Phenolic antioxidants, from plants

WILLIAMSON G, FAULKNER K, PLUMB G w (1998) Glucosuiolates and phenolics as antioxidants from plant foods. Eur J Cancer Prev. 7 17-21. 

Surveswaran S, Cai YZ, Corke H and Sun M. 2007. Systematic evaluation of natural phenolic antioxidants from 133 Indian medicinal plants. Food Chem 102(3) 938-953. 

During the course of screening antioxidants from plants, Baek et al. isolated a neolignan from the bark of M. officinalis [37]. A biphenyl compound, 5, 5 -di-2-propenyl-2-hydroxy-3, 2, 3 -trimethoxy-l-l -biphenyl (15), was found to have antioxidant activity similar to commercial synthetic antioxidants 2, 6-di-ter/-butyl-4-methylphenol (BHT) or 3-tert-butyl-4-hydroxyanisole (BHA). Antioxidants are compounds that inactivate free radicals in the body. Free radicals can cause cancer since it can promote the growth of cells by initiating spontaneous mitosis. Furthermore, phenolic antioxidants in wine, especially resveratrol (16), have demonstrated the ability to inhibit human low density lipid (LDL) oxidation in vitro [38]. Frankel mentions other studies suggesting... 

In the first published works, synthetic antioxidants like BHT, BHA, PEG, etc. were studied. Nevertheless, their presence in food is questionable due to potential risks and they require strict legislative control. An alternative that is being studied widely is the use of phenolic type natural antioxidants from plant species, including both integral extraets obtained by diverse methods and their purified components (such as catechin, quercetin, caffeic acid, etc.) obtained by chemical synthesis. 

Phytochemicals or phytonutrients are bioactive substances that can be found in foods derived from plants and are not essential for life the human body is not able to produce them. Recently, some of their characteristics, mainly their antioxidant capacity, have given rise to research related to their protective properties on health and the mechanisms of action involved. Flavonoids are a diverse group of phenolic phytochemicals (Fig. 6.1) that are natural pigments. One function of flavonoids is to protect plants from oxidative stress, such as ultraviolet rays, environmental pollution, and chemical substances. Other relevant biological roles of these pigments are discussed in other chapters of this book. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Other assays have been used to evaluate the antioxidant activity against H202 of several plant-based products, namely, fruit juices from different cultivars of berries (Wang and Jiao 2000), fractions rich in phenolics isolated from the aqueous by-products obtained during the milling of oil palm fruits (Balasundram and others 2005), cherry laurel fruit and its concentrated juice (Liyana-Pathirana and others 2006), and strawberries and blackberries treated with methyl jasmonate, allyl isothiocyanate, essential oil of Melaleuca alternifolia, and ethanol (Chanjirakul and others 2007). 

Parejo et al. (2004) identified caffeoyl-quinic acids, dicaffeoylquinic acids, flavonoids and rosmarinic acid among ten main antioxidant phenolic compounds from bitter fennel, F. vulgare, using a simple high-performance liquid chromatography (HPLC). Distilled fennel was found to contain a higher proportion of antioxidant phenolic compounds than non-distilled plant material. 

Oxidative transformations of hindered synthetic phenols and a-tocopherol are analogous to the oxidation of various mono- and dihydric phenols of plant origin. Natural phenols present in fruits or green tea leaves are oxidized on contact with air and/or during fermentation (a process characteristic of tea leaves) and are transformed into dark colored quinoid systems, not harmful for human beings. It may be extrapolated that trace amounts of discoloring quinones or quinone methides arising from phenolic antioxidants in plastics are harmless as well. 

Other Phenolic Antioxidative Compounds from Plants Higher plants are rich in a myriad of phenolic compounds in their secondary metabolite pool. Among these, phenolic acids and polyphenolic derivatives are found to be the most important series of hydrophilic-hydrophobic antioxidative compounds naturally present. In foods, these polyphenolic compounds act as radical scavengers... 

Antioxidants from Cereais, Oiiseeds, and Rotated Sources Seeds rich in oils are also abundant sources of various types of antioxidative compounds. Among these carotenoids, phenolic acids, and their derivatives, flavonoids, phytic acid, lignans, and tocopherols are predominantly found depending on the plant genera and species. Reviews by Wanasundara et al. (110) and Shukla et al. (111) discuss antioxidants of oilseeds and their products in detail. 

Fig. 2 Phenolic antioxidants isolated from plants 1. quercetin 2. silymarin 3. tranx-resveratrol 4. piceatanmol 5. chlorogenic acid methyl ester 6. l-(3, 4 -Dihydroxycinnamoyl)-cyclopenta-2,5-Diol 7. l-(3, 4 -Dihydroxycinnamoyl)-cyclopenta-2,3-Diol 8. kaempferol-3-O-neohespheridoside 9. 5,6,7,4 -Tetrahydroxyfiavonol-3-0-rutinoside 10. floribundones 1 11. fioribundones II 12. (-)-epicatechin-3-0-gallate and 13. curcumine. (From Refs. °l)...

Synthetic antioxidants, such as 2,6 di /art-butyl 4 methylphenol are not allowed in foods in Japan. In the United States they can be used in the wrapper around the cereal in small amounts, but not in the cereal itself. There is great interest in natural antioxidants that can be used to protect foods.28 That these natural phenols from plants may scavenge free radicals in the body and, thereby, reduce the incidence of heart attacks and cancer makes them especially important. Vitamin E (13.15) is the one that we must all have in our diets. 

Since water is perhaps the most environmentally friendly solvent available at high purity and low cost, it has been exploited for the extraction of avoparcin in animal tissue (53), fungicides in agricultural commodities (54), fragrances from clove (55), antioxidative compounds from sage (56), anthocyanins and total phenolics from dried red grape skin (48), and other bioactive compounds from plants (57). See also chapters 5 and 6 in this book uid a few review articles (51,58). 

Recent studies in biological systems have revealed the presence of a variety of compounds of many structural types that appear to function as antioxidants. The plant kingdom is especially rich in these materials (Larson, 1988). They include flavonoids and other phenolic compounds, alkaloids and other amines, reduced sulfur compounds, uric acid, ascorbic acid. Vitamin E, carotenoids, and many other substances. Often, their principal mechanism of action appears to be the quenching of peroxy radicals, removing them from the autooxidation chain. Vitamin E, for example, reacts with these radicals in a manner entirely analogous to that of BHT ... 

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