Abstract
The gel strengths of Ca-alginate gels made in situ with different
degree of cross-linking were determined by adapting three different
methods: FIRA Jelly Tester, initial deformation (Youngs modulus,
E) with a Stevens LFRA Texture Analyzer, and dynamic measurements
with a Bohlin VOR Rheometer (dynamic storage modulus, G'). The results
showed that there were relatively large differences in absolute values,
but that the deviations diminished when the results were expressed
as relative gel strengths. The deviations of the Youngs modulus (E)
from G' increased with decreasing gel strength. Only dynamic measurements
were suitable for quantifying low gel strengths. The gel strength
and the breaking point were also measured as a function of the molecular
weight of alginates isolated from stipes of Laminaria hyperborea.
In the present Ca limited system, both the gel strength and the breaking
point showed a marked increase with increasing molecular weight (Mw)
up to 320-340 kD. This is considerably higher than with gels made
by dialysis ('Ca saturated'), where the gel strength becomes independent
oil molecular weight around 100 kD. These results may have an impact
on applications of alginate gels where the source of Ca crosslinking
ions is limited.
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