Structural Characterization and In Vivo Gastric Mucosal Protective Activity of a Polysaccharide from Laoxianghuang (Fermented Finger Citron) in Mice.

PFCP-2-1 (polysaccharide-2-1 of Finger Citron-pickled products), a water-soluble polysaccharide enriched in galacturonic acid, was isolated from Laoxianghuang by hot water extraction and purified using DEAE-52 and agarose CL-6B chromatography. Structural analysis showed that PFCP-2-1 had a smooth surface, flakes of varying sizes and shapes, irregular ellipsoidal structures, and cylindrical-like forms, which likely represent aggregated assemblies formed by the association and curling of polysaccharide chains. It was determined to have an average molecular weight of 749.38 kDa and to consist of rhamnose, galactose, glucose, and galacturonic acid (molar ratio 0.147:0.238:0.059:0.556). FT-IR spectroscopy revealed both α- and β-pyranose configurations, while methylation and NMR analyses identified 16 types of glycosidic linkages, of which 9 were the main types, consistent with a pectic-type structure. In an ethanol-induced acute gastric ulcer mouse model, PFCP-2-1 exhibited significant mucosal protection by elevating prostaglandin E2 (PGE2), transforming growth factor-α (TGF-α), and mucin 5AC (MUC5AC) levels and upregulating Occludin and zonula occludens-1 (ZO-1) expression. It also modulated the gut microbiota by increasing the abundance of Bacteroides and Prevotella_UCG-001, and enhanced short-chain fatty acid (acetate and butyrate) levels. These findings suggest that PFCP-2-1 may exhibit a protective effect against ethanol-induced gastric damage under the conditions of this experiment, suggesting its potential for further development as a functional food ingredient.