Antioxidative functions

Selection of Proper Antidegradant. Because the various antioxidants function by different mechanisms, an antioxidant under one condition may become an oxidation promoter in a different condition. Therefore, an antioxidant should be carefully selected depending on service requirements. Most antioxidants are either amines, phenols, or phosphates. The following are some important properties in the selection of proper antidegradant that should be considered. 

Ultraviolet light absorbers will be discussed in more detail under another section. Suffice it to say that their incorporation into a polymer can provide a useful antioxidant function. 

In antioxidants, synergism appears to arise either from one antioxidant effectively regenerating another so that the latter does not become consumed or by the two antioxidants functioning by differing mechanisms. The latter is more important and it is easy to see how effective a combination of peroxide decomposer and chain-breaking antioxidant can be. 

When two antioxidants are used together, a synergistic improvement in activity usually results. Synergism can arise from three combinations (1) homosynergism — two chemically similar antioxidants (for instance, two hindered phenols) (2) autosynergism — two different antioxidants functions that are present in the same molecule (3) heterosynergism — the cooperative effect between mechanistically different classes of antioxidants, such as the combined effect of primary and secondary antioxidants. Thus, combinations of phenols and phosphites are widely used to stabilize synthetic rubbers. 

A cooperative interaction between two or more antioxidants (or antioxidant function) that leads to an overall antioxidant effect greater than the sum of the individual effects of each antioxidant is referred to as synergism. Synergism can be achieved in different ways. It may arise from the combined action of two chemically similar antioxidants, e.g., two hindered phenols (homosynergism), or when two different antioxidant functions are present in the same molecule (autosynergism) the latter is exemplified by many commercial antioxidants (e.g., Irgastab 2002, AO 29 Table lb), which have CB and UVA activity. 

In 1922, Evans and Bishop named the animal nutritional factor essential of reproduction Vitamin E . In the 1960s, vitamin E was associated with antioxidant function. Twenty-five years later, vitamin E has been found to possess functions that are independent of its antioxidant and free radical scavenging ability. a-Tocopherol specific molecular mechanisms were discovered which are still under investigation. 

Besides all the sensory and texturizing properties, GA has interesting antioxidant properties such as an efficient capacity for deactivation of excited electronic states and moderated radical scavenging capacity. There is increasing experimental evidence that associate the antioxidant function with its protein fraction, mainly by amino acid residues such as histidine, tyrosine and lysine, which are generally considered as antioxidants molecules (Marcuse, 1960,1962 Park et al., 2005). 

The antioxidant property of ferulic acid and related compounds from rice bran was reported by Kikuzaki et al, (2002). Their results indicated that these compounds elicit their antioxidant function through radical scavenging activity and their affinity with lipid substrates. Another recent study reported by Butterfield et al, (2002) demonstrated that ferulic acid offers antioxidant protection against hydroxyl and peroxyl radical oxidation in synaptosomal and neuronal cell culture systems in vitro. The effect of ferulic acid on blood pressure (BP) was investigated in spontaneously hypertensive rats (SHR). After oral administration of ferulic acid the systolic blood pressure (SBP) decreased in a dose-dependent manner. There was a significant correlation between plasma ferulic acid and changes in the SBP of the tail artery, suggesting... 

McGraw, K.J., The antioxidant function of many animal pigments are there consistent health benefits of sexually selected colourants Anim. Behav., 69, 757, 2005. 

Mulder, T.P.J., Verspaget, H.W., Janssens, A.R., de Bruin, P.A.F., Pena, A.S. and Earners, C.B.H.W. (1991). Decrease in two intestinal copper/zinc containing proteins with antioxidant function in inflammatory bowel disease. Gut 32, 1146-1150. 

Vitamin E, being first reported barely a century ago, is the biologically most important fat-soluble antioxidant and has become a commodity product and bulk chemical in the meantime. Besides its antioxidant function, several nonantioxidant actions of the compound have been recently identified and new ones are still being discovered.1... 

Krinsky, N. I. 1989. Antioxidant functions of carotenoids. Free Radic. Biol. Med. 7 617-35. 

Higdon JV and Frei B. 2003. Tea catechins and polyphenols health effects, metabolism, and antioxidant functions. Crit Rev Food Sci Nutr 43(1) 89—143. Review. 

Skulachev [117] proposed that the released cytochrome c oxidizes superoxide and, by this, exhibits an antioxidant function. This proposal was supported by recent experimental findings by Atlante et al. [118], who suggested that cytochrome c released from mitochondria by oxygen species protected mitochondria through a feedback-like process oxidizing superoxide. The most important physiological inhibitor of apoptosis is multifunctional protein Bcl-2,... 

Laskin, D.L. et al., Prooxidant and antioxidant functions of nitric oxide in liver toxicity, Antioxid. Redox. Signal, 3, 261, 2001. 

Sunda WG, Kieber D, Kiene R, Huntsman S (2002) An antioxidant function for DMSP and DMS in marine algae. Nature 418 317-320... 

Antioxidants act so as to interrupt this chain reaction. Primary antioxidants, such as hindered phenol type antioxidants, function by reacting with free radical sites on the polymer chain. The free radical source is reduced because the reactive chain radical is eliminated and the antioxidant radical produced is stabilised by internal resonance. Secondary antioxidants decompose the hydroperoxide into harmless non-radical products. Where acidic decomposition products can themselves promote degradation, acid scavengers function by deactivating them. 

Manganese performs significant antioxidative functions. It is included in the structure of Mn-dependent superoxide dismutase which is the only antioxidant based directly in the mitochondria where the intensive processes of oxidation and ATP synthesis occur. The Mn-dependent superoxide dismutase protects the mitochondria from oxidant stress. 

Another example is the tissues that are particularly rich in vitamin C, for example, the cortex of the suprarenal gland or the lens here, vitamin C fulfills both antioxidative functions and metabolic ones as it helps in the formation of collagen structures. Approximately 40% of the body s ascorbate is stored in skeletal muscle because this tissue is relatively abundant and its cellular concentration is tenfold higher than the plasma level. Similarly, the intracellular ascorbate concentration in the brain (3 mM) greatly exceeds the level in the extracellular fluid (200-400 zM). The majority of ascorbate is stored in the astroglial cells that are capable of reducing great quantities of DHAA to ascorbate, which then becomes available for release back into the extracellular fluid. 

Addition of an antioxidant to fuel will inhibit the fuel oxidation process most antioxidants function at treat rates from 5 to 50 ppm... 

Carotenoids produced in plants are used as colorants in foods and aiflmal feeds and can also have an antioxidant function. Production of phytoene synthase is the first committed step towards carotenoid biosynthesis in plants. When phytoene synthase is produced in B. napus, a 50-fold increase in carotenoid expression results. Therefore Brassica... 

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