Effects of modulated differential scanning calorimetry (MDSC) variables onthermodynamic and kinetic characteristics during gelatinization of waxy rice starch

The total, reversing, and nonreversing thermal properties during gelatiniza tion of waxy rice starch (starch-to-water ratio = 1:2, w/w) were examined b y modulated differential scanning calorimetry (MDSC). The effect of MDSC op erating variables (i.e., the amplitude and frequency of temperature modulat ion and the underlying heating rate) on these thermal properties was determ ined by response surface methodology (RSM) and statistical analysis. The fr equency of temperature modulation and the underlying heating rate significa ntly influenced the gelatinization temperatures and enthalpy changes in tot al and nonreversing endotherms. In addition, the combination of 0.025Hz and 4-8 degrees C/min with a properly low degree of oscillation was suitable f or characterization of starch gelatinization by MDSC. The enthalpy changes in the reversing (thermodynamic) endotherms increased, but those in the non reversing (kinetic) endotherms decreased with increasing periods (i.e., dec reasing frequencies) and underlying heating rates. However, the total entha lpy changes were only slightly influenced by the MDSC variables studied. In addition, the activation energies for the total and nonreversing events we re 281.8-417.3 and 386.3-739.7 kJ/mol, respectively, depending on the MDSC conditions. From the compensation relationship between the activation energ y and frequency factor, we concluded that the total and nonreversing endoth erms were linked to the same single transition.