Soybean Soluble Polysaccharides: Composition, Structure, and Protein Stabilization Mechanism in Acidic Milk Drinks

Soybean Soluble Polysaccharide (SSPS) is a natural anionic polysaccharide with protein content extracted from soybean residue. However, the impact of molecular weight and degree of esterification (DE) of soybean polysaccharides on protein stabilization remains a topic of debate. This study aimed to clarify the composition, macromolecular structure, and protein stabilization mechanism of SSPS and its various fractions with differing DEs and molecular weights (MWs). Nine polysaccharide fractions were isolated from three types of SSPSs with varying DEs and MWs using membrane ultrafiltration treatment. The analysis of monosaccharide composition and protein content reveals that the first component of soybean polysaccharides with high (847 kDa) molecular weight and low DE(SSPS20I) possesses the highest (7.25%) concentration of galacturonic acid (GalA) and a lower (0.83%) protein content compared to high-esterification SSPS. Meanwhile, the analysis of amino acids revealed that glutamic acid and aspartic acid were the primary amino acids across all protein components. It was also evident that alkaline treatment influenced the amino acid composition of SSPS. Atomic Force Microscopy (AFM) further substantiated that the components of SSPS exhibit distinct morphological and structural characteristics. The effects of SSPS fractions on the stability of Acidic Milk Drinks (AMDs) were investigated and evaluated using LUMi-Sizer. The results suggest that SSPS20I provided better stabilization in AMDs. This work establishes critical structure-property correlations, revealing that both DE and MW govern SSPS stabilization efficacy through synergistic effects of electrostatic repulsion, steric hindrance, and interfacial adsorption capacity.