Dynamic oscillation measurements of starch networks at temperatures above 100 °C Original Research Article

Small deformation oscillatory studies were performed on wheat flour paste with a starch content of 75.4%. Work focused on temperatures above 100 °C in an effort to seek molecular understanding of such high-temperature processes as bakery operations which are characterised by evaporation of water. The moisture content of the sample decreased from about 32% at 100 °C to 6.5% at 130 °C. Viscoelastic spectra produced a sigmoidal profile with a disproportionate viscous element also seen in the glass transition of semiamorphous synthetic polymers and high sugar/polysaccharide mixtures during cooling. It is argued that the loss of water upon heating reduces the available free volume between neighbouring chain segments, thus generating a high-density thermoplastic melt suspending granule fragments. The configurational rearrangements of the disordered chains contribute mainly to an energy-dissipating process, as observed in the vitrification of cooled high-solids systems. The equation of Williams, Landel, and Ferry was modified with a ‘moisture term’ in order to describe the temperature function of viscoelasticity.