Evaluation of free radical scavenging of dietary carotenoids by the stableradical 2,2-diphenyl-1-picrylhydrazyl

In order to avoid the interference of compounds with a chromophoric system when the 2,2-diphenyl-1-picrylhydrazyl (DPPH.) method is used, a new measur e of the decrease in absorbance at 580 nm was performed (correlation coeffi cient between absorbance and DPPH. concentration, 0.9979; p < 0.01). The an tioxidant effectiveness of dietary carotenes and xanthophylls towards the s table free radical DPPH. was measured. The antioxidant activity expressed a s the amount of antioxidant able to reduce the initial DPPH. concentration to 50% (EC50), given in terms of moles of antioxidant per mole of DPPH., ra nged from 0.16+/-0.01 (lycopene) to 3.29+/-0.31 (lutein). The parameter ant iradical efficiency (AE), which involves the potency (1/EC50) and the time taken to reach the steady state at EC50 (T-EC50), was calculated to discrim inate carotenoids with no significant difference between their EC50 Compari son of the structures of the carotenoids tested revealed that the scavengin g ability towards DPPH. was increased by the length of the effective conjug ated double-bond system and was modulated by the addition of chemical group s on the terminal rings (xanthophylls). (C) 2000 Society of Chemical Indust ry.