Antioxidant activity of 1,4-dihydropyridine derivatives in β-carotene-methyl linoleate, sunflower oil and emulsions

The antioxidant activity of six synthetic 1,4-dihydropyridine (DHP) derivatives was tested in an azobis-amidinopropane dihydrochloride initiated P-carotene-methyl linoleate peroxidation model system. Radical scavenging activity of the derivatives was estimated by measuring their reactivity with stable N,N-diphenyl-N'-picrylhydrazyl radicals. The antioxidant activity of these different derivatives was also evaluated in traditional sunflower oil and its 20% oil-in-water emulsion in the dark at 60 degrees C, as well as during storage of sunflower oil in the dark and with light exposure at ambient temperatures. The primary (conjugated diene hydroperoxides) and secondary (hexanal, pentanal) oxidation products were monitored during different periods of storage. Butylated hydroxytoluene was used as a standard antioxidant and different plant extracts were used for comparison of antioxidant activities throughout this study. All synthetic compounds showed antioxidant activity, while plant extracts acted as pro-oxidants upon light exposure. Three derivatives of DHP, without substitution at position 4, showed highest antioxidative activity in model system and sunflower oil and its emulsion in the dark at 60 degrees C as well as during storage of sunflower oil in the dark and with light exposure at ambient temperature. The hydrophilic derivative of DHP with a phenyl group at position 4 showed high radical scavenging activity, and high antioxidant activity in sunflower oil-in-water emulsion, but was less active in model system and sunflower oil. The hydrophobic derivatives of DHP with a phenyl group at position 4 showed high antioxidant activity in model system but were the lowest active derivatives in sunflower oil and its emulsion. (C) 1999 Elsevier Science Ltd. All rights reserved.