Determination of starch gelatinization temperature by ohmic heating

A method for measuring starch gelatinization temperature (T), determined from a change in electrical conductivity (sigma), was developed. Suspensions of native starches with different starch/water mass ratios and pre-gelatinized starches were prepared, and ohmically heated with agitation to 90 degreesC using 100 V by AC power at 50 Hz, and a voltage gradient of 10 V/cm. The results showed that sigma of native starch suspensions was linear with temperature (R-2 > 0.999) except for the gelatinization range, but the linear relationship was always present for the pre-gelatinized starch-water system. It was seen that the shape of dsigma/dT versus T curve was essentially similar to the endothermic peak on a DSC thermogram, and the gelatinization temperature could be conveniently determined from this curve. Thus, the segment profile on this curve was called the block peak. The reason for the decrease in sigma of native starch suspensions in the gelatinization range was probably that the area for motion of the charged particles was reduced by the swelling of starch granules during gelatinization. (C) 2003 Elsevier Ltd. All rights reserved.