Free radical interceptors

The antioxidant radical produced because of donation of a hydrogen atom has a very low reactivity toward the unsaturated lipids or oxygen therefore, the rate of propagation is very slow. The antioxidant radicals are relatively stable so that they do not initiate a chain or free radical propagating autoxidation reaction unless present in very large quantities. These free radical interceptors react with peroxy radicals (ROO ) to stop chain propagation thus, they inhibit the formation of peroxides (Equation 13). Also, the reaction with alkoxy radicals (RO ) decreases the decomposition of hydroperoxides to harmful degradation products (Equation 14). 

Most of the primary antioxidants that act as chain breakers or free radical interceptors are mono- or polyhydroxy phenols with various ring substitutions. 

Minimizing oxygen and prooxidants in a retail oil is not too difficult. In a formulated food, it is very difficult and often impractical. The important point is that by minimizing prooxidants, quality benefits. Oxidation will continue but is significantly retarded. Use of a synthetic antioxidant or natural extracts with antioxidant properties, such as tocopherol, rosemary, sage and tea, can be very helpful. Use of these free radical interceptors (FRIs) does not ordinarily prevent the oxidation reaction of Equation (2) since kinetics favor reaction of the lipid free radical with oxygen rather than with the FRI. 

Figure 7. Structure of free radical interceptors present in green tea and in rosemary.

The redox reactions of carbon free radicals and copper(II) compounds have been portrayed as ligand-transfer and electron-transfer processes 178). The electron-transfer oxidation of alkyl radicals by copper(II) complexes, which are efficient radical interceptors, is considered to proceed via a metastable alkylcopper species which is consumed primarily by oxidative elimination [Eq. (129)] and oxidative solvolysis [Eq. (130)] 143b). The anionic counterion exerts a dominant effect in the selection... 

Reactions Involved in Radical Interception. Some of the reactions which have been considered in the radical interceptor technique are shown in Reactions 1-8. Reactions 1 and 2 are schematic and do not describe the mechanism of formation of secondary free radicals in proteins by ionizing radiation. The reactions of the carbon radicals with tritiated scavengers (Reactions 3 and 3a) lead to the formation of carbon-tritium bonds. 

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