Identification of Intestinal Barrier-Protective Components from Bifidobacterium adolescentis YIT 13021: A Rhamnose-Rich Cell Wall Polysaccharide and UDP-MurNAc-L-Ala-D-Glu-L-Lys

Intestinal barrier dysfunction is associated with various diseases, including gastrointestinal disorders. Bifidobacteria strengthen intestinal barrier integrity and tight junction function by interacting with intestinal epithelial and immune cells. However, the components responsible for these effects remain to be determined. This study aimed to identify the active substances responsible for the barrier-enhancing activity of Bifidobacterium adolescentis YIT 13021. A cell wall polysaccharide-containing fraction was isolated from YIT 13021 and purified through ultrafiltration and hydrophilic interaction liquid chromatography-based high-performance liquid chromatography. Barrier-enhancing activity was evaluated using T84 epithelial cell monolayers by measuring transepithelial electrical resistance (TEER). Structural characterization was performed using nuclear magnetic resonance, mass spectrometry, monosaccharide composition analysis, and size-exclusion chromatography. Two active fractions, ≤10 and 10–30 kDa, were identified. The active component in the ≤10 kDa fraction was UDP-MurNAc-L-Ala-D-Glu-L-Lys, whereas that in the 10–30 kDa fraction was a rhamnose-rich cell wall polysaccharide. Both components significantly enhanced TEER in T84 cell monolayers, suggesting that they contribute to the barrier-enhancing activity of YIT 13021. These findings identify two cell wall-derived components associated with increased TEER in vitro and provide a basis for further investigation of their biological activities and physiological relevance.