Formation of Calcium-Mediated Junction Zones at the Onset of the Sol-Gel Transition of Commercial κ-Carrageenan Solutions

Gelling temperatures of commercial.-carrageenan solutions were measured using dynamic oscillatory shear rheometry, in response to varying polymer (0.4% to 1.6%, w/w) and added Ca2+ ( 5 to 20 mM) salts. Gelling temperatures were found to shift to higher temperatures with increased polymer and Ca2+ concentration. The Tang model was used to estimate the number of Ca2+-mediated cross-links formed with kappa-carrageenan at the onset of junction zone formation. Based on this model, 6 kappa-carrageenan double helices were estimated to be cross-linked by 5Ca(2+) ions through ionic bridging and electrostatic attraction, within a cross-linking region equivalent to one pitch of the double helix.