Nanoencapsulation of quercetin and curcumin in casein-based delivery systems

Direct incorporation of hydrophobic nutraceuticals into liquid foods faces different technological challenges, namely low water-solubility and limited physiochemical stability. Nanoencapsulation may facilitate dissolution and protection of lipophilic bioactives. In this study, a hierarchical approach (ligand binding to sodium caseinate and then either re-assembling the micellar nanostructures or formation casein nanoparticles) was used to encapsulate two phenolic compounds, including curcumin and quercetin. As determined by spectrofluorometry, the binding stoichiometry of quercetin and curcumin were 0.96 and 0.78, respectively. The average particle size of re-assembled casein micelles (r-CMs) was smaller than that of casein nanoparticles (CNPs). The effect of quercetin loading on increasing the particle size of r-CMs was higher than that of curcumin loading due to the higher binding affinity of quercetin. The entrapment efficiency of both ligands was higher than 90%. The ejection of ligands from the nanocarriers was negligible over time, but not as a function of pH in the case of quercetin-loaded nanocarriers. Both CNP and r-CM significantly improved the chemical stability of phenolic compounds during an accelerated shelf-life test. Formation of r-CMs was confirmed, likely for the first time, by measuring the changes in the relative viscosity during the re-assembly process. The aqueous solubility of curcumin and quercetin after loading in r-CMs was higher than that of free polyphenol molecules. Generally, the viability of MCF-7 human breast cancer cells in the presence of different samples followed this order: digested polyphenol-loaded r-CMs < non-digested polyphenol-loaded carriers < free polyphenol molecules. TEM images confirmed the formation of r-CMs.