Abstract
The purpose of this study was to investigate the rheological and thermal properties of yam starch. Yam starch had a hydrodynamic volume with the intrinsic viscosity,［$\eta$］, of 0.29dl/g deionized water. The values of the intrinsic viscosity of yam starch, determined to pH 2-11, varied between 0.07 to 0.18 dl/g. The highest intrinsic viscosity was obtained at pH 7. At salt concentrations 0-0.2 M NaCl, the intrinsic viscosity of yam starch was decreased up to 0.05 M NaCl concentration then increased to 0.07 M NaCl concentration and remained constant to reach 0.2 M NaCl concentration. The overlap parameter, calculated with the intrinsic vicosity data, was 3.45 g/dl in deionized water. The thermal properties of yam starch were investigated by Differential Scanning Calorimetry. Three endotherms were observed both pH solution and salt concentation. In the presence of pH 9, the onset temperature of gelatinization peak was the lowest temperature of 50.$32^{\circ}C$ and the enthalpy ($\Delta$H) was increased in this solution. The effect of salt on the thermal properties of yam starch was determined at salt concetration of 0-0.2 M NaCl. The enthalpy significantly decreased to salt concentration 0.07 M NaCl and the lowest onset temperature of this concentration was 52.$90^{\circ}C$.