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 CaCl(2)center dot 2H(2)O) on the mechanical, micro-structural and rheological properties of aqueous kappa (kappa) and iota (iota) 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 kappa-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 L-carrageenan gels with Ca(2+) demonstrated a similar trend to mechanical properties. However the syneresis observed in kappa-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. (C) 2010 Elsevier Ltd. All rights reserved.