Ultraviolet-C light-emitting diode (UVC-LED) is a new non-thermal sterilization technology. In this study, the inactivation effect of UVC-LED on A. acidoterrestris, a common juice spoilage bacterium, was investigated and the underlying mechanism was explored by measuring intracellular nucleic acid and protein leakage, membrane permeability, intracellular reactive oxygen (ROS) accumulation, and intracellular protein and DNA damage. The results showed that increasing the irradiation dose of UVC-LED enhanced its inactivation effect on A. acidoterrestris, and when the irradiation dose was increased to 50 mJ/cm², the number of viable cells in normal saline decreased by 4.6 (lg(CFU/mL)). By modeling of survival curves, it was observed that the inactivation effect of UVC-LED on A. acidoterrestris in normal saline was fitted to both the log-linear and Weibull models. The bacterium in different growth stages had different sensitivities to UVC-LED, in the logarithmic phase being more sensitive to UVC-LED. The irradiation treatment led to change in the membrane permeability and leakage of intracellular contents, indicating cell membrane damage, while intracellular ROS levels were not increased significantly (P > 0.05). Raman spectroscopic analysis and fluorescence microscopic analysis with acridine orange (AO) staining showed that the structures of intracellular proteins and DNA were changed. Overall, it was concluded that UVC-LED could inactivate A. acidoterrestris by causing DNA damage, structural change of intracellular proteins and the impairment of cell membrane permeability. According to the different degrees of damage, DNA damage may be the major reason for cell death.

Emulsions prepared using myofibrillar protein (MP) as an emulsifier have poor stability under low NaCl condition. The effect of high-intensity ultrasound (HIU) treatment (frequency of 20 kHz, and power of 450 W) for different periods of time (0, 3, 6, 9, and 12 min) on the emulsifying properties of chicken MP under low NaCl condition (0.15 mol/L NaCl) and the stability and rheological properties of MP emulsions were investigated. The results showed that compared with the control group, the emulsifying activity index (EAI) and emulsion stability index (ESI) of MP significantly increased with increasing ultrasonic treatment time (P < 0.05). The Turbiscan stability index (TSI) and particle size of MP emulsions decreased significantly with increasing ultrasonication time, and the absolute value of the zeta potential significantly increased (P < 0.05). The rheological analysis showed that ultrasound treatment significantly improved the viscoelasticity of MP emulsions. The oil-water interfacial tension analysis showed that ultrasound treatment effectively enhanced the mobility of MP, and rapidly decreased the interfacial tension. Meanwhile, ultrasound treatment significantly increased the amount of adsorbed protein in MP emulsions (P < 0.05), indicating that ultrasound treated MP contributed to emulsion stability. As observed by cold-field scanning electron microscopy, the emulsion prepared with MP treated by ultrasound for 12 min had the smallest droplet size. In conclusion, ultrasound treatment can significantly improve the emulsion stability of MP under low NaCl condition, which provides a theoretical reference for the application of ultrasound treatment to reduced-salt emulsified meat products.

The effects of ultrasound treatment at different powers (20 kHz for 6 min; 0, 150, 300, 450 and 600 W) on the structure, physicochemical properties and emulsifying properties of pale, soft and exudative-like (PSE-like) chicken meat myofibrillar protein (MP) were investigated. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed no significant changes in the composition of MP after ultrasound treatments; however, the band intensities of myosin heavy chain and actin were significantly increased at ultrasonic power of 450 and 600 W (P < 0.05). The α-helix content, surface hydrophobicity and solubility of MP increased and the β-fold content decreased as the ultrasonic power increased to 450 W. The α-helix content, surface hydrophobicity and solubility of MP decreased at 600 W ultrasonic power, but they were still significantly higher than those of the control group (P < 0.05). With an increase in ultrasound power, the fluorescence intensity of MP increased, and the particle size and zeta potential of MP and MP emulsion decreased significantly (P < 0.05). At ultrasonic power of 600 W, the highest emulsification activity index (EAI) and emulsion stability index (ESI) of MP, and the lowest oil/water interfacial tension and Turbiscan stability index of MP emulsion were obtained, indicating the highest emulsion stability. The cold field emission scanning electron micrograph confirmed that the oil droplets of the emulsion were smaller and more uniform. In summary, ultrasonic treatment can change the structure and physicochemical properties of PSE-like chicken MP, in turn improving the emulsion stability.

Myofibrillar protein (MP) and sarcoplasmic protein (SP) were extracted from pale, soft and exudative (PSE)-like chicken. The research investigated the differences in the heat-induced gel properties of SP-MP blends at 1:9, 2:8 and 3:7 ratios (m/m) and pure MP in order to select the appropriate SP/MP ratio. Furthermore, the differences in the gel properties, water distribution, intermolecular forces, gel electrophoresis pattern and microstructure of composite gels of SP treated with different ultrasonic powers (0, 300 and 600 W) at 20 kHz and MP were studied. The results showed that compared with the pure MP gel, the gel strength and water retention of the composite gel increased first and then decreased with the increase in SP addition, reaching the highest level at an SP/MP ratio of 2:8. After ultrasonic treatment at 600 W, the gel strength and water retention of the 2:8 composite gel were elevated by 113% and 47%, respectively, compared with those of the control group. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that SP had a certain promotion effect on the aggregation and cross-linking of myosin, but this effect became weaker when the ratio of SP to MP was 3:7. Both hydrophobic interactions and disulfide bond content reached their highest levels and the composite gel formed a denser network structure when the ratio of SP to MP was 2:8, and the ultrasonic power was 600 W. In conclusion, the effect of addition of ultrasonic-treated SP on the gel-forming capacity of PSE-like chicken MP was related to its concentration, and ultrasonic-treated SP favored the formation of MP gel structure, which effectively improved the gel characteristics of PSE-like chicken MP.

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.