Polysaccharide from Pleurotus nebrodensis: Physicochemical, structural characterization and in vitro fermentation characteristics.

A high Mw (5012 kDa) polysaccharide (PNPS) from the fruiting body of Pleurotus nebrodensis was isolated using water extraction followed by ethanol precipitation. The structural characteristics and in vitro fermentation behaviors of this polysaccharide was investigated. Chemical composition analysis showed the total sugar content of PNPS was up to 97.20 ± 1.80 wt%. Monosaccharide composition analysis showed PNPS contained mainly glucose (89.22 ± 5.70 mol%) while small percentage of mannose (5.60 ± 0.74 mol%) and galactose (5.18 ± 0.33 mol%) were also detected. According to the linkage pattern analysis (methylation analysis), PNPS comprised mainly 4-β-D-Glcp (58.90 mol%), while other residues including α-D-Glcp, 6-α-D-Galp, 3,6-α-D-Manp, 3-β-D-Glcp and 6-α-D-Glcp were detected with a comparable amount. Combined with results from 1D and 2D NMR spectrum, a proposed structure of PNPS was presented. In vitro fermentation of PNPS by gut microbiota showed total SCFA production of all treatment groups was higher than negative control group (NC) significantly (p < 0.05) after 48 h of fermentation. The formation of SCFAs was mainly acetic acid, followed by propionic acid and butyric acid, and the pH was decreased from 6.95 to 4.70. After 72 h, the total sugar content decreased from 5.813 ± 0.87 mg/L to 0.23 ± 0.065 mg/L, and the molecular weight of PNPS decreased.