Self-assembled Casein Nanostructures to Deliver Novel Functionalities

The nanoscale micellar structure of caseins can be manipulated by mechanical forces, solvent quality, and pH to reduce turbidity, encapsulate hydrophobic compounds, and improve dispersion stability and rheological properties. The goal of this dissertation was to control the nanostructure of self-assembled caseins to deliver functionalities. The combination of treatments at pH 11.0 and acidification with citric acid was first studied to produce translucent skim milk dispersions at pH 5.5-7.0, resulting from the significantly reduced dimensions of reassembled casein nanoparticles. Using sodium caseinate (NaCas), soluble soybean polysaccharide (SSPS), and high-speed homogenization, a food grade delivery system was studied to encapsulate thymol as transparent nanodispersions. The dispersions had the improved anti-listerial activity in milk than free thymol and SSPS enabled stability at an acidity around the isoelectric point of NaCas. To improve the encapsulation efficacy, a novel method was developed to encapsulate curcumin with improved dispersibility and bioactivity by spray-drying warm aqueous ethanol solution with co-dissolved NaCas and curcumin. Utilizing pH-dependent solubility properties of curcumin and self-assembly properties of NaCas, another scalable low-energy and organic solvent free encapsulation technology was studied. Curcumin was successfully encapsulated in self-assembled casein nanoparticles by pH-cycle treatment under only mild stirring, and showed significantly improved anti-proliferation activity against human colorectal and pancreatic cancer cells. The principle was then applied to stabilize zein by mixing with NaCas at pH 11.5 and the subsequent neutralization enabled the co-assembly of zein and NaCas, showing the promise of this novel method to prepare water dispersible zein nanoparticles for applications such as delivery systems and edible packaging films. Lastly, intrinsically disordered β [beta]- and κ [kappa]-caseins were found to form amyloid-like fibrils at pH 2.0 and 90 ºC, which had a Young’s modulus of 2.35 ± 0.29 GPa and 4.14 ± 0.66 GPa, respectively, as measured using quantitative nanomechanical atomic force microscopy. The dispersion with β-casein fibrils had a viscosity more than 10 and 5 times higher than those of κ-casein and β-lactoglobulin, respectively, at 0.1 s^-1 [1/second] and comparable concentrations. Self-assembled casein nanostructures in the present dissertation may found novel applications as functional materials.