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

The glass transition temperature (Tg) and change in heat capacity (ΔCp at Tg) of processed wheat gluten samples, including wet (casting) and dry processes (thermal treatment, mixing, thermomoulding and mixing followed by thermomoulding) were determined by modulated differential scanning calorimetry (MDSC) as a function of water content. An increase of Tg and a drastic decrease of ΔCp were observed when gluten was dry processed. Casting process gave a film with calorimetric properties close to those of native gluten. The molecular size distribution of proteins in native and processed glutens was measured by size exclusion chromatography. The thermomoulding and the use of chemical cross-linker during casting resulted in a drastic 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 applied to gluten, the modification of calorimetric parameters accounting for reticulation phenomena was not related to the SDS-insoluble protein content. Tg, ΔCp and protein SDS extractability could account for different kinds of protein networks.