Antioxidant, action

The development of the autoxidation theory, in which the propagating radicals, alkyl, and alkylperoxyl (R ROO ), and the hydroperoxide (ROOH) are the key intermediates, has therefore led to a comprehensive theory of antioxidant action Scheme 2 shows the two major... 

Scheme 9 Oxidative transformation products formed during the antioxidant action of BHT.

SCOTT B c, BUTLER J, HALLIWELL B and ARUOMA o I (1993) Evaluation of the antioxidant actions of ferulic acid and catechins , Free Radical Res Commun, 19, 241-53. 

VEDAVANAM K, SRIJAYANTA s, o reilly j, RAMAN A, WISEMAN H. (1999) Antioxidant action and potential antidiabetic properties of an isoflavonoid-containing soyabean phytochemical extract (SPE). Phytother Res. 13 601-8. 

The use of real food systems for detailed studies of antioxidants is complicated by a large number of factors which are often unknown or cannot be controlled due to the complex nature of foods. Using simplified model systems, which mimic the main features of a given food system, or antioxidant assays for quantifying the antioxidant action, can be very helpful in clarifying the action of potential antioxidants (Aruoma, 1996 Moller et al, 1999 Prior and Cao, 1999 Frankel and Meyer, 2000). The extrapolation of conclusions based on the behaviour of model systems or antioxidant assays to real complex food systems should generally be done with great care, and should ideally be based on results from more than one model system or assay (Frankel and Meyer, 2000). 

The terminology describing the action of antioxidants is unfortunately not clear. Terms such as antioxidant power , antioxidant effectiveness , antioxidant ability , antioxidant activity , and antioxidant capacity are often used interchangeably and without discrimination. Here we use the term antioxidant activity as meaning a measure of the rate of antioxidant action, and the term antioxidant capacity as meaning a measure of the extent of antioxidant action, i.e. the amount of radicals or intermediates and products produced during oxidation that are quenched by a given antioxidant. Thus antioxidant activity is related to the kinetics of the antioxidant action and antioxidant capacity to the stoichiometry. 

Quantification of antioxidant action usually relies on the reducing ability of antioxidants, measured either by electron transfer, reaction [16.15], or by hydrogen atom transfer reactions, reaction [16.16] ... 

ARUOMA o I (1996) Assessment of potential prooxidant and antioxidant actions, 73, 1617-25. 

The ability of carotenoids to act as antioxidants is closely related to their long-chain conjugated polyene structures (see Section 2.2 in Chapter 2). Two main types of antioxidant actions can be distinguished singlet oxygen quenching and reactions with radicals. The first mechanism occurs in vivo in plants and has been extensively studied in vitro. Reactions with radicals of different types have also been extensively studied in vitro under different conditions but their occurrence in vivo is still a matter of discussion. 

As mentioned earlier, physiological concentrations of carotenoids in vivo are in the micromolar range, mainly because of limited bioavailabiUty. Also, the antioxidant efficiencies of carotenoids after absorption are probably limited. Concentrations before absorption are much higher and can justify possible antioxidant actions in vivo. To test this hypothesis, Vulcain et al. developed an in vitro system of lipid peroxidation in which the oxidative stress is of dietary origin (metmyoglobin from meat) and different types of antioxidants (carotenoids, phenols) are tested. 

Vulcain, E. et al.. Inhibition of the metmyoglobin-induced peroxidation of hnoleic acid by dietary antioxidants action in the aqueous versus lipid phase. Free Rad. Res., 39, 547, 2005. 

Colorant containing annatto and Ca caseinate as carrier mixed with water to be added directly to cheese milk yielding uniform colored cheese mass Water-dispersible beadlet of p-carotene is mixed with oil to attein composition that remains stable even in presence of polyphosphates and with antioxidant action even in absence of ascorbic acid Blending carotenoid pigment and soybean fiber (wifii tomato juice) as effective ingredient for dispersion stability... 

Liebler, D.C. et al.. Antioxidant actions of beta-carotene in liposomal and microsomal membranes role of carotenoid-membrane incorporation and alfa-tocopherol, Arch. Biochem. Biophys., 338, 244, 1997. 

Wasil, M., Halliwell, B., Flutchinson, D. and Baum, FI. (1987). The antioxidant action of human extracellular fluids. Biochem. J. 243, 219-223. 

Scheme II.1 Mechanism of antioxidant action. After Grassie and Scott [1]. From N. Grassie and G. Scott, Polymer Degradation and Stabilisation, Cambridge University Press, Cambridge (1988). Reproduced by permission of Cambridge University Press...

In most assays designed to study antioxidant action of carotenoids, the effects of carotenoids were followed for a relatively short periods of time, while carotenoids were still present at substantial concentrations. Carotenoids, such as [1-carotene, lutein, and zeaxanthin, undergo rapid degradation upon exposure to oxidants or irradiation with ultraviolet and visible light (Ojima et al 1993 Siems et al 1999, 2005). 

Rozanowska, MB, Bigaj, J, Boulton, ME, Czuba-Pelech, B, Landrum, J, Rozanowski, B, and Zareba, M, 2004b. Uptake of carotenoids and their antioxidant action in ARPE-19 cells in culture. Invest Ophthalmol Vis Sci 45, U531. 

Plumb GW, Chambers SJ, Lambert N, Bartolome B, Heaney RK, Wangatunga S, Aruoma OI, Halhwell B and Wilhamson G. 1996b. Antioxidant actions of fruit, herb and spice extracts. JFood Lipids 3 171-178. 

Luximon-Ramma A, Bahorun T and Crozier A. 2003. Antioxidant actions and phenolic and vitamin C contents of common Mauritian exotic fruits. J Sci Food Agric 83(5) 496-502. 

CL accompanies many reactions of the liquid-phase oxidation of hydrocarbons, ketones, and other compounds. It was discovered in 1959 for liquid-phase ethylbenzene oxidation [219,220]. This phenomenon was intensively studied in the 1960s and 1970s, providing foundation for several methods of study of oxidation, decay of initiators, and kinetics of antioxidant action [12,17,221], Later this technique was effectively used to study the mechanism of solid polymer oxidation (see Chapter 13). 

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