Purification, structural characterization, and in vitro immunomodulatory activity of a low-molecular-weight polysaccharide from cultivated Chinese cordyceps.

Cultivated Chinese cordyceps, an optimal substitute for the endangered wild resource, has recently been produced on a large scale. This work sought to explore the structural features and immunomodulatory activity of a novel low-molecular-weight polysaccharide (CSP1a, 15.7 kDa) isolated from cultivated Chinese cordyceps. CSP1a was prepared with a multi-step process that encompassed hot water extraction, alcohol precipitation, and column chromatographic purification. The monosaccharide composition, infrared spectroscopy, methylation, and nuclear magnetic resonance results revealed that CSP1a was highly branched (with a branching degree of 49.21 %) and primarily constituted of galactose (30.60 %), glucose (12.87 %) and mannose (56.53 %), comprising 13 distinct types of glycosidic linkage fragments. The main chain of CSP1a consisted of different mannose residues, with several exposed β-d-Galf-(1→ residues in various side chains. The results from scanning electron microscopy and Congo red analyses revealed that CSP1a possessed a reticulated porous chain conformation, which enhanced its bioavailability and demonstrated its potential as a carrier. In vitro immunological investigations demonstrated that CSP1a significantly promoted splenic lymphocyte proliferation. Additionally, CSP1a increased RAW264.7 cell proliferation, improved phagocytic capacity, and stimulated the secretion of nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) in a dose-dependent manner. Collectively, CSP1a, a novel low-molecular-weight polysaccharide galactoglucomannan with a high branching degree and reticulated porous chain conformation, was isolated for the first time from cultivated Chinese cordyceps and showed promise as a potential immunomodulator or drug carrier. These findings contribute to elucidating the polysaccharide material basis for the immune activity of Chinese cordyceps and promote its industrial development as a functional food product.