Microbial resistance and resilience in a model sourdough ecosystem under environmental disturbance

Details

Supervisors

Stenuit, Benoît

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

enSourdough is a traditional fermented dough made from flour and water, maintained by naturally occurring lactic acid bacteria (LAB) and yeasts that drive leavening, acidification, and flavor development. Unlike baker’s yeast-based fermentation, sourdough develops more slowly, shaping bread texture, aroma, and acidity through a stable and complex microbial ecosystem. Puratos, a Belgian company that supplies ingredients to bakeries, patisseries, and chocolatiers, is currently the market leader in ready-to-use sourdoughs. This year, they launched the "NUTRIRISE" project with the final aim to create a new sourdough that is robust, stable, locally sourced, and also sustainable, by inoculating a synthetic microbial consortium. Sourdoughs are classified by inoculation method: Type 1 relies on repeated backslopping with flour and water, Type 2 on the addition of starter cultures under controlled conditions, and Type 3 combines starter cultures with backslopping. Designing robust Type 3 sourdoughs requires a clear understanding of Type 1 dynamics, as it represents the natural model from which stability principles can be derived. Although Type 3 sourdough offers reliability and robustness, its stability under abiotic (e.g., temperature) and biotic (e.g., microbial competition) stress is not well understood. This study examined the response of a wheat Type 1 sourdough (SD69), dominated by Fructilactobacillus sanfranciscensis, to abiotic and biotic disturbances. Fermentations were conducted at 17 °C (reference), 30 °C, and 40 °C to test thermal stress, and inoculated with Bacillus subtilis at 10³–10⁵ CFU/gFM to simulate microbial invasion and competition. At 30 °C, sourdough recovered its pre-disturbance state after 14 refreshments, with resistance and resilience indices of 0.98 and 0.90, based on the relative abundance of F. sanfranciscensis. In contrast, 40 °C caused community disruption, leading to new equilibrium states and very low indices (0.02 and 0.04). Inoculation with Bacillus subtilis showed little measurable effect (average resistance 0.84). These findings indicate that abiotic stress, particularly elevated temperature, is a stronger driver of sourdough community shifts than biotic disturbance with the chosen propagule pressure. Understanding such mechanisms is key to designing stable, predictable Type 3 sourdoughs from defined microbial consortia, supporting the development of sustainable and versatile fermentation cultures.