Structural and rheological characterisation of heteropolysaccharides produced by lactic acid bacteria in wheat and sorghum sourdough

Hydrocolloids improve the volume, texture, and shelf life of bread. Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) during sourdough fermentation can replace hydrocolloids. It was the aim of this study to determine whether heteropolysaccharides (HePS) synthesized intracellularly from sugar nucleotides by glycosyltransferases are produced in wheat and gluten-free sorghum sourdough at effective levels. The HePS-producing strains Lactobacillus casei FUA3185, L. casei FUA3186, and Lactobacillus buchneri FUA3154 were used; Weissella cibaria 10M producing no EPS in the absence of sucrose served as control strain. Cell suspensions of L. buchneri in MRS showed the highest viscosity at low shear rate. Glycosyltransferase genes responsible of HePS formation in LAB were expressed in sorghum and wheat sourdough. However, only HePS produced by L. buchneri influenced the rheological properties of sorghum sourdoughs but not of wheat sourdoughs. Sorghum sourdough fermented with L. buchneri exhibited a low |G∗| compared to the control, indicating a decrease in resistance to deformation. An increase in tan δ indicated decreased elasticity.The use of LAB producing HePS expands the diversity of EPS and increases the variety of cultures for use in baking.

Research highlights
► Heteropolysaccharide producing lactic acid bacteria are suitable starter cultures for wheat and sorghum sourdough.
► Rheological properties of sorghum sourdough were affected by HePS synthesized by Lactobacillus buchneri.
► The rheology of wheat sourdoughs was influenced by fermentation but unaffected by HePS synthesis.