Determination of the activity of an antioxidant by the DPPH° assay

The DPPH° test is used to measure the antiradical power of pure molecules or plant extracts in a model system (organic solvent, room temperature). It measures the capacity of an antioxidant (AH, generally phenolic compounds) to reduce the chemical radical DPPH° (2,2-diphenyl-1-picrylhydrazyl) by hydrogen transfer. DPPH°, which is initially violet, becomes DPPH-H, pale yellow.

DHHPº reduction is easily measured by spectrophotometry at 515 nm (λmax DPPH°). The reaction speed depends on the nature of the antioxidant, and the amount of DPPH-H formed depends on the concentration of the antioxidant.

Illustration of the DDPH° spectrum. On the abscissa the wavelength in nm, on the ordinate the absorbance. The stylized curve shows several peaks.

Two antyoxidant curves A and B, with time on the abscissa and residual DDPH° in % on the ordinate.

DDPH° kinetics of a green tea extract. 5 curves with the same origin but a more and more rapid decline represent 0.5, 1, 1.5, 2 and 3 mg/L.

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