Page 64 - Natural Antioxidants, Applications in Foods of Animal Origin

Natural Antioxidants: Occurrence and Their Role in Food Preservation 43
VetBooks.ir secondary or preventive antioxidants. The main difference with primary

antioxidants is that the secondary antioxidants do not convert free radicals
into stable molecules (Wanasundara & Shahidi, 2005). The primary anti-
oxidants consist mainly of hindered phenols and hindered aromatic amines.
They scavenge and destroy the chain propagating peroxy and alkoxy radi-
cals before they can react with the polymer. Gum guaiac was the first anti-
oxidant approved for the stabilization of animal fats, especially lard.

2.2 ANTIOXIDANTS VERSUS FREE RADICALS

The modes of action of an antioxidant can be broadly classified as preven-
tive/inhibitory and radical scavenging. Some examples of preventive/inhibi-
tory antioxidant enzymes are superoxide dismutase, catalase, and glutathione
peroxidase while radical scavenging antioxidants can be broadly classified
as hydrogen donating and iron-chelating antioxidants (ICA). Hydrogen
donating antioxidants (HDA) donate a hydrogen to peroxy radicals of lipid
or protein, which are mainly responsible for free radical chain reaction in a
biological system. Few examples of synthetic HDA are butylated hydroxy
anisole (BHA), butylated hydroxy toluene (BHT), propyl gallate (PG),
tertiary butyl hydroquinone (TBHQ), and so forth, while natural HDA are
AA (vitamin C), tocols (tocopherols and tocotrienols), carotenoids, polyphe-
nols, phenolics, phytosterols (PS), lignans, OZ, gossypol, and so forth. ICA
usually deactivate radically active trace metals by the formation of complex
ion. Examples of synthetic and natural ICA are ethylene diamine tetra acetic
acid (EDTA) and phytic acid, which form ions EDTA complex and phytate
complex, respectively. Several mechanisms by which antioxidants provide
defense mechanism against free radicals are:

1. Scavenging species that initiate peroxidation,
2. Chelating metal ions such that they are unable to generate reactive
species or decompose lipid peroxides,
3. Quenching O preventing formation of peroxides,
−
2
4. Breaking the autoxidative chain reaction, and/or
5. Reducing localized O concentrations (Nawar, 1996).
2
Several assays for quantifying antioxidant capacity are known and well
established. Few of them include:

1. ORAC (oxygen radical absorbance capacity).