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 o f 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 m easurements, samples were equilibrated at -25 degreesC for 15 20 min to all ow maximum ice formation, and then cooled at 1 degreesC/min to - 150 degree sC. The frequencies used were 0.1, 0.5, 1, 2.5, 5, 10, and 20 Hz for DMA an d 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 mel ting of ice, and all relaxation temperatures (alpha, beta and gamma) increa sed with increasing frequencies as measured by DEA. (C) 2000 Academic Press .