²³Na NMR molecular mobility studies of hydrocolloid—NaCl solutions as influenced by sodium concentration

²³Na NMR molecular mobility studies were performed to investigate the interaction between sodium ions and various hydrocolloid—water systems as affected by the nature of the hydrocolloid (ionic and non-ionic) and the concentration of added NaCl (0–5000 mg/100 ml). At low amounts of added NaCl (20–100 mg/100 ml) the transverse relaxation rates (R₂) for the ionic gums, kappa-carrageenan and xanthan, rapidly decreased and were larger than those for the non-ionic gums, guar and locust bean. At higher concentrations of added NaCl (>100 mg/100 ml), R₂ for the ionic gums gradually levelled off, approaching the R₂ values for the non-ionic gums. For the xanthan-water system, the R₂ for the endogenous Na⁺ concentration and very low added NaCl concentrations (<15 mg/100 ml) were also measured. This research suggests that gum type, NaCl and endogenous cation concentrations affect the binding of Na⁺ to the gums.