Effects of exopolysaccharide fractions with different molecular weights and compositions on fecal microflora during in vitro fermentation.

This study was to investigate the potential prebiotic function of exopolysaccharide (EPS) from a medicinal fungus and the relationship to the molecular properties by in vitro human fecal fermentation. The EPS from Cordyceps sinensis Cs-HK1 mycelial fermentation was processed into three fractions with different monosaccharide contents, a higher molecular weight (MW) and a lower MW attained by two-step ethanol precipitation, and an intermediate MW by ultrasound-degradation of EPS. All the EPS fractions were well utilized during 24-48 h of fecal fermentation, leading to significant increases in the short chain fatty acid (SCFA) production. The consumption rate and production level of SCFAs varied slightly with the different EPS fractions. The EPS also influenced the composition and diversity of the fecal microflora, increasing the relative abundance of Firmicutes but suppressing that of Proteobacteria, which may be a beneficial effect for human health. Overall the results have shown that the Cs-HK1 EPS has significant prebiotic activity which is dependent on its molecular properties.