The photochemical stability of oil from Evening Primrose seeds

Photochemical reactions taking place in oil to which was added chlorophyll a as well as P-carotene and subjected to illumination for different times, have been investigated by measuring the absorption, fluorescence emission and fluorescence excitation spectra. The addition of carotene was found to greatly lower chlorophyll degradation as a result of the quenching of chlorophyll triplet states; however, its presence also influence the generation of other oil photoproducts. A comparison of the photoreactions induced by the light absorbed predominantly by chlorophyll-like pigments with those induced by bright light covering practically the whole visible region implies that the majority of the photoreactions occur with the participation of excited chlorophyll molecules. The singlet excitation energy of beta-carotene is not transferred to chlorophyll. The quenching of photochemically active triplets of chlorophyll alters the extent of oil degradation imparted by this excitation. The absorption and emission spectra of the oil degradation products are superimposable and, therefore, the quantitative analysis of the products is not easy. The generation of malonic dialdehyde, which is the main product of oil degradation, is a little slower in the presence of carotenoids, which suggests that some components within the oil protect against photooxidation by the addition of carotenoids. (c) 2005 Elsevier Ltd. All rights reserved.