Multiscale analysis of the mechanisms underpinning interactions between biopolymers during high moisture extrusion of plant proteins

Understanding the structure-function relationship in high moisture extrusion (HME) remains a challenge. This work explored the mechanisms underpinning the interactions between biopolymers by studying the interplay of protein purity, starch concentration, and lamella alignment in HME.

Objectives

The research objective was to address structuring hypotheses using advanced rheological and microstructural tools and contrasting systems comprising pea protein isolate with and without added starch, against pea protein concentrate and fava bean protein concentrate.

Methods

The study employed a Parallel Twin-screw Extruder to prepare various structuring levels for different blends. Mechanical property evaluations were conducted through Texture Profile Analysis (TPA) and Dynamic Mechanical Analysis (DMA). Microstructural insights were obtained via Confocal laser scanning microscopy (CLSM) and Confocal Raman microscopy, while oscillatory rheology (SAOS and LAOS) assessed cross-link density.

Results

Confocal Raman microscopy uniquely revealed phase separation between protein-rich and water-rich domains. CLSM showcased a disruptive impact of the dispersed phase on the continuous protein network. Complementary rheological techniques are required to understand properties across length scales. Mechanical testing unveiled the effects of starch on elasticity and deformation, demonstrating increased internal tension and cross-linking with increased starch content. A notable correlation emerged between solubility and hydration development during extrusion, the total mechanical input (SME), and the velocity profile, collectively influence the obtained structure. Lamella angles exhibited parabolic V-shapes at high SME (264 KJ/kg) and softer U-shapes at lower SME values (188 KJ/kg), establishing a clearer link between process variables and resulting structural outcomes.