Extraction, Purification, Structural Characterization, Antioxidant and Hypoglycemic Activities of Polysaccharides from Fomitiporia yanbeiensis

Polysaccharides (FYP) from Fomitiporia yanbeiensis , an endemic fungus in Shanxi Province, are promising natural functional ingredients; however, how the extent of purification influences their structural features and bioactivity remains poorly understood. Herein, a pre-purified polysaccharide fraction (FYP-0, 73.2%) was obtained from crude polysaccharides by removing impurities (deproteinization, defatting, and decolorization), and two further fractions (FYP-1, 86.5%; FYP-2, 84.4%) were prepared from FYP-0 by ion-exchange chromatography. Structural characterization and multiple in vitro antioxidant assays, as well as α-amylase and α-glucosidase inhibitory assays, were performed on fractions representing successive purification stages. Counterintuitively, FYP-0 exhibited stronger bioactivity in most assays despite its lower polysaccharide purity, with the notable exception of α-amylase inhibition, for which FYP-1 showed the highest activity. The superior bioactivity of FYP-0 was potentially associated with a synergy between its polysaccharide structure and residual non-polysaccharide components (e.g., water-soluble protein), while its higher molecular weight and loose, fragmented morphology were identified as key structural attributes. This work demonstrates that exhaustive polysaccharide purification does not guarantee improved in vitro functionality and provides new insights into exploiting this endemic fungal resource as a source of functional food ingredients.