In order to study the effect of cold chain storage on the structural and functional properties of myofibrillar protein and the chemical interactions of surimi gel, the changes in the functional groups and secondary and tertiary structure of myofibrillar protein and the chemical interactions of surimi gel were investigated as a function of cold chain storage time, and the relationship between chemical interactions and myofibrillar protein was evaluated by principal component analysis (PCA) and correlation analysis. Results showed that the salt-soluble protein content, Ca²⁺-ATPase activity and total sulfhydryl content in surimi gel decreased, while the carbonyl content increased during storage. In addition, the secondary structures of myofibrillar protein transformed from an ordered to a disordered state, and the fluorescence intensity decreased, indicating changes in the polar environment of the protein. These findings demonstrate that the active groups in myofibrillar protein are closely related to the formation of gel chemical forces. Therefore, preventing protein oxidation and freeze denaturation at the initial stage of storage is an effective way to maintain the chemical interactions of surimi gel and the gel characteristics. This study can provide basic theoretical support for the quality maintenance of surimi during cold chain storage.

In order to reduce the amount of added sodium in myofibrillar protein (MP) gel, the effects of partial substitution of different chloride salts (CaCl₂, MgCl₂, and KCl) for NaCl on the gel strength, microstructure, water-holding capacity and rheological properties of MP gel were studied. The underlying mechanism of action of sodium substitutes was elucidated by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and intrinsic fluorescence spectroscopy as well as measuring surface hydrophobicity and sulfhydryl content. The results showed that KCl was the best substitute for NaCl, followed by CaCl₂, and MgCl₂ was least effective in replacing NaCl. The gel strength of the KCl substitution groups (0.5% KCl + 2.5% NaCl, 1.5% KCl + 1.5% NaCl, and 1.0% KCl + 2.0% NaCl; m/m) was better than that of the control group (3% NaCl), while no significant difference in water-holding capacity was found between the two groups (P > 0.05). The gel strength of the 1.5% CaCl₂ + 1.5% NaCl group decreased significantly (P < 0.05), and the water-holding capacity decreased first and then increased. The gel strength significantly decreased (P < 0.05) and the water-holding capacity increased in the MgCl₂ substitution groups. In terms of rheological properties, the storage modulus (G’) of the KCl substitution groups was significantly higher than that of the control group. Substitution of CaCl₂ and MgCl₂ increased the surface hydrophobicity of MP and decreased the sulfhydryl content. Substitution of CaCl₂, MgCl₂, and KCl resulted in a blue shift in intrinsic fluorescence spectra. At low substitution levels (0.5%), the microstructure of MP gel showed no significant difference from that of the control group. The above results indicate that CaCl₂, MgCl₂ and KCl can be used to partially substitute NaCl in surimi gel products.