RHEOLOGY AND MICROSTRUCTURE OF CA-K-CARRAGEENAN AND NA-K-CARRAGEENAN AND LOCUST BEAN GUM GELS

The viscoelastic and microstructural influences of 0.1-0.6% locust bea n gum on 0.5 or 1.0% kappa-carrageenan gels, in different ionic enviro nments, have been studied using small deformation oscillatory measurem ents and transmission electron microscopy (TEM). The results from the rheological measurements showed synergistic effects in the storage mod ulus, G', as locust bean gum, of two different mannose to galactose ra tios (3 and 5), was mixed with ion-exchanged Na-and Ca-kappa-carrageen an, in 0.25 M NaCl and 0.030 M CaCl2, respectively. The increase in G' was dependent on the mannose to galactose ratio, polymer concentratio ns, and ionic environment. At the supermolecular level, the microstruc ture of dilute samples has been visualised using low angle rotary meta l shadowing for TEM. In the presence of sodium and calcium ions, the s elf-association of kappa-carrageenan helices is moderate to low. Locus t bean gum did not influence the supermolecular structure of kappa-car rageenan to any large extent. The microstructure of the gels at the ne twork level was studied using plastic embedding and thin sectioning fo r TEM. In both sodium and calcium ionic environments, the mixed gels s howed a more homogeneous and connective network structure. (C) 1998 El sevier Science Ltd. All rights reserved.