Kinetics of gelatinization of potato starch studied by non-isothermal DSC

The kinetics of gelatinization of potato starch (starch:water weight ratio, 1:1) were investigated using differential scanning calorimetry (DSC). In the first stage, two isoconversional (Ozawa-Flynn-Wall and Friedman) methods were applied. It was found that the value of the activation energy (E) changes with 0 < alpha < 1 from approximately 75 to 138 kJ/mol. Further analysis using non-linear regression methods revealed that the best fit was found for a competitive double-step reaction, whereby the first step was attributed to the "n-order reaction" scheme and the second step was described by three-dimensional diffusion of Jander's type. The first step was attributed to the gradual formation of interchain and intrachain hydrogen bonding which restricts chain mobility and led at elevated temperature to the second diffusion-based rate-limiting step. For this model function, a spherical shape for the reacting bodies is the best stereogeometrical approximation; this corresponds well with observations concerning starch alignment at different microstructural levels and its behaviour during gelatinization. (C) 1998 Elsevier Science Limited. All rights reserved.