Structural Characteristics and Superior Ameliorative Effects of Low-Molecular-Weight Homogalacturonan Compared with Rhamnogalacturonan-I from Avicennia marina Fruit Pericarp on DSS-Induced Colitis

Pectic polysaccharides hold therapeutic potential for ulcerative colitis (UC). This study reports the first isolation of two structurally distinct pectins from Avicennia marina fruit pericarp: AMPP-2-1 (158 kDa), a rhamnogalacturonan-I (RG-I)-rich pectin with galactan branches and intricate arabinan side chains rich in β-Ara f terminals; and AMPP-2-2 (16 kDa), a low-molecular-weight homogalacturonan (HG)-rich pectin with unsaturated Gal p A at the nonreducing ends. Both pectins significantly ameliorated dextran sodium sulfate-induced UC by suppressing inflammation, restoring intestinal barrier integrity, and modulating gut microbiota to enrich beneficial bacteria while depleting pathogenic bacteria, alongside promoting short-chain fatty acid production. Low-molecular-weight HG showed greater ameliorative effects than RG-I under the present experimental conditions. These findings establish that pectins may contribute, at least in part, to the intestinal benefits of A. marina fruits in traditional use, expanding the structural diversity and biomedical applications of pectic polysaccharides from underexplored plant resources.