Designing biopolymer-coated Pickering emulsions to modulate in vitro gastric digestion: a static model study
The aim of this study was to restrict the degree of gastric destabilization of Pickering emulsions by using electrostatic deposition of a biopolymeric layer at the proteinaceous particle–laden oil–water interface. Pickering emulsions (20 wt% oil) were prepared using whey protein nanogel particles (WPN, Dh ∼ 91.5 nm) (1 wt%) and the emulsions were coated by a layer of anionic polysaccharide, dextran sulphate (DxS) of molecular weight (MW) of 40 or 500 kDa, respectively. The hypothesis was that DxS coating on the protein nanogel particle–laden interface would act as a steric barrier against interfacial proteolysis of WPN by pepsin. During static in vitro gastric digestion, the droplet size, ζ-potential, microstructure (confocal microscopy with fluorescently labelled dextran) and protein hydrolysis were monitored. The ζ-potential measurements confirmed that 0.2 wt% DxS was sufficient to coat the WPN-stabilized emulsion droplets with clear charge reversal from +35.9 mV to −28.8 (40 kDa) and −46.2 mV (500 kDa). Protein hydrolysis results showed a significantly lower level of free amino groups upon addition of 0.2 wt% DxS of either 40 or 500 kDa MW to the WPN (p < 0.05). Emulsions coated with DxS-500 kDa presented stable droplets with lower degree of pepsin hydrolysis of the adsorbed layer as compared to those coated with DxS-40 kDa or uncoated protein nanogel-stabilized interface after 120 min of digestion, highlighting the importance of charge density and molecular weight of the polymer coating. Insights from this study could enable designing gastric-stable emulsions for encapsulation of lipophilic compounds that require delivery to the intestine.