Isolation, structural characterization, and immunostimulatory activity of a new water-soluble polysaccharide and its sulfated derivative from Citrus medica L. var. sarcodactylis.

The homogeneous heteropolysaccharide CMSPW90-1 was first purified from bergamot by DEAE Sepharose Fast Flow and Sephadex G-75 column with a molecular weight of 18.8 kDa. The structure of CMSPW90-1 was elucidated with high-performance gel permeation chromatography, gas chromatography-mass spectrometry, infrared spectrum, methylation, nuclear magnetic resonance (NMR), Congo red test, and circular dichroism. In comparison with CMSPW90-1, the sulfated derivative CMSPW90-M1 showed significant ultra-structural differences with a molecular weight of 75.4 kDa. The antioxidant and immunomodulatory activities of CMSPW90-M1 were examined to determine the relationships of structure-bioactivity. CMSPW90-M1 exhibited stronger scavenging activities for DPPH and ABTS+ than those of CMSPW90-1. CMSPW90-M1 exhibited more immunomodulatory activity in vitro by promoting the proliferation of mouse splenocytes and the neutral red phagocytosis of RAW264.7 cells. The results demonstrated that CMSPW90-M1 could be developed as one of the potential free radical inhibitors and immunomodulators.