Multiscale characterization of plant protein-hydrocolloid soft-solids: Linking rheology, tribology, and mucoadhesion in texture-controlled formulations

Plant protein-hydrocolloid soft-solids exhibit coupled bulk and interfacial properties that cannot be described by steady shear viscosity alone. In this work, flaxseed- and hempseed-based formulations structured with carboxymethylcellulose, high-acyl gellan gum, or hydrolytic enzymes were investigated through a combined approach integrating steady and dynamic rheology, thixotropy, back extrusion, tribology, and ex-vivo mucoadhesion. Flow behavior was modelled using the Herschel-Bulkley equation, with yield stress ranging from 1.4 to 17.8 Pa and apparent viscosity at 50 s-1 from 0.7 to 2.9 Pa·s, highlighting the impact of structuring strategy on flow activation and low-shear resistance. Mechanical spectra revealed weak gel-like behavior (G’ > G’’), with formulation-dependent differences in network strength and frequency dependence. Structural recovery and large-deformation responses further differentiated protein-hydrocolloid interactions. Tribology revealed distinct boundary-to-hydrodynamic lubrication transitions and formulation-dependent friction coefficients. Ex-vivo mucoadhesion tests showed detachment forces between 0.03 and 0.5 N, evidencing interfacial retention mechanisms not predictable from bulk rheology alone. Hydrocolloid incorporation primary governed lubrication and adhesion under low shear conditions, whereas protein composition modulated network connectivity and recovery dynamics. Integrating yield stress, viscoelasticity, friction, and mucoadhesion enabled quantitative mapping of formulation-dependent performance, providing a structure-function framework for engineering of texture-controlled soft-solids with tunable mechanical and interfacial properties.