A diet, which is rich in carotenoids, offers health-related advantages with regard to degenerative diseases. This claim is associated to the antioxidative potential of the carotenoids which can be classified in carotenes and the oxygenated xanthophylls. For a better nutritional benefit of natural functional substances in food the bioavailability has to be enhanced. During food processing the disintegration of the matrix and the release of the functional substance from associations to proteins, lipids and membranes enhance the bioavailability while concomitantly Z-isomerization and oxidative degradation alter the qualitative and quantitative amounts of the carotenoids. In hen egg yolk lipophilic lutein and zeaxanthin are associated to the lipid core of the low-density lipoproteins (LDL) and to the lipid cavity of the high-density lipoproteins (HDL). Therefore, the impacts of heating and freeze-drying on the mass concentrations of the all-E- and 13-Z-isomers of lutein and zeaxanthin in egg yolk were investigated with regard to structural unfolding of the lipoproteins leading to a better extractability.

responsible : M.Sc. Severin R. Thierau