Antioxidant flavones

Fig. (2). General structures of antioxidant flavones, flavonols and anthocyanidins.

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Ferreres F, Sousa C, Valentao P, Andrade PB, Seabra RM and Gil-Izquierdo A. 2007b. New C-deoxyhexosyl flavones and antioxidant properties of Passiflora edulis leaf extract. J Agric Food Chem 55(25) 10187-10193. 

The application of flavonoids for the treatment of various diseases associated with free radical overproduction is considered in Chapter 29. However, it seems useful to discuss here some studies describing the activity of flavonoids under certain pathophysiological conditions. Oral pretreatment with rutin of rats, in which gastric lesions were induced by the administration of 100% ethanol, resulted in the reduction of the area of gastric lesions [157]. Rutin was found to be an effective inhibitor of TBAR products in the gastric mucosa induced by 50%i ethanol [158]. Rutin and quercetin were active in the reduction of azoxymethanol-induced colonic neoplasma and focal area of dysplasia in the mice [159], Chemopreventive effects of quercetin and rutin were also shown in normal and azoxymethane-treated mouse colon [160]. Flavonoids exhibited radioprotective effect on 7-ray irradiated mice [161], which was correlated with their antioxidative activity. Dietary flavones and flavonols protected against the toxicity of the environmental contaminant dioxin [162], Rutin inhibited ovariectomy-induced osteopenia in rats [163],... 

Synthetic analogues or derivatives of a-tocopherol which have better antioxidant properties can be introduced. Many natural antioxidants such as flavonols, flavones, tea leaf catechins, rosemary antioxidants and spice extracts have been reported to be more active than BHA, BHT or the tocopherols in model systems. The food applications of these compounds need to be explored further. 

The raison d etre for the proliferation of flavone and flavonol glycosides in nature continues to intrigue plant scientists. The ability of UV-B radiation to damage DNA, RNA, and proteins as well as to impair processes like photosynthesis is well known. Most flavonoids are very efficient antioxidants and chemoprotectants, and are therefore used in a plethora of food supplements and nutraceuticals [30]. Some flavonoids, however, have a Janus face - they could be excellent antioxidants but also have negative features. 

Bohm, FI. et al., Flavonols, flavone and anthocyanins as natural antioxidants of food and their possible role in the prevention of chronic diseases, Z. Ernahrungsw., 37, 147, 1998. 

The major types of bioactive constituents reported from Broussonetia papyrifera are the prenylated flavonoids, which include compounds of the diphenylpropane, chalcone, flavan, flavanone, flavone, flavonol, and aurone classes (Table 2), Fig. (7). An early study on B. papyrifera resulted in the isolation of two diphenylpropanes, broussonins A (29) and B (30), and a coumarin, marmesin (52), with antifungal activity [39]. Also, a diprenylated diphenylpropane derivative, kazinol F (31) [40], was reported as an antioxidant and tyrosinase inhibitory constituent [34]. 

Abbot, J. and Waite, R. 1962. The effect of antioxidants on the keeping quality of whole milk powder. I. Flavones, gallates, butylhydroxyanisole and nordihydroguaiaretic acid. J. Dairy Res. 29, 55-61. 

Quercetin and many 3-hydroxylated flavones, particularly those containing o- or />-quinol structure at ring C, such as (66), are strong antioxidants for unsaturated fatty acids and lipids of vegetable tissues [349-352]. The effect of antioxidant action is decreased when some of the hydroxy groups are methylated [353],... 

Different model systems and different methods are used to evaluate the antioxidant properties of flavonoids. The stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), which changes color after being reduced by an antiradical compound, was employed to study the antioxidant properties of isoflavones genistein (42) and daidzein (40), flavones apigenin (23) and lute-... 

Flavonols and flavones are present in many food products and medicinal plants and show relevant antioxidant activity in vitro. In this chapter, classical analytical methods sueh as thin layer ehromatography and two-dimensional paper chromatography together with modem methodologies such as HPLC-MS-MS are reported. Preparative ehromatography methods are also reviewed as well as spectroseopie methods used for flavonoid characterization and identification, including UV spectrophotometry and MS spectrometry. Chemical and enzymatic methods used in flavonoid identification are also reviewed. 

Flavones and flavonols are relevant phytochemicals in food products, spices and medicinal plants. They are secondary metabolites belonging to the polyphenols group, and have in common the general structure of two aromatic rings and often more than three phenolic hydroxyls. Flavones and flavonols often show high antioxidant activity in vitro, and they complex metal ions and scavenge free radicals. They have a planar structure that allows intermolecular interactions and stacking in... 

Flavones show antioxidant activity in different models. They neutralize free radicals, complex iron ions, and can prevent lipid oxidation (Pietta, 2000). This antioxidant activity is related to the phenolic hydroxyls present on the flavone nucleus, and the presence of ortho-dihydroxyl grouping (catechol groups) is known to be particularly effective for antioxidant activity. Conjugations with sugars always decrease the antioxidant activity, but can have positive effects on the solubility of the flavonoids in aqueous systems. 

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