Plant polyphenol flavones

Flavonoids are important group of polyphenols, widely distributed in plant flora. 4,000 flavonoids are known to exist and some of them are pigments in higher plants. Quercetin, kaempferol and quercitrin are common flavonoids present in nearly 70 percent of the plants. Soya flavones have recently gained importance due to variety of pharmacological activities. 

Bio active polyphenols are present in a variety of plants and are used as important components of human and animal diets [27]. Flavonoids are a broad class of low-molecular-weight secondary plant polyphenolics, which are benzo-y-pyrone derivatives consisting of phenolic and pyrane rings. Flavonoids are usually subdivided according to their substituents into fla-vanols, flavones, flavanones, chalcones, and anthocyanidines. 

Anthocyanins. Like the flavones. the anthocyanins are found throughout nature. This class uf polyphenolic compounds is responsible for the pink, red. violet, and blue colors found in plants. Like many other natural phenulic substances, anthocyanins occur in plants as glycosides the sugar-free anthocyanins are known as anihocyanidins. 

Plant-derived products Polyphenols (derivatives of hydroxycinnamic acid, hydroxybenzoic acid, flavonols,3 flavones,3 anthocyanidins,3 flavanols,3 isoflavones,3 flavanones,3 stilbenes, lignans), glucosynolates, carotenoids (am /3-, y-, 8-carotene, lycopene, luthein, xeaxantin, canthaxantin), phytic acid, allicin... 

Flavones and flavonols are relevant phytochemicals in food products, spices and medicinal plants. They are secondary metabolites belonging to the polyphenols group, and have in common the general structure of two aromatic rings and often more than three phenolic hydroxyls. Flavones and flavonols often show high antioxidant activity in vitro, and they complex metal ions and scavenge free radicals. They have a planar structure that allows intermolecular interactions and stacking in... 

The polyphenols are a series of phytochemicals synthesized by plants. They include the bioflavonoids anthocyanins, coumestanes, flavonoids, isoflavonoids, and stil-benes (Figure 4.1). Each bioflavanoid class is subdivided into other groups, e.g., flavones, flavans, flavanols, flavonols, and flavanones (Figure 4.2). Another class of polyphenol is the oligomeric polyphenols, such as the proanthocyanidins, found in the grape and various berries (black currant, blueberry, etc.). 

The LC/UV/MS analysis of Gentianaceae extracts gives useful structural information on-line for a partial identification of their metabolites. Indeed Gentianaceae plants contains UV active polyphenolic constituents such as xanthones and flavone... 

The actual explanation was given as a result of marty years of research. The pH of 4-6 in the vacuoles of plants would be consistent with the colorless pseudobase form of anthocyanins or a little bit of the violet anl drobase. This pseudobase, on the other hand, is understood to be rare in Nature. In addition to pH, the interactions of anthocyanins with each other, other polyphenol type pigments (such as flavonoids or flavons), and metal ions such as alirminum, gallium and iron(in) collectively determine the color. Desert bluebells Phacelia campanularia) are true to their name as their flowers are blue, which is caused by aggregation between phacelianin molecules and their interaction with aluminum(III) and iron(III) ions. 

Phenolic compounds are present separately from the substrates, predominantly located in the cell vacuoles. Particularly prominent substrates are caffeic acid and its esters, as well as some flavonoid substances, of which monomeric flavan-3-ols (catechins) are the most important. Other groups of phenolic compounds, such as condensed forms of flavan-3-ols and flavan-3,4-diols (tannins), flavonols, flavones, flavans, chalcones, dihydrochalcones and anthocyanins, are only partly oxidised. One of the reasons for this is probably the steric hindrance caused by the corresponding glycosides and substrate specificity of polyphenol oxidases. The content of phenohc compounds depends on genetic factors (on plant species and varieties), the degree of maturity and external (environmental) factors (hght, temperature, nutrients, use of pesticides and so on). The only substrate in animal tissues is the amino acid tyrosine. 

Members of the stilbene family which have the C6-C2-C6 structure (Table 1.1), like flavon-oids, are polyphenolic compounds. Stilbenes are phytoalexins, compounds produced by plants in response to attack by fungal, bacterial and viral pathogens. Resveratrol is the most common stilbene. It occurs as both the cts and the trans isomers and is present in plant tissues primarily as fra s-resveratrol-3-0-glucoside which is known as piceid and polydatin (Figure 1.14). A family of resveratrol polymers, viniferins, also exists. 

Flavonoids are a class of plant secondary metabohtes that are abundant components of fruit and vegetables. They are divided into five major subclasses flavonols, flavan-3-ols (monomers and proanthocyanidins), flavones, flavanones and anthocyanins (Manach etal. 2004). Isoflavones are a class of dietary polyphenols present in soya-based foods. The structiues of representative compounds from each of these polyphenol subclasses are shown in Figure 8.2 (also see Chapter 1). Flavonoids and isoflavones have received attention due to their potent antioxidant activity and possible role in the prevention of cancer, cardiovascular, neurodegenerative and infectious diseases as well as osteoporosis. 

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