(1 3),(1 6) and (1 3)--D-glucan physico-chemical features drive their fermentation profile by the human gut microbiota

Mushroom polysaccharides consist of a unique set of polymers that arrive intact in the human large intestine becoming available for fermentation by resident gut bacteria with potential benefits to the host. Here we have obtained four glucans from two mushrooms (Pholiota nameko and Pleurotus pulmonarius) under different extraction conditions and their fermentation profile by human gut bacteria in vitro was evaluated. These glucans were isolated and characterized as (1 -> 3),(1 -> 6)-beta-D-glucans varying in branching pattern and water-solubility. An aliquot of each (1 -> 3),(1 -> 6)-beta-D-glucan was subjected to controlled smith degradation process in order to obtain a linear (1 -> 3)-beta-D-glucan from each fraction. The four beta-D-glucans demonstrated different water solubilities and molar mass ranging from 2.2 x 10(5) g.mol(-1) to 1.9 x 10(6) g.mol(-1). In vitro fermentation of the glucans by human gut microbiota showed they induced different short chain fatty acid production (52.0-97.0 mM/50 mg carbohydrates), but an overall consistent high propionate amount (28.5-30.3 % of total short chain fatty acids produced). All glucans promoted Bacteroides uniformis, whereas Anaerostipes sp. and Bacteroides ovatus promotion was strongly driven by the beta-D-glucans solubility and/or branching pattern, highlighting the importance of beta-D-glucan discrete structures to their fermentation by the human gut microbiota.