Antioxidant behaviour of caffeine: Efficient scavenging of hydroxyl radicals

Considerable controversy exists in the literature regarding the toxicity of coffee, including its possible carcinogenic and anticarcinogenic properties. This study reports on the reaction of 1,3,7-trimethylxanthine (caffeine) with the hydroxyl radical (·OH), as investigated by electron spin resonance (ESR) spin trapping. The ·OH was generated by the Fenton reaction (Fe²⁺ + H₂O₂) as well as by the reaction of chromium(V) with H₂O₂. The results show that caffeine effectively scavenges ·OH with a reaction rate constant of ∼ 5.9 × 10⁹ m^-1 sec^-1 that is comparable with those of other efficient ·OH radical scavengers. ESR measurements provide evidence that a caffeine-derived oxygen-centred radical is formed in the reaction of caffeine with ·OH and suggest a biochemical basis for the understanding of the reported anticarcinogenic properties of caffeine and related methylxanthine compounds.