Dynamic oscillation measurements of starch networks at temperatures above 100 degrees C.
Small deformation oscillatory studies were performed on wheat flour paste with a starch content of 75.4%. Work focused on temperatures above 100 degrees 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 degrees C to 6.5% at 130 degrees 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.
Kasapis
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Department of Food Science & Nutrition, College of Agriculture, Sultan Qaboos University, Al-Khod, Oman. stefan@squ.edu.om
Sablani
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SS
Biliaderis
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CG
D002236:Carbohydrate Conformation / Q000187:drug effects; D004548:Elasticity / Q000187:drug effects; D006358:Hot Temperature; D009991:Oscillometry / Q000379:methods; D013213:Starch / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D014908:Triticum / Q000737:chemistry; D014783:Viscosity / Q000187:drug effects; D014867:Water / Q000378:metabolism / Q000494:pharmacology
D014867:Water; D013213:Starch