Extraction, structural characterization and biological activities of exopolysaccharides from Ruditapes philippinarum

This study investigated the extraction, structural characterization and biological activities of exopolysaccharides from clam meat. The aim of this is to develop low-cost and novel animal polysaccharides with potential medicinal or health benefits. A crude polysaccharide yield of 10 g/100 g was extracted by the ultrasonic-assisted method. Two fraction exopolysaccharides (RPP-1A and RPP-2A) were obtained through DEAE-52 column chromatography and HW-65F column. Glc, GalA, GlcA, Rha and Rib were the main monosaccharides components of RPP-1A, whereas RPP-2A was primarily composed of GlcA, Rha and Rib. RPP-1A and RPP-2A were further investigated using Fourier transformed infrared (FT-IR) and nuclear magnetic resonance (NMR) that the results showed that RPP-1A comprised a main chain of residues represented as: [→6-α-Glc-(1 → 4)-β-GalA-(1 → 6)-α-Glc-(1 → 4)-β-GalA-(1→]. The side chain repeating unit structure is [β-GlcA-(1 → 4)-α-Glc-(1 → 3)-α-Rib-(1 → 4)-α-Rha-(1→], attached to the main chain at the C-2 position of Glc. RPP-2A represents the side chain portion of RPP-1A [β-GlcA-(1 → 4)-α-Glc-(1 → 3)-α-Rib-(1 → 4)-α-Rha-(1→]. Scanning electron microscopy (SEM) analysis revealed that the characteristic morphology of different fractions. X-ray diffraction showed that the polysaccharides consisted of crystalline and amorphous regions. Furthermore, assays of antioxidant activity showed that any one of RPP-1A and RPP-2A had antioxidant effects against DPPH radical, ABTS radical cation, hydroxyl radical, among which RPP-2 was stronger. In addition, they significantly inhibited the proliferation of Hela, and HepG2 cancer cells, and HepG2 was more sensitive to RPP-2A. In general, the results demonstrated that RPPs had great potential as a natural antioxidant in the functional food, and they are promising candidates for cancer treatment.