Yeast vs Plant Protein Isolates: Structure–Function for Food Interfaces, High-Solids Rheology, Thermal Stability, and In Vitro Digestibility

Single-cell proteins can complement plant isolates, yet mechanism-driven comparisons under identical conditions are scarce. We benchmarked a Saccharomyces yeast protein isolate (YP) against soy, potato, pumpkin seed, and oat isolates using complementary structural analyses (scanning electron microscopy, circular dichroism/Fourier transform infrared spectroscopy, X-ray diffraction, fluorescence, and particle size/ζ-potential) and food-relevant tests (solubility, surface hydrophobicity, emulsification/foaming, 15% w/w rheology, and in vitro digestibility) at standardized conditions (pH 7, low ionic strength). YP was β-sheet-rich, compact, and the most hydrophobic. YP showed the highest emulsifying activity and strong foaming, whereas soy showed the highest emulsion stability index over 10 min, indicating a formation–stability trade-off. At 15% solids, YP dispersions had the lowest viscosity and high digestibility. Interfacial extensional rheology, droplet size evolution in multicomponent matrices, and functionality across pH/ionic strength were not quantified; therefore, conclusions about dynamic stability are limited. Findings link structure and surface chemistry to interfacial behavior, guiding formulation and blend strategies coupling rapid formation (YP) with higher short-term stability (soy).