Effects of Astragalus polysaccharide on the solubility and stability of 15 flavonoids

Poor solubility and stability are limitation factors of flavonoids application. Polysaccharides from herbs have been proven to be functional foods and potential promising natural supplements with large molecular weight and complex structures. Astragalus polysaccharides (APS) are the main components of Astragalus membranaceus (Fisch.) and novel synergistic pharmacological effects between Astragalus polysaccharides and flavonoids have been reported. However, the general effects of polysaccharides when co-administered with flavonoids are currently unknown. Herein, the influences of APS on aqueous solubilities and stabilities of fifteen flavonoids were systematically investigated, and the mechanism of effects of polysaccharides on flavonoids was further considered. The results showed that APS could significantly enhance the solubilities and stabilities of the flavonoids, with solubilization effect improved by 68.88-fold for quercetin and negatively correlated with the aqueous solubility of the flavonoid itself. A phase solubility study and Differential scanning calorimetry characterization indicated that APS could form complexes with flavonoids at 1:1 ratio with K values ranging from 1491 to 55,395 L·mol-1, a tendency to improved solubilization at higher association constant values was also observed. Those findings could provide the basis for a new approach to solving the problems of poor solubility and stability of flavonoids through the application of natural macromolecules.