Structural modification of soybean β-conglycinin by low/medium frequency ultrasound: impacts on oil-water interface adsorption and stability

This study investigated the effects of ultrasound treatments at different frequencies (20 and 207 kHz) and power densities (65 and 130 W/L) on the structure and interfacial properties of β-conglycinin in soybean. Ultrasound-induced cavitation effectively disrupted noncovalent interactions within proteins, with the effect most pronounced at 20 kHz and 130 W/L. SDS-PAGE profile indicated that ultrasound treatment did not cleave peptide bonds and disulfide bonds, suggesting that the overall structural integrity was preserved. Amino acid analysis further indicated changes in the detected amino acid concentrations after acid hydrolysis, while the primary structure of β-conglycinin was not substantially altered. Spectroscopic analyses revealed conformational rearrangements, including increased α-helix content, reduced β-sheet content, and altered tertiary structures. Specifically, 20 kHz tended to promote aggregate dissociation and moderate unfolding, whereas 207 kHz more readily induced local rearrangements and enhanced quenching. Meanwhile, the increased zeta potential and reduced particle size facilitated faster protein diffusion and adsorption at the oil-water interface, while the increased contact angle indicated enhanced conformational flexibility and interfacial adaptability. Dynamic interfacial tension measurements further confirmed that these changes favored the development of a stable interfacial film. Molecular dynamics simulations corroborated these findings, showing that 20 kHz ultrasound more markedly altered protein flexibility, global conformation, and hydrophilic-hydrophobic characteristics, thereby deepening mechanistic understanding at the molecular level. These findings provide a theoretical foundation for the application of ultrasound as a sustainable and efficient physical modification technique to enhance the functional properties of plant proteins.