Effects of the Hofmeister anion series salts on the rheological properties of Sesbania cannabina galactomannan

Abstract

Sesbania cannabina galactomannan (2%) solutions added with strongly hydrated ions (Na₂CO₃, NaH₂PO₄, NaCl) and weakly hydrated ions (NaNO₃) at different ionic strengths were rheologically characterized. The four selected salts dramatically decreased the intrinsic viscosity of galactomannan solution in the following order of effectiveness: Na₂CO₃ < NaH₂PO₄ < NaCl < NaNO₃. This conforms effectively to the Hofmeister anion series. Moreover, salt addition increased the viscosity of galactomannan solution when the ionic strength was 1 mmol/kg, which related to an increased occurrence of intermolecular interactions. As increasing ionic strength, galactomannan chains may tend to contract or expand due to the presence of strongly or weakly hydrated ions, thereby decreasing the viscosity. These phenomena were demonstrated by zeta potential measurement and again observed in dynamic viscoelasticity measurement. Overall, this property can be used to manipulate the rheological properties of galactomannan in food gums to obtain gums of high quality for enhancing consumer goods.

Keywords: Galactomannan; Hofmeister anion series salts; Viscosity.