Antioxidative activity, sulfur-containing

The mechanisms of inhibition by peroxide decomposers, metal deactivators, and ultraviolet absorbers are fairly well understood in general terms, although many details of the individual reactions remain to be elucidated. Classifying a preventive antioxidant into one of the three categories above will only rarely describe its entire function. The dual behavior of dialkyl dithiophosphates in the liquid phase has been mentioned. Many other phosphorus- and sulfur-containing antioxidants commonly classified as peroxide decomposers can also act as chain breakers. Similarly, the structure of many metal deactivators and ultraviolet absorbers indicates that they must also have some chain-breaking activity. 

Garlic has been reported to have lipid- and blood-pressure-lowering properties, as well as antiplatelet, antioxidant, and fibrinolytic effects. In animal models and human cell cultures, it has been shown to have antiatherosclerotic activity (see Chapter 50). The sulfur-containing component, allicin, is considered to be the principal active ingredient of garlic, but several other bioactive ingredients have also been isolated. 

Selenium is an essential trace element and an integral component of heme oxidase. It appears to augment the antioxidant action of vitamin E to protect membrane lipids from oxidation. The exact mechanism of this interaction is not known however, selenium compounds are found in the selenium analogs of the sulfur-containing amino acids, such as cysteine and methionine. Se-cysteine is found in the active sites of the enzyme glutathione peroxidase, which acts to use glutathione to reduce organic hydroperoxides. 

Sulfur-Containing Heterocyclic Compounds with Antioxidative Activity Formed in Maillard Reaction Model Systems... 

Antioxidative Activity of Thiazoiidine and 1,3-Ditiiiolane. Saturated cyclic sulfides represent another common class of sulfur-containing heterocyclic compounds formed in model systems and cooked foods. We have selected thiazoiidine and 1,3-dithiolane as model compounds for which to evaluate the antioxidative activity of this class of compounds and the results are shown in Figure 6. 1,3-Dithiolane appears to exhibit slightly higher activity than that of thiazoiidine. Both, however, inhibit heptanal oxidation for a longer period than do the thiophene derivatives presumably due to their different structural characteristics and hence potentially different mechanisms of antioxidative action. 

Many sulfur-containing PD antioxidants, especially the metal dithiolates, are very effective long-term thermal stabilizers (also melt and photo antioxidants see later). This versatility in antioxidant action is the direct consequence of their highly effective PD activity (54,105,107,136-140). Moreover, the effectiveness of dithiolate antioxidants, within any one series depends strongly on their solubility in the polymer. For example, in the case of nickel dialkyldithiophosphate (NiDRP, AO 23, Table 3) series, the lower molecular weight members of the series are less soluble, and less effective than the higher members (see Fig. 3) (141). The zinc dialkyl dithiocarbamate (ZnDRC, AO 21) series too show similar behavior (142). 

Sulfur-containing amino acids like cysteine, methionine and tripeptide glutathione are very powerful antioxidants that participate in different stages of free-radical chain reactions of biomolecule oxidation [18]. For example, cysteine participates in the synthesis of taurine, the substance that effectively blocks the peroxide oxidation of lipids by binding hypochlorite anion to form chloramine complex. In any organism, cysteine and glutathione reduces the oxidized form of vitamin C to its initial active form while methionine (being an... 

X-Ray fluorescence spectroscopy (XRF) is another commonly used method for the analysis of additives in pol3rmers. As the technique is not suitable for use with elements of lower atomic number than fluorine, primary antioxidants which contain either oxygen or nitrogen as the active element cannot be analyzed by XRF. Secondary antioxidants, however, which contain either phosphorus or sulfur as the active element, can be readily analyzed by this method. 

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