Antioxidant activity of phenols

PEYRAT-MAiLLARD M N, BONNELY s and BERSET c (2000) Determination of the antioxidant activity of phenolic compounds by coulometric detection, Talanta, 51, 709-16. 

The stability of oxygen-centered radicals has been studied repeatedly in recent years in search of quantitative descriptors of antioxidant activity. The antioxidant activity of phenols is indeed so well correlated with O - H BDEs and the ionization potential that these two energies can be used as the guiding... 

The antioxidant activity of phenolic substances makes them easily prone to oxidation. Thus, the analytical techniques must be aimed at not applying pH and temperature variations that cause oxidation. 

Heinonen, M. et al., Effect of protein on the antioxidant activity of phenolic compounds in a lecithin-liposome oxidation system, J. Agric. Food Chem., 46, 917, 1998. 

Stalmach A, Mullen W, Nagai C, Crozier A. On-line HPLC analysis of the antioxidant activity of phenolic compounds in brewed, paper-filtered coffee. Brazilian Journal of Plant Physiology. 2006 18(1) 253-262. 

Utkina, N. K., Makarchenko, A. E., Shchelokova, . V., and Virovaya, M. V. (2004). Antioxidant activity of phenolic metabolites from marine sponges. Chem. Nat. Compd. 40,... 

Foti, M., Piattelli, M., Amico, V., and Ruberto, G. 1994. Antioxidant activity of phenolic meroditerpenoids from marine algae. J. Photochem. Photobiol. B Biol., 26, 159-164. 

BCristinova, V. Mozuraityte, R. Storro, I. Rustad, T. 2009. Antioxidant activity of phenolic acids in lipid oxidation catalyzed by different prooxidants. J. Agric. Food Chem. 57 10377-10385. 

The antioxidant activity of phenolic acids and their esters depends on the number of hydroxyl groups in the molecule, and this would be strengthened by steric... 

Direct Measurements—UVNIS Techniques. The conjugated diene (CD) formed among the polyene hydroperoxide products that are formed as a result of oxidation of polyunsaturated fatty acids (PUFAs) have a UV absorbance that can be monitored to follow the progress of the oxidation. The effect of antioxidants on the suppressed rate of product formation can be followed with time. For example, conjugated dienes from oxidation of linoleate lipid molecules absorb at 234 nm and can be monitored directly , or else after HPLC separation (via normal phase or reverse phase j of the individual isomers. In order to use these findings to calculate the antioxidant activity of phenols and relate it to oxygen uptake studies (equations 7 and 14), one also has to make a correction to account for loss of absorbance due to loss (from decomposition) of hydroperoxides (equation 22) . 

Quantitative kinetic studies of absolute rate constants for hydrogen atom transfer from substituted phenols to polystyrene peroxyl radicals by Howard and Ingold in the 1960s provided the first reliable data on substiment effects on antioxidant activities of phenols. Later, a very detailed report appeared providing data on substituent and structural effects on various classes of monohydroxy phenols. In addition, detailed reviews were given of substituent etfects ". These reports provide the basis for understanding how substituent and strucmral effects control the antioxidant activities of phenols and will be summarized in part below. 

TABLE 10. Antioxidant activities of phenolic antioxidants in different media... 

Calculations of molecular geometry are important when intramolecular hydrogen bonding is involved, and more complex, polycyclic molecules are being considered for calculations, such as the flavonoids. Some specific examples will be reviewed briefly to illustrate how the various methods have been applied to elucidate the mechanisms and in particular predict the effects of substituents and overall structure on the antioxidant activities of phenols. 

The antioxidant activity of phenolic compounds is related to their structure, in particular the number of hydroxy-substituents in the aromatic ring and the nature of the substituents in the para or ortho position. In particular the addition of a hydroxyl or methoxy group in the ortho position increases the antioxidant activity due to a strong electron delocalizing effect and this helps to... 

Gunduc, N. and El, S.N., Assessing antioxidant activities of phenolic compounds of common Turkish food and drinks on in vitro low density lipoprotein oxidation, J. Food Sci., 68, 2591-2595, 2003. 

Luximon-l amma A, Bahorun T, Soobrattee MA, Aruoma OI. (2002). Antioxidant activities of phenolic, proanthocyanidin, and flavonoid components in extracts of Cassia fistula. J. Agric. Food Chem, Vol. 50, pp. 5042-5047... 

The antioxidant activity of phenols used and standards was determined according to die ferric thiocyanate method with minor modifications. Each sample of treated wool (200 mg) was mixed with 2 mL distiUed water and 5 mL linoleic acid emulsion (0.02 M, pH 7.0) and 5 mL phosphate bufier (0.2 M, pH 7.0). Linoleic acid emulsion was prepared by mixing 0.5608 g of linoleic acid with 0.5608 g of Tween 20 as emulsifier, and 100 mL phosphate buffer (0.2 M, pH 7.0), and then the mixture was homogenised. The reaction mixture was incubated at 37 C. Aliquots of 0.1 mL wm taken at different intervals during incubation. The degree of oxidation was measured by sequentiaUy adding 4.7 mL ethanol (75%), 0.1 mL ammonium diiocyanate (30 %), 0.1 mL sample solution and 0.1 mL ferrous chloride (0.02 mg, in 3.5% HCl). The mixture was... 

Table 10.13. Effect of bovine semm albumin (BSA) on inhibition (%) of lipid and protein oxidation on the antioxidant activity of phenolic compounds (5 /uM) in lecithin...

Han, D., Yi, O-S. and Shin, H-K. Solubilization of vitamin C in fish oil and synergistic effect with vitamin E in retarding oxidation. J. Am. Oil Chem. Soc. 68, 740-743 (1991). Heinonen, M., Rein, D., Satue-Gracia, M.T., Huang, S-W., German, J.B. and Frankel, E.N. Effect of protein on the antioxidant activity of phenolic compound in a lecithin-Uposome oxidation system. J. Agric. Food Chem. 46, 917—922 (1998). 

Several recent studies have produced mixed results in indicating in vivo antioxidant activity of phenolic compounds in red wine. However, the results of these studies are unconvincing because non-specific assays were used for antioxidant action that may be inadequate due to the confounding and indirect effects of many semm and plasma components. The effect of in vivo supplementation of polyphenols in red wine on the oxidizability of LDL cannot be tested ex vivo because, like vitamin C, these hydrophilic compounds are removed from LDL during isolation from plasma (Table 13.6). Not surprisingly red wine consumption showed no effect on LDL oxidation ex vivo. 

Zou, K., and R.-Y. Zhang Constituents from Glycyrrhiza inflata and Antioxidant Activities of Phenols from the Roots of Glycyrrhiza Spp. (Abstract of Master thesis of K. Zou). J. Chin. Pharm. Sci., 3, 90 (1994) Chem. Abstr., 122, 51291r (1995). 

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