Anthocy anidins

Flavonoids are one of the largest classes of phenylpropanoid-derived plant specialized metabolites, with 10,000 different members. They consist of two main groups, the 2-phenylchromans (flavonoids flavanones, flavones, flavonols, flavan-3-ols, anthocy-anidins) and the 3-phenylchromans (isoflavonoids isoflavones, iso-flavans, pterocarpans). Some flavonoids and their metabolites exhibit positive effects for disease therapy and chemoprevention [218,219],... 

The pH of cell sap of most flowers is such that many antho-cyanin-containing flowers should be colorless, yet the presence in nature of colorless anthocyanins is rare. Anthocy-anidins undergo a series of complex color changes in water at varying pH (Brouillard, 1988). The flavylium cation of natural anthocyanins behaves as a weak diacid, whereas a neutral quinonoid base is at the same time a weak acid and a weak base. The pH of crude extracts of flowers varies from 2,8 to 6.2. 

A similar dihydroquercetin reductase activity has been shown to be a key step in the biosynthesis of anthocyanidins (Stafford, 1989). The enzyme from Dahlia has a molecular weight of about 41,000. However, there is evidence that the specificity of 3-hydroxyflavanone reductases of anthocy-anidin biosynthesis are distinct from those of flavan-3,4-diol biosynthesis (Stafford, 1989) see Chapter 11). 

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