Page 215 - Natural Antioxidants, Applications in Foods of Animal Origin

194 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir and odor and able to distinguish them for different meat species. Amongst

the chemical methods, total AOA is measured by ferric reducing antioxidant
power (FRAP) assay. FRAP assay uses antioxidants as reductants in a redox-
linked colorimetric method, employing an easily reduced oxidant system
present in stoichiometric excess. At low pH, reduction of ferric tripyridyl-
triazine (Fe III–TPTZ) complex to ferrous form (which has an intense blue
color) can be monitored by measuring the change in absorption at 593 nm.
The reaction is non-specific, in that any half reaction that has lower redox
potential, under reaction conditions, than that of ferric ferrous half reac-
tion, will drive the ferrous (Fe III to Fe II) ion formation. The change in
absorbance is, therefore, directly related to the combined or “total” reducing
power of the electron donating antioxidants present in the reaction mixture.
The ability to scavenge DPPH radical by added antioxidant can be measure
at 517 nm wavelength to know efficacy of antioxidant compound. DPPH
can make stable free radicals in aqueous or ethanol solution. However,
fresh DPPH solution should be prepared before every measurement. Super-
oxide anion radical scavenging assay is based on the reduction of nitro blue
tetrazolium (NBT) in the presence of nicotinamide adenine dinucleotide
(NADH) and phenazonium methosulfate (PMS) under aerobic condition
at room temperature under the dark. Oxygen radical absorption capacity
(ORAC) assay is the measure of the oxidative degradation of the fluores-
cent molecule (either beta-phycoerythrin or fluorescein) after being mixed
with free radical generators such as azo-initiator compounds. Azo-initiators
are considered to produce the per-oxiradical by heating, which damages the
fluorescent molecule, resulting in the loss of fluorescence. Antioxidants are
considered to protect the fluorescent molecule from the oxidative degenera-
tion. The degree of protection is quantified using a fluorometer. Fluorescein
is currently used most as a fluorescent probe. Equipment that can automati-
cally measure and calculate the capacity is commercially available. ABTS
method is based on the ability of antioxidants to quench the long-lived
ABTS radical cation, a blue/green chromophore with characteristic absorp-
tion at 734 nm, in comparison to that of standard antioxidants. ABTS was
dissolved in water to a 7 mM concentration. ABTS radical cation (ABTS )
+
was produced by reacting ABTS stock solution with 2.45 mM potassium
persulfate (final concentration) and allowed the mixture to stand in the dark
at room temperature for 16 h before use. As ABTS and potassium persul-
fate react sterio-chiometrically at a ratio of 1:0.5 (mol mol ), this results
-1
in complete oxidation of ABTS. Oxidation of ABTS commenced immedi-
ately, but the absorbance was not maximal and stable until 6 h had elapsed.