Viscoelastic properties of κ-carrageenan in saline solution

Viscoelastic properties of κ-carrageenan in saline solution at various concentrations and pH were investigated by dynamic rheological techniques, viscosity, elasticity measurements, and IR spectrometry. The viscosity and elasticity at low concentrations of κ-carrageenan do not depend on pH, confirming that κ-carrageenan is in a disordered conformation. At 0.7% κ-carrageenan, the disordered confirmation transforms into an ordered helical confirmation with the possibility of weak-type gel formation. The transformation is also confirmed by dynamic measurements of loss and storage moduli. Furthermore, at this concentration, the viscosity and elasticity are highly dependent on pH. At higher concentrations of NaCl (0.5 M) at some pHs, we observed that storage moduli is greater than loss moduli for the entire frequency region. Hence, there is a possibility of structure transformation from weak-type gel to a somewhat intermediate gel. The lowest viscosity and elasticity were obtained at extreme pH, confirming that there are structural changes occurring at these pHs due to hydrolysis. This is confirmed by IR data.