Zymomonas mobilis: an alternative dough leavener for the production of yeast-free baked doughs

Background: adverse responses to Saccharomyces cerevisiae occur in particular in people with Inflammatory Bowel Disease and with Crohn’s disease, in which anti-S. cerevisiae antibodies directed against the phosphopeptidomannan of the yeast cell wall have been identified. Zymomonas mobilis, a Gram-negative bacterium GRAS classified by the FDA, can represent an interesting candidate for producing yeast-free fermented goods. Objectives: as Z. mobilis does not utilize maltose present in flour, different strategies were applied to improve its leavening ability in dough: glucose or sucrose addition, or exploitation of the maltose hydrolytic activity of Lactobacillus sanfranciscensis. Methods: five Z. mobilis and one L. sanfranciscensis strains were used in dough leavening trials. Experiments were set up with different dough consistency and inoculum (107-109 UFC/g), leavening temperature (25 - 30 ± 0.5 °C) and time (6 to 24 h), with or without sugars (3-5%) and NaCl (1%). Dough leavening properties (e.g., CO2 production, dough volume increase, lag leavening time and rates) as well as time course of microbial population, sugars consumption and ethanol production were evaluated. Results: the addition of glucose or sucrose as well as the highest leavening temperature increased the gaseous production and retention and consequently the dough development. L. sanfranciscensis contribution was fickle: the productivity gain showed positive performance only at high inoculum and short leavening time (3-4 h). NaCl worsened Z. mobilis fermentation performance but this behavior seems to be strain-related. Results highlight that developing a dough leavened by Z. mobilis and thus suitable for yeast-sensitive people is possible.