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Relaxations Below Glass Transition Temperature in Bread and Its Components

¹Laboratoire de Biochimie, Physico-Chimie et Propriétés Sensorielles des Aliments. Ecole Nationale Supérieure de Biologie Appliquée à la Nutrition et l'Alimentation 1, Esplanade Erasme - F-21000 Dijon. France. ²Corresponding author. Fax: 00 33 3 80 39 66 11. E-mail: roudaut@u-bourgogne.fr ³Laboratoire de Physique de l'Université de Bourgogne. Bâtiment Mirande, Campus Universitaire - F-21000 Dijon. France.

Dry glassy bread, cooked gluten, and gelatinized wheat starch-sucrose mixtures were prepared. Dielectric properties were studied as a function of temperature at different frequencies ranging from 100 to 1,000 kHz. Both bread and starch samples exhibited a tan δ peak at -53°C at 10 kHz, which is associated with a secondary relaxation characterized by an activation energy of 50 kJ/mol. The gluten sample did not show any relaxation in the temperature range studied. The magnitude of the relaxation peak was sensitive to the sucrose concentration of the starch sample. The higher the sucrose content, the greater the amplitude of the peak. Such an effect is attributed to a greater β-relaxation induced by an increasing number of relaxing units or increasing size of the loosely packed regions of the glass. However, it cannot be concluded whether the relaxation is associated with a group present on both starch and sucrose or that the sucrose has an enhancing effect on starch mobility.