Structural characterization and prebiotic activity of Bletilla striata polysaccharide prepared by one-step fermentation with Bacillus Licheniformis BJ2022

Bletilla striata polysaccharide (BP) is one of the main active ingredients in Orchidaceae plant Bletilla striata. BP has a high molecular weight, high viscosity, and complex diffusion, which is not conducive to the absorption and utilization of the human body. For the first time, we produced fermented Bletilla striata polysaccharide (FBP) with a low polymerization degree using Bacillus licheniformis BJ2022 one-step fermentation. FBP was a neutral polysaccharide with the molecular weight of 6790 Da. It was composed of glucose and mannose at a molar ratio of 1:2.7. The glycosidic bonds of FBP were composed of β-1,4-linked mannose, β-1,4-linked glucose and β-1,6-linked mannose according to methylation and NMR analysis. Compared with BP, FBP has a lower viscosity and higher solubility. The scanning electron microscopy results showed that the surface of FBP was porous and honeycomb-like. The rheology properties of FBP solution were close to non-Newtonian fluid. Using in vitro fermentation, we proved that FBP could regulate human gut microbiota and significantly increase the content of Bifidobacterium and Bacteroides. Our results suggested that Bacillus licheniformis fermentation significantly improved the physical and prebiotic properties of FBP. This study provides a new strategy for developing and utilizing Bletilla striata resources in China.