Synergistic interactions of plant protein microgels and cellulose nanocrystals at the interface and their inhibition of gastric digestion of Pickering emulsions

Pickering emulsions have possibilities for optimizing transport of nutraceuticals, pharmaceuticals and other bioactive compounds in human physiology. So-called ultra-stable Pickering emulsions can often get destabilized in the gastric digestion regime if the particles are proteinaceous in nature. The present study seeks to test how the interfacial structure can be engineered via synergistic particle-particle interactions to impact gastric coalescence of Pickering emulsions. In this study, we designed plant-based protein particle stabilized oil-in-water emulsions (PPM-E, with 20 wt% sunflower oil,) via pea protein microgels (PPM at 1 wt%). The PPM hydrodynamic diameter ≈ 250 nm. In vitro gastric digestion of PPM-E confirmed droplet coalescence within 30 min of pepsin addition. Supposedly surface active cellulose nanocrystals (CNCs, at 1-3 wt%) were added to PPM-E at pH 3.0, to see if could act as a barrier to interfacial pepsinolysis, due to the CNC and PPM being oppositely charged at this gastric pH value. A combination of confocal microscopy, zeta-potential and Langmuir trough measurements suggested that CNCs and PPMs might form a combined layer at the O/W interface, owing to the electrostatic attraction between them. CNCs at > 2 wt% inhibited pepsinolyis of the adsorbed PPM film and thus droplet coalescence. However, increasing concentrations of CNC also increased the bulk viscosity of the PPM-E and eventually caused gelation of the emulsions, which would also delay their gastric breakdown. In conclusion, tuning bulk and interfacial structure of Pickering emulsions via synergistic interactions between two types of particles could be an effective strategy to modify enzymatic breakdown of such emulsions, which would have important applications in pharmaceuticals, foods and other soft matter applications.