This study investigated the effects of ultrasound treatment at different powers (0, 150, 300, 450 and 600 W) and a 20 kHz frequency for different durations (0, 5, 10 and 15 minutes) on the structure, physicochemical properties and emulsifying performance of sarcoplasmic proteins (SP) extracted from pale, soft and exudative (PSE)-like chicken meat. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed no significant changes in the composition of SP before and after ultrasound treatment. Circular dichroism (CD) spectroscopy showed that sonication did not alter the secondary structure of PSE-like chicken SP. Both ultrasonic treatment time and power had significant effects on the particle size, turbidity, potential, surface hydrophobicity, fluorescence intensity, ultraviolet (UV) absorption spectrum, solubility, and emulsifying properties of SP. With increasing ultrasonication time and ultrasonic power, the average particle size and turbidity of SP decreased significantly (P < 0.05), reaching minimum values of 237.2 nm and 0.018, respectively. The absolute value of zeta potential, solubility, surface hydrophobicity, and fluorescence intensity significantly increased. Experimental results showed that the most pronounced effects were observed at a 600 W power and 15 min, resulting in an up to 44.72% increase in solubility compared with the control group. In addition, ultrasonication could significantly increase the emulsifying activity index (EAI) and emulsion stability index (ESI) of SP, and reduced the Turbiscan stability index (TSI) of the emulsion stabilized by SP (P < 0.05). The highest emulsifying performance of SP was observed after ultrasonication at 20 kHz, 300 W for 15 min, with a 79.18% increase in EAI and a 44.87% increase in ESI. In summary, ultrasonication changed the structural properties of PSE-like chicken SP and effectively improved its solubility and emulsifying properties.

In order to investigate the effect of ultrasound on the structure and physical stability of chicken myofibrillar protein (MP) under low-salt conditions (0.15 mol/L NaCl), as well as the oxidizing effect of free radicals generated by ultrasound on MP, this study investigated the changes in the structure and oxidative properties of MP under low-salt conditions after ultrasound treatments (20 kHz, 450 W for 0, 3, 6, 9, and 12 min). The results showed that compared with the control group, the solubility, physical stability, and absolute ζ-potential of MP under low-salt conditions increased significantly (P < 0.05) with ultrasonic treatment time, whereas the turbidity and particle size decreased significantly (P < 0.05). The solubility was increased to 58.5% after 12 min of ultrasonic treatment. After ultrasonic treatment, the surface hydrophobicity and molecular flexibility were significantly increased, indicating that ultrasonic treatment caused the highly aggregated structure of myofibrillar protein to unfold and the internal hydrophobic groups to be exposed under low-salt conditions. After ultrasonic treatment for more than 6 min, the free sulfhydryl content of MP began to gradually decrease, whereas the content of disulfide bonds increased. After ultrasonic treatment for 12 min, the contents of free radicals, carbonyl groups and dimerized tyrosine (by 20.55%) were significantly increased (P < 0.05), while the free amino group content was decreased significantly (P < 0.05). In conclusion, ultrasonic treatment changed the structural properties of MP under low-salt conditions and increased its physical stability, thereby contributing to the formation of emulsions. Ultrasonic treatment can generate free radicals; ultrasonic treatment time for 6 min can exacerbate the oxidation of MP. So, attention should be paid to the oxidizing effect of free radicals generated by ultrasound on MP when applying ultrasonic treatment to improve the functional properties of MP.