Reactivity of beta-carotene towards peroxyl radicals studied by laser flash and steady-state photolysis.
Peroxyl radicals, as model for peroxyl radicals formed during autoxidation of lipids, have been generated in three solvent systems (cyclohexane, tetrahydrofuran and tert-butanol/water) by steady-state and laser flash photolysis, and their reaction with beta-carotene studied. Steady-state photolysis experiments showed that alkyl, alkoxyl and alkylperoxyl radicals all react with beta-carotene. However, laser flash photolysis experiments indicated that the reaction with peroxyl radicals (second-order rate constant estimated to be less than 10(6) M(-1) s(-1)) is slower than with alkyl and alkoxyl radicals, and that beta-carotene is hence a poor direct scavenger of peroxyl radicals. Scavenging of peroxyl radicals by beta-carotene is suggested not to proceed via electron transfer but rather by adduct formation and/or hydrogen abstraction. For different phenoxyl radicals, differences in reactivity towards beta-carotene seem to be correlated with standard reduction potential.
Mortensen
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Food Chemistry, Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark. am@kvl.dk
Skibsted
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LH
D003510:Cyclohexanes / Q000737:chemistry; D016166:Free Radical Scavengers / Q000737:chemistry; D005663:Furans / Q000737:chemistry; D007834:Lasers; D010545:Peroxides / Q000737:chemistry*; D010782:Photolysis; D012997:Solvents; D014867:Water / Q000737:chemistry; D019207:beta Carotene / Q000737:chemistry*; D020002:tert-Butyl Alcohol / Q000737:chemistry
D003510:Cyclohexanes; D016166:Free Radical Scavengers; D005663:Furans; D010545:Peroxides; D012997:Solvents; D019207:beta Carotene; D014867:Water; C111570:di-tert-butyl peroxide; C049375:perhydroxyl radical; C018674:tetrahydrofuran; D020002:tert-Butyl Alcohol