Antioxidative systems

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

D. Burdick, S. Laermer, S. Young, and P. Zambetti, "A New Primary Antioxidant System for Polyolefins," presented 2l. ddditives 95 Clearwater,... 

The electrical properties of polypropylene are very similar to those of high-density polyethylenes. In particular the power factor is critically dependent on the amount of catalyst residues in the polymer. Some typical properties are given in Table 11.3 but it should be noted that these properties are dependent on the antioxidant system employed as well as on the catalyst residues. 

There are a number of occasions where a transparent plastics material which can be used at temperatures of up to 150°C is required and in spite of its relatively high cost, low impact strength and poor aging properties poly-(4-methylpent-1 -ene) is often the answer. Like poly(vinyl chloride) and polypropylene, P4MP1 is useless without stabilisation and as with the other two materials it may be expected that continuous improvement in stabilising antioxidant systems can be expected. 

The FAD-dependent enzyme glutathione reductase plays a role in the antioxidant system. Glutathione reductase restores reduced glutathione (GSH), the most important antioxidant in erythrocytes, from oxidized glutathione (GSSG) [1, 2]. 

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

During ischaemia, the activity of cellular antioxidant systems may be reduced (Ferrari et al. 1985 GaUnanes etal. 1992). In addition, a number of cellular pathways that produce free radicals are primed during ischaemia such as the xanthine/xanthine oxidase system (McCord, 1987), catecholamine auto-oxidation (Jackson et al., 1986) and the arachadonic acid pathway (Halliwell and Gutteridge, 1989). Thus, during early reperfusion there is a burst of free radical production (see Fig. 4.1) that may overwhelm the antioxidant systems of the cells. 

Corrocher, R, Casaril, M., Bellisola, G., Gabrielli, G.B., Nicoli, N., Guidi, G.C. and DeSandre, G. (1986). Severe impairment of antioxidant systems in human hepatoma. Cancer 58, 1658-1662. 

Takeuchi, K., Nishiwaki, H., Niida, H., Ueshima, K. and Okabe, S. (1991b). Duodenal ulcers induced by diethyl-dithiocarbamate, a superoxide dismutase inhibitor, in the rat role of antioxidative system in the pathogenesis. Jpn. J. Pharmacol. 57, 299-310. 

Robertson, J.D., Maughan, R.J., Duthie, G.G. and Mortice, P.C. (1991). Increased blood antioxidant systems of runners in response to training load. Clin. Sci. 80, 611-618. 

Amantuni, V.G. and Safarian, M.D. (1984). Determination of the correlations between oxidant and antioxidant systems in bronchial asthma. Ter. Arkh. 56, 81-85. 

The natural endogenous physiological antioxidant systems for controUing the potentially injurious elFects of environmentally exacerbated oxidative stress, may be modulated by a number of various nutritional and pharmacological supplementary interventions. 

High-MW hindered amine thermal stabiliser (HATS) formulations are designed for advanced extraction resistant long-term stabilisation, i.e. for use in extractive environments such as polyolefin pipes, fulfilling the stringent requirement of guaranteeing product lifetime of more than 50 years [565], These systems offer much better gas and hot water resistance than the low-MW phenolic antioxidant systems. Ethanox 330... 

Stablizers. Stabilizers are ingredients added to a formula to decrease the rate of decomposition of the active ingredients. Antioxidants are the principal stabilizers added to some ophthalmic solutions, primarily those containing epinephrine and other oxidizable drugs. Sodium bisulfite or metabisulfite are used in concentration up to 0.3% in epinephrine hydrochloride and bitartrate solutions. Epinephrine borate solutions have a pH range of 5.5 7.5 and offer a more difficult challenge to formulators who seek to prevent oxidation. Several patented antioxidant systems have been developed specifically for this compound. These consist of ascorbic acid and acetylcysteine, and sodium bisulfite and 8-hydroxyquinoline. Isoascorbic acid is also an effective antioxidant for this drug. Sodium thiosulfate is used with sodium sulfacetamide solutions. 

Felton G. W. and Summers C. B. (1995). Antioxidant systems in insects. Arch Insect Biochem Physiol 29 187-197. 

Lendieric I, Pinto E, Vendrell M and Larrigaudiere C. 1999. Harvest date affects die antioxidative system in pear fruits. J Hort Sci Technol 74(6) 791—795. 

The antioxidant system in humans is a complex network composed by several enzymatic and nonenzymatic antioxidants. In addition to being an antioxidant, lycopene also exerts indirect antioxidant properties by inducing the production of cellular enzymes such as superoxide dismutase, glutathione S-transferase, and quinone reductase that also protect cells from reactive oxygen species and other electrophilic molecules (Goo and others 2007). 

Yahia EM, Soto-Zamora G, Brecht JK and Gardea A. 2007. Postharvest hot air treatment effects on the antioxidant system in stored mature-green tomatoes. Postharvest Biol Technol 44 107—115. 

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