Oxidation of -catechin

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

Catechin-immobilizing polymer particles were prepared by laccase-catalyzed oxidation of catechin in the presence of amine-containing porous polymer particles. The resulting particles showed good scavenging activity toward stable free l,l-diphenyl-2-picryl-hydrazyl radical and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation. These particles may be applied for packed column systems to remove radical species such as reactive oxygen closely related to various diseases. 

Jiang, Y. and Miles, P.W., Generation of H2O2 during enzymic oxidation of catechin. Phytochemistry 33, 29, 1993. 

Oszmianski, J., Cheynier, C., and Moutounet, M., Iron-catalyzed oxidation of (+)-catechin in wine-like model solutions. J. Agric. Food Chem. 44, 1972, 1996. 

Similarly, catechin polymers formed upon horseradish peroxidase-catalyzed oxidation of catechin or polycondensation of catechin with aldehydes prove much more efficient than catechin (at identical monomer concentration) at inhibiting XO and superoxide formation. A more detailed investigation with the catechin-acetaldehyde polycondensate (which is expected to form in wine because of the microbial oxidation of ethanol to acetaldehyde) shows that inhibition is noncompetitive to xanthine and likely occurs via binding to the FAD or Fe/S redox centers involved in electron transfers from the reduced molybdenum center to dioxygen with simultaneous production of superoxide. 

Clark, A.C., Scollary, G.R. (2002). Copper(II)-mediated oxidation of (+)-catechin in a model white wine system. Au. J. Grape Wine Res. 8, 186-195. 

As is the case for other phenols, the peroxidase-catalyzed oxidation of (+)-catechin involves a one-electron oxidation [36] and yields unstable... 

Class in plant peroxidases, such as that purified from strawberries, are able to oxidize (+)-catechin with ki values of 0.57 pM s at pH 5.0 [36]. The peroxidase-mediated oxidation of (+)-catechin leads to the formation of dimers such as dehydrodicatechin A and B4, trimers, tetramers and oligomers of different degrees of polymerization [146,147],... 

It yields a reddish-brown compound on oxidation with potassium bichromate, probably identical with the japonic acid formed on oxidation of catechin. 

The content of catechins is mostly influenced by PPO and POD. The oxidation of catechins nnder the action of PPO and POD results in the decrease of catechins dnring the withering stage. The amount of catechins remains steady during terminal withering stage, while PPO and POD activities are inhibited. ... 

In addition to the enzymatic pathway of aroma formation, a thermal route also exists. At high temperatures, interactions of amino acids and sngars resnlt in the formation of various aldehydes. After thermal treatment, the tea becomes more tasty and pleasant, and has a better aroma. An essential source of secondary volatiles, formed during tea leaf processing, is oxidative. o-Quinone resulting from the oxidation of catechins can oxidize, besides amino acids and carotenes, unsaturated fatty acids as well. Linoleic and linolenic acids can be converted into hexenal and trans-hex-2-enal, respectively, and in addition, small amounts of other volatile compounds, especially hexanoic acid and trani-hex-2-enoic acid, can be formed from the same acids, respectively. Also the monoterpene alcohols, linalool and geraniol, play an important role in the formation of the aroma of black tea [38]. 

Tyrosinase is an oxygenase with a molecular weight of 33,000. In contrast to laccase, there are only one or two copper atoms per molecule. Tyrosinase catalyzes the oxidation of catechins to the respective quinones with the reduction of O2 to H2O. Since one of the cooper ions is presnet in the form not detected by EPR, it is assumed that it is a diamagnetic Cu " ion. The essentially different structure of the active center of tyrosinase and of laccase points also to a different mechanism of their operation. Apparently, in the case of tyrosinase a progressive transport of electrons takes place from the substrate... 

Hathway, D.E., and Seakins, J.W.T., 1957b, Enz3nnic oxidation of catechin to a polymer structurally related to some phloba-tannins, Biochem. J., 67 239. 

In a mice model of Parkinson s disease, catechins are thought to chelate metal ions such as copper (II) and iron (II) and therefore prevent the generation of potentially damaging free radicals, to suppress the translation of APP mRNA, to reduce holo-APP, and to decrease Ap levels. After the oxidation of catechins by free radicals, a dimerized product is formed with an increased iron-chelating potential and ability to scavenge superoxide anions [56-58]. 

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