Chemical and biological properties of the novel exopolysaccharide produced by a probiotic strain of Bifidobacterium longum.

Bifidobacterium longum W11 is a commercialized probiotic that has an exopolysaccharide (EPS) layer covering its surface which could play a role in the beneficial properties attributed to the strain; thus, we have carried out chemical and biological analyses of this polymer. The eps cluster putatively involved in the polymer synthesis presented a unique structural organization not previously reported in bifidobacteria. B. longum W11 produced a complex polysaccharide blend with the main component composed of glucose and galactose. An exhaustive structural analysis identified two different repeating units: one linear [→6)-β-Galf-(1→3)-α-Galp-(1→] and one, more abundant, with the same backbone in which the β-Galf is 5-substituted by a β-Glcp unit. The antioxidant capability and the lack of toxicity of the whole EPS W11 mixture, as well as some functional characteristics of the producing strain, such as the in vitro resistance to gastrointestinal conditions and the adhesion of colonocytes, were also determined.