Curcumin is a potent bioactive polyphenolic compound but its bioavailability when orally administered is limited because of its low solubility in aqueous environments and chemical/ metabolic degradation during gastrointestinal transit. Oil-in-water emulsions have been extensively used as delivery systems for curcumin to target physiological sites. Particularly, emulsions stabilized by solid particles, also known as Pickering emulsions, have gained remarkable research interest as delivery vehicles due to their exceptional resistance to coalescence over prolonged periods of time and the fact that these particles are not desorbed by intestinal biosurfactants (bile salts) because of their high detachment energies. This thesis focuses on the design of complex particulate Pickering interfaces using two types of interactions (i.e. electrostatic and covalent) between whey protein and polysaccharides (dextran sulphate or dextran). Hence, three different Pickering emulsions; whey protein isolate nanogel particle-stabilized (EWPN), dextran sulphate coated-whey protein isolate nanogel particle-stabilized (DxS-EWPN) and whey protein isolate-dextran conjugated (or Maillard) microgel particle-stabilized (EWPDxM) Pickering emulsions were created as delivery vehicles for curcumin.
For EWPN, controlled retention of curcumin was associated with the effect of pH and ionic strength on the partitioning of curcumin between the oil phase and the nanogel particle-laden interface. Also, by using an in vitro gastric model, pepsin hydrolysis was restricted in DxS-EWPN compared to EWPN. In addition, Maillard conjugation was used to engineer novel conjugated microgel particles (WPDxM) that could stabilize Pickering emulsions (EWPDxM) that exhibited gastric-stable properties as opposed to non-conjugated systems. Finally, the bioaccessibility and cellular uptake of curcumin by Caco-2 cells in the three different Pickering interfaces was evaluated after in vitro digestion. All three systems offered similar bioaccessibility due to similar degree of free fatty acid release during in vitro intestinal digestion. Nevertheless, the uniqueness was that DxS-EWPN and EWPDxM had better cell viability and cellular internalization of curcumin in comparison to EWPN.
In summary, findings from this PhD ranges from colloidal design of novel biocompatible Pickering emulsion-based delivery vehicles, to identifying the vehicles that offer optimized gastric stability of emulsions and cellular delivery of bioactives (curcumin). These insights can be used for rational design of functional foods, food supplements, and for oral pharmaceutical and cosmetic applications in the future.
