From the seaweeds' carrageenan composition to the hybrid carrageenans' hydrogel elasticity: Identification of a relationship based on the content in iota-carrageenan

The carrageenan composition of 12 commercial seaweeds used in the production of hybrid carrageenans (HC) is estimated from the analysis of solid-state NMR spectra and is systematically compared with the chemical structure of HC extracted in hot water. 1H NMR showed that the isolated HC contain from 5 to 80 mol% kappacarrageenan, from 90 to 10 mol% iota-carrageenan, while from 8 to 23 mol% biological precursors are present in the copolymer's chain. A good correlation is found between the iota-carrageenan content in the seaweeds and in the extracted HC. The shear elastic modulus of 1 wt% HC gels in the presence of 0.1 M KCl is significantly weaker and gels form at lower temperatures when the iota-content in the seaweed is larger than the kappa-content. However, these weaker gels show strain hardening. A cut-off of 30 mol.% of iota-carrageenan in the polysaccharide is identified that separates strain softening stiffer gels from strain hardening softer gels. Overall, the set of data suggests that the carrageenan gel elasticity is ruled by the self-assembly of iota-carrageenan moieties in the HC, and HC gel elasticity can be directly linked to the iota-carrageenan composition of seaweeds.