Spectroscopic Analysis and Electron Microscopic Observation of Lutein Dispersed in Bile Acid Solutions

Spectroscopic and electron microscopic studies of lutein dispersed in aqueous solutions of the bile acids, sodium cholate (CA), sodium deoxycholate (DCA), and sodium chenodeoxycholate (CDCA) were done. The bile acids caused the lutein molecules to form water-soluble aggregates of right-handed helices, which gave characteristic ellipticities in the wavelength range of 350-450 nm. The molar ellipticity of lutein increased during aggregation. The ellipticities of lutein wax maximum at about 26 mM CA, 3 mM DCA, and 7 mM CDCA. The maximum ellipticity of lutein in CA was larger than those in the two other bile acids. This means that CA makes more regular lutein aggregate than DCA or CDCA. The binding ratio of CA to lutein was estimated to be 1000-3000 mol/mol, but that of DCA to lutein was 80 mol/mol. In the CA solution, large rod-shaped lutein aggregates 1.5-3μm long and 0.2-0.8μm in diameter were observed under the electron microscope. Small spherical particles 0.3μm in diameter adhered to the lutein aggregates. The number of these particles increased as the CA concentration increased, indicating that they were CA micelles. Therefore, lutein seemed to interact with the CA micelles.