Loading of lutein in egg-sphingomyelin vesicles as lipid carriers: thermotropic phase behaviour, structure of sphingosome membranes and lutein crystals

Abstract Lutein is a xanthophyll carotenoid provided exclusively by the diet, that has protective functions and beneficial effects on human health. Supplementation in lutein is necessary to reach the recommended daily dietary intake. However, the introduction of lutein into foods and beverages is a real challenge since this lipophilic nutrient has a poorly aqueous solublility and a low bioavailability. In this study, we investigated the capacity of egg-sphingomyelin (ESM) vesicles called sphingosomes to solubilise lutein in the bilayers. The thermal and structural properties of ESM bilayers were examined in presence of various amount of lutein by differential scanning calorimetry (DSC) and temperature-controlled X-ray diffraction (XRD), the structures of sphingosomes and lutein crystals were observed by microscopic techniques. ESM bilayers were in the fluid Lα phase above the phase transition temperature Tm = 39.6°C and in the lamellar ripple Pβ’ phase below Tm where ESM sphingosomes exhibited ondulations and were facetted. Lutein was successfully incorporated into the ESM bilayers and induced a desorganisation in their packing. For ESM/lutein 90/10 % mol (91.8/8.2 %wt ; 89 mg lutein / g ESM), lutein partitioning occured with the formation of lutein crystals in the aqueous phase together with lutein-loaded ESM vesicles. This study highlighted the capacity of new lipid carriers such as egg-sphingosomes to solubilise lutein and opens perspectives for the formulation of effective lutein-fortified functionnal foods and beverages providing health benefits.