Influence of pH and ionic strength on the physicochemical and structural properties of soybean β-conglycinin subunits in aqueous dispersions

Understanding the impact of pH and ionic strength on the physicochemical and structural properties of soy proteins at subunit level is essential for design and fabrication of many plant-based foods. In this study, soybean beta-conglycinin and its subunit fractions alpha alpha ' and beta were dispersed in solutions with different pH values (3.7, 7.6, and 9.0) at low (5 mM NaCl) and high (400 mM NaCl) ionic strengths, respectively. The solubility, rheology, particle size, zeta potential, microstructure, secondary structure, and tertiary structure of the different dispersions were analyzed using a range of analytical methods. The beta-conglycinin, alpha alpha '- and beta-subunits aggregated near the isoelectric point (pH 3.7). Increasing the ionic strength led to the assembly of more homogeneous units. An increase in ionic strength at pH 7.6 and pH 9.0 led to electrostatic screening, which promoted dissociation of the aggregates. The beta-subunit showed a greater sensitivity to pH and ionic strength than the alpha alpha '-subunits. Based on the evidence from a range of analytical methods, the highly hydrophilic extension region of the alpha alpha '-subunits played an important role in determining the stability of the beta-conglycinin dispersions under different environmental conditions. Moreover, the N-linked glycans appeared to impact the conformation and aggregation state of the beta-conglycinin.

Automated summary

Understanding the impact of pH and ionic strength on the physicochemical and structural properties of soy proteins at subunit level is essential for design and fabrication of plant-based foods. The study shows that soybean beta-conglycinin and its subunits are sensitive to pH and ionic strength, exhibiting different stability and aggregation states under different conditions. The highly hydrophilic extension region of the alpha alpha '-subunits and N-linked glycans play important roles in determining the stability and conformation of beta-conglycinin dispersions.