Characterisation of glass transition of durum wheat semolina using modulated differential scanning calorimetry

The glass transition of wheat durum semolina was characterised at different moisture contents using modulated differential scanning calorimetry. The t otal, reversing and non-reversing heat flows were quantified during heating , cooling and re-heating. An endothermic peak was observed on the nonrevers ing heat Row during first heating and was not greatly affected by changes i n moisture content (below 20 g water/100 g dry matter). This peak was assoc iated with endothermic relaxation of the protein fraction in wheat semolina . An endothermic baseline shift was observed on the reversing heat Row duri ng first heating, cooling and re-heating. The temperature at baseline shift decreased (from 110 degreesC to 27 degreesC) when moisture content increas ed (from 6% to 27% db). The measured heat capacity change (0 . 100 25J/g/de greesC) was not significantly affected by moisture content. This endothermi c baseline shift was presumed to be the glass transition of amorphous polym ers in wheat durum semolina. The plasticising effect of water on the glass transition temperature (Tg) was described using Gordon Taylor and Kwei mode ls and compared with Tg of the main wheat components. (C) 2001 Academic Pre ss.