Dynamic oscillation measurements of starch networks at temperatures above 100 degrees C

Small deformation oscillatory studies were performed on wheat flour paste w ith a starch content of 75.4%. Work focused on temperatures above 100 degre es C in an effort to seek molecular understanding of such high-temperature processes as bakery operations which are characterised by evaporation of wa ter. The moisture content of the sample decreased from about 32% at 100 deg rees C to 6.5% at 130 degrees C. Viscoelastic spectra produced a sigmoidal profile with a disproportionate viscous element also seen in the glass tran sition of semiamorphous synthetic polymers and high sugar/polysaccharide mi xtures during cooling. It is argued that the loss of water upon heating red uces the available free volume between neighbouring chain segments, thus ge nerating a high-density thermoplastic melt suspending granule fragments. Th e configurational rearrangements of the disordered chains contribute mainly to an energy-dissipating process, as observed in the vitrification of cool ed high-solids systems. The equation of Williams, Landel, and Ferry was mod ified with a 'moisture term' in order to describe the temperature function of viscoelasticity. (C) 2000 Elsevier Science Ltd. All rights reserved.