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Natural Antioxidants in Poultry Products 171
VetBooks.ir 5.2.4 ANTIOXIDANTS IN PREVENTING LIPID OXIDATION

Antioxidants are organic molecules of either synthetic origin or natural
origin, which can avoid or delay the progress of oxidative rancidity. It is
mainly imparted to their phenol-derived structure. Antioxidants work by
donating hydrogen to the lipid free radical to reform the fat molecule or by
donating one hydrogen to a peroxide free radical to form a hydroperoxide
and a stable antioxidant free radical. They “sacrifice themselves” by giving
up a hydrogen atom, then rearrange to a stable conformation.

A: H + RO• → A• + ROH (5.8)

Antioxidants can be classified according to their protective properties
at different stages of the oxidation process and since they act by different
mechanisms, they are divided into two main types: primary and secondary
antioxidants.

a) Primary antioxidants can inhibit or retard oxidation by scavenging
free radicals by donation of hydrogen atoms or electrons, which
converts them to more stable products, for example vit. C and E,
phytochemicals like flavonoids.
b) Secondary antioxidants function by many mechanisms, including
binding of metal ions, scavenging oxygen, converting hydroperox-
ides to non-radical species, absorbing UV radiation, or deactivating
singlet oxygen, for example butylated hydroxyl anisole (BHA),
butylated hydroxyrotoluene (BHT), propyl gallate (PG), and metal
chelating agent (EDTA).

5.3 SOURCES OF NATURAL ANTIOXIDANTS

Natural antioxidants are presumed to be safe and are available in variable
amounts in plant and animal kingdoms. Plant phenolics, “phytochemicals,”
are multifunctional and can act as reducing agents, free radical terminators,
metal chelators, and singlet oxygen quenchers. Flavonoids and other classes
of phenolic compounds are important phytochemicals. Extracts from plants
which contribute health benefits to consumers, arising from protection from
free radical-mediated deteriorations, and which cause retardation of lipid
oxidation have stronger antioxidant activity (AOA) than that of synthetic
antioxidants (Table 5.1).