Oxidation control, antioxidants

Wade et al. (1986) reported that BHA and BHT were effective in retarding oxidation of anhydrous milk fat but DL-a-tocopherol acted as a pro-oxidant. Natural antioxidants in betel and curry leaves have also been reported to retard oxidation of anhydrous milk fat (Sharma, 1981 Parmer and Sharma, 1986). Amr (1991) reported that turmeric and wheat grits were as effective as BHA and BHT in controlling oxidative rancidity in sheep s anhydrous milk fat for up to 4 months. However, rosemary, sage, rue and fennel exerted pro-oxidant effects. Quercetin and rutin are reported to be efficient antioxidants in butter (Eriksson, 1987). 

Levonen AL, Landar A, Ramachandran A, Ceaser EK, Dickinson DA, Zanoni G, Morrow JD, Darley-Usmar VM (2004) Cellular mechanisms of redox cell signalling role of cysteine modification in controlling antioxidant defences in response to electrophilic lipid oxidation products. Biochem J 378(Pt 2) 373-382... 

To study quantitatively the kinetics of lipid oxidation and antioxidation, a standard way of controlling and measuring the rate of free radical initiation is to use thermally labile azo compounds. These artificial initiators generate radicals at a reproducible, well-established and constant rate. In the presence of initiators such as a,a-azobisisobutyronitrile (AIBN) or benzoyl peroxide, the overriding initiation can be directly related to the rate of production of the initiator radical. Also, by using either water-soluble or lipid-soluble azo dyes, these compounds can initiate radicals at known specific micro-environments. 

This book discusses these and other pitfalls inherent in basic studies that use artificial radical initiators with unrealistic models and homogeneous systems. The application of simple research models may lead to numerous problems in the ultimate interpretation of results, because lipid oxidation proceeds by a complex sequence of reactions influenced by many factors, all of which become extremely difficult to unravel in real food and biological systems. These systems are multi-phased and controlled by complex colloidal phenomena affecting different sites of oxidation and antioxidation. In interpreting the effects of prooxidant and antioxidant compounds their effective concentrations in different phases must be considered. A dimension of lipid oxidation that is important to better understand control methods deals with the relative partition of oxidants and antioxidants in multiphase systems. This topic has not received sufficient attention. 

Expansion is desirable for snacks and breakfast cereals, but the increased surface area formed by the numerous air cells favors oxidation. However, antioxidants derived from Maillard reaction products may help reduce oxidation rates. Oatmeal cookies containing potato peels showed lower peroxide values than control cookies, and extruded peels had greater antioxidant activity than did non-extruded peels (Arora and Camire, 1994). 

The phosphonate esters, HP(=0(OR)2, of alkylated phenols are used extensively as lubricating-oil additives to control bearing corrosion and oxidation, and to impart antimst properties as stabilizers, as antioxidants (qv) and flame retardants in plastics, as specialty solvents, and as intermediates (see Corrosion AND corrosion control Heat stabilizers). 

PTMEG is a polymeric ether susceptible to both thermal and oxidative degradation. It usually contains 300—1000 ppm of an antioxidant such as 2,6-di-/ f2 -butyl-4-hydroxytoluene (BHT) to prevent oxidation under normal storage and handling conditions. Thermal decomposition in an inert atmosphere starts at 210—220°C (410—430°E) with the formation of highly flammable THE. In the presence of acidic impurities, the decomposition temperature can be significantly reduced contact with acids should therefore be avoided, and storage temperatures have to be controlled to prevent decomposition to THF (261). 

It has been proposed that the development of the complications of diabetes mellitus may be linked to oxidative stress and therefore might be attenuated by antioxidants such as vitamin E. Furthermore, it is discussed that glucose-induced vascular dysfunction in diabetes can be reduced by vitamin E treatment due to the inactivation of PKC. Cardiovascular complications are among the leading causes of death in diabetics. In addition, a postulated protective effect of vitamin E (antioxidants) on fasting plasma glucose in type 2 diabetic patients is also mentioned but could not be confirmed in a recently published triple-blind, placebo-controlled clinical trial [3]. To our knowledge, up to now no clinical intervention trials have tested directly whether vitamin E can ameliorate the complication of diabetes. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

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