on hepatic drug-metabolizing enzymes and benzo [fl]pyrene-DNA adduct formation (Sabatier et ah, 1992 Siess et ah, 1996). 

Application of HPLC-MS to the analysis of a black tea liquor was studied in a paper by Bailey 39 a great deal of useful information could be obtained without sample pretreatment. A tea liquor was applied to a wide-pore HPLC column connected to a mass spectrometer by a VG Plasmaspray interface. Pseudo-molecular ions were obtained from the flavanols, flavanol gallates, chlorogenic acids, 4-coumarylquinic acids, and caffeine, but the flavanol glycosides were extensively fragmented by the interface. Fragments were obtained from unresolved polymer that supported its previous designation as a flavanol polymer. 

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. 

Tea oxidation is generally referred to as fermentation because of the erroneous early conception of black tea production as a microbial process.66 Not until 1901 was there recognition of the process as one dependent on an enzymically catalyzed oxidation.67 This step and further reactions result in the conversion of the colorless flavanols to a complex mixture of orange-yellow to red-brown substances and an increase in the amount and variety of volatile compounds. Extract of oxidized leaf is amber-colored and less astringent than the light yellow-green extract of fresh leaf and the flavor profile is considerably more complex. 

The initial oxidation of the flavanol components of fresh leaf to quinone structures through the mediation of tea polyphenol oxidase is the essential driving force in the production of black tea. While each of the catechins is oxidizable by this route, epigallocatechin and its galloyl ester are preferentially oxidized.68 Subsequent reactions of the flavonoid substances are largely nonenzymic. 

A large proportion of the hot-water extractable solids obtained from black tea is derived from tea flavanols but is not accounted for by the known oxidation products previously described. 

All steps in black tea manufacturing are designed to expedite the oxidation of the tea flavanols and to control the reaction so that the end products are optimized with respect to flavor as well as to leaf and beverage appearance. 

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