Catechin oxidation

Peroxidase is found in tea leaf and has been recently recognized to play a role in the catechin oxidation system and in the further oxidation of the initial components produced.57... 

Jimenez-Atienzar M, Cabanes J, Gandia-Herrero F and Garcia-Carmona F. 2004. Kinetic analysis of catechin oxidation by polyphenol oxidase at neutral pH. Biochem Biophys Res Commun 319 902-910. 

Cheynier, V., Basire, N., and Rigaud, J., Mechanism of trans-cziitoyl tartaric acid and catechin oxidation in model solutions containing grape polyphenoloxidase. J. Agric. Food Chem. 37, 1069, 1989. 

Guyot, S., Vercauteren, J., and Cheynier, V., Colourless and yellow dimers resulting from (+)-catechin oxidative coupling catalysed by grape polyphenoloxidase. Phytochemistry 42, 1279, 1996. 

Nakayama T, Enoki I, Hashimoto K. 1995. Hydrogen peroxide formation during catechin oxidation is inhibited by superoxide dismutase. Food Sci Technol Int 1 65-69. 

Guyot, S., PeUerin, P, Brillouet, J., Moutounet, M., Cheynier, V. (1996a). Inhibition of b-glucosidase (Amygdalae Dulces) by (-l-)-catechin oxidation products and procyanidin dimers. Biosci., Biotech. Biochem., 60, 1131-1135. 

Since the 1950s, many efforts have been made to isolate polyphenols directly from black tea, and the structures of the major phenolic compounds characteristic of fermented tea have been elucidated." ° However, the composition of black tea polyphenols is so complex that the minor phenolic substances, which cumulatively account for a substantial portion of black tea polyphenols, are difficult to separate even by high-performance liquid chromatography (HPLC). This difficulty associated with the purification is mainly due to the presence of uncharacterized substances that are detected as a broad hump on the baseline during HPLC analysis but do not produce any clear spots on thin-layer chromatography. These snbstances are probably a complex mixture of catechin oxidation products with higher molecular sizes, and usually account for the majority of black tea polyphenols. 

FIGURE 5.2 Time course of catechin oxidation with banana homogenate. 

FIGURE 15.2. A proposed mechanism of theaflavins formation from catechin oxidation. 

Quinones themselves are coloured compounds. Simple quinones are usually red when they contain an o-quinoid structure (such as o-benzoquinone) in the molecule, while compounds with the p-chinoid arrangement are yellow (e.g. p-benzoquinone). The catechin oxidation product is bright yellow, quinone formed of chlorogenic acid has a yeUow-orange colour and quinone derived from amino acid dopa (dopaquinone) is pink. 

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. 

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... 

Therefore depending upon the conditions used to simulate either in vitro or in vivo oxidation, catechins or other phenolic compounds display differences in their antioxidant properties. Catechins also limited the consumption of a-tocopherol, allowing it to act as a scavenger within cell membranes whilst the catechins scavenged aqueous peroxyl radicals near the membrane surface (Pietta and Simonetti, 1998). 

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. 

TANG s z, KERRY J p, SHEEHAN D, BUCKLY D J and MORRISSEY p A (2001) Antioxidative effect of dietary tea catechins on lipid oxidation of long-term frozen stored chicken meat , Meat Sci, 56, 285-90. 

HAYEK T, FURHMAN B, VAYA J, ROSENBLAT M, BELINRY P, COLEMAN R, ELIS A, AVIRAM M (1997) Reduced progression of atherosclerosis in apolipoprotein E-deficient mice following consiunption of red wine, or its polyphenols quercetin or catechin, is associated with reduced susceptibility of LDL to oxidation aggregation, Arteriosclerosis, Thrombosis and Vascular Biology, 17, 2744-52. 

LOTiTO s B, FRAGA c G (1998) (+)-Catechin prevents human plasma oxidation, Free Radical Biology and Medicine, 24, 435-41. 

Nowadays, consumers would like those antioxidants present in food products not only to stabilise food lipids, but also to be absorbed through the intestinal wall and protect the lipids of blood plasma against oxidation. This effect is relatively evident in the case of tocopherols (which are liposoluble) or ascorbic acid (which is hydrophilic), but much less evidence is available on antioxidants of medium polarity, such as flavonoids, rosemary oleoresins or green or black tea catechins. 

NICOLI M c, CALLIGARIS s and MANZOCCO L (2000) Effect of enzymatic and chemical oxidation on the antioxidant capacity of catechin model systems and apple derivatives , JAgric Food Chem, 48 (10) 4576-80. 

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