Identification of galacturonic acid-rich polysaccharide with intestinal immune system modulating activity via Peyer's patch from postbiotics of Phellinus linteus mycelial submerged culture

Interests in the development and exploration of industrial applications of medicinal mushrooms as postbiotics have lately increased. We recently reported the potential use of Phellinus linteus mycelial-containing whole culture extract (PLME) prepared by submerged cultivation as a postbiotic that promotes immune system activation. Here, we aimed to isolate and structurally elucidate the active ingredients in PLME by activity-guided fractionation. The intestinal immunostimulatory activity was evaluated by bone marrow (BM) cell proliferation activity and related cytokine production in C3H-HeN mouse-derived Peyer's patch (PP) cells treated with polysaccharide fractions. The initially crude polysaccharide (PLME-CP) of PLME prepared using ethanol precipitation was further fractionated into four fractions (PLME-CP-0 to -III) by anion-exchange column chromatography. BM cell proliferation and cytokine production of PLME-CP-III were significantly improved compared to those of PLME-CP. PLME-CP-III was then fractionated into PLME-CP-III-1 and PLME-CP-III-2 by gel filtration chromatography. Based on the molecular weight distribution, monosaccharide, and glycosyl linkage analyses, PLME-CP-III-1 was revealed as a novel galacturonic acid-rich acidic polysaccharide and further shown to play an important role in facilitating PP-mediated intestinal immunostimulatory activity. This is the first study demonstrating the structural characteristics of a novel intestinal immune system modulating acidic polysaccharide from P. linteus mycelium-containing whole culture broth postbiotics.