The effects of magnetic field (MF)-assisted freezing at different intensities (0, 1, 2, 3, 4, and 5 mT) on the physicochemical properties and structure of myofibrillar protein (MP) from prepared chicken breast were investigated in terms of secondary structure, surface hydrophobicity, solubility, and degree of oxidation. The results showed that compared with the control group, the solubility of MP in all MF treatments significantly increased, while the turbidity, surface hydrophobicity, and average particle size significantly decreased (P < 0.05). Additionally, all MF treatments significantly increased the absolute value of the zeta potential of MP relative to the control group, enhanced the surface charge density, and consequently inhibited the growth of heterogeneous aggregates in MP solutions. The results of circular dichroism (CD) spectroscopy revealed that MF treatments increased the content of α-helix, inhibited the unfolding of protein structure, and reduced the exposure of internal groups. Concurrently, MF treatment at 3 mT significantly reduced the generation of carbonyl compounds (P < 0.05), reflecting the inhibition of oxidative modification and abnormal cross-linking of MP. Overall, 3 mT MF-assisted freezing had a significantly positive effect on preserving the structure and physicochemical properties of MP from prepared chicken breasts and further improved its processing quality.

Myofibrillar protein (MP) extracted from thawed pork was treated with plasma-activated water (PAW) generated by low-temperature plasma treatment. The effect of PAW obtained at different discharge times (0, 5, 10, 15, 20 and 25 s) on the emulsifying activity, emulsion stability, particle size, zeta potential, amount of adsorbed protein and rheological properties of MP-stabilized emulsion was investigated. The results showed that compared with the control group, PAW treatments significantly improved the emulsifying activity and emulsion stability, and reduced the turbiscan stability index (TSI) (P < 0.05). Additionally, after PAW treatments, the particle size of MP-stabilized emulsion significantly decreased and the zeta potential increased; PAW 20 s resulted in the smallest particle size and the highest absolute value of the zeta potential, 34.22 μm and 11.36 mV. Compared with PAW 20 s, PAW 25 s reduced the emulsion stability. The results of rheological properties showed that after PAW treatments, the elasticity, apparent viscosity and viscoelasticity increased. In conclusion, PAW treatment could significantly improve the emulsifying properties of MP from thawed pork, the effect being most pronounced with PAW 20 s.

Postmortem ovine Longissimus dorsi muscle was treated by dielectric barrier discharge (DBD) low-temperature plasma with different intensities (0, 30, 60, 90 and 120 s) and then stored 4 ℃. The changes in the pH, color, juice loss, shear force, total bacterial count and protein oxidation indicators of the samples during storage were analyzed to explore the effect of DBD low-temperature plasma treatment on the quality of lamb meat. The results showed that during storage, the pH of the treated samples was lower than that of the untreated ones. The L^* and b^* values of the samples increased firstly and then decreased with treatment time. DBD low-temperature plasma treatment had no significant influence on the color or shear force, but could accelerate protein oxidation in lamb meat. Furthermore, this treatment significantly (P < 0.05) reduced the total count of bacteria during storage. After five days of storage, the total count of bacteria in the control group was 6.10 (lg (CFU/g)), which was far beyond the limit. However, the total count of bacteria the treatment group exceeded the limit value after seven days, indicating that DBD low-temperature plasma treatment can extend the shelf life of lamb meat. DBD low-temperature plasma treatment for 60 s had the least negative impact on lamb meat quality during storage.

In this study, magnetic field was applied at different intensities (0, 1, 2, 3, 4 and 5 mT) during the freezing of prepared chicken breast to explore the effect of magnetic field-assisted freezing on the freezing rate, water-holding capacity, moisture distribution, microstructure, and physicochemical properties of prepared chicken breast. The results showed that magnetic field at appropriate intensities (3 and 4 mT) significantly accelerated the freezing process, shortened the freezing time, reduced the size of ice crystals formed during freezing, and caused less tissue damage to muscle fibers. In addition, it reduced juice loss and lipid oxidation, maintained color stability, improved the overall water-holding capacity, and resulted in more uniform moisture distribution inside chicken breast. Compared with the control group, prepared chicken breast under magnetic field assisted freezing had better eating quality.

The Longissimus dorsi muscle of sheep was treated at different times postmortem with dielectric barrier discharge (DBD) low temperature plasma and evaluated for pH, total number of bacteria, myofibrillar fragmentation index (MFI) and myofibril ultrastructure during postmortem storage. Our aim was to determine the effects of DBD low temperature plasma treatment at different times after slaughter on mutton tenderness. The results showed that after 12 h of postmortem storage, the pH of mutton treated with DBD low-temperature plasma at 6 and 12 h postmortem was significantly lower than that of the other treated groups (P < 0.05); the total number of bacteria in mutton treated at 12-72 h after slaughter decreased significantly compared with the untreated group. As the storage time increased, MFI gradually increased, showed a significant upward trend during 6-72 h (P < 0.05), and then tended to be stable after 72 h for all treated groups. DBD low temperature plasma treatment at 6-24 h postmortem significantly increased the growth rate of MFI than the other treatments (P < 0.05). After 24 h storage, the sarcomere length of mutton treated at the early postmortem stage (6-24 h) was significantly reduced and shorter than that of the other treated groups (P < 0.05), and the sarcomere length of mutton in the 24 h postmortem treatment group was the shortest. In conclusion, DBD low-temperature plasma treatment at 12 to 24 h postmortem had the least effect on the tenderness of mutton while reducing the number of bacteria.

Postmortem mutton longissimus dorsi was minced and treated separately with phosphatase inhibitor, kinase inhibitor, S-nitrosoglutathione and nitric oxide synthase (NOS) inhibitor to control the degrees of phosphorylation and S-nitrosylation. The effect of interaction between protein phosphorylation and S-nitrosylation on mutton tenderness during postmortem storage were investigated by analyzing the changes in the phosphorylation level, S-nitrosylation level, pH, myofibrillar fragmentation index (MFI), desmin and troponin-T degradation of the treated mutton samples during storage at 4 ℃. The results indicated that phosphorylation levels were significantly higher (P < 0.05) in the phosphorylation-controlled group than in the phosphorylation and S-nitrosylation-controlled group in the early (0-12 h) and late (48-72 h) stages of storage, suggesting that protein S-nitrosylation inhibited its phosphorylation. When phosphorylation and S-nitrosylation modifications acted simultaneously, phosphorylation modification was dominant in affecting pH and its effect could be further enhanced by S-nitrosylation. On the contrary, S-nitrosylation played a major role in destroying the internal structure of myofibrillar proteins in mutton longissimus dorsi. When they occurred simultaneously, protein phosphorylation inhibited its S-nitrosylation; conversely, protein S-nitrosylation may promote the inhibitory effect of protein phosphorylation on desmin degradation. During postmortem storage, the interaction between protein phosphorylation and S-nitrosylation varied at different reaction periods, but both ultimately resulted in a decrease of troponin-T degradation. In conclusion, the interaction between protein phosphorylation and S-nitrosylation negatively influences the tenderness of mutton during postmortem aging.

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.