Modulation of gel characteristics in surimi-curdlan gel system by different valence metal cations: Mechanical properties, ionic distribution and microstructure visualization

The valence state of metal cations is a potential factor in regulating the structural properties of surimi gels. In this study, Surimi-Curdlan dual network (SCDN) gel was prepared by NaCl, KCl, CaCl2, and MgCl2, combined with the concept of dual network hydrogel. The effects of different valence metal cations on mechanical properties, water state, microstructure, protein structure and composition of SCDN gel were studied. The results showed that the monovalent metal cations conferred higher G' and G" to the SCDN gel and promoted the unfolding of the alpha-helix structure in the proteins, providing more binding sites for adequate binding of protein and curdlan. It also increased the compatibility of proteins and curdlan, forming a regular and tight three-dimensional network structure. The monovalent metal cations enhanced the gel's mechanical properties such as strength and hardness, and retained more water through the net-trapping effect. However, the divalent metal cation-mediated SCDN gels had low G' and G", inadequate unfolding of the protein secondary structure and the aggregates formed by each of them were dispersed in the gel system, resulting in an inhomogeneous gel structure and texture. This structural feature reduced water retention and gel strength. After comprehensive comparative analysis, K+ has the potential to replace Na+ in preparing SCDN gel. This study provides some insights into the development of sodium alternatives for the surimi gel industry.