Response of sourdough lactic acid bacteria and yeast to low temperatures exposure

During the “resting step” (between two consecutive back-slopping-fermentation cycles) low temperatures are frequently applied by sourdough users to control over metabolic activities and standardize sourdough performances. This study aimed to assess the effect of low temperatures on Lactiplantibacillus plantarum, Fructilactobacillus sanfranciscensis and Saccharomyces cerevisiae in both a model system (Wheat Flour Hydrolyzed, WFH) and a sourdough simple mock community (dough fermented with the two lactobacilli and yeast strains). Transcriptomics and meta-transcriptomics revealed the metabolic pathways affected by exposure to low temperatures. In WFH and sourdough L. plantarum and S. cerevisiae were not affected by exposure to low temperatures during the resting step, whereas F. sanfranciscensis in WFH was intrinsically more sensitive to exposure to 4 or 10°C. A shift of the main carbon sources was found for both L. plantarum and S. cerevisiae when exposed to 10 °C. Low temperatures did not affect the concentration of the main metabolites of fermentation. The resting step of sourdough at 15 °C was unfavourable to F. sanfranciscensis, whereas after resting performed at 4 °C, F. sanfranciscensis reached in the backslopped sourdough a cell density that did not significantly differ from that reached after no resting step-low temperature had been applied. Results of metatranscriptomics offered an interesting view about the observed behaviour of sourdough lactobacilli and yeast.