Multiscale study of structure formation in high moisture extruded plant protein biopolymer mixes

While high moisture extrusion (HME) of plant proteins is known to result in anisotropic structures, there are still gaps in understanding the principles underlying structure formation, as well as how to study the interactions between biopolymers in mixed systems. This study aims to employ advanced rheological and microstructural tools to better characterize the structure of various HME systems and to derive some general principles for their structure formation. Pea protein isolate, with and without starch, and less refined protein fractions from pea and faba bean were used to produce extrudates with varying structures. Mechanical properties were assessed using Texture Profile Analysis, Dynamic Mechanical Analysis (DMA), and oscillatory rheology, while microstructural insights were obtained through Confocal Laser Scanning and Confocal Raman Microscopy. The addition of maize starch resulted in softer extrudates with clear partitions between protein and starch domains. The different formulations used in this study also suggest the important role of different complex carbohydrates in structure formation. Distinct parabolic shapes were observed in the extrudates, suggesting that lamellae formed during cooling, influenced by melt viscosity and the laminar flow profile resulting from the temperature gradient across the cooling die. DMA was particularly useful in evaluating differences in mechanical behavior and anisotropy. Raman microscopy proved to be valuable in assessing spatial distribution of various components and providing insights of water mobility related to competition. Evaluating various biopolymer mixes allowed for a more general view into the mechanisms of formation of structure in HME, important to enhance the development of plant-based foods.