The method of dynamic oscillation was employed to investigate changes
in the mechanical properties of deacylated gellan gels in the presence
of sucrose-corn syrup blends. The effect of sugar, at concentrations
between 0 and 50% in the mixture, is to raise gradually the gelling te
mperature and the mechanical strength of the gellan network. However,
there is a sharp increase in thermal stability (formation of a structu
re at the highest experimentally accessible temperature of 90 degrees
C) and substantial reduction in shear modulus development at 60% co-so
lute in the system which is discussed in terms of a disproportionate c
onformational ordering and diminishing water-supported, intermolecular
junction zones of the gellan strands in a low solvent environment. Th
e dramatic change in physical properties of the gellan-solute blends a
t 90 degrees C produces a spectacular temperature dependence of the in
-phase and out-of-phase viscoelastic components during subsequent cool
ing. Thus, the high-solids gellan network undergoes transformation fro
m a rubber-like consistency to a glassy state in the manner observed f
or entangled networks of high molecular weight synthetic polymers. The
onset of glass transition is enhanced by increasing amounts of sugars
, occurring at about 37 degrees C for the 0.5% gellan plus 85% solute
system at an experimental frequency of 10 rad/s, Mechanical spectra of
sucrose-corn syrup mixtures at this concentration remain Newtonian at
5 degrees C, the lowest experimentally accessible temperature. Accord
ing to the time-temperature superposition principle, vitrification of
the above gellan sample commences at approximate to 17 Hz at 90 degree
s C. Following the empirical procedure developed by Williams, Landel a
nd Ferry, the temperature at which the gellan-solute glass forms (Tg)
was found to be close to the vitrification temperature of a sucrose pr
eparation at 15% moisture content (approximate to-25 degrees C).