Effect of polysaccharides on the rheological behaviour of soy-wheat protein aggregation and conformational changes during high-moisture extrusion.

Background: Due to the extrusion black box effect, polysaccharides determine the formation of meat-like fibrous structures by modulating the flow behaviour and structural changes of plant proteins under high-moisture extrusion conditions. However, there is limited knowledge on the mechanism of resolution. This study simulated the rheological properties of soy protein-wheat protein under 57% moisture conditions with addition of 4% sodium alginate (SA), 2% xanthan gum (XG), and 2% maltodextrin (MD). The effect of these polysaccharides on the aggregation behaviour and conformation of raw protein during high-moisture extrusion was investigated.

Results: It was revealed that the three polysaccharides were effective in increasing the interaction between proteins and between proteins and water. Among them, 4% SA elicited a significantly stronger storage modulus (gelation behaviour) compared to the control. Analysis of different zones of extrudates by protein electrophoresis, particle size, and turbidity showed that SA-4% was able to form more high molecular protein aggregates (> 245 kDa) and promoted crosslinking of low molecular subunits (< 48 kDa), resulting in moderately sized protein aggregated particles. Fluorescence and ultraviolet spectra showed the transformation of protein tertiary structures in different extrusion zones, confirming that the key extrusion zone for protein conformational transformation by polysaccharides is the die-cooling zone. Furthermore, stretching of polypeptide chains and accelerated protein rearrangement facilitated the formation of more fibrillar structures.

Conclusion: Theoretical support for polysaccharide modulation of plant protein quality in high moisture extruded products is provided by this study. © 2023 Society of Chemical Industry.