Antioxidant distribution

The activity of antioxidants in food [ 1 ] emulsions and in some biological systems [2] is depends on a multitude of factors including the localisation of the antioxidant in the different phases of the system. The aim of this study is determining antioxidant distributions in model food emulsions. For the purpose, we measured electrochemically the rate constant of hexadecylbenzenediazonium tetrafluorborate (16-ArN,BF ) with the antioxidant, and applied the pseudophase kinetic model to interpret the results. 

Figure 4.23 Antioxidant distribution in BAN copolymer as a function of elution volume. After Gupta and Salovey [816]. Reprinted with permission from Rubber Chemistry and Technology. Copyright (1985), Rubber Division, American Chemical Society, Inc.

Establishing reliable criteria for selecting the most efficient antioxidant, AO, for a particular application is a major unsolved problem in food emulsions and dispersions and one of general importance in nutrition and health. Recent reviews " point to multiple factors that affect activities of antioxidants including the properties and reactions of the antioxidant and the polyunsaturated lipids being oxidized the locations or distributions of the antioxidant within emulsified food the effect of other components on antioxidant activity and the relevance of the model system to real food. Frankel and Meyer s summarized the antioxidant distribution problem highlighthing the crucial role of the antioxidant distributiOTi into emulsifier-rich interfacial layers in hetero-phasic food emulsions[9, 17],... 

Finally, the rate craistant for reaction in the interfacial region, k, between 16-ArN2 and TBHQ, Scheme 1, can be determined by using equation 4 and the estimated Pq value, k - 0.063 s. No similar values have been reported up to date for this antioxidant and emulsion, hence no reliable comparisons of the k values can be made. Determining k values should help to lay the basis for a scale of antioxidant activity that is independent of the antioxidant distribution in the emulsion. 

Given that most of antioxidants bear -OH groups in their chemical structures, the distribution of antioxidants is expected to depend on a number of parameters including its chemical structure, HLB, the acidity of the solution, temperature, etc. The effects of these and other parameters such as oil polarity, emulsifier HLB, etc. on antioxidant distributions are being investigated and will be part of future communications. 

Romsted LS, Zhang J Determining antioxidant distributions in model food emulsions development of a new kinetic method based on the pseudophase model in micelles and opaque emulsions 182... 

Most of the resin systems used in commodity composites are slight modifications of the standard commercial mol ding grade material. Usually certain selected properties, such as purity or molecular weight range or distribution, are enhanced or carehiUy selected. In addition, special additives, such as flow controllers, thermal stabilizers, or antioxidants, are often added by the resin manufacturer prior to shipment. Many of the conventional or commodity-type resins used in thermoplastic composites are Hsted in Table 1 and the preparation of each of these is described. AH resins and blends described in the hterature are not Hsted, and the synthesis described is not the only procedure available, but is usually the most common commercial process. 

Neuromelanin, a dark colored pigment and product of the oxidative metabolism of dopamine, is found in the cytoplasm of dopaminergic neurons of the human substantia nigra pars compacta. Neuromelanin deposits increase with age, matching the age distribution of Parkinson s disease. In the absence of significant quantities of iron, neuromelanin can act as an antioxidant in... 

The term vitamin E describes a family of eight antioxidants, four tocopherols, alpha (a), beta ((3), gamma (y) and delta (8), and four tocotrienols (also a, (3, y, and 8). a-Tocopherol is present in nature in only one form, RRR a-tocopherol. The chemical synthesis of a-tocopherol results in eight different forms (SRR, SSR, SRS, SSS, RSR, RRS, RSS, RRR), only one of which is RRR a-tocopherol. These forms differ in that they can be right (R) or left (S) at three different places in the a-tocopherol molecule. RRR a-tocopherol is the only form of vitamin E that is actively maintained in the human body and is therefore the form of vitamin E found in the largest quantities in the blood and tissue. A protein synthesized in the liver (a-TTP alpha-tocopherol transfer protein) preferentially selects the natural form of vitamin E (RRR a-tocopherol) for distribution to the tissues. However, the mechanisms for the regulation of vitamin E in tissues are not known... 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

The solubility of antioxidants determines their phase distribution in foods. It has been observed that compared to lipid-soluble antioxidants water-soluble antioxidants like ascorbate yield better protection to strongly lipophilic food systems like pure oils. In contrast, antioxidants soluble in lipids like the tocopherols yield better protection to oil-in-water emulsions when compared to water-soluble antioxidants (Porter, 1993). The explanation offered for this... 

Tesoriere, L et al., Absorption, excretion, and distribution of dietary antioxidant betalains in LDLs potential health effects of betalains in humans. Am. J. Clin. Nutr., 80, 941, 2004. 

Injury (either physical or chemical) to the comeal endothelial cells has a marked efiect on occular function as these cells are responsible for maintaining the thickness and clarity of the cornea, yet they cannot be replaced if damaged. Immunohistochemical studies have revealed that enzymatic antioxidant defences, SOD, CAT and GSHPx, are similarly distributed in the corneal epithelium and endothelium (Rao etal., 1985 Attala et d., 1987, 1988). Other antioxidants include ascorbate, carotenoids and vitamin E (Fleath, 1962). 

More recently, the same author [41] has described polymer analysis (polymer microstructure, copolymer composition, molecular weight distribution, functional groups, fractionation) together with polymer/additive analysis (separation of polymer and additives, identification of additives, volatiles and catalyst residues) the monograph provides a single source of information on polymer/additive analysis techniques up to 1980. Crompton described practical analytical methods for the determination of classes of additives (by functionality antioxidants, stabilisers, antiozonants, plasticisers, pigments, flame retardants, accelerators, etc.). Mitchell... 

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