Structure-antioxidant activity relationships of flavonoids and phenolic acids

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

Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study.

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

Resveratrol, a constituent of red wine, has long been suspected to have cardioprotective effects. Interest in this compound has been renewed in recent years, first from its identification as a chemopreventive agent for skin cancer, and subsequently from reports that it activates sirtuin deacetylases and extends the lifespans of lower organisms. Despite scepticism concerning its bioavailability, a growing body of in vivo evidence indicates that resveratrol has protective effects in rodent models of stress and disease. Here, we provide a comprehensive and critical review of the in vivo data on resveratrol, and consider its potential as a therapeutic for humans.

Therapeutic potential of resveratrol: the in vivo evidence.

Inhibition of oxidation of human low-density lipoprotein by phenolic substances in red wine

This study was aimed at evaluating the effectiveness of alpha- and gamma-tocopherols in inhibiting the formation and decomposition of hydroperoxides in bulk corn oil stripped of natural tocopherols and in 10% oil-in-water emulsion systems Whether alpha-tocopherol acted as an antioxidant or as a prooxidant depended on the test system, the concentration, the oxidation time, and the method used to determine lipid oxidation On the basis of hydroperoxide formation, alpha-tocopherol showed maximum antioxidant activity at 100 ppm in bulk oil and at 250-500 ppm in emulsions, while gamma-tocopherol showed maximum activity at 250-500 ppm in bulk oil but showed no significant difference in antioxidant activity between 250 and 1000 ppm in emulsions alpha-Tocopherol had a slight, initial prooxidant effect at 250 ppm or higher concentrations in bulk oil and at 500 ppm or higher concentrations in emulsions, whereas gamma-tocopherol showed no prooxidant activity in either system However, gamma-tocopherol showed less antioxidant activity than alpha-tocopherol at 100 ppm but higher antioxidant activity at higher concentrations in both systems In contrast to hydroperoxide formation, the ability of both alpha- and gamma-tocopherols in inhibiting hexanal formation improved with increased concentration and oxidation time

Antioxidant activity of alpha- and gamma-tocopherols in bulk oils and in oil-in-water emulsions

This study was aimed at evaluating the antioxidant effectiveness of α-tocopherol and its water-soluble analogue, Trolox, in different lipid systems. The oxidative stability of lipids in bulk and emulsion systems at 37 °C decreased in the order corn oil triglycerides > methyl linoleate > linoleic acid. In both bulk and emulsified linoleic acid, Trolox was a better inhibitor of hydroperoxide formation and decomposition than α-tocopherol. However, in bulk methyl linoleate and corn oil triglycerides, although Trolox was a better inhibitor of hydroperoxide formation, in emulsions, α-tocopherol was a better inhibitor of both the formation and decomposition of hydroperoxides. In emulsified methyl linoleate and corn oil, the partition coefficients of Trolox between lipids and water at high concentrations were not affected by Tween 20, and the antioxidant activity of Trolox decreased because it partitioned into the water phase and Tween 20 micelles. In contrast, in linoleic acid emulsified with Tween 20, the forma...

Antioxidant activity of α-tocopherol and Trolox in different lipid substrates : Bulk oils vs oil-in-water emulsions

The activity of alpha-tocopherol, Trolox, propyl gallate, gallic acid, methyl carnosoate, and carnosic acid was studied in two oil-in-water (o/w) emulsions, in two water-in-oil (w/o) emulsions, and in bulk oil with and without added emulsifiers. All antioxidants had either moderate or higher activity in bulk oil than in the emulsions. In most emulsions, the most polar antioxidants, propyl gallate and gallic acid, exhibited either prooxidant activity or no antioxidant activity. Methyl carnosoate was the most active antioxidant in w/o emulsions but was less active than Trolox in o/w emulsions. alpha-Tocopherol was less active in bulk oil than in emulsions, but its activity in bulk oil was markedly enhanced by the addition of o/w emulsifiers. Partitioning of antioxidants, hydrogen bonding, interphase transport, surface accessibility, and interaction of emulsifier with antioxidants are considered to be important parameters that determine antioxidant activity in lipid-containing systems.

Activities of antioxidants are affected by colloidal properties of oil-in-water and water-in-oil emulsions and bulk oils.

Lactoferrin is an iron transport protein present in human milk at an average concentration of 1.4 mg/mL. Commercially modified infant formulas based on cow's milk contain much lower amounts of lactoferrin (0.1 mg/mL lactoferrin) and soy based formulas have none. In addition to its role in iron transport, lactoferrin has bacteriostatic and bactericidal activities. Infant formulas are supplemented with relatively large amounts of iron (up to 12 mg/L). The effect of various concentrations of added lactoferrin and supplemental iron on lipid oxidation was tested in two different infant formulas. The extent of oxidation in the formulas as a function of time was determined by formation of hydroperoxides, production of hexanal, and fluorescence. On the basis of all three of these determinations, lactoferrin acted as an antioxidant in the absence and presence of different concentrations of supplemented iron. Lactoferrin inhibited oxidation in a concentration-dependent manner even at concentrations beyond its capacity to bind iron at its two high affinity binding sites. Lactoferrin can be used, therefore, as a dual purpose additive in infant formulas and similar food products for its antioxidant and its antimicrobial properties.

J. B. German

Papers

Inhibition of oxidation of human low-density lipoprotein by phenolic substances in red wine

Antioxidant activity of alpha- and gamma-tocopherols in bulk oils and in oil-in-water emulsions

Antioxidant activity of α-tocopherol and Trolox in different lipid substrates : Bulk oils vs oil-in-water emulsions

Activities of antioxidants are affected by colloidal properties of oil-in-water and water-in-oil emulsions and bulk oils.

Lactoferrin in infant formulas: effect on oxidation.