Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.