Atomic force microscopy imaging of carrageenans from red algae of Gigartinaceae and Tichocarpaceae families

In the present article, the atomic force microscopy was applied to investigate macromolecular structures of various carrageenan types including hybrid polysaccharides (κ-, κ/β-, κ/ι-, λ-, and X-carrageenans) depending on polysaccharide concentration. The structures dependence on a polysaccharide concentration also was focused. κ-Carrageenan forms both single and two stranded structures at a low concentration. At high concentrations κ-, κ/β-, and κ/ι-carrageenans form fibrous network-like structures by a side-by-side association type at the same time for κ/ι-carrageenan end-to-end association type also was found. Comparably to κ-carrageenan, κ/β-carrageenan network was more open with coarser fibers while κ/ι-carrageenan structure is characterized with a more flexible network. Honeycombed structures due to end-to-end and side-by-side association types were observed for X-carrageenan, while λ-carrageenan formed honeycombed structures only at high concentrations. In order to investigate topographical parameters of the carrageenans macromolecular structure a new method of the autocorrelation function analysis was used for the first time.

► K-, κ/β- and κ/ι-carrageenans form fibrous network-like structures.
► Compared to κ-carrageenan, κ/β-carrageenan network was more open with coarser fibers.
► λ-Carrageenan formed honeycombed structures at high concentrations.