Flavonoids From Argentine Tagetes (Asteraceae) With Antimicrobial Activity

The flavonoids, constituting one of the most numerous and widespread groups of natural plant constituents, are important to humans not only because they contribute to plant colors but also because many members are physiologically active. These lowmolecular-weight substances, found in all vascular plants, are phenylbenzopyrones. Over 4000 structures have been identified in plant sources, and they are categorized into several groups (Fig. 1 ). Primarily recognized as pigments responsible for the autumnal burst of hues and the many shades of yellow, orange, and red in flowers and food, the flavonoids are found in fruits, vegetables, nuts, seeds, stems, flowers, and leaves as well as tea and wine and are important constituents of the human diet (1). They are prominent components of citrus fruits and other food sources. Flavonols (quercetin, myricetin, and kaempferol) and flavones (apigenin and luteolin) are the most common phenolics in plant-based foods. Quercetin is also a predominant component of onions, apples, and berries. Such flavanones as naringin are typically present in citrus fruit, and flavanols, particularly catechin, are present as catechin gallate in such beverages as green or black tea and wine. Some major sources of flavonoids are outlined in Table 1 (2). The daily intake of flavonoids in humans has been estimated to be approx 25 mg/d, a quantity that could provide pharmacologically significant concentrations in body fluids and tissues, assuming good absorption from the gastrointestinal tract (3).

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Flavonoid	Source
Catechins	Tea, red wine
Flavanones	Citrus fruits
Flavonols (e.g., quercetin)	Onions, olives, tea, wine, apples
Anthocyanidins	Cherries, strawberries, grapes, colored fruits
Caffeic acid	Grapes, wine, olives, coffee, apples, tomatoes, plums, cherries