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 (T-g) 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 T-g values are 164 and 209 degrees C, respectively. The calculated T-g 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 T-g(Delta Cp) with a single heating scan, avoiding sample alteration, and Delta Cp values are 0.365 J/g per K for zein and 0.184 J/g per K for glutelin. The differences observed in T-g, relaxation temperatures, Delta Cp and tan delta peak height are related to differences in the structure of the proteins, through the cross-linkages and hydrogen or van der Weals 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. (C) 1999 Elsevier Science B.V. All rights reserved.