Morphology and Structure of Solid Lipid Nanoparticles Loaded with High Concentrations of β-Carotene

Solid lipid nanoparticles (SLNs) containing up to 37.S wt % all-trans beta-carotene in the lipid phase are potential water-dispersible food colorants. SLNs have been made by hot-melt high-pressure homogenization with fully hydrogenated sunflower oil and with polysorbate 80 and sunflower lecithin as stabilizers. Atomic force microscopy revealed the SLNs had thin platelet structures most likely derived from the triglyceride crystal beta-form, as detected by X-ray diffraction. No indications of crystalline beta-carotene were detected. High-performance liquid chromatography analysis showed the extensive isomerization of beta-carotene into more than 10 cis isomers, suggesting that it is present as an amorphous mixture. The high beta-carotene loadings did not affect the triglyceride crystal structure and the morphology of the SLNs. It is suggested the SLNs consist of a platelet core of crystalline triglyceride surrounded by an amorphous beta-carotene-containing layer. The layered structure is suggested to affect the coloring power of the SLNs at beta-carotene loadings above 15 wt % of the lipid phase.