WATER SELF-DIFFUSION COEFFICIENTS AND DIELECTRIC-PROPERTIES DETERMINED FOR STARCH-GLUTEN-WATER MIXTURES HEATED BY MICROWAVE AND BY CONVENTIONAL METHODS

The effect of microwave and conventional heating on water mobility (self-diffusion coefficient, D) and dielectric properties was investigated. Wheat starch and vital wheat gluten were mixed in various proportions (100:0, 80:20, 50:50, 20:80, and 0:100) at three different moisture contents (54, 100, and 186%). Measurements were made for the individual powders and for each of the 15 combinations of starch, vital wheat gluten, and water before heating, after conventional heating, and after microwave heating. For the dry powders, no differences were found in dielectric properties, but differences were found in the mobility by pulsed gradient spin-echo nuclear magnetic resonance. For nearly all of the mixtures, two D values were obtained at all three moisture contents. Moisture content had a significant effect on D values, as did heating. The difference between conventionally heated and microwave-heated samples was not great. The dielectric properties were affected by heating method-the dielectric constant was more dependent on moisture content than was dielectric loss, which showed very tittle variation over the three moisture contents.