Structure of β-glucan from Tibetan hull-less barley and its in vitro fermentation by human gut microbiota

Background: The influence of beta-glucan on the human gut microbiota is closely related to the physicochemical structure of beta-glucan. We purified a homogeneous water-soluble polysaccharide from Tibetan hull-less barley 25 and studied its structure and the in vitro fermentation profile. Results: Analysis by gas chromatography (GC), Fourier-transformed infrared (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and atomic force micrograph (AFM) helped determine the hull-less barley polysaccharide to be a beta-glucan (molecular weight: 3.45 x 10(4) Da), which was further characterized as mixed-linkage (1 -> 3)(1 -> 4)-linked beta-d-glucans. SEM images demonstrated an intricate web structure of the hull-less barley polysaccharide, while the AFM images revealed the presence of small spherical particles in its structure. In addition, the microbiota composition of the hull-less barley polysaccharide group was found to be altered, wherein the abundance of Pantoea, Megamonas, Bifidobacterium, and Prevotella-9 were increased. On the other hand, in vitro fermentation revealed that hull-less barley polysaccharide significantly decreased the pH value and increased the production of acetate, propionate, and butyrate. Conclusions: Hull-less barley polysaccharide is a type of dietary fiber, and its analysis suggested that it may serve as a prebiotic food supplement for the regulation of the gut microbiota.