Thermal properties of raw and processed wheat gluten in relation with protein aggregation

The glass transition temperature (T-g) and change in heat capacity (Delta C -p at T-g) of processed wheat gluten samples, including wet (casting) and d ry processes (thermal treatment, mixing, thermomoulding and mixing followed by thermomoulding) were determined by modulated differential scanning calo rimetry (MDSC) as a function of water content. An increase of T-g and a dra stic decrease of Delta C-p were observed when gluten was dry processed. Cas ting process gave a film with calorimetric properties close to those of nat ive gluten. The molecular size distribution of proteins in native and proce ssed glutens was measured by size exclusion chromatography. The thermomould ing and the use of chemical cross-linker during casting resulted in a drast ic drop of SDS-soluble proteins. In contrast, mixing of gluten, even using high specific mechanical energies, gave only a slight polymerisation of the proteins. Therefore, except for treatments where a high temperature was ap plied to gluten, the modification of calorimetric parameters accounting for reticulation phenomena was not related to the SDS-insoluble protein conten t. T-g, Delta C-p and protein SDS extractability could account for differen t kinds of protein networks. (C) 2000 Elsevier Science Ltd. All rights rese rved.