Rheology and microstructure of Ca- and Na-K-carrageenan and locust bean gum gels

The viscoelastic and microstructural influences of 0.1-0.6% locust bean gum on 0.5 or 1.0% κ-carrageenan gels, in different ionic environments, have been studied using small deformation oscillatory measurements and transmission electron microscopy (TEM). The results from the Theological measurements showed synergistic effects in the storage modulus, G', as locust bean gum, of two different mannose to galactose ratios (3 and 5), was mixed with ion-exchanged Na- and Ca-κ-carrageenan, in 0.25 M NaCl and 0.030 M CaC1₂, respectively. The increase in G' was dependent on the mannose to galactose ratio, polymer concentrations, and ionic environment.

At the supermolecular level, the microstructure of dilute samples has been visualised using low angle rotary metal shadowing for TEM. In the presence of sodium and calcium ions, the self-association of κ-carrageenan helices is moderate to low. Locust bean gum did not influence the supermolecular structure of κ-carrageenan to any large extent. The microstructure of the gels at the network level was studied using plastic embedding and thin sectioning for TEM. In both sodium and calcium ionic environments, the mixed gels showed a more homogeneous and connective network structure.