Microwave Permittivities Of Cracker Dough, Starch and Gluten

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Abstract
An open-ended coaxial probe technique was used to measure the real and imaginary dielectric components of wheat starch, wheat gluten, and a commercial cracker dough. The permittivity or dielectric constant (ε) and the dielectric loss (ε“) or loss factor were determined as a function of moisture and frequency at constant density and temperature. The permittivity was measured over a continuous frequency range from 0.2 GHz to 20 GHz. The moisture range is 20% to 40%, typical of a normally processable dough. Two discrete areas of dispersion are observed at moisture contents above 30% correlating with the appearance of free water in the material, as measured by differential scanning calorimetry (DSC). The static (εS) and optical (ε∞) dielectric constants for associated water are predicted. The semicircular plot thus obtained is consistent with the Debye model for predicting dielectric behavior of polar substances. εS and ε∞ found to increase with increasing moisture content for starch, gluten, and cracker dough. This result is consistent with a shift of the relaxation time of bound water to higher frequencies. This is expected due to the greater mobility of the mixture with increasing amount of water as a plasticizer.

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