RELATIVE STABILITY OF CAROTENOID RADICAL CATIONS AND HOMOLOG TOCOPHEROXYL RADICALS - A REAL-TIME KINETIC-STUDY OF ANTIOXIDANT HIERARCHY

Real time detection following laser flash photolysis of transient caro tenoid radical cations and tocopheroxyl radicals formed in chloroform and bleaching of the carotenoids has allowed interaction between carot enoids and tocopherols to be studied. It is found that alpha-, beta-, and gamma-tocopherol reduce all the carotenoid radical cations investi gated whereas the delta-tocopheroxyl radical can be reduced by lycopen e and beta-carotene, Astaxanthin, canthaxanthin, and beta-apo-8'-carot enal radical cations are scavenged rapidly by all four tocopherol homo logues whereas the other carotenoid radical cations react much more sl owly with the tocopherols. The results allow the antioxidant hierarchy to be established: alpha-tocopherol > lycopene similar to beta-tocoph erol similar to gamma-tocopherol > beta-carotene > zeaxanthin similar to delta-tocopherol > lutein > echinenone much greater than canthaxant hin similar to beta-apo-8'-carotenal > astaxanthin. (C) 1997 Federatio n of European Biochemical Societies.