Relationship between rheological parameters and structure formation in high moisture extrusion of plant protein biopolymers

Summary

High moisture extrusion (HME) is widely employed to texturize plant-derived protein ingredients, but its development is still much based on trial and error. In this project, it was hypothesized that the rheological properties of plant-based mixtures analyzed when in the molten state and during their cooling can aid in understanding their structure formation. To test this hypothesis, biopolymer formulations containing pea protein isolate (PPI) were examined at different moisture and starch contents, and their rheological properties were analyzed using a closed cavity rheometer (CCR) at temperatures relevant to those applied during HME processing. The results obtained with the CCR were then contrasted with the mechanical properties of HME obtained using a lab scale extruder, measured using oscillatory rheology, large deformation, and dynamic mechanical analysis. Low moisture (55 %) HMEs were stiff and brittle, while high moisture (65 %) HMEs formed more flexible and anisotropic structures. Addition of starch created softer structures. The viscoelastic properties of the biopolymer mixes measured with the CCR were correlated with the mechanical parameters of the final extrudates. Strong correlations were found between small deformation rheological parameters measured in the CCR and the hardness values, while non-linear viscoelastic parameters were correlated with anisotropy indexes. Results demonstrated that the material properties measured at the early cooling stages strongly influence the structural heterogeneity in HMEs. This study highlights the potential to use the viscoelastic properties of the biopolymer mix measured with the CCR to predict their structural features when processed by extrusion.