Dynamic changes in interfacial and emulsifying properties of soy protein during fibrillation

The fibrillation process endows food proteins with exceptional techno-functional properties; however, these properties can be unstable owing to alterations in the structure and composition of a fibril system during fibrillation. This study comprehensively evaluated the interfacial and emulsification properties of the soy protein fibril system during the 24-h incubation under acid heating conditions (pH 2.0, 85 °C). Thioflavin T fluorescence and sodium dodecyl sulfate–polyacrylamide gel electrophoresis confirmed that the formation of soy protein nanofibrils (SPNFs) involved hydrolysis and self-assembly processes, ultimately transforming SPNFs into mature fibrils with a contour length of 276.7 nm and a β-sheet-rich structure after 18 h. Protein fragments formed during the initial stage (0–4 h) increased the diffusion rate of the fibril system to the oil–water interface. Prolonged incubation enhanced both the penetration and rearrangement of the fibril system accompanied by significant increases in the dynamic dilatational elastic and surface dilatational moduli. The fibril component was separated by ultrafiltration centrifugation and was proved crucial for maintaining high interfacial stability. Mature fibrils (18–24 h) were robustly adsorbed at the oil–water interface, forming a cream layer reinforced with hydrogen bonds, which significantly enhanced the emulsion stability. These findings elucidate the structural and interfacial property transformations of soy protein during fibrillation and provide a theoretical foundation for its strategic application in food processing.