Synthetic antioxidants physical properties

Natural rubber (NR) and guttapercha consist essentially of polyisoprene in cis-l, 4 and trans-1,4 isomers, respectively. Commercially produced synthetic polyisoprenes have more or less identical structure but reduced chain regularity, although some may contain certain proportions of 1,2- and 3,4-isomers. Microstructure differences not only cause the polymers to have different physical properties but also affect their response to radiation. The most apparent change in microstructure on irradiation is the decrease in unsaturation. It is further promoted by the addition of thiols and other compounds.130 On the other hand, antioxidants and sulfur were found to reduce the rate of decay of unsaturation.131 A significant loss in unsaturation was found, particularly in polyisoprenes composed primarily of 1,2- and 3,4-isomers.132,133... 

Table 6 Physical Properties of Synthetic Phenolic Antioxidants... 

TABLE 6. Physical Properties of Synthetic Antioxidants Used in Foods (18, 88, 89). 

In most countries, use of synthetic antioxidants is regulated and the safety of the compounds involved has been tested based on long-term toxicity studies. The ability of an antioxidant to withstand thermal treatment (e.g., frying or baking) and to retain sufficient stabilizing activity for the food (fried or baked) is termed as carry through property. Table 6 provides a summary of physical properties of commonly used synthetic antioxidants. Several researchers have smdied the effectiveness of these compounds in suppressing lipid oxidation in fats and oil, and Tables 7 and 8 provide comparative effects of synthetic antioxidants (82). 

Antioxidants are one of the main families of additives where much work has been carried out during the past few years. They preserve chemical and physical-mechanical properties of polymers both during processing and under in-use conditions. In particular, natural antioxidants, mostly hindered phenols, are chosen to replace synthetic ones mainly in biopolymer and biocomposites formulations to render them completely compatible with different biologically active environments (e.g., natural environments and human body). Side effects of some synthetic antioxidants, such as butyl hydroxytoluene (BHT) and butyl hydroxyanisole (BHA), have been documented, and this has stimulated the substitution of synthetic antioxidants by natural ones. Among them, tocopherol, ferulic acid, sorbic acid, ascorbic acid, ° and vegetable oil with essential fatty acids are those most commonly found in biopolymer formulations. 

The main constituents just referred to are responsible for the physical properties (structure, texture, and color) as well as the flavor of foods. Sometimes, specific natural or synthetic ingredients (such as salt or antioxidants) are added to improve the food properties [1-3]. 

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