Bifidogenic properties of polysaccharides isolated from mushroom Lentinula edodes and enhanced immunostimulatory activities through Bifidobacterial fermentation

Polysaccharides from Lentinula edodes mushrooms (LePS) are well-known for their immunomodulatory activities, which may have a functional connection with probiotic fermentation in the gut microbiota. This study was to evaluate the bifidogenic properties and impact of Bifidobacterial fermentation on the LePS molecules and immunoactivities. Two LePS fractions, LePS-40 (3.97 × 10⁷ Da) and LePS-80 (1.43 × 10⁵ Da) with differences in molecular weight (MW) and chemical composition were isolated from the mushroom hot-water extract and fermented with a Bifidobacterium breve strain. The higher-MW fraction LePS-40 was more significantly consumed and utilized by the bacteria for growth and acetic acid production during the fermentation, due probably to its higher total carbohydrate content and glucose-abundant composition. The Bifidobacterial fermentation caused a notable MW reduction of both LePS fractions and, more interestingly, also led to a higher immunostimulatory activity in RAW 264.7 macrophage cells. Further assessment of the separated fractions by ultrafiltration of the fermentation liquid (digesta) suggested that the immunoactivity was mainly attributed to the partially degraded LePS instead of the small-molecule metabolite products derived from the Bifidobacterial fermentation. In summary, monosaccharide composition was a more significant determinant than MW on the bifidogenic properties of LePS and the immunomodulatory activities after fermentation.