Structural characterization of κ-carrageenan by acetylation modification and its effect on intestinal inflammation

This study aimed to investigate the effect of acetylation on the structure and intestinal inflammation of κ-carrageenan of different molecular weights (around 6455-5.9 kDa) through acid hydrolysis-ultrafiltration. Results indicated that with molecular weight decreased from approximately 6455 kDa to 5.9 kDa, the surface structure of κ-carrageenan loosened with the pore size increased, while the total sugar content was reduced. Acetylation modification resulted in a more loose surface of κ-carrageenan, which became rough with crystal particles attached, but did not affect the type of monosaccharide composition. Acetylation modification introduced acetyl groups and reduced sulfate content of κ-carrageenan, where the characteristic peak of acetyl groups appeared at 1740 cm^-1 in the FT-IR spectra and 2.04 ppm in the NMR hydrogen spectra. Importantly, acidolyzed F-κ-CA promoted the production of TNF-α, IL-1β, and ICAM-1 in Caco-2 cells and down-regulated tight junction proteins such as Occuldin and Claudin-1, which was more pronounced in the lower molecular weight κ-carrageenan. Acetylated κ-carrageenan downregulated cytokines (TNF-α, IL-1β, and ICAM-1) and promoted the expression of tight junction proteins, exhibiting a clear regulatory effect on the inflammatory response of intestinal epithelial cells, which laying the foundation for the further validation of its immunomodulatory functions. The results are beneficial to the future utilization and development of κ-carrageenan.