Multiscale Analysis of Kluyveromyces lactis SCP in a Fermented Soy Protein Matrix

This study evaluated the impact of incorporating single-cell protein (SCP) from Kluyveromyces lactis into soy protein isolate (SPI) matrices for the development of a yogurt analog, applying a multiscale analytical framework. Four formulations were prepared by substituting SPI with 0, 25, 50, and 75% SCP. SCP addition accelerated fermentation, modified the organization of the protein network, and affected texture and water-holding capacity (WHC). At 25% replacement, SCP produced a more open structure with larger pores while sustaining SPI network continuity, yielding the highest firmness and consistency, alongside increased storage modulus and viscosity, indicating a reinforced, more elastic gel network. At this concentration, firmness increased by 54% (from 30.5 to 47.0 g, p < 0.05) compared with the control. Higher SCP levels (≥50%) weakened mechanical properties, reducing firmness and consistency, while WHC increased significantly only at 75% SCP. These results support the potential of SCP as a sustainable ingredient in fermented plant-based foods.