Anti-adhesion bioactivity of soybean tempeh against enterotoxigenic Escherichia coli F4 through supplementation with exopolysaccharide-producing Leuconostoc mesenteroides

Soybean tempeh can reduce the adhesion of diarrheagenic enterotoxigenic Escherichia coli (ETEC) to the intestinal surface due to the presence of carbohydrates that can bind to the pathogen's fimbrial adhesin. Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) such as Leuconostoc mesenteroides also exhibit anti-adhesion bioactivity against ETEC. Tempeh supplemented with EPS-producing L. mesenteroides strains (LmWA and LmWN) to improve its anti-adhesion bioactivity was produced. Both strains persisted in the fermentation process and produced dextran (α-1,6-linked glucan) in the supplemented tempeh. LmWN supplementation resulted in a higher amount of dextran in tempeh (0.44% w /w) compared to LmWA (0.22% w/w). The dextrans obtained from both LAB supplementations consisted of two molecular weight (Mw) populations of ~750 to >1000 kDa and ~ 5 kDa. Although both strains are known to also produce levan (β-2,6-linked fructan), such EPS was not detected in LAB-supplemented tempeh. LAB-supplemented tempeh reduced adhesion of pig-associated ETEC F4 to porcine mucin by three to four times compared to non-supplemented tempeh. The role of dextran in such bioactivity was confirmed by increased adhesion upon treatment of the tempeh extract with dextranase. In conclusion, the production and presence of bioactive dextran with anti-adhesion bioactivity against ETEC in tempeh made with the supplementation of EPS-producing LAB strain to soybean fermentation has been demonstrated. This study demonstrates that co-fermentation with EPS-producing LAB is a viable strategy to develop food products with an anti-adhesion bioactivity against ETEC.