Starch gelatinization in ohmic heating
1997
Wang, W.C. | Sastry, S.K.
The effect of starch gelatinization on electrical conductivity (sigma) was investigated in this study. Suspensions of corn and potato starch were prepared with a starch:water ratio of 1:5 (w/w) by mixing with the appropriate amount of water. Suspensions were ohmically heated with agitation to 90 degrees C by AC at 60 Hz, and a voltage gradient of 20 V/cm. Partially gelatinized and fully gelatinized samples, prepared by preheating suspensions to or beyond the gelatinization ranges, were also tested. Gelatinization energy (delta H(G)) and degree of gelatinization (%SG) of each sample were determined by differential scanning calorimetry (DSC) at a scanning rate of 10 degrees C/min. The results showed that endothermic gelatinization peaks were found on both DSC thermograms and electrical conductivity curves, with similar shapes and temperature ranges. Data of %SG obtained from conductivity curves and DSC thermograms were in agreement in low and mid-gelatinization ranges but were different when %SG was high, due to high ohmic heating rate. Electrical conductivity increased with temperature, but decreased with degree of gelatinization, apparently caused by structural changes and an increase in bound water.
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