Effects of Ingredients on Phase and State Transitions of Frozen Wheat Doughs

Effects of ingredients on frozen state properties of wheat doughs were investigated using different thermal analysis techniques. Also, the water sorption properties and glass transition temperatures for different cereal materials were determined. DSC thermograms were obtained for different dough samples annealed at a few degrees below the onset temperature of ice melting of the material, then cooled to −100 °C, and scanned at a heating rate of 5 °C/min from −100 to 10 °C. Dough samples were also analyzed with DMA and DEA at a heating rate of 1 °C/min from −150 to 10 °C. Before analysis, the samples were annealed a few degrees below the onset of ice melting for all doughs with different ingredients to obtain maximally freezeconcentrated samples. Added ingredients decreased the onset temperature of ice melting (Tm') and increased the relative amount of unfrozen water (Wg') with increasing concentrations in all doughs, as measured by DSC. Tan δ of DEA showed that the melting of ice occurred extremely sharply, in all doughs with the same moisture content, at small frequencies. Peaks of the ice melting were moved closer to 0 °C with increasing frequency, as measured by DEA and DMA. The tan δ of DMA and DEA showed also α-, βand γ-relaxations. At higher frequencies the glass transition (α-relaxation) coincided with ice melting measured by DEA. The glass transition temperature (Tg') of maximally freeze-concentrated doughs, could be observed only at small frequencies in doughs measured by DEA. Added sucrose increased the Tg', and decreased the onset temperature of ice melting, Tm'. Added salt decreased the Tg' and Tm', as measured by DEA. Added sucrose and NaCl increased the Tg' measured by DMA. Using DEA, doughs with sucrose and NaCl showed intermediate Tg'. Added WEA (1%) increased the Tg' of dough, derived from α-relaxation, with different ingredients, when DMA or DEA was used. Addition of WEA may decrease the effect of lower molecular weight solutes shifting the transition to a higher temperature. On the other hand, the Tg' decreased with increasing concentration (>1%) of WEA. Added WEA (>1%) increased the relative amount of unfrozen water in the concentrated matrix, and thereby the Tg' of the material decreased with increasing concentration (>1%) of WEA. Steady state water contents and glass transition temperatures of materials used in the present study were typical for cereal materials.