Characterization, antioxidative and bifidogenic effects of polysaccharides from Pleurotus eryngii after heat treatments

• Freeze drying is optimal to preserve contents of Pleurotus eryngii polysaccharides.
• Monosaccharide composition of Pleurotus eryngii polysaccharides were HPLC analyzed.
• Microstructures of Pleurotus eryngii polysaccharides were analyzed by FTIR and CLSM.
• Polysaccharides of freeze dried Pleurotus eryngii had highest antioxidant activity.
• Polysaccharides stimulated Bifidobacterium longum growth in soymilk significantly.

Polysaccharides were extracted from freeze-dried-, oven-dried- and boiling-treated Pleurotus eryngii (FDPEPS, ODPEPS and BTPEPS). Yield of FDPEPS and its total carbohydrates, total polysaccharides, reducing sugars, phenolics and protein content were higher than ODPEPS and BTPEPS. High performance liquid chromatography (HPLC) identified that FDPEPS, ODPEPS, and BTPEPS were composed of mannose (5.75%, 5.52%, 6.97%), glucose (88.90%, 89.31%, 87.68%) and galactose (5.34%, 5.17%, 5.35%). All three polysaccharides showed typical saccharic absorption bands in FT-IR. The FDPEPS showed the highest antioxidant activities in ferric reducing antioxidant power (FRAP), ABTS, superoxide anion and hydroxyl radical scavenging tests. Denser aggregates and larger serum pores were observed in confocal micrographs of soymilk added with ODPEPS. Viability of Bifidobacterium longum in soymilk added with polysaccharides was significantly higher (p < 0.01) than those without polysaccharides during fermentation. Heat treatments applied before extraction affected the properties, composition and microstructures of FDPEPS, ODPEPS and BTPEPS.