Composition and effect of salt on rheological and gelation properties of Enterolobium contortisilliquum gum exudate

The composition, structure and rheological properties and metal ions intera ction with Enterolobium contortisilliquum gum were investigated. This gum c ontains galactose, arabinose, rhamnose and glucuronic acid as main monosacc haride components. C-13 nuclear magnetic resonance spectroscopy revealed th at the anomeric composition is similar to the Enterolobium cyclocarpum exud ate, however no 4-O-methylglucuronic acid was detected for E. contortisilli quum. The rheological experiment resulted in a very similar flow behaviour to that found for E. cyclocarpum gum. The empirical stiffness parameter, B was determined (B = 0.090) and suggested that the polysaccharide possesses semi-flexible chains. Cation affinity of the gum aqueous solution was deter mined by intrinsic viscosity measurements and gelation. The melting tempera ture of gels pointed to a charge/ionic radius ratio dependence for metal io ns. Thermodynamic parameters (enthalpy and entropy) at the melting temperat ure were also calculated. (C) 2001 Elsevier Science B.V. All rights reserve d.