Structural characterization, rheological properties, and skin bioactivities of a glucomannan from Bletilla striata

Bletilla striata is highly regarded in traditional Chinese medicine and has also gained widespread attention as a valuable medicinal plant resource. However, the molecular composition and bioactive potential of its polysaccharides present a significant knowledge gap. Herein, a specific glucomannan fraction, designated as BSP60, was purified from Bletilla striata tubers and subsequently subjected to structural, rheological, and biological evaluations. Comprehensive characterization via methylation-GC-MS, monosaccharide composition analysis, and 1D and 2D NMR techniques demonstrated that BSP60 possesses a β-(1 → 4)-linked backbone featuring alternating mannosyl and glucosyl units, with the mannose moieties exhibiting partial O-acetylation at their C-2 or C-3 positions (with an acetylation rate of 23.54%). Rheological studies showed that BSP60 aqueous solutions exhibit shear-thinning behavior and form an elastic-dominated viscoelastic network, with higher viscosity and storage modulus than dextran of comparable molecular weight, indicating enhanced intermolecular interactions. Biological assays revealed that the BSP60 effectively decreased the level of NO, IL-6, and TNF-α in LPS-triggered macrophages (RAW264.7). Furthermore, the scavenge ability of BSP60 to superoxide anion (O₂^•-) and ABTS^⁺• radicals are significantly higher than that of hyaluronic acid. This study systematically characterizes the structural features of glucomannan derived from Bletilla striata, thereby establishing a robust scientific basis for its expanded utilization in the development of biomedical materials and functional cosmetic ingredients.