The role of ethylene glycol (EG) in the gelation mechanisms of acid pi
gskin gelatin and high methoxy pectin has been monitored and used as a
baseline for the investigation of mixed gelatin-pectin gels in variou
s mixed ethylene glycol-water solvents. The addition of EG did not alt
er the gelation (t(gel) approximate to 14 degrees C) and melting (t(me
l) approximate to 28 degrees C) temperatures of an aqueous gelatin net
work, the strength of which, however, was first increased, and then re
duced at concentrations of co-solute higher than 30%. The reduction in
values of storage modulus (G) was attributed to a decrease in the pro
portion of polypeptide chains involved in the formation of junction zo
nes. By contrast, increasing levels of ethylene glycol encouraged form
ation of pectin gels at high temperatures (e.g. t(gel) was 63 degrees
C at 80% EG) which largely retained their structure upon subsequent he
ating. The network strength increased rapidly and peaked at 60% co-sol
ute followed by a subsequent reduction in storage moduli at conditions
of low water activity (60-80% EG). On the basis of a model for gel fo
rmation involving a two-step process, it was proposed that ethylene gl
ycol promotes the ordered structure of contiguous pectin chains (first
stage) but 'dissolves' the hydrophobic clusterings of methyl groups (
second stage). Differential scanning calorimetry demonstrated that the
rmodynamic incompatibility between the two polymers is the driving for
ce behind the phase behaviour of mixed preparations. Based on the mech
anical properties of single components, it was argued that increasing
amounts of EG, within the 0-25% range, promote pectin's conformational
ordering, which becomes more and more effective in excluding concentr
ating up and strengthening the continuous gelatin phase. At higher lev
els of co-solute (from 30 to 70%), pectin can form a thermally stable
network and during cooling it does so before gelatin's gelation at low
er temperatures. Light microscopy work strongly suggests that gelatin
also forms a continuous network throughout the body of the sample. The
refore, the latter mixtures can be described as phase-separated, bicon
tinuous arrangements.