Phenolic compounds, classification flavonoids

There is growing evidence from human feeding studies that the absorption and bioavailability and thus bioactivity of phenolic compounds and flavonoids are very much dependent on the nature of their chemical structure. Their chemical classification and dietary occurrence is briefly discussed in the following section. 

Tanacetum species contain mainly sesquiterpenoids and flavonoids, whereas the other terpenoids and phenolic compounds are rarely found. Sesquiterpenoids which are the main constituents of the genus, supposed to be bioactive principles of the plants. Flavonoids and essential oils are also pointed out as active substances in some species. On the other hand, there is a confusion on the systematic position and classification of several species of Asteraceae, therefore chemotaxonomy of the species will help the systematic studies. 

The phenolic compounds present in these three commodities fall into two general classifications, cinnamic acid derivatives and flavonoids. Included in the former are chlorogenic acid and its isomers, free cinnamic acids such as caffeic and p-coumaric acid and various esters of those two acids. Included among the flavonoids are the following ... 

A straightforward classification attempts to divide the broad category of phenolics into simple phenols and polyphenols, based exclusively on the number of phenol subunits present, but many plant phenolic compounds are polymerized into larger molecules. Thus, the term plant phenolics encompasses simple phenols, phenolic acids, coumarins, flavonoids, stilbenes, hydrolyzable and condensed tannins, lignans, and hgnins [4]. 

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