Flavanols distribution

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. 

Polyphenoloxidase (PPO, EC 1.14.18.1) is one of the most studied oxidative enzymes because it is involved in the biosynthesis of melanins in animals and in the browning of plants. The enzyme seems to be almost universally distributed in animals, plants, fungi, and bacteria (Sanchez-Ferrer and others 1995) and catalyzes two different reactions in which molecular oxygen is involved the o-hydroxylation of monophenols to o-diphenols (monophenolase activity) and the subsequent oxidation of 0-diphenols to o-quinones (diphenolase activity). Several studies have reported that this enzyme is involved in the degradation of natural phenols with complex structures, such as anthocyanins in strawberries and flavanols present in tea leaves. Several polyphenols... 

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). 

Dihydroflavonols. Widely distributed 2,3-dihydroflavon-3-ols include the antioxidant 2,3-dihydroflavonols aromadendrin (3,5,7,4 -tetrahydroxyflavanone 2,3-dihydrokaempferol), ampelopsin (3,5,7,3, 4, 5 -hexahydroxyflavanone 2,3-dihydromyricetin), fustin (3,7,3, 4 -tetrahydroxyflavanone 2,3-dihydrofisetin) and taxifolin (3,5,7,3, 4 -pentahydroxy-flavanone 2,3-dihydroquercetin). Some flavanols are sweet-tasting, notably 6-methoxy-aromadendrin 3-O-aceate, 6-methoxytaxifolin and taxifolin 3-0-acetate. Taxifolin and fustin inhibit NADH and succinate dehydrogenases and taxifolin inhibits 5-LOX. 

Although flavanols, also called catechins, seem to be widely distributed in plants, they are rich only in tea leaves, where catechins may contribute up to 30% of dry leaf weight. The antioxidative and antitumor properties of green and black teas and their tea polyphenols are extensively studied. It seems that tea polyphenols are important not only for plants but also for humans. Therefore, this brief review will discuss the current data with a particular emphasis on the effects of tea polyphenols on the cellular oxidative stress and cancer chemopreventive properties. The action mechanisms of several phytopolyphenols on cancer chemoprevention will be elaborated. 

The flavonoids are a group of secondary metabolites widely distributed in the plant kingdom [63]. In 1984, more than 4000 flavonoids were identified in plants [64]. The major dietary sources of flavones are spices and pot herbs, such as parsley, rosemary, and thyme [65], whereas flavonols are predominantly found in onions, kale, broccoli, apples, berries and cherries, and in tea and red wine [66]. The flavanones are mainly restricted to citrus fruits [67], and flavanols are found in considerable amounts in tea, apricots, apples, and cherries [66]. 

The distribution of these molecules is perfectly consistent with their antifungal properties, as they stop the mycelial development of fungi lacking in laccase, the only enzyme capable of breaking them down without being deactivated. The skin also contains phenolic acids and flavanols in the cell vacuoles. Phenolic acids are the main phenol components of the flesh. 

Serra, A., Blade, C., Arola, L., Macia, A., and Motilva, M. J. 2013. Flavanol metabolites distribute in visceral adipose depots after long-term intake of grape seed proanthocyani-din extract in rats. J. Br. Nutr. 110 1411-1420. 

When discussing the biological activity of flavonoids in general, and flavanols in particular, there are some major factors to be considered bioavailabDity from food, matrix effects, absorption and metabolism in the gastrointestinal tract, tissue and cellular distribution after absorption, possible interactions and/or accumulation, which are the chemical form(s) biologically available to the cell/tissue and their potential metabolism at cellular level [3, 42, 69, 70]. 

The flavanol metabolites that exist in vivo need to be eharacterized further as they are the major determinants of biologieal aetivity. Significant amounts of ring-fission metabolites are Ukely present in vivo, but many of the specific structures and levels in humans are not known. Additional information is also needed on the positions of the glucuronide and sulfate moieties in human metabolism. Determining the identities of speeifie metabolites and their distribution within tissues and cells will be a key to accessing their biological activity, the major task at hand. 

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