Structural characterization of a galacturonic acid-rich polysaccharide from Ziziphus Jujuba cv. Muzao

Jujube (Zizyphus jujuba Mill.) have been widely used as a health food and medicinal herb in oriental medicine. In the present study, a novel galacturonic acid-rich polysaccharide (PZMP3-2) was isolated from Zizyphus Jujuba cv. Muzao through hot water extraction, ethanol precipitation, and purification with DEAE-Sepharose Fast Flow and Sephacryl S-300 column chromatography. The chemical structures of PZMP3-2 were elucidated by methylation analysis, along with HPGPC, FT-IR spectroscopy, GC-MS, 1D NMR spectroscopy, and 2D NMR spectroscopy. Its morphological properties were further characterized by SEM, AFM, and XRD. Monosaccharide compositional analysis of PZMP3-2 revealed the presence of rhamnose, arabinose, galactose, and galacturonic acid at a molar ratio of 1.74:2.00: 1.00:18.69, and the HPGPC data demonstrated an average molecular weight of 58.21 kDa. Structural and linkage analysis by GC-MS and NMR spectroscopy suggested that PZMP3-2 was a homogalacturonan (HG)-like pectic polysaccharide branched at C-2 with some Araf and Rhap residues. Such unique structure of PZMP3-2 may indicate distinct bioactivities and further application in food and even clinic.