Comparison of Extraction, Isolation, Purification, Structural Characterization and Immunomodulatory Activity of Polysaccharides from Two Species of Cistanche

This study focuses on polysaccharides from Cistanche deserticola and Cistanche tubulosa, medicinal plants renowned for their health benefits. The “water extraction and alcohol precipitation” method was used to obtain the crude polysaccharides of the wine-making residues of C. deserticola (CDP) and C. tubulosa (CTP), respectively. Then, ultrafiltration membrane (UFM), DEAE-52, and Sephadex-G75 or Smartdex-G100 gel chromatography were used to separate and purify the crude polysaccharides, yielding the homogeneous fractions CDP1-5-1, CDP2-2-2, CDP2-3-2, CTP1-5-1, and CTP1-5-3. Structural analysis was conducted by using Fourier-transform infrared spectroscopy (FT-IR), high-performance anion-exchange chromatography coupled with multi-angle laser light scattering and refractive index detection (HPAEC-MALLS-RID), gas chromatography–mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), congo red, and scanning electron microscopy (SEM). CDP1-5-1 was found to be an arabinan, while CDP2-2-2 and CDP2-3-2 were agavin-like fructans with different molecular weights. CTP1-5-1 and CTP1-5-3 were identified as a heteropolysaccharide and a galacturonan, respectively. Immunological evaluation using RAW264.7 macrophages showed that they all significantly enhanced nitric oxide (NO) production, with CDP1-5-1 exhibiting the most potent activity. The structural–activity relationship is summarized as follows: the arabinose was a key active unit with NO stimulatory effects. This research provides foundational data on the structure and immune-enhancing potential of Cistanche polysaccharides, supporting their further development and application.