Effect of pH on the Stability of Dairy Beverages Stabilized with Soluble Soybean Polysaccharides

This study aimed to elucidate the effect of pH on the stability of soluble soybean polysaccharide (SSPS)-stabilized dairy beverages. A single-factor experimental design was employed using model systems containing 1.0% (w/v) protein and 0.4% (w/v) SSPS, with pH values adjusted from 3 to 7. System stability was comprehensively evaluated through centrifugation sedimentation rate, particle size distribution, ζ-potential, viscosity, and LUMisizer analysis. As pH increased from 3 to 7, the stability first decreased and then increased, showing the lowest stability at pH 5 and the highest stability at pH 6–7. At pH 5, large SSPS–protein aggregates formed due to the proximity to the isoelectric point (pI) of milk proteins, resulting in increased viscosity (6.83 mPa·s) and reduced ζ-potential (−5.8 mV). Conversely, at pH 6–7, strong electrostatic repulsion and steric stabilization led to small, uniformly dispersed particles and minimal transmittance change (<5%) in LUMisizer analysis. These findings clarify the stabilizing mechanism of SSPS and provide practical guidance for pH regulation in the formulation of dairy beverages.