Viscoelastic properties of pectin - co-solute mixtures at iso-free-volume states

Small-deformation oscillatory measurements were performed on pectin-sucrose -glucose syrup systems at a total level of solids of 81%, with the polysacc haride content being fixed at levels of industrial use (1%). The experiment al temperature range was between 50 and - 50 degreesC. Analysis of the temp erature dependence of viscoelastic processes by the equation of Williams, L andel, and Ferry provides values of fractional free volume for the temperat ures covering the glass transition region. The shift factors used in the co nversion of mechanical spectra into master curves were normalised at suitab ly different temperatures so that their temperature dependence becomes coin cident. The treatment implies an iso-free-volume state and relates to chang es in the monomeric friction coefficient with increasing levels of intermol ecular interactions in the mixture. A free-volume related glass transition temperature was defined and manipulated markedly by introducing pectin of v ariable degrees of esterification to the sucrose-glucose syrup system. (C) 2000 Elsevier Science Ltd. All rights reserved.