Molecular Characteristics and Gelling Properties of the Carrageenan Family, 1. Preparation of Novel Carrageenans and their Dilute Solution Properties

The carrageenans are a family of sulfated polysaccharides extracted from red seaweed, and are conventionally classified into three major groups as κ‐, ι‐ and λ‐carrageenan according to the maximum number (1, 2 and 3, respectively) of sulfate groups per disaccharide repeating unit in corresponding ideal structures. β‐ and θ‐carrageenan (not available in nature) possessing none and two sulfate groups per repeating unit, respectively, were prepared from κ‐ and λ‐carrageenan by desulfonation. Here the aqueous solutions of κ‐, ι‐, β‐ and θ‐carrageenans undergo the thermoreversible gelation by lowering temperature, whereas the aqueous solution of λ‐carrageenan forms no gel.Light scattering and small‐angle X‐ray scattering were observed from the aqueous solution of κ‐, ι‐, λ‐, β‐ and θ‐carrageenans, and the results were analyzed conventionally and by adapting the molecular model in order to elucidate the effect of sulfate groups and anhydrous residue on the conformational characteristics of carrageenans.