Simulated human digestion and fermentation of a high-molecular weight polysaccharide from Lentinula edodes mushroom and protective effects on intestinal barrier.

Lentinula edodes (Shiitake) is an important edible mushroom and polysaccharides are its major constituents with proven health benefits. The study was to investigate the gut bacterial fermentation and subsequent effects on gut barrier function of a glucan-rich polysaccharide, LePS40 precipitated from the mushroom water extract with 40 % (v/v) ethanol. LePS40 consisted of a ß-(1→3)-glucan main chain with substitution in the C-6 position with side chains mainly composed of (1 → 6)-linked ß-Glcp residues, (1 → 6)-linked α-Galp residues and terminal residues of ß-Glcp. LePS40 was found highly resistant to digestive enzymes and gastric acid in simulated human gastrointestinal tract, but highly fermentable during in vitro human fecal fermentation. The fecal fermentation degradation of LePS40 appeared to selectively break the glucoside linkage in view of the dramatic decrease in the glucose molar ratio (12.68 to 1.07). Compared with the prebiotic reference FOS, LePS40 led to much higher levels of butyric, and propionic acid and a lower level of acetic acid. Moreover, LePS40 enhanced the abundance of some beneficial bacterial populations, but decreased the bacteria possibly linked with fatty-liver disease and colorectal cancer. Furthermore, the fecal fermentation products of LePS40 showed a potential protective effect on intestinal barrier function against inflammatory damage in Caco-2/Raw264.7 co-culture model. These findings suggest the potential of LePS40 for improvement of gut health through modulation of gut microbiota.

Efficient isolation of immunostimulatory polysaccharides from Lentinula edodes by autoclaving-ultrasonication extraction and fractional precipitation.

A hyphenated process, autoclaving followed by ultrasonication (AU), was evaluated for efficient extraction of polysaccharides (PS) from Lentinula edodes (Shiitake) mushroom. The PS yield (w/w) was 8.44 % from hot-water extraction (HWE), 11.01 % by autoclaving extraction (AE), and 16.3 % by AUE. The AUE water extract was subject to fractional precipitation in four-steps with increasing ethanol concentration of 40 %, 50 %, 70 % and 80 % (v/v), yielding four PS fractions in descending molecular weight (MW), PS40 > PS50 > PS70 > PS80. All the four PS fractions were composed of four monosaccharide residues, mannose (Man), glucose (Glc) and galactose (Gal) but in different mole ratios. The PS40 fraction with the highest average MW (4.98 × 106) was the most abundant fraction, accounting for 64.4 % of the total PS mass and also had the highest glucose molar ratio (~80 %). PS40 also most significantly enhanced the NO, and ROS generation and phagocytic activity in RAW 264.7 cells. The results proved that AUE followed by fractional ethanol precipitation is an efficient strategy with reduced solvent expenditure for isolation of the major immunostimulatory PS from L. edodes mushroom.