Milk protein-based carrier system for encapsulation of dietary polyphenol rutin: Molecular-level interactions and enhanced bioactivities

The self-assembly process of proteins provides plenty of potential for redesigning and combining them into supramolecular assemblies for real-time applications. The present study demonstrates the encapsulation of dietary polyphenol rutin in beta-casein (beta CN) micellar cavity followed by their molecular interactions and biological implications. The prepared rutin-loaded beta CN particles (DLS: 274.2 +/- 3.86 nm; TEM: similar to 200 nm) appeared to be smoothly spherical. Isothermal titration calorimetry (ITC) studies indicated that the encapsulation process was thermodynamically favorable and a typical example of entropy-driven hydrophobic interaction (Delta H: 38.1 kJ mol(-1); T Delta S = 51.9 kJ mol(-1) K-1). The molecular interaction of rutin with beta CN was characterized by absorption, steady-state fluorescence, and time-resolved fluorescence spectroscopic studies. The intrinsic fluorescence of beta CN was quenched by rutin via a static mechanism with a favorable binding affinity. Molecular docking studies suggested the involvement of hydrophobic and hydrogen bonding interactions between the concerned entities. A sustained release mechanism followed by significant improvement in the cytotoxicity of rutin was observed after encapsulation. An in vitro digestion model mimicking gastric and intestinal phases was also employed to study the bioaccessibility. Our study may assist in formulating more efficient casein-based carrier systems to enhance the bio-efficacy of polyphenols.