Antioxidants free radical trapping

The exterior durabiHty of relatively stable coatings can be enhanced by use of additives. Ultraviolet absorbers reduce the absorption of uv by the resins and hence decrease the rate of photodegradation. Eurther improvements can be gained by also adding free-radical trap antioxidants (qv) such as hindered phenols and especially hindered amine light stabilizers (HALS). A discussion of various types of additives is available (113). 

The main function of vitamin E is as a chain-breaking, free radical trapping antioxidant in cell membranes and plasma lipoproteins. It reacts with the lipid peroxide radicals formed by peroxidation of polyunsaturated fatty acids before they can establish a chain reaction. The tocopheroxyl free radical product is relatively unreactive and ultimately forms nonradical compounds. Commonly, the tocopheroxyl radical is... 

The mechanistic basis of the neuroprotective activity of FAEE appears to rely not only on its general free-radical trapping or antioxidant activity per se, but also on its activity in mediating the induction of stress response proteins (HO-1 and F1SP72), cytoprotective (phase 2) proteins, and the parallel suppression of genes induced by pro-inflammatory cytokines, such as nitric oxide synthase (iNOS). 

D12. Durken, M., Agbenu, J., Finckh, B., Hubner, C., Pilchmeier, U., Zeller, W., Winkler, K., Zander, A., and Kohlschutter, A., Deteriorating free radical-trapping capacity and antioxidant status in plasma during bone marrow transplantation. Bone Marrow Transplant. 15, 757-762 (1995). 

K4. Kharb, S., Total free radical trapping antioxidant potential in pre-eclampsia. Int. J. Gynaecol. Obstet. 69,23-26 (2000). 

L4. Langley, S. C., Brown, R. K., and Kelly, F. J., Reduced free-radical-trapping capacity and altered plasma antioxidant status in cystic fibrosis. Pediatr. Res. 33, 247-250 (1993). 

Antioxidant in the lipid phase free radical trap... 

Antioxidants work by being a free-radical trap, i.e. they readily combine with oxygen free-radicals to produce stable compounds. Any compound which has this ability is a potential antioxidant. Of course, not all such compounds are suitable for use in foods to be used a compound has to be non-toxic and also must have legal approval. Some antioxidants are synthetic, a few are natural and a few are nature-identical. 

Gum bases normally contain a permitted antioxidant. Typically, buty-lated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) or toco-pherols are used. The reason that these substances are used is that the gum base is subject to oxidation, and antioxidants work because they act as free-radical traps. Oxidation normally occurs via a free-radical mechanism, and because of this, oxidation is a zero free energy process and relatively unaffected by the ambient temperature. 

Gray, D.A. Clarke, M.J. Baux, C. Bunting, J.P. Salter, A.M. 2002. Antioxidant aetivity of oat extraets added to human LDL particles and in free radical trapping assays. J. Cereal Sei. 36 209-218. 

In addition to its provitamin A role, p - carotene is a radical trapping antioxidant and may be nutritionally important in its own right both as an antioxidant and possibly also through direct actions that are independent of retinoids. Other carotenoids that occur in foods, and circulate in the bloodstream, also have free radical trapping activity, and, hence, potential metabolic significance, whether or not they are metabolic precursors of vitamin A. 

In order to improve the stability of synthetic diesels and biodiesels it is necessary to add free-radical trapping additives known as antioxidants (such as DTBHQ, lONOX 220, Vulkanox ZKF, Vulkanox BKF, and Baynox). Butylated hydroxy toluene (BHT) in particular prevents oxidation and radical polymerization reactions that can lead to diesel fuel ageing. 

Antioxidants are used to stabilize fats and fat-containing products against oxidation and thereby prolong their stability and storage time. An antioxidant (AH) acts as a free radical trap to terminate oxidation chain reactions ... 

Chain-breaking antioxidants (a) free-radical traps, (b) electron donors, (c) hydrogen donors. 

Table 9.19. Free radical trapping methods to evaluate natural antioxidants ...

The chemical stmctures of flavonols and procyanidins might be important for antioxidant activity because of free radical trapping and chelation of redox-active metals properties. Adamson et al. [32] indicated that polyphenol content positively correlated with antioxidant properties as measured by ORAC. AU polyphenols possess antioxidant properties in vitro but this activity is not well characterized in human. 

The radical A is a stable unreactive free radical which is not capable of propagating the chain reaction. However, a disadvantage for hindered phenols and aromatic amines is that they do not trap carbon free radicals. Carbon free radical trapping reduces hydroperoxide formation to a great extent and is preferable to peroxy radical trapping. Hindered amines, which are well known as photostabilizers, can trap alkyl radicals and constitute a new class of radical trapping antioxidants. 

The HNBR base formulation and initial properties are shown in Table 14.1. The initial properties indicate that Naugard 445 signihcantly lowers maximum torque, as determined by a rheometer, and as would be expected for a primary, radical trap antioxidant in a peroxide-cured compound (see Figure 14.7). Since zinc 2-mercap-totoluimidazole (ZMTl) does not act as a free radical trap, it is surprising that the total level of antioxidant is a better single predictor of the maximum rheometer torque than is the level of Naugard 445, see Table 14.2. 

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