Dynamic oscillatory data on deacylated gellan and high methoxy pectin,
in the presence of sucrose and glucose syrup, are presented over a wi
de temperature range. High levels of the co-solute induce a transition
from rubberlike to glasslike consistency in the two biopolymers. The
time-temperature superposition method is employed to construct composi
te curves, around the glass transition region, covering a nine-decade
frequency range. The shift factors thus derived are fitted against the
experimental temperatures using the Williams, Landel and Ferry equati
on. These observations are interpreted on the basis of the free volume
theory which allows calculation of thermal expansion coefficient and
fractional free volume parameters, at the glass transition temperature
s of the high solids gellan and pectin systems. Values are in excellen
t agreement with those for synthetic polymers, a result which emphasiz
es the universal utility of the above approach (experiment and theory)
in studying glasses of synthetic or biological origin. (C) 1997 Elsev
ier Science Ltd.