Sulfation and carboxymethylation of Citrus medica 'Fingered' polysaccharides: Physicochemical properties and protective effects against LPS-induced intestinal barrier injury in Caco-2 cells.

It is well known that Citrus medica 'Fingered' is an important industrial crop resource. Our previous study found that Citrus medica 'Fingered' polysaccharides via hot water extraction (HWE-CP) can alleviate ulcerative colitis by enhancing intestinal barrier and regulating intestinal flora. However, the large molecular weight of HWE-CP (35.15 kDa) limits its absorption by intestinal cells, thereby restricting its protective effects on the intestinal barrier. In this study, HWE-CP was chemically modified to obtain sulfated derivatives (S-HWE-CP) and carboxymethylated derivatives (C-HWE-CP). Subsequently, we investigated the physicochemical, structural characteristics, and protective abilities of these derivatives on the intestinal barrier. The results indicated that chemical modification led to significant changes in the molecular weight, monosaccharide composition and molar ratio, proportion of HG domains, Zeta potential, and thermal stability of HWE-CP. C-HWE-CP, with a degree of substitution of 1.12, most effectively promoted Occludin protein expression and enhanced the integrity of the cell barrier. Further analysis using RNA-seq revealed that C-HWE-CP may alleviate damage to Caco-2 cells through pentose and glucuronate interconversion pathways. These findings provide a theoretical basis for the role of HWE-CP functional group derivatives of HWE-CP in preventing chronic diseases associated with the intestinal barrier and facilitating the development of related functional foods.