Viscometric Properties of Solutions of Amylose and Amylopectin in Aqueous Potassium Thiocyanate

Abstract

Solutions of commercial potato amylose (1.65%, w/v) in dimethyl sulfoxide (DMSO) /water mixtures formed gels on standing when the water content was equal to or greater than 60% (w/v). These gels did not form when the water was replaced with aqueous potassium thiocyanate solution (KSCN, 2 mol/L). Commercial amylose did not dissolve completely in aqueous KSCN, unlike commercial potato and corn amylopectins, which formed more stable solutions than those in water alone. Solutions of amylopectin in mixtures of DMSO and aqueous KSCN showed a maximum relative viscosity (flow viscometer) at 80% (v/v) DMSO, like those in DMSO/water. Solutions of amylopectin in 25% (v/v) DMSO/75% (v/v) aqueous KSCN (2 mol/L) could be used for estimation of molecular weight by flow viscometry using the Mark-Houwink-Sakurada Equation. Sigma corn amylopectin gave a weight average molecular weight of 12.1 x 106, lower than that obtained using DMSO alone, and likely to be due to a lower degree of hydrogen bonding in the presence of KSCN, consistent with its chaotropic effect. This effect was also reinforced by the observation that formation of the amylose/iodine complex is inhibited by KSCN at concentrations as low as 0.2 mol/L.