Abstract: This study investigated the stability and interfacial tension of soybean oil emulsions stabilized by chicken breast myofibrillar protein (MP) subjected to ultrasonic treatment (frequency of 20 kHz, power of 450 W, and intensity of 30 W/cm2) for different durations (0, 3 and 6 min), as well as the zeta potential, solubility, turbidity, viscosity, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) profile, secondary structure and morphplogical structure of the treated MP samples. Also, this study explored the mechanism by which ultrasonic treatment may improve the emulsifying properties of MP. The results showed that ultrasonic treatment reduced the Turbiscan stability index (TSI) and interfacial tension of the MP-stabilized emulsions. The solubility and the absolute value of zeta potential were increased significantly (P < 0.05), while the turbidity and viscosity were significantly reduced by ultrasonic treatment (P < 0.05). SDS-PAGE analysis showed that ultrasonic treatment had no effect on protein bands. Circular dichroism (CD) spectroscopy showed that the content of ordered α-helices in MP was significantly decreased, while the contents of loose β-turn, β-sheet and random coil were significantly increased (P < 0.05). Atomic force microscopy (AFM) showed that the structure of MP was destroyed, the morphology was characterized by dispersed particles with smaller particle size, and the surface roughness was significantly reduced. These results indicated that the low-frequency and high-intensity ultrasonic treatment made the MP structure more disordered, promoting the breakup of MP aggregates to form small soluble ones. Moreover, it enhanced the electrostatic interaction and fluidity, enabling the protein to quickly adsorb oil droplets during the emulsification process and consequently reducing the oil-water interfacial tension and enhancing the emulsion stability. This study provides a theoretical basis for the application of ultrasonic in the processing of emulsified meat products.

Key words: low-frequency ultrasound; myofibrillar protein; interfacial tension; atomic force microscopy