Antioxidants oxidation, mechanism

Epidemiological studies and intervention trials with food and beverages rich in flavonoids are not conclusive although flavonoids were recognized to display numerous antioxidant, anti-inflammatory, anti-tumoral, and anti-microbial activities. The antioxidant capacity of flavonoids has been largely reported in numerous in vitro and ex vivo systems. Numerous reviews "" have been published on the antioxidant properties of flavonoids. Degenerative diseases are largely associated with oxidative mechanisms that may be counteracted by flavonoids. 

Zitnanova I, Korytar P Aruoma Ol, et al. Uric acid and allan-toin levels in Down syndrome antioxidant and oxidative mechanism Clin Chim Acta 2004 341 139-146. 

PEG can be severely degraded in air. Its melting point and heat of fusion are reduced by as much as 13 °C and 32 kJ kg"1, respectively [81]. The thermal degradation of PEG in air follows a random chain scission oxidation mechanism, and could be suppressed by addition of an antioxidant, 2, 2,-methylene-bis (4-methyl-6-tert-butylphenol) (MBMTBP), due to the reaction of MBMTBP with ROO radicals formed in the propagation step [79]. Low-molecular-weight esters including formic esters are produced as the main products of the thermal degradation of PEG (Scheme 3.17) [80]. 

Free radical formation is an important contributor to cell death and brain injury in many neurological diseases. Shortly after brain damage by hypoxia-ischemia, hemorrhage, or trauma, excessive reactive oxygen species (ROS) production occurs, and at the same time, there is an impairment of antioxidant protective mechanisms, which leads to oxidative stress (Heo et al 2005). 

Reactive aldehydes generated from hpid peroxidation are involved in CVD (266). Another example lies with the role of oxidative stress in the pathophysiology of asthma (267). Lipid peroxidation, as determined by plasma iso-prostanes, is related to disease severity in mild asthma. Tumor cell lines are sensitive to PUFA and to associated oxidation products (268). This sensitivity depends on the antioxidant defense mechanism, as well as on culture conditions. Hydroperoxy docosahexaenoic acid is a major metabolite, responsible for the cytotoxicity of DHA. 

In native state, proteins exist as either fibrous or globular form. Protein should be denatured and unfolded to produce an extended chain structure to form film. Extended protein chains can interact through hydrogen, ionic, and hydrophobic bonds to form a three-dimensional stmcture (24). Protein films are excellent gas barriers but poor moisture barriers because of their hydrophilic nature. Mechanical properties and gas permeability depend on the relative humidity (1). Al-ameri (25) smdied the antioxidant and mechanical properties of soy, whey and wheat protein, and carrageenan and carboxymethyl cellulose films with incorporated tertiary-butylhy-droquinone (TBHQ), butylated hydroxytoluene (BHT), fenugreek, and rosemary extracts. Armitage et al. (26) studied egg albumin film as a carrier of natural antioxidants to reduce lipid oxidation in cooked and uncooked poultry. 

There is considerable body of (indirect) evidence which makes oxidative stress one of the best accepted hypothesis for explaining the cause of Parkinson s disease. For example, the Fe(II)/Fe(III) ratio in the substantia nigra is shifted from 2 1 in the normal brain to 1 2 in Parkinsonian brain.131,132 In the Parkinsonian brain several enzymes which constitute the antioxidative defence mechanisms (glutathione peroxidase, catalase) have a decreased activity, while the activity of superoxide dismutase is increased, relative to the normal brain.133 Furthermore, specific products of radical damage, such as lipid hydroperoxides, were detected at a 10-fold increased level in the Parkinsonian brain.134... 

L. Packer and A. S. H. Ong (Eds.), Biological Oxidants and Antioxidants. Molecular Mechanisms and Health Effects, AOCS Press, Champaign, lUinois, 1998. 

Al-Malaika, S. Antioxidants preventive mechanisms. In Atmospheric Oxidation and Antioxidants, Scott, G., Ed. Elsevier Applied Science London, 1993 Vol. 1, 161-224. 

Reiter RJ. 1995. Oxidative processes and antioxidative defense mechanisms in the aging brain. FASEB J 9 526-533. 

Product stability and performance can be affected by exposure to several oxidative sources, including oxygen, free radicals, UV radiation, oxidative enzymes, catabolic oxidation, and chemical oxidation. Many antioxidants are also good UV absorbers due to their conjugated chemical structure. Typical antioxidants found in cosmetic products are flavonoids, polyphenols, carotenoids, thiols, tocopherol (vitamin E) and ascorbic acid (vitamin C) [71,72], According to Black [73], a combination of antioxidants from different classes is more effective than a single antioxidant due to an antioxidant cascade mechanism. 

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