Abstract
Gellan gum is a microbial polysaccharide produced by Sphingomonas elodea. The gelation mechanism of mixed gellan gum solutions of native gellan gum (=NG) and deacylated gellan gum (=DG) with divalent cations has been studied by dynamic rheological measurements and gradient NMR measurements. For 1 % mixed gellan solutions with 5 mM CaCl2 at various mixing ratios, complex modulus increased around 70 ℃ and 40 ℃ in two stages on cooling. The temperature dependence of echo peak intensities in the NMR measurements indicated that NG and DG formed aggregates with restricted molecular mobility at around 70 ℃ and 40 ℃, respectively. These results suggest that NG chains and DG chains form aggregates individually in the mixed solution and the gels have an interpenetrating structure by networks of NG and DG. From the GPC measurements, it was found that the powdered sample of NG included an aggregate and the aggregate was dissociated by heat treatments at 90 ℃ for 12 hours. In order to clarify the effect of the aggregate in the mixed gellan solution, the dissociate NG was mixed with DG in 1 % solution with 5 mM CaCl2 and studied by dynamic rheological measurements and gradient NMR measurements showing the individual aggregation at each aggregation temperature. This result indicates that the severalty in the gelation process for the mixed solution of NG and DG is attributable to the difference in chemical structures of the polysaccharide chains.
