Comparison of Physicochemical Properties of Soybean Proteins under Different Ultrasound Treatment Conditions

This study examined the effects of ultrasound treatment on the structural and physicochemical properties of soybean proteins, generating fundamental data for their use as functional food materials.Two soybean cultivars, Daewonkong and Miso, were subjected to different ultrasound conditions.Compared with the control, the protein extraction yield decreased under the 30 min-23 μm treatment but increased under the 30 min-46 μm treatment in both soybean cultivars, suggesting that the ultrasound treatment affected the protein structural modification and recovery behavior differently depending on processing intensity.The changes in free amino acid composition were observed under different ultrasound treatment conditions.The highest values were generally detected under the 30 min-23 μm condition in both cultivars.The in vitro protein digestibility reached a maximum of 84.18% in Daewonkong at 30 min-23 μm, while Miso showed the highest digestibility (87.36%) at 15 min-46 μm.Secondary structure analysis indicated increased α-helix and β-turn contents and reduced β-sheet proportions under 30 min-23 μm.In addition, the bound bromophenol blue content, reflecting surface hydrophobicity, increased under this condition, indicating changes in surface-exposed hydrophobic residues and suggesting tertiary structural rearrangement.Overall, ultrasound treatment induced cultivar-dependent structural and functional changes in soybean proteins depending on the processing intensity.