Structural characteristics of carrageenan gels: temperature and concentration dependence

κ- and ι-carrageenan in aqueous solution undergoes reversible sol/gel transition by cooling or increasing concentration. The small-angle X-ray scattering profiles from carrageenans were observed at different temperatures and concentrations. The results were analyzed by means of molecular models of double helix or associated double helices. It was found that κ-carrageenan formed two or three associated double helices by gelation, although gelation took place in ι-carrageenan mostly by the transition from single chain to double helix without association. λ-carrageenan exhibited the normal scattering behavior of polyelectrolyte in solution.