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

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.