Electrical conductivity of heated cornstarch-water mixtures

Electrical conductivity (EC) of cornstarch-water mixtures in the range 10:90 to 70:30 (w/w) was studied as a function of temperature. An external resistive heating system equipped with an electronic device capable of monitoring EC in real time was used and EC of the mixtures was measured while heated at a rate of 5C/min. Results showed that EC went through four different temperature-dependent stages (A, B, C and D). Stage B (41C to 64C) showed a lower EC increasing rate when compared with that of Stage A (from 25C to 41C), probably as a result of starch granule swelling. In Stage C (64C to 78C), EC behavior was found to be dependent on water content. When water content was more than 50%, the value for EC increased. On the other side, EC decreased when water content was less than 50%. Stage C was related to starch gelatinization, according to differential scanning calorimetry results obtained in this study. In Stage D (78C to 92C), a steady increase in EC was observed, probably as a result of the total solubilization of starch in water. It was concluded that Stage C in EC graphs corresponded to cornstarch gelatinization, so it might be possible to use EC monitoring as an alternative technique to measure cornstarch thermal characteristics with different contents of water.