Page 294 - Natural Antioxidants, Applications in Foods of Animal Origin

Application of Natural Antioxidants in Dairy Foods 273
VetBooks.ir proteins, whose oxidation leads to an inevitable deterioration of the organo-

leptic qualities of a food due to the formation of undesirable substances like
aldehydes, ketones, and organic acids that yield off-flavors, is considered
to be an antioxidant (Saad et al. 2007; Andre´ et al. 2010). However, to
be used in foods, antioxidants must be nontoxic, inexpensive, effective at
low concentrations (0.001–0.02%), capable of surviving processing (carry-
through), stable in the finished products, and devoid of undesirable color,
flavor, and odor effects (Shahidi & Zhong, 2010). These days, there is an
extensive use of natural and synthetic antioxidants in the food and pharma-
ceutical industry.
Antioxidants can be divided into primary or chain-breaking antioxidants
and synergists or secondary antioxidants based on their mechanisms of
action. Primary antioxidants include hindered phenols and secondary aryl
amines, while secondary antioxidants include organophosphites and thioes-
ters. All the primary antioxidants commonly used in foods, have either two—
OH groups or one—OR group in the ortho or para positions (Hudson, 1990).
They are effective at extremely low concentrations of 0.01% or less and for
some of them the effectiveness decreases as concentration is increased. It
is reported that at high concentrations, they may act as pro-oxidant due to
their involvement in the initiation reactions (Cillard et al., 1980). Phenolic
(primary) antioxidants, whether naturally occurring, for example, tocoph-
erols or flavonoids or permitted synthetic compounds, such as hindered
phenolic (e.g., BHT, BHA, and TBHQ) and polyhydroxy phenolic (e.g.,
gallates), inhibit chain reactions by acting as hydrogen donors or free radical
acceptors, resulting in the formation of more stable products. They interfere
directly with the free radical propagation process and thus block the chain
reaction.
Secondary antioxidants or synergist can be accounted for metal chela-
tion (Khokhar & Owusu Apenten, 2003). They have little direct effect on
the autoxidation of lipids but are able to enhance considerably the action
of primary antioxidants. Chelating agents and sequestering agents like
citric acid and isopropyl citrate, amino acids, phosphoric acid, tartaric
acid, ascorbic acid and ascorbyl palmitate, ethylenediaminetetraacetic acid
(EDTA) chelate metallic ions (such as copper and iron) that promote lipid
oxidation through a catalytic action. The chelators are referred to as syner-
gists since they greatly enhance the action of phenolic antioxidants. Thus,
antioxidants slow down the oxidation rates of foods by a combination of
mechanisms like, scavenging free radicals; chelating pro-oxidative metals;
quenching O and photo-sensitizers, and inactivating lipoxygenase (Thorat
1
2
et al., 2013). The effectiveness of antioxidants to scavenge free radicals