KINETICS OF GELATINIZATION OF POTATO STARCH STUDIED BY NONISOTHERMAL DSC

The kinetics of gelatinization of potato starch (starch:water weight r atio, 1:1) were investigated using differential scanning calorimetry ( DSC). In the first stage, two isoconversional (Ozawa-Flynn-Wall and Fr iedman) methods were applied. It was found that the value of the activ ation energy (E) changes with 0 < alpha < 1 from approximately 75 to 1 38 kJ/mol. Further analysis using non-linear regression methods reveal ed that the best fit was found for a competitive double-step reaction, whereby the first step was attributed to the ''n-order reaction'' sch eme and the second step was described by three-dimensional diffusion o f Jander's type. The first step was attributed to the gradual formatio n 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 th e reacting bodies is the best stereogeometrical approximation; this co rresponds well with observations concerning starch alignment at differ ent microstructural levels and its behaviour during gelatinization. (C ) 1998 Elsevier Science Limited. All rights reserved.