Structural characterization of blueberry fruit polysaccharides and assessment of its hypolipidemic and immunological activity

In this study, polysaccharides were extracted from blueberry fruit (BFP) and isolated to 3 components (BFP-1, BFP-2 and BFP-3). The molecular weight, monosaccharide composition, characteristic groups, microscopic morphology, and triple helical conformation of the polysaccharides were characterized using high performance permeation chromatography, high performance liquid chromatography, gas chromatographymass spectrometry, Fourier transform infrared spectrometer, scanning electron microscope and Congo red staining. Moreover, the hypolipidemic and immunological activities of the polysaccharides were also assessed. Results showed that the molecular weights of polysaccharides BFP-1, BFP-2, and BFP-3 were 5.547 × 10⁴, 5.671 × 10⁴, and 3.951 × 10⁴ Da, respectively, the main monosaccharides were glucose (Glc), galactose (Gal) and arabinose (Ara), but BFP-3 was mainly composed of galacturonic acid (GalA), Glc, Gal, and Ara. The backbone of BFP-1 was →4)-Glcp-(1→, which branches to Ara and xylose (Xyl) residues, while the backbone of BFP-2 was →5)-Araf-(1→, which branches to Xyl, Glc, rhamnose (Rha) and Gal residues, in particularly, BFP-3 has a more complex branching with a →3, 6)-Galp-(1→) backbone, the side chain is dominated by Araf-(1→). Blueberry polysaccharides are pyran-type polysaccharides with α-glycosidic bonds, and BFP-1 has a typical triple-helical structure. The activity assay revealed that the binding of BFP-3 to sodium glycylcholate hydrate and sodium taurocholate was 79.95% and 78.50%, respectively, indicating that it had better hypolipidemic activity than the others. Immunoactivity assay showed that BFP promoted NO secretion through activating the NF-κB signalling pathway in RAW264.7 cells, which played a role in enhancing the immune function of the organism. These findings may provide a reference for the development and application of blueberry polysaccharides in functional food and medicine.