Particle-stabilized emulsions, known as Pickering emulsions (PEs), have garnered significant research attention due to the high detachment energy of the particles that imparts high resistance to droplet coalescence, unlike conventional emulsions stabilized by small, low molecular weight emulsifiers. Protein-based particles are well-established in literature to act Pickering stabilizers. Besides single protein-based particles, there has been increasing attention towards hybrid particles where the particles are combinations of proteins with other natural molecules (often macromolecules) to provide enhance particle adsorption and stabilizing properties, as well as to improve other properties such as dual delivery of encapsulated bioactives and modulation of lipid digestion. In nature, plant-derived phenolic compounds such as flavonoids tend to co-exist in self-assembly with proteins in biological systems, particularly in food matrices. Therefore, in this thesis, plant proteins and flavonoids have been employed to design hybrid particles via non-covalent interactions to enhance not only the particle properties and thus the physicochemical stability of the emulsions that they stabilize, but also to potentially deliver the health-promoting properties of the flavonoids, i.e., dual functionality.
Potato protein (PoP) and the flavonoid quercetin (QC) were used to form the hybrid (PoPQC) particles, at different mass ratios (PoP: QC) at pH 7.0. Complex formation between PoP and QC appeared to be primarily via hydrophobic and hydrogen bonding interactions, conjugation resulting in conformational changes in the protein structure. The mass ratio markedly affected the PoPQC particle size of and consequently their effectiveness as stabilizers of Pickering emulsions (E-PoPQC).
The interfacial properties of the PoPQC and the stability of the corresponding E-PoPQC were studied, also when subjected to in vitro gastrointestinal digestion. Physicochemical and microstructural properties across various length scales were evaluated and compared to conventional oil-in-water emulsions stabilized by native PoP. The PoPQCs were superior in inhibiting droplet coalescence compared to conventional emulsions, attributed to the Pickering effect plus bridging between PoPQC in the bulk aqueous phase. In addition, the PoPQC imparted higher resilience in acidic pH and raised ionic strength (by addition of NaCl). In vitro digestion studies, E-PoPQC also showed slowing of lipolysis, which also enhanced delivery of QC. Thus, such particles might be particularly advantageous in the nutraceutical and functional food industries, among other colloidal applications.
