Rheological behavior and 3D printing performance of high internal phase emulsions stabilized by Maillard-type...

High internal phase emulsions (HIPEs) are structured, semi-solid systems with high dispersed-phase volume fractions and complex viscoelastic behavior, making them attractive for advanced food applications. In this study, Maillard-type hazelnut protein isolate (HPI) conjugates with gum Arabic (GA) or sodium alginate (SA) were used to stabilize highly concentrated emulsions and HIPEs formulated at different water:oil ratios (20:80-40:60, w/w) and conjugate concentrations (2.5-3.5%, w/w). All formulations exhibited PDI values ≤1 and negative ζ-potential values (-27 to -41 mV), indicating acceptable colloidal stability and droplet dispersion within the emulsion systems. Polysaccharide type markedly influenced emulsion structure, with HPI-SA formulations yielding smaller droplet sizes, whereas HPI-GA systems supported higher oil loadings. Steady-shear analysis showed that increasing oil fraction and conjugate concentration increased apparent viscosity and consistency in both systems, with HPI-SA formulations exhibiting higher viscosity levels. In contrast, HPI-GA systems showed stronger shear sensitivity (lower n), indicating a more shear-responsive structure favorable for extrusion. Frequency sweep analysis further revealed that HPI-GA-stabilized systems exhibited a more elastic and weakly frequency-dependent response, whereas HPI-SA formulations showed greater frequency sensitivity. Lower shift factor (α_SF) values for HPI-GA-stabilized HIPEs indicated a stronger deviation from the Cox-Merz rule, reflecting a more elastic and structurally organized network. These rheological differences were reflected in extrusion-based 3D printing performance, with HPI-GA conjugates favoring cohesive, gel-like HIPE networks, while HPI-SA conjugates primarily contributed to droplet-level stabilization via reduced droplet size and enhanced electrostatic repulsion.