Texture and rheological characterization of kappa and iota carrageenan in the presence of counter ions

The effect of cation concentration and ion valency (0–0.2% (w/v) of KCl or CaCl2·2H2O) on the mechanical, micro-structural and rheological properties of aqueous kappa (κ) and iota (ι) carrageenan dispersions were investigated using a texture analyzer, cryo-SEM and an oscillatory rheometer, respectively. The probe penetration method demonstrated a decrease in “hardness” of carrageenan systems with increasing cation concentration, after exhibiting an initial maximum. The Young's modulus (E) of κ-carrageenan gels was determined using the uniaxial compression method. E was approximately 3 times the shear modulus recorded under the same experimental conditions; indicating the elimination of slip by the use of roughened parallel plates. The storage modulus of ι-carrageenan gels with Ca2+ demonstrated a similar trend to mechanical properties. However the syneresis observed in κ-carrageenan systems with storage, may have reduced the sensitivity of probe penetration method. Cryo-SEM observation of gels revealed a microstructure consistent with the observed mechanical properties.