Free Radical Mediated Oxidative Degradation of Carotenes and Xanthophylls

Abstract

This article reviews the excited-state quenching, pro-vitamin A activity and anticarcinogenicity of carotenes and xanthophylls in relation to their chemical structures. Excited-state quenching improved with the length of the conjugated chain structure. Pro-vitamin A activity was dependent on the presence of at least one beta-ionyl ring structure. The effectiveness of carotenoids as antioxidants depended on their ability to trap peroxyl radicals with production of resonance-stabilized carotenyl radicals. The products identified from oxidations of carotenes and xanthophylls with molecular oxygen and other oxidizing agents are presented. The free radical-mediated mechanisms that have been proposed to account for the different classes of products are reviewed.

Keywords

• free radicals
• carotenoids
• xanthophylls
• oxidation
• β-carotene
• canthaxanthin
• β-ionone
• retinal
• apo-carotenoids