Effects of Thermal Denaturation on the Interactions Between Soluble Soybean Polysaccharides and Casein and Whey Protein

This study aimed to investigate the interactions between soluble soybean polysaccharides (SSPS) and milk proteins, namely, casein and whey protein, and to evaluate their effects on the stability of acidified milk beverages under different degrees of thermal denaturation. Casein, whey protein, and SSPS were used as raw materials to prepare mixed solutions under varying pH conditions. A combination of analytical techniques, including centrifugal sedimentation rate, particle size distribution, ζ-potential measurement, differential scanning calorimetry (DSC), size-exclusion chromatography (SEC), and LUMisizer stability analysis, was employed to systematically examine the interactions between SSPS and the two proteins, as well as the influence of thermal treatment at 120-140 °C (casein) and 65-78 °C (whey protein). The results demonstrated that under acidic conditions (pH 3.5-4.5), SSPS formed compact complexes with casein, effectively stabilizing casein dispersions through steric hindrance and electrostatic repulsion. In contrast, SSPS exhibited a limited stabilizing ability toward whey protein due to its strong tendency to aggregate, which hindered the formation of uniform complexes. Regarding thermal denaturation, casein heated at 140 °C for more than 40 min showed pronounced κ-casein dissociation and aggregation, resulting in reduced stability of the SSPS-casein system. For whey protein, increasing thermal denaturation (complete denaturation at 78 °C for 30 min) led to the formation of larger aggregates, with particle size increasing from 198.23 nm to 213.33 nm and ζ-potential decreasing from -3.77 mV to -2.01 mV, thereby diminishing the stability of the SSPS-whey protein system. Overall, this study elucidates the interaction mechanisms of SSPS with casein and whey protein, and highlights the role of thermal denaturation, thereby providing theoretical guidance for the effective application of SSPS in acidified milk beverages.