The rheology of gelatin hydrogels modified by κ-carrageenan

- Carrageenan is a modifying co-gelator for gelatin gels.
- Carrageenan increases the strength, rigidity, and melt temperature of gels.
- Carrageenan forms (bio)polyelectrolyte complexes with gelatin.

We studied the impact of anionic polysaccharide (κ-carrageenan) as a co-gelator of gelatin at different physico-chemical and by varying the κ-carrageenan/gelatin ratio. It has been shown that increasing κ-carrageenan concentration accelerates the gelation and leads to significant increase in the viscoelastic parameters of the modified gels. Non-linearity of viscoelastic properties becomes evident in much lower deformations in comparison with those of native gelatin gels. The strength of gels characterized by the yield stress also increases along with κ-carrageenan concentration. The deformation (but not flow) of gels happens along the rupture surfaces appearing at the apparent yield stress. The melting temperature increases until 45 °C for high κ-carrageenan/gelatin ratio. The suggested explanation of the observed changes in properties of modified gels relates these effects with formation of complexes of gelatin and polysaccharide. FT-IR spectroscopy data show that (bio)polyelectrolyte complex formation is due to electrostatic interaction between positively charged groups in gelatin and negatively charged sulfate groups in κ-carrageenan that leads to conformation changes of gelatin macromolecules. Micrographs (scanning electron microscopy) show that addition of even a small quantity of polysaccharide leads to radical changes in supramolecular structure of modified gels.