Inhibition of oxidation in 10% oil-in-water emulsions by beta-carotene with alpha- and gamma-tocopherols

The effects of low concentrations of beta-carotene, alpha-, and gamma-tocopherol were evaluated on autoxidation of 10% oil-in-water emulsions of rapeseed oil triacylglycerols. At concentrations of 0.45, 2, and 20 mu g/g, beta-carotene was a prooxidant, based on the formation of lipid hydroperoxides, hexanal, or 2-heptenal. In this emulsion, 1.5, 3, and 30 mu g/g of gamma-tocopherol, as well as 1.5 mu g/g of alpha-tocopherol, acted as antioxidants and inhibited both the formation and decomposition of lipid hydroperoxides. Moreover, at a level of 1.5 mu g/g, gamma-tocopherol was more effective as an antioxidant than a tocopherol. At levels of 0.5 mu g/g, both alpha- and gamma-tocopherol significantly inhibited the formation of hexanal but not the formation of lipid hydroperoxides. Oxidation was effectively retarded by combinations of 2 mu g/g beta-carotene and 1.5 mu g/g gamma- or alpha-tocopherol. The combination of beta-carotene and alpha-tocopherol was significantly better in retarding oxidation than a-tocopherol alone. While gamma-tocopherol was an effective antioxidant, a synergistic effect between beta-carotene and gamma-tocopherol could not be shown. The results indicate that there is a need to protect beta-carotene from oxidative destruction by employing antioxidants, such as alpha- and gamma-tocopherol, should beta-carotene be used in fat emulsions.