Catechin

Phloroglucinol (42) is a colorless and odorless solid which is only spariagly soluble ia cold water (82). It was discovered ia 1855 ia the hydrolysis products of the glucoside phloretia, which was obtained from the bark of fmit trees. Phlorogluciaol occurs ia many other natural products ia the form of derivatives such as flavones, catechins, coumaria derivatives, anthocyanidins, xanthins, and glucosides. 

PPO from tea reacts effectively with both 3 -4 and 3 -4 -5-hydroxylated catechins, with specificity for the o-diphenol (43,44). Studies defining the kinetics of PPO from tea in relation to substrate type are lacking as of this writing (ca 1997). Tea PPO has good functionaUty in the pH range 4.6—5.6 (43,45-48). 

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. 

There are four main theaflavins common to black teas, and a second group of minor theaflavins, including the isotheaflavins (55) and neotheaflavins (57) (Table 5). The total theaflavin concentration in black tea leaves does not usually exceed 2% and can be as low as 0.3%. At most, only 10% of the catechins in tea flush can be accounted for as theaflavins in black tea and the fate of the remaining catechins is less clear. Theaflavins can be readily determined by direct hplc analysis of tea beverages (48,58,59). 

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... 

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. 

Extraction of the catechin and epicatechin from the green tea was carried out by liquid extraction with methanol. 

Fig. Electropherogram of a) catechin standards, b) green tea sample prepared in 50 % methanol using liquid extraction...

Sample is in deionized water. Peak identification (1) (-)-epicatechin, (2) (-i-)-catechin... 

Brenz-. pyro-. -apfelsaure, /. maleic acid, -cain, n. Pharm.) pyrocain. -catechin, n. pyrocatechol, pyrocatechin. 

Katechln, n. catechol, catechin. -gerbstoff, m, catechol tan. -saurej /. catechuic acid (catechol). 

Catechin (+)-Catechol Cianidol Cyanidanol Cyanidol Dexcyanidanol)... 

Classical examples of this type of reaction are the various dimethylaminobenz-aldehyde reagents (q.v.) and vanillin-acid reagents, of which one, the vanillin-phosphoric acid reagent, is already included in Volume 1 a. The aldol condensation of estrogens is an example for the reaction mechanism (cf. Chapter 2, Table 6). According to Maiowan indole derivatives react in a similar manner [1]. Longo has postulated that catechins yield intensely colored triphenylmethane dyes [2]. 

In the presence of strong acids catechins react with aromatic aldehydes to yield triphenylmethane dyes [14] according to Malowan [15] indole derivatives form the following condensation product ... 

Alkaloids produce variously colored chromatogram zones (yellow, pink, brown, purple) on a light background [2]. Indole and the catechins appear red [4, 5, 8, 9, 12, 16]. If the catechins are acetylated it is necessary to heat to 105 °C for 5 min after treatment with the reagent [8]. Lysergic acid derivatives should also be heated to 75 °C for 5 min. 

Note The reagent can also be applied by first treating the chromatogram with an unacidified solution of vanillin and then exposing it to hydrochloric acid vapor [3, 9], Catechin derivatives should be evaluated rapidly (within 10 min), since the red coloration is not stable in daylight and fades relatively quickly [5, 9]. 

The general aspects of the aldehyde-acid reaction were discussed in Chapter 2. Thus it is readily understood that catechins, for example, can react with aromatic aldehydes in the presence of strong acids to yield colored triphenylmethane dyes [26]. 

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