Galactan from the Lactarius hatsudake Tanaka mycelium: structural characterization and in vitro biological evaluation

Lactarius hatsudake Tanaka (L. hatsudake) fruiting body polysaccharides possess diverse bioactivities but are limited by fruiting body scarcity. Therefore, this study investigated the potential of mycelial polysaccharides as a sustainable alternative. Four fractions (LHMPs) were isolated and characterized by methylation analysis, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy. The LHMPs (35-1788 kDa) consisted primarily of glucose and galactose. Bioactivity evaluation identified LHMP-4 as the key fraction in in vitro antioxidant and cytotoxicity assays. Structural analysis showed that the backbone consisted of →6)-α-Galp-(1→, →2,6)-α-Galp-(1→, and →3,5)-α-Araf-(1→ residues. α-L-Fucp-(1→ was attached to O-5 of the →3,5)-α-Araf-(1→ residue, while →6)-α-Galp-(1→ side chains were linked to O-2 of →2,6)-α-Galp-(1→ via α-(1→ 2) linkages, each with α-L-Fucp-(1→ attached at O-6. LHMP-4 resembled bioactive fruiting body polysaccharides but showed a higher degree of branching and arabinose content, supporting L. hatsudake mycelia as a potential alternative source of bioactive polysaccharides for functional food and pharmaceutical applications.