Understanding antioxidant mechanisms in preventing oxidation in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 233

10.2.2 Synthetic phenolic antioxidants
The major synthetic antioxidants are substituted phenols of varying polarity
(Fig. 10.4). These include butylated hydroxytoluene (nonpolar), butylated
hydroxyanisole (nonpolar), tertiary butylhydroquinone (intermediate polarity)
and propyl gallate (most polar). Synthetic phenolics can be extremely effective
in food systems but their utilization by the food industry is declining due to
consumer demand for all natural products.
The antioxidant mechanism of the synthetic phenolics involves the formation
of a phenolic radical which neither rapidly catalyzes the oxidation of other
unsaturated fatty acids nor reacts with oxygen to form antioxidant hydro-
peroxides which decompose into free radicals (Shahidi, 1992). Synthetic
phenolic radicals can potentially react with each other in mechanisms similar to
-tocopherol resulting in the formation of hydroquinones and phenolic dimers.
The phenolic radicals can also react with other peroxyl radicals in termination
reactions resulting in formation of phenolic-peroxyl species adducts. In addition,
oxidized synthetic phenolic undergo numerous degradation reactions (for a
review, see Shahidi, 1992) to form compounds that still contain active hydroxyl
groups and thus can further scavenge free radicals. Therefore, the net antioxidant
activity of synthetic phenolics in food actually represents the activity of the
original phenolic plus some of its degradation products.
Fig. 10.4 Structures of several important synthetic free radical scavengers approved for
use in foods.