Capacity of peroxyl radical scavenging and inhibition of lipid peroxidation by β-carotene, lycopene, and commercial tomato juice

Carotenoids have received much attention as natural antioxidants. The role and action of carotenoids as singlet oxygen quenchers have been well demonstrated. The radical scavenging is another function of carotenoids as antioxidants, but the method to assess the radical scavenging capacity has not been established and previous studies have given inconsistent results. Carotenoids have strong absorptions in the visible light region and, unlike phenolic antioxidants, they do not have a reactive hydrogen to donate to radicals, which make it difficult to use conventional probes for the assessment of their radical scavenging capacity. In the present study, a method for the assessment of peroxyl radical scavenging capacity by carotenoids was re-examined and applied for beta-carotene, lycopene, and commercial tomato juice. The capacity for scavenging peroxyl radicals was assessed from the effect of alpha-tocopherol on the bleaching of carotenoids being tested. Total content of carotenoids was also assessed from the rate of bleaching under constant flux of peroxyl radicals. The peroxyl radical scavenging capacity of beta-carotene and lycopene exhibited was about one-tenth of that observed for alpha-tocopherol, and the efficacy of lipid peroxidation inhibition was much smaller.