88C-4 |
Using the modulated differential scanning calorimetry to determine the glass transition of durum wheat semolina |
B. CUQ, Ecole Nationale Supérieure Agronomique de Montpellier, Institut National de la Recherche Agronomique, 2, Place P. Viala, Bât. Administratif, Cedex 1, Montpellier, 34060, France Construction of state diagrams for wheat durum semolina could be useful to describe the physico-chemical changes involved during the pasta process, and more particularly during the steps involving changes in moisture and temperature (hydration, extrusion, drying and cooking). The objective of the current study was to identify and characterize the glass transition of wheat durum semolina using modulated differential scanning calorimetry. Glass transition temperatures of semolina were determined using a differential scanning calorimeter. The total, reversing and non reversing heat flows were quantified during heating, cooling and re-heating. An endothermic peak, observed on the non reversing heat flow during first heating was associated with endothermic relaxation of the protein fraction. An endothermic baseline shift was observed on the reversing heat flow during first heating, cooling and re-heating. The temperature at baseline shift decreased (from 110°C to 27°C) when moisture content increased (from 6% to 27 % db). The measured heat capacity change (0.10 - 0.25 J.g-1.°C-1) was not significantly affected by moisture content. This endothermic baseline shift was presumed to be the Tg of amorphous polymers in wheat durum semolina. The plasticizing effect of water on the Tg was described using Gordon Taylor and Kwei models and compared with Tg of the main wheat components. The glass transition of wheat durum semolina was characterized at low water contents by using modulated DSC. However, the Tg was difficult to detect using modulated DSC at high water contents due to the very low energy associated with the baseline shift and baseline disturbances on the reversing heat flows.
Session 88C, Food Engineering: Physical and Chemical Properties
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