Rheological properties and interactions of fish gelatin-κ-carrageenan polyelectrolyte hydrogels: The effects of salt

This study mainly explored the effects of low-concentration salts (0.1, 0.5 mM NaCl and Na2SO4) on the gel, rheological and structural properties of fish gelatin (FG)-kappa-carrageenan (kappa C) polyelectrolyte hydrogels. The results showed that kappa C could increase the gel strength, hardness, and chewiness of the FG-kappa C polyelectrolyte hydrogels, while the addition of salts had a negative effect. The rheological behaviors showed that the addition of salts reduced the apparent viscosity, gel, and melting points of the FG-kappa C polyelectrolyte hydrogels. Compared with NaCl, Na2SO4-treated FG-kappa C had lower gel strength, hardness, viscosity, gelation, and melting points, while the addition of salts increased the fluorescence intensity by unfolding FG molecules. The secondary structure analysis results showed that the addition of NaCl and Na2SO4 decreased alpha-helix and beta-sheet contents of FG-kappa C by destroying the hydrogen bond of FG-kappa C.