Antioxidants phase distribution

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... 

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. 

The selection of an appropriate antioxidant depends on factors such as stability, toxicity, efficiency, odor, taste, compatibility with other ingredients, and distribution phenomena between the two phases. Antioxidants that give protection primarily in the aqueous phase include sodium metabisulfite, ascorbic acid, thioglycerol, and cysteine hydrochloride. Oil-soluble antioxidants include lecithin, propyl gal-late, ascorbyl palmitate, and butylated hydroxytoluene. Vitamin E has also been used, but its virtue as a natural antioxidant has been the subject of some controversy. 

About one-third of the phospholipids in freshly drawn milk are located in the milk serum as small lipoprotein particles, sometimes referred to as milk microsomes. Their proportion in milk serum can be increased in processed milk as a result of disruption of the MFGM and release of membrane phospholipids into the aqueous phase (Mulder and Walstra, 1974 McPherson and Kitchen, 1983). Modification of the MFGM by processing treatments that may alter the distribution of pro-oxidants and antioxidants can markedly affect the stability of milk (McPherson and Kitchen, 1983). 

Polyolefin resins contain only carbon and hydrogen, and additives, such as some antioxidants and UV stabilizers. Moreover, the presence of hetero-elements, such as chlorine and bromine is undesirable, as these elements distribute over the three product phases-gas, liquid, and solids, reducing the market potential and value of each of these. Studying their elimination is a major consideration in developing processes for mixed plastics. 

In order to inhibit the oxidation of polymers, the antioxidant has to be present in sufficient concentration at the various oxidation sites. In this respect, both the distribution of antioxidants and the morphology of the host polymer assume greater significance. Examination of the distribution of photo-antioxidants in typical commercial semi-crystalline polymers, such as polyolefins, has shown " " " that they are rejected into the amorphous region on the boundaries of spherulites. Such nonuniform distribution of antioxidants leads to an increase in their concentration in the amorphous region, which is most susceptible to oxidation (the crystalline phase is normally impermeable to oxygen). However, in the case of polymer blends, a nonuniform distribution of antioxidants can undermine the overall stability of the blend, especially when the more oxidizable component of the polymer blend is left unprotected. 

In gas chromatography (GC), the separation of analytes is based on a distribution between a mobile gas phase and a stationary phase. It is a technique with high resolution, high selectivity and high sensitivity. A range of different detectors can be used. This technique has nevertheless certain limitations in the characterization of antioxidants, since many antioxidants are thermally sensitive. GC analysis is also limited to lower molar mass compounds, additives, oligomers, etc., since the analytes must have a boiling point below... 

Additive and impurity rejection at the growing crystal front leads to uneven distribution in a crystalline polymer. This redistribution process has been studied by UV and fluorescence microscopy and by an electron microscope with energy dispersive x-ray analysis. In polymer samples which are quenched after rapid crystallization, the additive distribution is kinetically determined and may be modeled in a computer as a three-dimensional zone-refining process. In annealed polymer samples, low molecular weight additives are uniformly concentrated in the amorphous phase. The additive distribution reflects that of crystalline material within the polymer. Antioxidant and uv stabilzer redistribution probably does not have a major effect on polymer stability, but the redistribution of partially oxidized, impure polymer may be important... 

Thermal or oxidative degradation of the gel alters the swell characteristics and changes the pore size distribution, eventually breaking down the particle. Although ultimately some degradation can be expected under such aggressive conditions, this can be substantially reduced by the addition of antioxidants to the mobile phase. 

The broad spectrum of effectiveness and the high antimicrobial activity of iso-propyl-methylphenols is enlightened by the MIC in Table 57. In spite of that the isopropyl-methylphenols have not gained much importance as preservatives for material protection or as active ingredients in disinfectants. The reason for this is the distinctive odour of these phenol derivatives, their poor water solubility and their unfavourable distribution between water and organic phases. Last but not least they are more expensive than other phenol derivatives with more favourable properties. Worthy of note are antioxidant actions of the isopropyl-methylphenols (Aeschbach et ak, 1994). 

This is one of the hydrolysis products of the aliphatic GSL called sinigrin, which is broadly distributed widely throughout the Brassica-ceae family (Fahey et al. 2001). Allyl nitrile appears to be a more active inducer of phase II enzymes compared with other nitriles. This compound has the ability to induce the phase II antioxidant and detoxification enzymes in the liver, kidneys, and small intestine. 

A comparison of LC methods for determination of cis-trans isomers of P-carotene was made on Vydac C18 201 TP and calcium hydroxide columns (186). The purity and relative distribution of P-carotene and its isomers in several commercially available products were evaluated by HPLC on several columns using a mobile phase of methanol/water (97 3) (187). Because carotenoids and chlorophylls are very sensitive to the nature of injection solvent, such as acetone, sample-solvent interaction may give rise to distorted and even false peaks (188). Because metal column frits may damage carotenoids. Teflon column frits should be used (189). Also artifacts may be produced on the column by reactions among the carotenoids, injection solvents, and mobile phase. Losses that occur during extraction and saponification can be reduced by use of suitable antioxidants (189). 

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