This method measures the ability of antioxidants to reduce ferric
iron. It is based on the reduction of the complex of ferric
iron and 2,3,5-triphenyl-1,3,4-triaza-2-azoniacyclopenta-1,4-
diene chloride (TPTZ) to the ferrous form at low pH. This
reduction is monitored by measuring the change in absorption
at 593 nm, using a diode-array spectrophotometer. Antioxidant
assay can be conducted by the method developed by Benzie
and Strain (1999). Three milliliter of prepared FRAP
reagent is mixed with 100 lL of diluted sample; the absorbance
at 593 nm is recorded after a 30 min incubation at 37 C.
FRAP values can be obtained by comparing the absorption
change in the test mixture with those obtained from increasing
concentrations of Fe3+ and expressed as mM of Fe2+ equivalents
per kg (solid food) or per L (beverages) of sample.