Modulation of soy flour bioactivity against enterotoxigenic Escherichia coli by fermentation with exopolysaccharides-producing lactic acid bacteria

Enterotoxigenic Escherichia coli (ETEC)-mediated diarrhea can be mitigated by inhibiting bacterial adhesion to intestinal surface. Some lactic acid bacteria (LAB) produce exopolysaccharides (EPS) that can inhibit ETEC adhesion. In this study, we fermented soy flour-based dough (SoyD) with EPS-producing LAB strains Pediococcus pentosaceus TL (PpTL), Leuconostoc citreum TR (LcTR), Leuconostoc mesenteroides WA (LmWA) and L. mesenteroides WN (LmWN) to improve anti-adhesive activity of the dough against ETEC. The strains LcTR, LmWA and LmWN produced EPS in SoyD fermentation with similar polysaccharide yields and compositions as when grown in liquid medium, whereas PpTL was unable to produce EPS in SoyD. LcTR produced high molecular weight (Mw) dextran (∼900 kDa) while LmWA and LmWN produced dextran and levan with diverse Mw (∼20–1000 kDa). SoyD fermentation by EPS-producing LAB increased the capability of the SoyD extracts to adhere to ETEC cells and block ETEC adhesion to porcine mucin. After Mw-based fractionation, all extract-fractions (>3 kDA) of LmWA- and LmWN-fermented SoyD retained their blocking activity indicating that various Mw populations of the EPS contributes to bioactivity against ETEC. This study shows the potential of EPS-producing LAB strains as fermenting microorganisms in the development of a functional food product with anti-diarrheal properties.