Effect of Molecular Weight and Protein Content on the Air–Water Interfacial and Foaming Properties of Soybean Soluble Polysaccharides

This study systematically investigated the influence of molecular weight (MW) and protein content (PC) on the interfacial behavior and foaming properties of soluble soybean polysaccharide (SSPS), aiming to elucidate the structure–function relationship for the targeted design of SSPS-based foam stabilizers. The results demonstrated that the low-MW group, particularly the LH sample (low MW, high PC), exhibited the highest foam expansion (FE = 272.5%), attributed to its smallest particle size, lowest zeta potential, and minimal surface tension, which facilitated rapid adsorption at the interface. Interfacial rheology revealed that all SSPS samples formed an elastic-dominated interfacial film (G′ > G″). The HM sample (high MW, moderate PC) showed the most rapid increase in G′ and the highest mechanical strength, while the LH sample (low MW, high PC) exhibited the strongest elastic response within the low-MW group, which contributed to its relatively high foam stability (FS = 69.9%). The interfacial viscoelasticity and foaming performance of SSPS are synergistically governed by its MW and PC. Low MW facilitates rapid adsorption and superior foam expansion, while high PC enhances interfacial film elasticity. Moreover, the long-term stability of foam depends not only on reduced interfacial tension but more critically on the mechanical strength and viscoelasticity of the interfacial film. These findings provide a crucial theoretical basis for optimizing SSPS applications in aerated foods.