Determination of the thermo-mechanical properties in starch and starch/gluten systems at low moisture content – A comparison of DSC and TMA

• Heating rate affects the temperature of transitions in starch as measured by DSC.
• The optimum heating rate for starch Tg measurement by DSC was 5 °C/min.
• Tg of starch changes upon ageing and is lowered by use of an initial heating scan.
• Gluten plasticises starch and results in a lower Tg compared to starch alone.
• TMA is a useful alternative to DSC for determining Tg in starch up to 80 °C.

The impact of heating rate on the glass transition (Tg) and melting transitions observed by differential scanning calorimetry (DSC) on starch and a starch/gluten blend (80:20 ratio) at low moisture content was examined. The results were compared to those determined by thermo-mechanical analysis (TMA). Comparison with dynamic mechanical thermal analysis (DMTA) and phase transition analysis (PTA) is also discussed. Higher heating rates increased the determined Tg as well as the melting peak temperatures in both starch and the starch/gluten blend. A heating rate of 5 °C/min gave the most precise value of Tg while still being clearly observed above the baseline. Tg values determined from the first and second DSC scans were found to differ significantly and retrogradation of starch biopolymers may be responsible. Tg values of starch determined by TMA showed good agreement with DSC results where the Tg was below 80 °C. However, moisture loss led to inaccurate Tg determination for TMA analyses at temperatures above 80 °C.