The Ferric Reducing Antioxidant Power (FRAP) assay is a biochemical method used to measure the total antioxidant capacity of a sample by evaluating its ability to reduce ferric iron.
Understanding the FRAP Assay
The FRAP assay is a widely recognized and simple spectrophotometric method for assessing the antioxidant power of various substances, including biological fluids, foods, and plant extracts. It quantifies the overall reducing potential of a sample, indicating its capacity to donate electrons and neutralize free radicals.
Principle of the Assay
The core principle of the FRAP assay relies on a redox reaction. At a low pH environment, the assay measures the reduction of a ferric-tripyridyltriazine complex (Fe3+-TPTZ) to its ferrous form (Fe2+-TPTZ).
Here's a breakdown of the chemical transformation:
- Initial State: The assay mixture contains ferric-tripyridyltriazine (Fe3+-TPTZ), which is typically yellow or colorless.
- Reduction by Antioxidants: Antioxidants present in the sample donate electrons to the Fe3+-TPTZ complex.
- Color Change: This electron donation reduces the ferric iron (Fe3+) to ferrous iron (Fe2+), forming an intense blue colored ferrous-tripyridyltriazine (Fe2+-TPTZ) complex.
- Measurement: The formation of this blue complex leads to an increase in absorbance, which is measured spectrophotometrically at an absorption maximum of 593 nm. The intensity of the blue color and thus the absorbance at 593 nm is directly proportional to the total reducing power (antioxidant capacity) of the sample.
Key Components of the FRAP Assay
| Component | Role in Assay | Chemical Form | Color Change / Measurement |
|---|---|---|---|
| Ferric Ions | Electron acceptor; reduced by antioxidants | Fe3+ | N/A (Part of complex) |
| Tripyridyltriazine (TPTZ) | Chelating agent; forms complex with iron ions | TPTZ | N/A (Forms complex) |
| Antioxidants | Electron donors; reduce Fe3+ to Fe2+ | Various (e.g., ascorbic acid, polyphenols) | Directly correlated to color intensity at 593 nm |
| Low pH Environment | Optimizes the reduction reaction | Typically achieved with an acetate buffer (pH ~3.6) | Essential for the specificity and sensitivity of the assay |
Applications and Significance
The FRAP assay is widely used in various fields due to its simplicity, speed, and reproducibility. Its applications include:
- Nutritional Science: Evaluating the antioxidant content of fruits, vegetables, beverages, and other food products. This helps in understanding the potential health benefits of dietary components.
- Clinical Research: Assessing the total antioxidant status in biological samples like plasma, serum, and urine. This can provide insights into oxidative stress levels in relation to various diseases. Further information on the Ferric Reducing Antioxidant Power Assay can be found in scientific literature.
- Pharmacology: Screening potential antioxidant compounds from synthetic or natural sources.
- Environmental Science: Analyzing the antioxidant capacity of water or soil samples.
By providing a quantifiable measure of a sample's antioxidant power, the FRAP assay contributes significantly to understanding the role of antioxidants in health, disease, and food quality.
