Application of a shear cell for the simulation of extrusion to test the structurability of raw materials

The required raw material properties and the mechanisms behind fibrous structure formation during high moisture extrusion cooking (HMEC) to produce plant-based meat analogues are not sufficiently understood. The implementation of new raw materials is therefore a labour-intensive, empirical endeavour. Hence, this research explores the potential of a high-pressure shear cell (HPSC) as a tool for rapid screening of raw materials for HMEC suitability. During these texturisation tests, material viscosity was monitored to gain deeper mechanistic insights. For that, hydrated pea protein isolate (PPI) and soy protein concentrate (SPC) were sheared at 5-40 s⁻¹ in the HPSC with a cone-plate or plate-plate geometry under extrusion-like conditions at 140–160 °C and 20 bar. Fibrous structures were successfully generated with both tested plant proteins, but reproducibility was limited to trials with SPC. Monitoring of viscoelastic properties revealed an onsetting polymerisation, followed by a decrease in viscosity, indicating fracturing of the forming network as underlying structuring mechanism. The suggested fracturing of an emerging network aligns with an observed increase in fibrousness in the plate-plate geometry compared to the cone-plate geometry due to the radial shear rate gradient. Finally, this research showcased a high similarity of the process-structure response pattern for SPC between the applied HPSC process and HMEC. Yet, further modifications, such as increasing the mechanical energy input capacity, are required to effectively apply HPSC processing for the prediction of the structuring behaviour in HMEC for the broad range of existing raw materials.