Characterization of Low-Sodium Myofibrillar Protein Gels with Substitution of Human Essential Metal Salts and Their Mechanisms of Action

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.