The effect of salt content on the structure of iota-carrageenan systems: (23)Na DQF NMR and rheological studies.

(23)Na NMR spectroscopy has been used to study the effects of Na(+) ion concentrations on the structure of 1% (w/w) iota-carrageenan systems, a natural gelling polysaccharide used as a thickener in the food industry. Rheological and (23)Na T(1) relaxation time measurements revealed that gel formation correlates with decreases in ion mobility over the range of 0-3% (w/w) sodium content. (23)Na single-quantum (SQ) and double-quantum-filtered (DQF) NMR experiments performed on these systems provided evidence for a 'bound' sodium ion fraction in a specifically ordered environment. These results have allowed us to propose a model for the carrageenan gelation mechanism in the presence of Na(+) ions.