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

The antioxidant activity of six synthetic 1,4-dihydropyridine (DHP) derivat ives was tested in an azobis-amidinopropane dihydrochloride initiated P-car otene-methyl linoleate peroxidation model system. Radical scavenging activi ty of the derivatives was estimated by measuring their reactivity with stab le N,N-diphenyl-N'-picrylhydrazyl radicals. The antioxidant activity of the se different derivatives was also evaluated in traditional sunflower oil an d its 20% oil-in-water emulsion in the dark at 60 degrees C, as well as dur ing 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 peri ods of storage. Butylated hydroxytoluene was used as a standard antioxidant and different plant extracts were used for comparison of antioxidant activ ities throughout this study. All synthetic compounds showed antioxidant act ivity, while plant extracts acted as pro-oxidants upon light exposure. Thre e derivatives of DHP, without substitution at position 4, showed highest an tioxidative 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 deriva tive of DHP with a phenyl group at position 4 showed high radical scavengin g activity, and high antioxidant activity in sunflower oil-in-water emulsio n, but was less active in model system and sunflower oil. The hydrophobic d erivatives of DHP with a phenyl group at position 4 showed high antioxidant activity in model system but were the lowest active derivatives in sunflow er oil and its emulsion. (C) 1999 Elsevier Science Ltd. All rights reserved .