The induction period (IP) of ethyl linoleate stressed at 60 °C was monitored via the formation of hydroperoxides. The addition of lycopene (1% w/w) increased the IP from 7.0 to 10.0 h to prove the strong antioxidative potential in contrast to β-carotene with pro-oxidative effects (IP: 6.0 h), both showing strong scavenging activity under fast degradation. When peroxidation was induced by singlet oxygen, both carotenoids effectively inhibited the formation of hydroperoxides, with quenching activity only observed at low singlet oxygen concentrations, while scavenging still dominated. Thus, carotenoids did not interact with the introduced singlet oxygen but rather with the radical intermediates of fat oxidation. These experiments were then transferred to lecithin-based micelles more related to biological systems, where singlet oxygen was generated in the outer aqueous phase. Lycopene and β-carotene delayed or inhibited lipid peroxidation depending on concentration. In this setup, β-carotene showed exclusively quenching activity, while lycopene was additionally degraded to about 70%.
Keywords: carotenoids; hydroperoxides; induction period; isomerization; lipid peroxidation; micellar system; scavenging and quenching activity.