Thermal, dynamic-mechanical, and dielectric analysis of phase and state transitions of frozen wheat doughs

The physical state of wheat dough at sub-zero temperatures was investigated using Differential Scanning Calorimetry (DSC), Dynamic-mechanical Analysis (DMA) and Dielectric Analysis (DEA). Also, the water sorption properties of freeze-dried dough were investigated. DMA and DEA measurements were made at a heating rate of 1 degreesC/min from - 150 to 10 degreesC. Before the measurements, samples were equilibrated at -25 degreesC for 15 20 min to allow maximum ice formation, and then cooled at 1 degreesC/min to - 150 degreesC. The frequencies used were 0.1, 0.5, 1, 2.5, 5, 10, and 20 Hz for DMA and 0.1, 0.5, 1, 5, 10, 20, 50, 100 and 1000 Hz for DEA. The DSC thermograms were obtained for annealed samples by scanning from -80 to 20 degreesC at 5 degreesC/min, and they showed only ice melting starting at - 18 degreesC. The tail delta of DMA and DEA showed an alpha -relaxation (glass transition), two low temperature relaxations (beta and gamma) and melting of ice, lit rho higher frequencies (>0.5 Hz), the alpha -relaxation coincided with melting of ice, and all relaxation temperatures (alpha, beta and gamma) increased with increasing frequencies as measured by DEA. (C) 2000 Academic Press.