Rheological and DSC studies on the interaction between gellan gum and konjac glucomannan

Abstract

Interaction between gellan gum (GELL) and konjac glucomannan (KGM) has been studied by dynamic viscoelastic measurements and differential scanning calorimetry (DSC). Three fractions of konjac glucomannan with different molecular weights (1.17 × 10 6 (ND), 9.5 × 10 5 (LM-1) and 2.51 × 10 5 (LM-2)) were used in this study. Mechanical spectra showed that 1.6% solutions of GELL alone and of LM-2 alone behaved like a dilute polymer solution whilst 1.6% solutions of ND alone and LM-1 alone behaved like a concentrated polymer solution where molecular entanglements play an important role. Thermal scanning rheological measurements showed a step-like change in the loss modulus which is attributed to helix-coil transition, and subsequent aggregation of helices, and an exothermic and endothermic peak appeared in cooling and heating DSC curves at the same temperature of transition. The transition temperature shifted to lower temperatures, and the transition enthalpy decreased with increasing KGM content in the mixture. The elasticity of mixtures originates mainly from aggregated helices of gellan gum molecules for GELL/LM-2 systems whilst the contribution from KGM is more important for GELL/LM-1 and GELL/ND systems. Although the storage modulus of GELL/LM-1 and GELL/ LM-2 as a function of mixing ratio showed a maximum, it is concluded that KGM inhibit the formation of the ordered structure of gellan gum.