Rutin-casein co-precipitates as potential delivery vehicles for flavonoid rutin

The purpose of this research was to develop a simple, cost-effective, biocompatible, and biodegradable delivery system for delivering high concentrations of rutin as a health-promoting polyphenolic compound. A concentrated solution (10% w/v) of sodium caseinate (NaCas) was brought to alkaline pH, and rutin (10% w/v) and trehalose (0, 2.5, or 5% w/v) were added. The mixture was then acidified, which caused NaCas, rutin, and trehalose to co-precipitate, and the product was lyophilised. The high-performance liquid chromatography (HPLC) results showed a very high entrapment efficiency and loading capacity for rutin (98.1% and 48.6%, respectively). Dispersibility experiments with static light scattering suggested that pH treatment, NaCas, and trehalose all improved the dispersibility of the powders in the aqueous medium (phosphate buffer, pH 7.0). Scanning electron microscopy (SEM) revealed some considerable morphological changes for rutin because of the pH-treatment so that the degree of crystallinity of rutin crystals changed substantially in the case of both rutin precipitate and the rutin-NaCas co-precipitates. SEM micrographs also showed that the addition of trehalose resulted in a porous microstructure of resultant lyophilised and milled powders. These effects were further confirmed by X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy analyses, which revealed an amorphous structure of rutin after pH-treatment and trehalose addition. Overall, the pH-treatment of rutin and its co-precipitation with NaCas in the presence or absence of trehalose resulted in a highly-dispersible powder containing a high concentration of rutin that is suitable as a delivery system for rutin-fortified foods.