FRAP (Ferric Reducing Antioxidant Power)
Definition and meaning of FRAP (Ferric Reducing Antioxidant Power) in chemistry.
FRAP (Ferric Reducing Antioxidant Power) is a spectrophotometric assay that measures a sample's antioxidant capacity by tracking the reduction of a colorless ferric-TPTZ complex to its intensely blue ferrous form. The assay quantifies total reducing power rather than any single antioxidant compound.
In more detail
At low pH, electron-donating antioxidants in a sample reduce the Fe3+-tripyridyltriazine (Fe3+-TPTZ) complex to Fe2+-TPTZ, and the resulting color change is monitored as absorbance at 593 nm after a fixed incubation time. The absorbance increase is compared against a calibration curve made with a known reductant, usually ferrous sulfate or ascorbic acid, and results are reported as a FRAP value. Because it relies purely on single-electron transfer, FRAP only detects reducing antioxidants and misses species that work mainly by radical scavenging (hydrogen-atom transfer) without strong reducing power. It is popular in food and nutrition science for comparing antioxidant capacity across fruits, vegetables, teas, and plasma samples because it is fast, cheap, and needs only a standard spectrophotometer.
Key facts
| Full name | Ferric Reducing Antioxidant Power |
|---|---|
| Key reagent | Fe3+-TPTZ complex (2,4,6-tri(2-pyridyl)-1,3,5-triazine) |
| Detection wavelength | 593 nm |
| Field | Analytical Chemistry |
To measure the FRAP value of a green tea extract, the extract is mixed with FRAP reagent, incubated 4 minutes, and its absorbance at 593 nm is compared to a ferrous sulfate standard curve to calculate ferrous-equivalent reducing capacity.
Frequently asked questions
What does a higher FRAP value mean?
A higher FRAP value means the sample reduced more Fe3+-TPTZ to Fe2+-TPTZ, indicating greater overall reducing (antioxidant) capacity.
Does FRAP measure all antioxidants equally?
No. FRAP detects only single-electron-transfer reducing agents, so it underestimates or misses antioxidants such as thiols and carotenoids that act mainly through radical scavenging rather than reduction.