Soluble chitosan–carrageenan polyelectrolyte complexes and their gastroprotective activity

•The soluble polyelectrolyte complexes κ-carrageenan–chitosan were obtained.•The binding constant of carrageenan with chitosan is 2.11×107mol−1.•The transformation of supramolecular structure of the complexes was shown.•Gastroprotective activity of complexes depending on their composition was found. The soluble polyelectrolyte complexes (PEC) κ-carrageenan (κ-CG):chitosan was obtained. Binding constant value (2.11×107mol−1) showed high affinity of κ-CG to chitosan. The complex formation of κ-CG:chitosan 1:10 and 10:1w/w was shown by centrifugation in a Percoll gradient. Using atomic force microscopy we showed that the supramolecular structure of the complexes is different from each other and from the macromolecular structure of the initial polysaccharides. The gastroprotective and anti-ulcerogenic effect of κ-CG, chitosan and their complexes was investigated on the model of stomach ulcers induced by indometacin in rats. PEC κ-CG:chitosan have gastroprotective properties which depend on their composition. Complex κ-CG:chitosan 1:10w/w possesses higher gastroprotective activity than the complex 10:1w/w. These results suggest that the gastroprotective effect of complexes can be associated with their protective layer on the surface of the mucous membrane of a stomach, which avoids a direct contact with the ulcerogenic agent.