Associative phenomena in galactomannan-deacetylated xanthan systems

Abstract

The interaction between mesquite seed galactomannan (MSG; D-mannose to D-galactose ratio (M/G) ~1.1) and deacetylated xanthan (DX) in 5 mM NaCl leading to synergistic gel formation at 25 °C was investigated and compared with the far more studied system made of xanthan and locust bean gum (LBG; M/G ~3.5). Rheology and differential scanning calorimetry were used to measure temperatures of gel formation and transition enthalpy as a function of polymer composition, while circular dichroism was used to probe the conformation of DX in the LBG– DX system. MSG and DX associate at 25 °C with a well defined stoichiometry of 0.6:1.0 (w/w) at low ionic strength favouring the disordered coil state of DX. When LBG was used in place of MSG in water or 5 mM NaCl, two types of mechanisms of interpolymeric association are envisaged.