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FRAP
FRAP stands for Ferric Reducing Antioxidant Power (FRAP). At low pH, reduction of
ferric tripyridyl triazine (Fe(III)(TPTZ)
2) complex to ferrous form (which has an intense
blue color) can
be monitored by measuring the change in absorption at 593nm. The
reaction is non specific, in that any half reaction that has lower redox potential,
under reaction conditions, than that of ferric ferrous half reaction, 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. But this method does not come without
any shortcomings. One is that the reaction is carried out on a rather acidic environment.
The other is that the
main reagent Fe(III)(TPTZ)
2 is not the only oxidant, many metal chelators
in food extract could bind Fe(III) and form complexes that are also capable of reacting
with antioxidants.
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