Polyphenol free-radical scavenging antioxidants

Rice-Evans C. Plant polyphenols free radical scavengers or chain-breaking antioxidants Biochem Soc Symp 1995 61 103-116. 

There are numerous other polyphenolic compounds possessing in vitro and in vivo antioxidative activity. Several examples of these compounds are cited below. One of nonflavonoid polyphenols of particular interest is resveratrol (3,5,4 -trihydroxy-Znmv-stilbcne, Figure 29.8), which has been identified as a potential cancer chemopreventive agent and an antimutagen [182]. It has been found that resveratrol is the efficient inhibitor of cyclooxygenase and the inhibitor of free radical-mediated cellular processes. For example, resveratrol is a better free radical scavenger than a-tocopherol or ascorbic acid but has nearly the same activity as... 

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

Benefits Japanese studies in the 1980s showed that the polyphenol components had antioxidant properties similar to superoxide dismutase (SOD), an enzyme that is a free radical scavenger and is thought to slow down the ageing process. The herb has less tannin than oriental tea, so tastes less bitter, and it is caffeine free. 

The quality of the phenol antioxidants was assessed by Vinson et al. (1999) using the IC50 for LDL + VLDL (very low density lipoprotein) oxidation, with smaller values indicating a higher quality. Quality of the antioxidants was due to free-radical scavenging activity and not chelation as the concentration of polyphenols for 50% inhibition was < 1 xM and cupric ion 25 xM in the oxidation medium. There was less percent variation within the groups for this parameter than for the total polyphenol content. The quality order was dark chocolate > cocoa > milk chocolate. The dark chocolate and cocoa were significantly different from the milk chocolate (p < 0.05), but not... 

Most stilbenoids possess antioxidant activities because they possess polyphenol functions in the molecules. Some of their beneficial effects, hepatoprotective action, cardiovascular protection, for instance, are in close relation to their antioxidant activities. Several models have been employed in the assay such as lipid peroxidation system, human low-density lipoprotein model, xanthine oxidase system and l,l-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging model, which is the most commonly used protocol. 

Commercial extracts of green tea are marketed for the prevention of heart disease and of cancer because of the powerful antioxidant and free radical scavenging properties of the polyphenols. In the case of heart disease it is known that in rats green tea extracts decrease plasma cholesterol and lipid levels. Epidemiological studies in Japan suggest a relationship between lower LDL-cholesterol and increased green tea drinking. 

As polyphenolic compounds, flavonoids have the ability to act as antioxidants by a free radical scavenging mechanism [140, 141, 142], This involves the formation of less reactive flavonoid phenoxyl radicals (Eq 1 and 2) on the other hand, through their known ability to chelate transition metals [143,144], these compounds may inactivate iron ions, and bivalent... 

Antioxidant plant polyphenols have received increasing attention of late owing to their multifunctional properties, which have been shown to be beneficial to human health. Antioxidant polyphenols are believed to reduce the risk of chronic diseases such as cancer, diabetes, and coronary heart disease. As each of these diseases is associated with long-term accumulation of cellular damage due to oxidative stress, the antioxidant and free radical scavenging activities of polyphenols are believed to underlie the beneficial actions of these substances in humans. 

Ningappa MB, Dinesha R, Srinivas L (2008) Antioxidant and free radical scavenging activities of polyphenol-enriched curry leaf (Murraya koenigii L.) extracts. Food Chem 106(2) 720-728... 

Details about structure, biosynthesis, and classification of phenolics are described in the other chapters in this handbook. Plant phenolics have a distinctive ability to form non-covalent, intermolecular complexes with each other and with both large and small molecules. Recognition of the antioxidant activities of many polyphenols has established correlation with the health benefits by such compounds [34]. This leads to the development of commercial products containing free-radical-scavenging phytochemical mixtures, for example, Pycnogenol (procyanidin extracted from Pinus maritima). Table 82.2 represents a list of polyphenolic compounds used in nutraceuticals and their biologic effects on human health. 

An infusion of the pods inhibited the in vitro proliferation of mouse hepatocellular tumor (Tl) cells and induced apoptosis in the cells. The crude polyphenol fraction of carob pods exhibits in vitro lipid peroxidation-inhibiting, antioxidant, and free radical scavenging activities. ... 

Naturally occurring compounds such as phytochemicals, which possess anticar-cinogenic and other beneficial properties, are referred to as chemopreventers. One of the predominant mechanisms of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. Among the most investigated chemopreventers are some vitamins, plant polyphenols, and pigments such as carotenoids, chlorophylls, flavonoids, and betalains. Resolution of the potential protective roles of... 

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