A sensitive in-house rheometer and two measuring configurations were e
mployed to examine the structural properties of gellan/sugar preparati
ons at stoichiometric levels of added calcium ions. Perforated cylinde
rs allowed recording of the gelation process in slippery gellan gels (
from 0 to 40% sucrose) whereas systems with greater amounts of co-solu
te could also be analysed with a flat cone-and-plate geometry. The sha
rp sigmoidal transition of the highly enthalpic aggregated helices in
aqueous or low sucrose (up to 30%) gellan gels was observed at tempera
tures below 60 degrees C upon cooling (1 degrees C/min). This gave way
at 60% sucrose and beyond (high solids regime of sucrose plus corn sy
rup) to a thermally stable structure with a low modulus monotonic temp
erature profile (from 90 to 5 degrees C). At the intermediate range of
co-solute (30 to 60%) a bimodal cooling profile was recorded which wa
s rationalised on the basis of a composite network comprising lightly
cross-linked and therefore flexible gellan chains, and rigid aggregate
s. In the absence of external calcium, at the intermediate level of so
lids, only the aggregated type of network was formed at the low temper
ature end, apparently supported by the batch salts. Therefore, the add
ed calcium facilitated stabilisation at the top temperature end of lim
ited intermolecular associations between the thermally vibrant gellan
chains in a sugar (>40%) environment. (C) 1997 Elsevier Science Ltd.