Thermal behavior of native and hydrophobized wheat gluten, gliadin and glutenin-rich fractions by modulated DSC

The glass transition temperature (T-g) of hydrophobized and native wheat gl uten and its protein fractions, with water mass fraction from 0 to 0.2, was studied using modulated differential scanning calorimetry. The T-g values of unplasticized products were similar to 175 degrees C whatever the treatm ent (hydrophobization) or the fraction tested, except for the gliadin-rich fraction (162 degrees C). Experimental change in heat capacity at the glass transition (Delta C-p) ranged from 0.32 to 0.50 J/g/degrees C depending on the gluten fractions. The Gordon-Taylor fit of T-g evolution as a function of water content showed that glutenin-rich fractions were more sensitive t o water plasticization than the gliadin-rich fraction. The Kwei equation ga ve better fit to experimental data and demonstrated that the water plastici zation of gluten and its fractions is influenced by secondary interactions. However, the application of the Couchman-Karasz equation without fitting p redicts satisfactorily the plasticization of gluten proteins by water. (C) 2000 Elsevier Science B.V. All rights reserved.