Page 373 - Natural Antioxidants, Applications in Foods of Animal Origin

352 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir 9 compatibility with the food and ease of application

9 survive after processing and be stable in the finished product
9 available at low cost.

The compound and its oxidation products must also be nontoxic, even at
doses much larger than those that normally would be ingested in food.
Antioxidants can be classified according to the mechanism of action into
two groups:

9.2.1.4.1 Primary Antioxidants

Primary antioxidants interfere with autoxidation by interrupting the chain
propagation mechanism. Primary antioxidants are free radical acceptors
(Wasowicz et al., 2004). The best-known and most effective primary anti-
oxidant substances are polyphenols. They react with the chain-propagating
radical species, which results in the formation of radical species incapable of
extracting hydrogen atoms from unsaturated lipids (Coma & Kerry, 2012).
Tocopherols inhibit lipid oxidation by scavenging of aqueous and
lipophilic free radicals as well as physical effects on membrane structure
(Buettner, 1993; Atkinson et al., 2008). Dietary antioxidant treatments (i.e.,
the inclusion of antioxidants in animal feed) have been shown to stabi-
lize lipids in membranes and reduce the extent of lipid oxidation in meat
during storage, but antioxidant effects in meat can differ between muscle
types (Morrissey et al., 1997; Ahn et al., 2006). Vitamin E in livestock diets
has been shown to reduce lipid oxidation in meats (Morrissey et al., 1998;
Álvarez et al., 2009). Batifoulier et al. (2002) reported that supplementation
of turkeys with α-tocopheryl acetate increased vitamin E content of micro-
somal membranes and had also a protective effect on lipid oxidation.
Some endogenous enzymes also have an antioxidant effect such as super-
oxide dismutase, catalase or glutathione peroxidase. These enzymes inhibit
lipid oxidation through the following mechanisms:

- Superoxide dismutase is present in cells and extracellular fluids
to remove •O resulting in formation of oxygen and hydrogen
−
2
peroxide.
- Catalase, a heme-containing enzyme reacts with H O to form water
2
2
and oxygen (Goth, 1987; Richards, 2006).
- Glutathione peroxidase reduces hydrogen peroxide and lipid
hydroperoxides to alcohols (Gong et al., 2010).