Dynamic viscoelastic, calorimetric and dielectric characteristics of wheat protein isolates

Dynamic oscillatory theology of two wheat protein isolate (Prolite 100 and Prolite 200) doughs ( approximate to 48% moisture content, wet basis) were studied over a frequency range of 0.1-10 Hz during temperature sweep from 20 to 90 degrees C at a heating rate of 2 degrees C/min. Both doughs behaved similarly during heating; showed a threshold value and increased sharply, thereafter. Prolite 200 dough had a higher elastic modulus (G') and lower phase angle (delta) whereas Prolite 100 showed a distinct gel point at 52.2 degrees C followed by significant increase up to 90 degrees C. Rheological data of doughs after isothermal heating at 90 degrees C for 15 min followed by cooling to 20 degrees C resulted in strong mechanical strength. However, Prolite 100 dough showed more viscoelastic characteristics with significant transformation from liquid-like to solid-like behavior after heating than Prolite 200. Thermal analysis of isolates indicated distinct endothermic peaks in wider temperature range (50-130 degrees C) at various moisture levels. Lower temperatures could be associated with denaturation of various fractions of proteins whereas higher temperature linked to glass transition temperature of isolates. SDS-PAGE did not show any clear distinction among protein subunits between two isolates. Dielectric measurements of isolates at frequencies from 500 to 3000 MHz and temperature range between 30 and 80 degrees C indicated Prolite 200 had higher dielectric constant (epsilon') and loss factor (epsilon '') than Prolite 100. Isolates showed significant changes in dielectric properties above 50 degrees C indicating protein denaturation and supported theological and calorimetric data. (C) 2007 Elsevier Ltd. All rights reserved.