Rheological modulation of egg white protein-based capillary suspensions via synergistic capillary bridging and...

Capillary suspensions are ternary solid-liquid-liquid systems formed by introducing a secondary fluid into a suspension of solid particles in a bulk liquid. While previous studies have established the concept of polymer-enhanced capillary suspensions, systematic quantitative correlations between polymer concentration and rheological performance remain lacking, and the potential of cationic biopolymers in edible systems has received limited attention. This study investigates capillary suspensions comprising corn oil (bulk phase), water (secondary phase), and egg white protein (EWP) microgel (particle phase), with chitosan (CS) introduced into the aqueous phase to modulate rheological properties. The results show that the capillary-force-driven particle network can be tuned by adjusting EWP content and water fraction, with optimal solid-like behavior achieved at water saturation > 0.15 and EWP content >30 wt%. At Φ_P = 30%, increasing water content from S = 0.05 to 0.19 led to a three-orders-of-magnitude increase in viscosity with shear-thinning behavior. Notably, at a CS concentration of 0.15 wt% in the aqueous secondary phase, the yield stress increased 6.69-fold, and the oil constraint capacity and network stability were also enhanced. Confocal laser scanning microscopy reveals a denser EWP particle network, while Fourier transform infrared spectroscopy confirms more extensive hydrogen bonding upon CS addition, consistent with the enhanced viscoelasticity. This enhancement is attributed to synergistic effects between capillary bridging and CS-mediated hydrogen bonding. Overall, this work establishes a quantitative correlation between CS concentration and rheological reinforcement, and demonstrates the feasibility of employing a cationic biopolymer to tailor edible capillary suspension networks for food applications.