  Carrageenans comprise linear sulfated high molecular weight polysaccharides
obtained from seaweeds and are routinely used in food and home/personal care
industries. Various kinds of carrageenans differ from others based on the ester
sulfate group location on the polysaccharide chains. Pure and mixed systems of
Kappa Carrageenan and Iota Carrageenan undergo a three-dimensional gel network
structure formation or dissociation with a change in temperature. During the
sol-gel and gel-sol transitions, the Carrageenan systems pass through a unique
critical gel state, where dynamic moduli are scale-invariant owing to the
self-similar structure of the three-dimensional network. In this work, we
obtain the critical gel state associated with pure and mixed systems of Kappa
and Iota Carrageenan during cooling and heating by exploring the material
behavior for a range of frequencies. Interestingly, on the one hand, the mixed
gels show a higher critical sol-gel transition temperature compared to the pure
systems at equal individual concentrations. On the other hand, the low
temperature moduli of mixed gels are closer to that of Kappa Carrageenan when
the concentration of the same is more than half in the mixture. The rheological
measurements demonstrate that the Kappa Carrageenan strongly affects the nature
of aggregation of double helices of Iota Carrageenan, but Iota Carrageenan does
not have a significant influence on that of Kappa Carrageenan. These results
suggest an associative, interactive network formation between Kappa and Iota
Carrageenan in the mixture, such that the gel behavior is predominantly
influenced by Kappa Carrageenan.
