ORGANIZATION AND ASSOCIATION OF KAPPA-CARRAGEENAN HELICES UNDER DIFFERENT SALT CONDITIONS

Mixtures of the added salts NaI and CsI can be used to gradually 'tune ' the propensity of kappa-carrageenan (KC) helices to aggregate in sol ution. We show that this method can be used to resolve the molecular e vents by which helix formation, under certain conditions, leads to gel ation. We also present an overview of the various states of aggregatio n and organisation that appear for helical KC (non-degraded or ultraso nically degraded) when the NaI/CsI ratio and the concentration of KC a re varied. A transition to rigid, superhelical rods is found above a w ell-defined fraction of cesium. This transition is reflected in a rang e of experimental measurements, such as cryo-transmission electron mic roscopy, optical rotation, viscometry and small deformation oscillator y measurements. The superhelical-rod state also seems essential for th e association of KC with locust bean gum, and locust bean gum is found to stabilise this state. Novel states of KC alone have been found at cesium contents below the transition threshold. Non-degraded KC forms weak gels at sufficiently high concentrations (> ca, 1%). In contrast, ultrasonically degraded KC forms a chiral nematic liquid crystalline phase at sufficiently high concentrations (> ca. 5%) under these salt conditions. (C) 1997 Elsevier Science B.V.