Thermal properties of corn gluten meal and its proteic components.

Thermal properties of corn gluten meal (CGM) and of its extracted proteic components (zein and glutelin) at 0% moisture content, is studied by dynamic mechanical thermal analysis (DMTA) and modulated differential scanning calorimetry (MDSC). The glass transition temperature (Tg) on first heating, is measured at 176 and 174 degrees C, respectively, for hot-air-dried and native CGM. For zein and glutelin isolated fractions, the measured Tg values are 164 and 209 degrees C, respectively. The calculated Tg from using Matveev's method (Matveev YI. Spec Publ R Soc Chem 1995;156;552) is in good agreement with experimental data for zein, a well defined protein. MDSC allows the measurement of change in heat capacity at Tg (deltaCp) with a single heating scan, avoiding sample alteration, and deltaCp values are 0.365 J/g per K for zein and 0.184 J/g per K for glutelin. The differences observed in Tg, relaxation temperatures, deltaCp and tan delta peak height are related to differences in the structure of the proteins, through the cross-linkages and hydrogen or van der Waals interactions. Experimental data from DMTA and MDSC, and the Couchman-Karasz thermodynamic approach indicate that CGM behaves as a miscible blend of its components, with high non-polar interactions between zein and glutelin proteins.