Dietary Fibers from Mushroom Sclerotia:  3. In Vitro Fermentability Using Human Fecal Microflora

The in vitro fermentability of three novel dietary fibers (DFs) prepared from mushroom sclerotia, namely, Pleurotus tuber-regium, Polyporous rhinocerus, and Wolfiporia cocos, was investigated and compared with that of the cellulose control. All DF samples (0.5 g each) were fermented in vitro with a human fecal homogenate (10 mL) in a batch system (total volume, 50 mL) under strictly anaerobic conditions (using oxygen reducing enzyme and under argon atmosphere) at 37 °C for 24 h. All three novel sclerotial DFs exhibited notably higher dry matter disappearance (P. tuber-regium, 8.56%; P. rhinocerus, 13.5%; and W. cocos, 53.4%) and organic matter disappearance (P. tuber-regium, 9.82%; P. rhinocerus, 14.6%; and W. cocos, 57.4%) when compared with those of the cellulose control. Nevertheless, only the W. cocos DF was remarkably degraded to produce considerable amounts of total short chain fatty acids (SCFAs) (5.23 mmol/g DF on organic matter basis, with a relatively higher molar ratio of propionate) that lowered the pH of its nonfermented residue to a slightly acidic level (5.89). Variations on the in vitro fermentability among the three sclerotial DFs might mainly be attributed to their different amounts of interwoven hyphae present (different amounts of enzyme inaccessible cell wall components) as well as the possible different structural arrangement (linkage and degree of branching) of their β-glucans. Keywords: In vitro fermentability; human fecal microflora; mushroom dietary fiber