Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Characterization and Measurement of Anthocyanins by UV-Visible Spectroscopy

The biochemistry and medical significance of the flavonoids.

Proanthocyanidins (syn condensed tannins) are complex flavonoid polymers naturally present in cereals, legume seeds and particularly abundant in some fruits and fruit juices. They share some common structural features—phenolic nature and high molecular weight—with phenolic polymers found in black tea and red wine (called here tannin-like compounds). The polymeric nature of proanthocyanidins makes their analysis and estimation in food difficult. For this reason, little is known about their consumption, although they likely contribute a large part of the daily polyphenol intake. They also share common physicochemical properties: they form stable complexes with metal ions and with proteins and are, like other polyphenols, good reducing agents. Many of their biological effects of nutritional interest derive from these properties. As metal ion chelators, they influence the bioavailability of several minerals. The nutritional significance of the non-specific complexation of proteins is less clear. As reducing agents, they may participate in the prevention of cancers, both of the digestive tract and inner organs. They may also protect LDLs against oxidation and inhibit platelet aggregation and therefore prevent cardiovascular diseases. In vitro, animal and human studies on the prevention of these chronic diseases are reviewed with particular attention to wine and tea polyphenols. The lack of data on their bioavailability and the paucity of human studies are emphasised.

© 2000 Society of Chemical Industry

Proanthocyanidins and tannin-like compounds – nature, occurrence, dietary intake and effects on nutrition and health

Copigmentation is a solution phenomenon in which pigments and other noncolored organic components form molecular associations or complexes. It generally results in an enhancement in the absorbance and in some cases, a shift in the wavelength of the maximum absorbance of the pigment. Copigmentation has not previously been taken into account in traditional wine color measures, in the relationship between color and pigment analysis, or in spectrophotometric assays for anthocyanin content. It is now apparent that copigmentation can account for between 30 and 50% of the color in young wines and that it is primarily influenced by the levels of several specific, noncolored phenolic components or cofactors. Copigmentation is of critical importance in understanding the relationship between grape composition and wine color, the variation in color and pigment concentration between wines, and in all reactions involving the anthocyanins during wine aging. This review focuses on the importance of the individual pigments and cofactors, the strength of their interactions, and their relative abundance in grapes and wines. A simple mathematical analysis of the solution equilibrium is developed to explain the nonlinear deviation from Beer’s law. When solved for typical wines, this function provides estimates of the apparent association constant, K, and the apparent molar extinction of the copigmented form, Ec, in natural mixtures. These measures allow the fraction of the anthocyanins which is in the copigmented form to be estimated. The significance of this phenomenon on pigment extraction and color retention during fermentations, on the rate of subsequent pigment polymerization, on the possible protection of anthocyanins from oxidation, and in the possible involvement on perceived mouthfeel and astringency of wines are suggested. Aspects of the copigmentation phenomenon that are poorly understood are identified and some research directions are suggested.

The copigmentation of anthocyanins and its role in the color of red wine: A critical review

40 compounds structurally related to the plant flavonol quercetin were tested for mutagenic activity in Salmonella typhimurium strain TA98. 10 flavonols, quercetin, myricetin, rhamnetin, galangin, kaempferol, tamarixetin, morin, 3'-O-methylquercetin, 7,4'-di-O-methylquercetin and 5,7-di-O-methyl-quercetin, exhibited unequivocal mutagenic activity. 4 compounds, quercetin, myricetin, rhamnetin and 5,7-di-O-methylquercetin, were active without metabolic activation, although metabolic activation markedly enhanced their activity. All 4 have free hydroxyl groups at the 3' and 4' positions of the B ring. The other active compounds required an in vitro rat-liver metabolizing system for significant activity. Structural features which appear essential for mutagenic activity in this strain are a basic flavanoid ring structure with (1) a free hydroxyl group at the 3 position, (2) a double bond at the 2, 3 position, (3) a keto group at the 4 position, and (4) a structure which permits the proton of the 3-hydroxyl group to tautomerise to a 3-keto compound. The data are consistent with the requirement for a B ring structure that permits oxidation to quininoid intermediates. Free hydroxyl groups in the B ring are not essential for activity if a rat-liver metabolic activating system is employed. Data from 12 compounds which differ only at the essential sites described above indicate that the structural requirements for mutagenicity in strain TA100 are the same as those for activity in strain TA98. Based on the above structural requirements, a metabolic pathway for flavonol activation to DNA-reactive species is proposed.

Leonard Jurd

Papers

Mutagenicity of plant flavonoids: structural requirements for mutagenic activity in Salmonella typhimurium.

The formation of metal and “co-pigment” complexes of cyanidin 3-glucoside

Antimicrobial properties of 6,7-dihydroxy-, 7,8-dihydroxy-, 6-hydroxy- and 8-hydroxycoumarins

Anthocyanidins and related compounds—XI: Catechin-flavylium salt condensation reactions

The formation of xanthylium salts from proanthocyanidins