Structure-antioxidant activity relationships of flavonoids and phenolic acids

Antioxidant properties of phenolic compounds

Polyphenols constitute one of the most numerous and ubiquitous groups of plant metabolites and are an integral part of both human and animal diets. Ranging from simple phenolic molecules to highly polymerized compounds with molecular weights of greater than 30,000 Da, the occurrence of this complex group of substances in plant foods is extremely variable. Polyphenols traditionally have been considered antinutrients by animal nutritionists, because of the adverse effect of tannins, one type of polyphenol, on protein digestibility. However, recent interest in food phenolics has increased greatly, owing to their antioxidant capacity (free radical scavenging and metal chelating activities) and their possible beneficial implications in human health, such as in the treatment and prevention of cancer, cardiovascular disease, and other pathologies. Much of the literature refers to a single group of plant phenolics, the flavonoids. This review offers an overview of the nutritional effects of the main groups of polyphenolic compounds, including their metabolism, effects on nutrient bioavailability, and antioxidant activity, as well as a brief description of the chemistry of polyphenols and their occurrence in plant foods.

Polyphenols: Chemistry, Dietary Sources, Metabolism, and Nutritional Significance

The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is approximately 1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 microM after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.

Dietary Intake and Bioavailability of Polyphenols

Phenolic compounds in plants and agri-industrial by-products: Antioxidant activity, occurrence, and potential uses

The phenolic antioxidant phytochemicals in wines have been implicated for the lower rates of cardiac disease mortality among people drinking wine regularly in certain European populations. The activities of 20 selected California wines in inhibiting the copper-catalyzed oxidation of human lowdensity lipoproteins (LDL) were determined. This antioxidant activity was related to the major phenolic compounds and not to resveratrol analyzed in wines by HPLC and GC-MS. The relative inhibition of LDL oxidation varied from 46 to 100% with the red wines and from 3 to 6% with the white wines. When compared at the same total phenol concentration, the inhibition of LDL oxidation varied from 37 to 65% with the red wines and from 27 to 46% with the white wines. The relative antioxidant activity correlated with total phenol contents of wines (r = 0.94) and with the concentrations of gallic acid (r = 0.921, catechin (r = 0.761, myricetin (r = 0.701, quercetin (r = 0.681, caffeic acid (r = 0.631, rutin (r = 0.50), epicatechin (r = 0.451, cyanidin (r = 0.431, and malvidin 3-glucoside (r = 0.38). Therefore, the activity of wines to protect LDL from oxidation appeared to be distributed widely among the principal phenolic compounds.

Principal Phenolic Phytochemicals in Selected California Wines and Their Antioxidant Activity in Inhibiting Oxidation of Human Low-Density Lipoproteins

Current research suggests that wine contains substances that may reduce the mortality rate from coronary diseases. The oxidation of low-density lipoprotein (LDL) is thought to be a key step in the development of atherosclerosis. Phenolic fractions of a Petite Syrah wine were evaluated for their antioxidant activity in inhibiting LDL oxidation in vitro. The more active fractions contained components of the catechin family. The catechin oligomers and the procyanidin dimers (B 2 , B 3 , B 4 , B 6 , B 8 ) and trimers (C 1 , C 2 ) were extracted, isolated and purified from grapes seeds. These compounds were tested for their inhibition of LDL oxidation, along with other monomeric wine phenolics. The procyanidin dimers B 2 and B 8 , and trimer C 1 , and the monomers catechin, epicatechin and myricetin had the highest antioxidant activity. The procyanidin dimers B 3 , B 4 and C 2 and the monomers gallic acid, quercetin, caffeic acid, and rutin, and a group of compounds that included the dimer B 6 , ellagic acid, sinapic acid, cyanidin had lower antioxidant activity and α-tocopherol had the least activity. Thus, the numerous phenolic compounds found in wine are potent antioxidants in inhibiting LDL oxidation in vitro.

Inhibition of in vitro human LDL oxidation by phenolic antioxidants from grapes and wines

Delayed tumor onset in transgenic mice fed an amino acid-based diet supplemented with red wine solids.

En 1992, le Groupe Amorim a cree l'Academie Amorim, un lieu d'echanges entre oenologues, ingenieurs, professeurs, sommeliers, auteurs, artistes... tous animes d'une meme passion du vin. Chaque annee, cette Academie encourage et soutient la recherche en oenologie par la remise d'un Prix a un chercheur ou a une equipe de chercheurs ayant fait paraitre des travaux significatifs qui concourent a la defense de la qualite du vin. Cette annee, une « Mention d'Honneur » a ete decernee aux travaux d'une equipe, reunissant des chercheurs americains et francais, sur les liens controverses du vin et de la sante. De nombreuses enquetes epidemiologiques realisees au cours des vingt dernieres annees dans les pays industrialises ont confirme que les populations consommatrices de vin presentaient des taux bas de mortalite par les maladies cardio-vasculaires.

Pierre L. Teissedre

Papers

Principal Phenolic Phytochemicals in Selected California Wines and Their Antioxidant Activity in Inhibiting Oxidation of Human Low-Density Lipoproteins

Inhibition of in vitro human LDL oxidation by phenolic antioxidants from grapes and wines

Delayed tumor onset in transgenic mice fed an amino acid-based diet supplemented with red wine solids.

Composés phénoliques du raisin et du vin et santé