Effect of Dry Heating on Physicochemical Properties of Pregelatinized Rice Starch

Abstract

Japonica and indica rice starches (10% w/w) were pregelatinized in a boiling water bath for 5 or 10 min and subsequently heat-treated in a dry state for 0, 1, 2, or 3 h at 130 degrees C to examine the effects of dry heating on pasting viscosity, paste clarity, thermal properties, X-ray diffraction pattern, and gel strength of pregelatinized starches. Heat treatment obviously changed the physicochemical properties of pregelatinized rice starch. The pregelatinized rice starches had higher peak viscosity and final viscosity than the corresponding native rice starches. Heat treatment of pregelatinized rice starch for 1 h increased the peak viscosity, but treatment for 2 or 3 h decreased the peak viscosity compared with the unheated pregelatinized rice starch. The indica rice starch exhibited more substantial changes in pasting viscosity than did japonica rice starch during heat treatment. The melting enthalpy of the endothermic peak occurred at 90-110 degrees C, and the intensity of the X-ray diffraction peak at 20 degrees was increased by dry heating, possibly owing to the enhanced amylose-lipid complexes. The dry heat treatment of pregelatinized starch caused an increase in paste clarity and a decrease in gel strength.