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 this study, the effects of ultrasonic-assisted immersion freezing (UIF) with different ultrasonic powers on beef quality were measured. The changes in freezing rate, cooking loss, thawing loss, tenderness, color difference, moisture distribution and microstructure of beef were analyzed after traditional air cooling or ultrasonic-assisted freezing at different ultrasonic powers (0, 200, 400 and 600 W). Fresh beef was used as control. The results showed that UIF could significantly increase the freezing rate of beef, affect the color and water state, and reduce the structural destruction of muscle tissue and quality deterioration during the freezing process. At an ultrasonic power of 400 W, the fastest freezing rate was obtained, as well as the lowest cooking loss and thawing loss of 32.44% and 1.66%, respectively, and shear force closest to that of the fresh meat. In addition, the minimum freezable water of 51.11% was observed. Low-field nuclear magnetic resonance (NMR) analysis showed that the amplitude of T₂₁ was the highest, and the amplitude of T₂₂ was relatively small, indicating a more uniform water distribution. Microscopic observation showed that an appropriate ultrasonic power reduced the structural damage caused by freezing to muscle fibers, thereby improving the quality of frozen meat.

The longissimus dorsi muscle of sheep was treated with cold plasma (CP) induced by dielectric barrier discharge (DBD) at different time points (6, 12, 24, 48, 72 and 120 h) after slaughter. By analyzing changes in the color, myoglobin content, fat oxidation, total sulfhydryl content and surface hydrophobicity of samples during postmortem cold storage, the effects of DBD-CP treatment at different time points after slaughter on the color and oxidation stability of mutton at different time points after slaughter were determined. The results showed that DBD-CP treatment at different time points after slaughter had no significant effects on L^* or a^* values of mutton (P > 0.05), but significantly increased the b^* value compared to the untreated control group (P < 0.05). DBD-CP treatment reduced the color stability of the meat and accelerated the deterioration of meat color. DBD-CP treatment at 6 and 12 h postmortem had little impact on the color stability. DBD-CP treatment at all selected time points after slaughter had no significant effect on the myoglobin content of mutton (P > 0.05). The thiobarbituric acid reactive substances (TBARS) value of the DBD-CP treatment group was higher than that of the control group (P < 0.05), and the treatment significantly reduced the total sulfhydryl content in mutton and increased the surface hydrophobicity (P < 0.05). In summary, DBD-CP treatment at 6 to 12 h after slaughter had the most significant effect on stabilizing and maintaining meat color. In addition, it could accelerate the oxidation of myofibrillar protein (MP). Therefore, DBD-CP treatment has potential application value in improving the quality of mutton.

The objective of the study was to investigate the effect of radio frequency parameters on the thawing time and the uniformity. During the radio frequency thawing of frozen chicken breast at 27.12 MHz and 6 kW, the effects of operating parameters such as electrode gap (8, 9, 10, and 11 cm), voltage (70%, 75%, and 80%) and sample thickness (4, 5, and 6 cm) on the pattern of temperature rise and the uniformity were examined. The results showed that with decreasing electrode gap and increasing voltage and sample thickness, the temperature rise accelerated and the uniformity index decreased. The optimum parameters were determined as 9 cm and 75% for electrode gap and voltage, respectively based on the thawing time and temperature distribution. Compared with thawing at ambient temperature (20 ℃, 6 h), the thawing time with radio frequency was shortened to 54.67 min, and the total viable count, the drip loss and total volatile basic nitrogen (T-VBN) content were significantly reduced (P < 0.05). The results of this study provide a theoretical basis and technical support for the practical application of radio frequency technology in the field of meat thawing.

In this study, the effects of high-intensity ultrasound (HIU, frequency 20 kHz, amplitude 60%, power 450 W) for 0, 6, and 9 min on the emulsifying properties of chicken myofibrillar protein (MP) under different NaCl concentrations (0.2, 0.3, 0.4, and 0.5 mol/L) were investigated. The results showed that the increasing NaCl concentration and prolonged HIU treatment time significantly enhanced the emulsifying activity, the emulsifying stability and storage stability of MP emulsion were increased significantly (P < 0.05), and the particle size of MP emulsion were decreased significantly (P < 0.05). HIU pretreatment decreased the interfacial tension, and increased the apparent viscosity and the absolute zeta-potential of reduced-NaCl MP emulsions. Compared with the non-HIU group at 0.5 mol/L NaCl, the emulsions stability was significantly improved when the HIU time was extended to 9 min under 0.3 mol/L NaCl (P < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis result of interfacial MP showed that the band strength of myosin heavy chain and actin significantly increased after 9 min-HIU treatment at both 0.3 and 0.5 mol/L NaCl. Circular dichroism analysis showed that the random coil relative content of interfacial MP was decreased significantly (P < 0.05), and the relative content of α-helix and β-sheet were increased (P < 0.05) after HIU. Extended HIU time could partially alternative the effect of NaCl on the emulsification properties of MP, and improve the stability of the interfacial protein structure and MP emulsion in reduced-salt conditions, which facilitated the processing of lower salt emulsion-based meat products.

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.