Double emulsion derived from kafirin nanoparticles stabilized Pickering emulsion: Fabrication, microstructure, stability and in vitro digestion profile

Edible colloidal particles stabilized Pickering emulsions have gained renewed research interest during the past ten years. The concept of stabilizing at least one interface of a double emulsion with a layer of colloidal particles, or Pickering double emulsion, has been realized only in very few cases. Unique properties of Pickering double emulsions, such as interfacial structure, instability mechanism and digestion profile after oral intake have scarcely been investigated. In this work, a water-in-oil-in-water (W/O/W) Pickering double emulsion utilizing kafirin nanoparticles as outer layer stabilizer (KDE) was formulated. The effects of formulation parameters, including lipophilic emulsifier content, volume ratio of inner water phase (W1) to oil phase (O), volume ratio of W1/O to external water phase (W2) and kafirin particle concentration, on the formation of KDE were systematically investigated. The cross-section structure and the attachment of protein particles at the external interface were revealed via cryo-scanning electron microscopy (cryo-SEM). Its structural instability during storage was then studied by monitoring the leakage of encapsulated dye and structural evolution via confocal laser scanning microscopy. Finally, the digestion profiles in simulated gastric and intestinal fluids were assessed by microscopic analysis and in vitro lipolysis. Results suggest that osmotic pressure gradients-driven swelling is the major challenge for long-term stability of KDE during storage and processing. Under simulated gastric digestion process, KDE underwent structural collapse and its lipid digestion profile in simulated intestinal fluids followed similar trend as the kafirin particles-stabilized single Pickering emulsion.