Dynamics of Enterobacteriaceae and lactobacilli in model sourdoughs are driven by pH and concentrations of sucrose and ferulic acid

This study aimed to assess, in model sourdough fermentations, the relevance of physico-chemical features of flour for the interactions between Enterobacteriaceae and lactobacilli, and for the interactions within the latter microbial group. Initially, model sourdoughs made with white wheat flour, whole wheat flour or wheat bran were inoculated with Cronobacter sakazakii, Klebsiella pneumoniae, Lactobacillus plantarum and Lactobacillus sanfranciscensis. Subsequently, white wheat sourdoughs were prepared with phosphate buffer, ferulic acid, maltose, sucrose or baker's yeast. During sourdough propagation, C. sakazakii and K. pneumoniae disappeared after few fermentation cycles in white wheat and whole wheat sourdoughs, but persisted in phosphate buffered or in wheat bran sourdoughs. Sucrose, maltose or ferulic acid did not impact on the ecological fitness of Enterobacteriaceae, whereas baker's yeast inhibited these bacteria. In white wheat and in whole wheat sourdoughs, L. sanfranciscensis outcompeted L. plantarum. A variation of sucrose level and the presence of ferulic acid reduced the competitiveness of L. sanfranciscensis, thus favoring L. plantarum.This study demonstrated that the pH is key contributor to the elimination of Enterobacteriaceae in cereal fermentation. In addition, L. sanfranciscensis prevails in wheat sourdoughs, but minor perturbations of the ecosystem reduce its competitiveness.