pH-regulated preparation and structural characterization of non-covalent complexes of soybean isolate proteins with different charged polysaccharides

• Published in: International journal of biological macromolecules 2025-04, Vol.298, p.140004, Article 140004
• Main Authors: Chen, Jiaying, Wang, Yilin, Pu, Mingxia, He, Shan, Ninan, Neethu, Cheng, Ming
• Format: Article
• Language: English
• Subjects: Charge density; chitosan; emulsions; glucans; heat treatment; hydrogen; hydrophobicity; ionic strength; isoelectric point; Non-covalent interaction; pH-regulated; Protein and polysaccharide complexes; protein isolates; protein solubility; protein structure; sodium alginate; soy protein; soybeans; Stability; temperature
• ISSN: 0141-8130; 1879-0003; 1879-0003
• DOI: 10.1016/j.ijbiomac.2025.140004

Soybean protein isolate (SPI) exhibits limited functional properties in processing applications due to environmental stressors such as pH, salt ion, and temperature. The present study was devoted to exploring the non-covalent assembly of SPI with chitosan (CS), glucan (GL) and sodium alginate (SA) under different pH conditions. At a fixed mixing ratio (1:1), the phase behavior, protein solubility, and surface hydrophobicity (H0) of the resulting protein-polysaccharide complexes (PPCs) exhibited great differences due to the diversity of polysaccharide charge density and structure. Specifically, CS and SA primarily incorporated with SPI through electrostatic interactions, resulting in a pronounced enhancement of SPI solubility near the isoelectric point, with increases of 37.1 % and 51.6 %, respectively. In contrast, the combination of GL with SPI dominated by hydrophobic interactions and hydrogen bonds, yielding a similar protein solubility and H0 to SPI itself under different pH. Further analysis in charge density indicates that heat treatment promotes the electrostatic complexation of proteins with polysaccharides, whereas an increase in ionic strength inhibits the non-covalent assembly, and this effect was pronounced in the anionic polysaccharide system. In addition, the formation of electrostatic complexes exerted a positive effect on the stability of the emulsions, while the co-soluble systems tended to produce emulsion particles with smaller particle sizes. In summary, the charged polysaccharides showed great potential to modulate protein structure and enhance the stability of protein emulsions compared with the nonionic polysaccharides. [Display omitted] •Construction of PPCs with differently charged polysaccharides and SPI over a wide range of pH•Determination of charge density of polymers before and after pretreatment•Charged polysaccharides exhibit superior performance in improving protein solubility and emulsification.•Electrostatic complexes provide better emulsion stability than co-solubles.•Proposing mechanisms for PPC formation and Pickering emulsion stabilization.