Conjugate microgel-stabilized Pickering emulsions: Role in delaying gastric digestion

In this study, a new class of microgels called ‘conjugate microgels’ was designed, where whey protein isolate (WPI) was conjugated with dextran (Dx, 500 kDa) (WPI-Dx) via Maillard reaction before fabricating the microgel particles. Such microgel particles were assessed for their abilities to act as Pickering stabilizers for oil-in-water emulsions and also checked if they offered gastric stability to the Pickering emulsions during in vitro digestion against interfacial pepsinolysis. WPI-Dx conjugates were obtained by controlled dry heating (60 °C, 79% RH, 24–48 h incubation). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and ortho-phthaldialdehyde (OPA) profile revealed that the degree of conjugation ranged from 11.6 to 28.1%. The WPI-Dx conjugates were re-dispersed and heat-treated to form heat-set gels with moduli ranging from ~45 to 250 kPa. Microgel particles (hydrodynamic diameters of 130–150 nm, ζ-potentials of −4.5 to −8.0 mV) were created by controlled shearing of these heat-set gels. Interfacial shear rheology measurements and microscopic examination confirmed that conjugated microgel particles with lower degree of conjugation (WPDx₁₀M) were effective as Pickering stabilizers. When present in an aqueous dispersion, WPDx₁₀M had reduced degree of gastric proteolysis (120–130 μM free NH₂) as compared to non-conjugated counterparts (187–205 μM free NH₂). When present at the droplet surface, cross-correlation image analysis revealed that WPDx₁₀M was successful in delaying interfacial gastric proteolysis. Insights from this study suggest that conjugate microgel particles might be useful to design gastric-stable Pickering emulsions in the future for effective delivery of lipophilic compounds to the intestines.