Page 67 - Natural Antioxidants, Applications in Foods of Animal Origin

46 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir positions suitable for molecular oxygen attack. Both synthetic (BHA, BHT,

and PG) and natural antioxidants contain phenolics (flavonoids) function in
this manner. Natural extracts with antioxidant activity generally quench free
radical oxygen with phenolic compounds (POH) as well. Because bivalent
transition metal ions, Fe in particular, can catalyze oxidative processes,
2+
leading to formation of hydroxyl radicals, and can decompose hydroper-
oxides via Fenton reactions, chelating these metals can effectively reduce
oxidation (Halliwell et al., 1987; Brewer, 2011). Food materials containing
significant amounts of these transition metals (red meat) can be particularly
susceptible to metal-catalyzed reactions. Food tissues, because they are (or
were) living, are under constant oxidative stress from free radicals, ROS, and
pro-oxidants generated both exogenously (heat and light) and endogenously
(H O and transition metals). For this reason, many of these tissues have
2
2
developed antioxidant systems to control free radicals, lipid oxidation cata-
lysts, oxidation intermediates, and secondary breakdown products (Naka-
tani, 2003; Agati et al., 2007; Brown & Kelly, 2007; Chen, 2008; Iacopini
et al., 2008; Brewer, 2011). These antioxidant compounds include flavo-
noids, phenolic acids, carotenoids, and tocopherols that can inhibit Fe /AA
3+
induced oxidation, scavenge free radicals, and act as reductants (Khanduja,
2003; Ozsoy et al., 2009; Brewer, 2011). Spices and herbs, used in foods for
their flavor and in medicinal mixtures for their physiological effects, often
contain high concentrations of POH that have strong H-donating activity
(Lugasi et al., 1995; Muchuweti et al., 2007; Brewer, 2011).

2.5 ROLE OF LIPID FRACTIONS IN RADICAL SCAVENGING AND
ANTIOXIDANT ACTIVITY

Radical scavenging activity (RSA) tests are used to evaluate the health
impact of many bioactive compounds found in foods. RSA tests like DPPH
and galvinoxyl free radicals are generally used for seed oils and their free
radical quenching ability are measured by spectrophotometric and ESR
assays. Generally, it is accepted that the higher the degree of unsaturation of
an oil, the more susceptible it is to oxidative deterioration. RSA of seed oil
fractions like neutral lipids (NL), glycolipids (GL), and PL is also studied.
The results revealed that the PL fraction had the strongest antiradical action
followed by GL and NL, respectively (Ramadan et al., 2003). The radical
quenching property of GL was expected to be due to reducing sugars in
all GL components and the sterol moiety in steryl glucoside. Moreover,
less polar POH that have been extracted with GL may be responsible for