Relating the protein denaturation degree and solubility of soy protein isolates to the structure of high moisture extrudates

Commercial soy protein isolates (SPI) with high protein denaturation degrees and low solubilities are often used raw materials for the production of meat analogues with high moisture extrusion (HME). The impact of such SPI properties on structure formation and protein-protein interactions/reactions that occur during HME processing is not well-understood. Therefore, SPI with (i) native and soluble proteins, (ii) denatured and aggregated proteins or (iii) blends thereof were subjected to lab-scale HME processing. Most native and soluble SPI proteins took part in the formation of new non-covalent interactions and disulfide bonds during HME processing, which resulted in a layered extrudate microstructure. In addition, even after disruption of non-covalent and covalent bonds, high MW aggregates (>100 kDa) were present in the extrudate. SPI with highly aggregated protein had low protein extractability and HME did not cause a pronounced further reduction in this regard. HME did, however, result in the formation of a fibrous extrudate structure. Extrusion of blends with intermediate content of both SPIs resulted in the highest extrudate hardness and cutting strength. These findings demonstrate a significant impact of SPI protein denaturation degree and solubility on high moisture extrudate structure and texture. Hence, in-depth evaluation of the protein physical properties of raw materials used for HME processing will aid in controlling product properties.