Effect of viscoelastic properties of soluble and insoluble soy protein isolate on the fiber formation and the distribution of insoluble dietary fiber in extrudates

Blends of soy proteins isolate (SPI) and insoluble dietary fiber (IDF) are promising due to their ability to produce fibrous products resembling meat texture. In this study, model blends of SPI-IDF (SPI: IDF = 90:10, based on dry mass) with varying proportions of soluble (SSPI) and insoluble SPI (ISPI) were produced through high-moisture extrusion. The rheological behaviors of the SPI-IDF blends, as well as the morphology and mechanical properties of the extrudates, were investigated. The results showed that the ISS-40 extrudate (ISPI: SSPI = 4:0) exhibited pronounced fibrous structures with superior mechanical anisotropy. This was attributed to the even distribution of numerous small-sized voids or honeycomb areas, which were deformed along the extrusion flow direction. In contrast, ISS-04 extrudate (ISPI: SSPI = 0:4) exhibited a gel-like structure with the coalescence of IDF domains. These morphological and mechanical differences were attributed to the viscoelastic properties of protein matrix, which affected the distribution of dispersed IDF domains. Thus, these insights into the interactions between the continuous and dispersed phases in SPI-IDF blends provide guidance for developing meat analogue products with desired textural properties.