Changing the Structure of Casein Micelles to Improve the Delivery of Bioactive Compounds
This thesis is an investigation of binding of casein micelles to polyphenols such as epigallocatechin gallate (EGCG), resveratrol, and curcumin. The incorporation of the bioactive molecules in casein micelles seems to be beneficial. The results from this study clearly demonstrated that casein micelles can incorporate polyphenols. There is a difference in the binding behaviour between curcumin and resveratrol. Curcumin is able to penetrate the core of the micelles, but resveratrol has less affinity for the hydrophobic sites, instead, it can be bind in the core of the micelles through the water channels. The processing of milk (heating, cooling, static high pressure and microfluidization) alters the surface or the internal structure of the casein micelles resulting in increased incorporation. The release of β-casein caused alteration to the core of the casein micelles, without any effect on the colloidal calcium phosphate composition and any changes in the surface properties of the micelles. These internal rearrangements lead to an increase in the affinity of the hydrophobic sites for curcumin and resveratrol in the inner core of the micelles. This work clearly confirmed that β -casein plays a role in stabilizing internal structures in the casein micelle and its release causes an increase in the micellar size by increasing the hydration and repulsion occurring within the water pockets present in the inhomogeneous inner structure of the casein micelles. Inner core of casein micelles undergoes rearrangements during application of static high pressure and microfluidization. In the case of static high pressure, the results indicated that the persistent rearrangement of the amino acid residues induced by high-pressure treatment result in an increase in the amount of curcumin association with milk proteins. It was shown that in both untreated and microfluidized milk, the presence of polyphenol molecules significantly affects rennet induced gelation, by delaying the gelation. However, the behavior of casein micelles incorporated with resveratrol is different comparing to curcumin, as resveratrol strongly affected the surface interactions during rennet-induced gelation. Further research is needed to explain the practical aspect ( functionalities such as acid gelation, emulsification and foaming) of application of casein micelles as natural nanocarrier of bioactive compounds.