DPPH Radical Scavenging Assay — Antioxidant Capacity Measurement
2,2-Diphenyl-1-Picrylhydrazyl Radical Scavenging Assay · Also known as: DPPH antioxidant assay, DPPH free radical scavenging method, DPPH decolorization assay, radical scavenging activity test
The DPPH radical scavenging assay is a rapid, widely used spectrophotometric method for measuring the antioxidant capacity of foods, plant extracts, and purified compounds. It quantifies how effectively a sample neutralises the stable synthetic free radical DPPH (2,2-diphenyl-1-picrylhydrazyl) by measuring the resulting colour change from deep violet to yellow, making it a cornerstone technique in food science, nutraceutical research, and phytochemistry.
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When to use it
Use the DPPH assay when you need a fast, low-cost, and reproducible estimate of the hydrogen-atom or electron-donation antioxidant capacity of a sample, particularly in the early screening phase of food science, phytochemistry, or nutraceutical research. It is well-suited for comparing antioxidant activity across multiple extracts or fractions. Do not rely on DPPH alone as the sole measure of antioxidant capacity: because the radical is dissolved in organic solvent, results may not reflect behaviour in aqueous or lipid biological environments. Complement with ABTS, FRAP, or ORAC assays for a fuller profile, and pair with total phenolic content (Folin-Ciocalteu) to contextualise the findings chemically.
Strengths & limitations
- Simple, rapid protocol executable in standard laboratory settings without specialised equipment beyond a UV-Vis spectrophotometer.
- Stable DPPH radical allows extended reaction windows and high reproducibility between replicates.
- Quantitative output (% RSA, IC50, Trolox Equivalents) enables direct comparison across studies when standardised protocols are followed.
- Compatible with a wide range of sample matrices including plant extracts, beverages, oils, and isolated phenolic compounds.
- Well-established method with decades of literature, facilitating benchmarking against published reference values.
- Low reagent cost and small sample volumes make it amenable to high-throughput microplate-format screening.
- DPPH is soluble only in organic solvents (methanol, ethanol), so hydrophilic antioxidants in aqueous food matrices may be underestimated or require solvent extraction that can alter sample composition.
- Results are not directly comparable across studies that use different DPPH concentrations, solvent systems, incubation times, or wavelengths — lack of universal standardisation is a persistent criticism.
- The assay measures only hydrogen-atom transfer and electron-transfer mechanisms; it does not capture antioxidant activities such as metal chelation or enzyme inhibition.
- DPPH is a synthetic, non-physiological radical, so results do not necessarily predict in vivo antioxidant efficacy in biological tissues or food systems.
- Coloured or turbid samples can interfere with absorbance readings, requiring correction blanks or alternative detection methods.
Frequently asked
Why do results differ between studies using the same extract?
DPPH assay results are sensitive to reagent concentration, solvent type, sample-to-reagent ratio, incubation time, temperature, and the wavelength used for measurement. Even small deviations in protocol produce different % RSA or IC50 values. Always report all conditions in full and, where possible, express results as Trolox Equivalents using a freshly prepared calibration curve to improve cross-study comparability.
Can I use DPPH alone to conclude that a food is a good antioxidant?
No. The DPPH assay captures only a subset of antioxidant mechanisms (hydrogen-atom and electron transfer in organic solvent) and uses a synthetic, non-physiological radical. International consensus recommends using at least two complementary assays — for example DPPH with ABTS or FRAP — and correlating results with total phenolic content before drawing conclusions about overall antioxidant capacity.
What is IC50 and why does a lower value indicate stronger antioxidant activity?
IC50 is the concentration of the test sample needed to reduce the initial DPPH absorbance by 50%. Because it represents the dose required to achieve half-maximal inhibition, a lower IC50 means that less sample is needed to neutralise the same amount of radical — indicating higher antioxidant potency. IC50 values should always be accompanied by the exact DPPH concentration and conditions used.
What solvent should I use for the DPPH stock solution?
Methanol is the most commonly used solvent in the literature following the Brand-Williams et al. (1995) protocol. Absolute ethanol is an acceptable alternative and is preferred when methanol toxicity is a concern. The important rule is to use the same solvent for both the DPPH solution and the sample extract to avoid solvent-mixing artifacts that can alter radical stability and reaction kinetics.
Sources
- Blois, M. S. (1958). Antioxidant determinations by the use of a stable free radical. Nature, 181(4617), 1199–1200. DOI: 10.1038/1811199a0 ↗
- Brand-Williams, W., Cuvelier, M. E., & Berset, C. (1995). Use of a free radical method to evaluate antioxidant activity. LWT — Food Science and Technology, 28(1), 25–30. DOI: 10.1016/S0023-6438(95)80008-5 ↗
How to cite this page
ScholarGate. (2026, June 3). 2,2-Diphenyl-1-Picrylhydrazyl Radical Scavenging Assay. ScholarGate. https://scholargate.app/en/food-science/dpph-assay