Rheology of plant protein–polysaccharide gel inks for 3D food printing: Modeling and structure–property relations

Plant protein–polysaccharide composite hydrogels and emulsion gels are attractive materials for production of edible inks for 3D food printing. Their ability to satisfy the printability requirements is conventionally evaluated in small- and large-amplitude oscillatory shear tests. A model is derived that describes experimental data in linear and nonlinear rheological tests on protein gels in a unified manner. The model is based on the population-balance approach and involves a reasonably small number of adjustable parameters. Fitting observations on soy protein isolate–xanthan gum, peanut protein–gellan gum, peanut protein–carrageenan, pea protein–carrageenan and pea protein isolate–flaxseed gum gels demonstrates that material parameters evolve consistently with composition of the gels. The governing equations describe adequately the effects of pH and ionic strength of aqueous solutions on the mechanical properties of the gels and predict the stress–strain Lissajous curves and the crossover amplitudes for transition from the solid-like to fluid-like response. Based on the analysis of observations in large-amplitude oscillatory tests with various frequencies, a mechanism is proposed for transition from the type-I (strain thinning) to type-III (weak strain overshoot) response of protein–polysaccharide gels.