The efficiency of the generation of photochemically active triplet states in oils containing various amounts of natural pigments

Absorption, fluorescence emission and excitation spectra as well as time resolved photothermal signals of oils, obtained by pressing the following types of seeds: evening primrose seeds, rapeseeds, borage seeds and viper's bugloss seeds, were measured. It was found that the oils differed in the compositions of fatty acids, acid values, peroxide values and contents of pigments. The oils contained not only various tocopherols and sterols but also different amounts of chlorophylls and carotenoid pigments. The chemical bleaching procedure used causes a decrease in the pigment content and changes acid values in the bleached oils in comparison with natural (unbleached) oils. The bleached oils exhibit predominantly fluorescence of fatty acids and products of their degradation. In natural oils, a high pigment and low fatty acid emission is observed, because of the excitation energy transfer from these acids to pigments that takes place. The ratios of fast thermal deactivations of natural oils to those of the bleached ones were different for various oils. This suggests that also the change in the efficiencies of triplet state generation due to bleaching differed for these oils. On the basis of the results presented it is possible to predict the influence of the oils' bleaching procedure on their stability during storage.