Solubilization and stabilization of macular carotenoids by water soluble oligosaccharides and polysaccharides

Abstract

Xanthophyll carotenoids zeaxanthin and lutein play a special role in the prevention and treatment of visual diseases. These carotenoids are not produced by the human body and must be consumed in the diet. On the other hand, extremely low water solubility of these carotenoids and their instability restrict their practical application as components of food or medicinal formulations. Preparation of supramolecular complexes of zeaxanthin and lutein with glycyrrhizic acid, its disodium salt and the natural polysaccharide arabinogalactan allows one to minimize the aforementioned disadvantages when carotenoids are used in food processing as well as for production of therapeutic formulations with enhanced solubility and stability. In the present study, the formation of supramolecular complexes was investigated by NMR relaxation, surface plasmon resonance (SPR) and optical absorption techniques. The complexes increase carotenoid solubility more than 1000-fold. The kinetics of carotenoid decay in reactions with ozone molecules, hydroperoxyl radicals and metal ions were measured in water and organic solutions, and significant increases in oxidation stability of lutein and zeaxanthin in arabinogalactan and glycyrrhizin complexes were detected.

Keywords: Arabinogalactan; Carotenoid oxidation; Glycyrrhizic acid; Lutein; NMR relaxation; Oxygen radicals; Ozone; Surface plasmon resonance; Water-soluble complexes; Zeaxanthin.

Fig. 1

Structural formulas of zeaxanthin and lutein.

Fig. 2

Structural formulas of glycyrrhizic acid (GA) arabinogalactan (fragment).

Fig. 3

The echo decay kinetics of zeaxanthin CH protons in CPMG experiment in pure form in deuterated methanol and in the complex with sGA (5 mM) in deuterated methanol and D₂O.

Fig. 4

SPR sensorgram showing interaction of Siberian arabinogalactan (top) and Sigma arabinogalactan (bottom) with zeaxanthin.

Fig. 4

SPR sensorgram showing interaction of Siberian arabinogalactan (top) and Sigma arabinogalactan (bottom) with zeaxanthin.

Fig. 5

Kinetics of lutein concentration decay in 75% water-ethanol solution during oxidation by ozone in free form and in the presence of AG, 0.1 mM, and GA, 1 mM.

Fig. 6

Kinetics of lutein concentration decay in 75% water-ethanol solution during oxidation by ozone in free form and in the presence of AG, 0.05 mM (a), and sGA, 1 mM (b), prepared by “liquid state, ls” and “mechanochemical, ss” methods.

Fig. 6

Kinetics of lutein concentration decay in 75% water-ethanol solution during oxidation by ozone in free form and in the presence of AG, 0.05 mM (a), and sGA, 1 mM (b), prepared by “liquid state, ls” and “mechanochemical, ss” methods.

Fig. 7

Kinetics of zeaxanthin concentration decay in DMSO solution during oxidation by Fe³⁺ ions in the absence and in the presence of 1 mM of GA and sGA.

Fig. 8

Kinetics of zeaxanthin concentration decay in DMSO solution during oxidation by •OOH radicals (Fenton reaction with excess of H₂O₂) in the absence and in the presence of 1 mM of GA and sGA. [H₂O₂] = 125 mM, [Fe²⁺] = 1 mM.

Fig. 9

Decay kinetics (in logarithmic scale) of the NMR signal of zeaxanthin 4-H protons in T₂ relaxation experiment in DMSO. [Zea] = 2 mM, [GA] = 5 mM.