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, D∼ 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.