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

Abstract

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 ( R 2) 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), R 2 for the ionic gums gradually levelled off, approaching the R 2 values for the non-ionic gums. For the xanthan-water system, the R 2 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.