EFFECT OF POTASSIUM-IONS ON THE THEOLOGICAL AND THERMAL-PROPERTIES OFGELLAN GUM GELS

To clarify the effect of cations on the gelling ability of gellan gum, the cation-free gellan gum was prepared by treating with ethylenediam inetetraacetic acid and ethanol. Storage Young's modulus E' and mechan ical loss tangent tan a were observed for cation-free gellan gum (F1) gels, non-treated gellan gum (F2) gels and potassium added F1 gels. E' increased and tan delta decreased in the presence of potassium ions i ndicating the increase of the number of junction zones, and the critic al polymer concentration below which no gelation occurs shifted to low er concentrations by adding cations. An endothermic peak accompanying gel-to-sol transition in heating differential scanning calorimetry cur ves shifted to higher temperatures by adding potassium ions. It was co nfirmed that potassium ions increase the number of junction zones and make the junction zones more heat resistant. F2 gels containing sodium , calcium and magnesium ions in addition to potassium ions showed mult iple broad endotherms in addition to a main endothermic peak indicatin g that junction zones are made from various aggregations of double hel ices with different bonding energies and/or different degrees of rotat ional freedom of parallel links consisting a single zipper.