Structural Characterization, Antioxidant and Antibacterial Activities of Polysaccharides from Blueberry

A neutral polysaccharide (BPN1) was obtained from blueberry by citric acid-assisted extraction followed by purification through cellulose DEAE-52 and Sephadex G-100 column chromatography. The average weight molecular mass (m_w) of BPN1, as determined by high-performance size exclusion chromatography with multi-angle laser light scattering (HPSEC-MALLS) detection, was 2.991 × 10⁴ Da, the polydispersity index (PDI) was 1.163, and the molecular mass distribution ranged narrowly. Monosaccharide composition analysis performed using 1-phenyl-3-methyl-5-pyrazolone derivatization followed by high performance liquid chromatography (HPLC) showed that BPN1 was mainly composed of glucose, galactose, xylose and araban. The glycosidic bond configuration and linkage of BPN1 were analyzed by infrared spectroscopy and gas chromatography-mass spectrometry (GC-MS) after methylation. Combining the obtained results with two-dimensional nuclear magnetic spectroscopy (NMR) analysis, it was inferred that the polysaccharide was composed of a backbone chain of 1→4 linked dextran, some of which were substituted at position C6 by araban, xylose and galacto-oligosaccharide. The in vitro antioxidant assays showed that BPN1 had stronger scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl, 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) cation and hydroxyl radicals than hot water-soluble blueberry polysaccharide. The antibacterial test showed that the minimum inhibitory concentration (MIC) of BPN1 against Staphylococcus aureus and Escherichia coli was in the range of 2.5 to 5 mg/mL, and it exerted antibacterial activity against S. aureus and E. coli by destroying the cell membrane. This study provides a basis for the structural analysis, development and utilization of blueberry polysaccharides.