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 Na2 SO4 ) on the gel, rheological and structural properties of fish gelatin (FG)-κ-carrageenan (κC) polyelectrolyte hydrogels. The results showed that κC could increase the gel strength, hardness, and chewiness of the FG-κC 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-κC polyelectrolyte hydrogels. Compared with NaCl, Na2 SO4 -treated FG-κC 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 Na2 SO4 decreased α-helix and β-sheet contents of FG-κC by destroying the hydrogen bond of FG-κC.