Influences of Ingredients and Bakers on the Bacteria and Fungi in Sourdough Starters and Bread

Abstract

Sourdough starters are naturally occurring microbial communities in which the environment, ingredients, and bakers are potential sources of microorganisms. The relative importance of these pools remains unknown. Here, bakers from two continents used a standardized recipe and ingredients to make starters that were then baked into breads. We characterized the fungi and bacteria associated with the starters, bakers’ hands, and ingredients using 16S and internal transcribed spacer (ITS) rRNA gene amplicon sequencing and then measured dough acidity and bread flavor. Starter communities were much less uniform than expected, and this variation manifested in the flavor of the bread. Starter communities were most similar to those found in flour but shared some species with the bakers’ skin. While humans likely contribute microorganisms to the starters, the reverse also appears to be true. This bidirectional exchange of microorganisms between starters and bakers highlights the importance of microbial diversity on bodies and in our environments as it relates to foods. IMPORTANCE Sourdough starters are complex communities of yeast and bacteria which confer characteristic flavor and texture to sourdough bread. The microbes present in starters can be sourced from ingredients or the baking environment and are typically consistent over time. Herein, we show that even when the recipe and ingredients for starter and bread are identical, different bakers around the globe produce highly diverse starters which then alter bread acidity and flavor. Much of the starter microbial community comes from bread flour, but the diversity is also associated with differences in the microbial community on the hands of bakers. These results indicate that bakers may be a source for yeast and bacteria in their breads and/or that bakers’ jobs are reflected in their skin microbiome.

Fermentative Foods: Microbiology, Biochemistry, Potential Human Health Benefits and Public Health Issues

“…The bacterial and fungal species present in sourdough originate from (a) the microflora of the flour, (b) the bakeries' environment microbiota, (c) the water used and, according to some researchers, (d) the bakers themselves (their bodily microbiome) [178]. Typically, in the biomass of sourdough, it is mostly the Lactobacillus strains producing acid and yeasts who undertake the production of carbon dioxide.…”

“…Some studies, however, have highlighted a different population dynamic and point to a greater variety of bacteria and yeasts other than Lactobacillus and Saccharomyces [179][180][181][182]. Other studies have revealed that, at the genus level, Enterococcus, Lactococcus, Lactobacillus, Leuconostoc, Pediococcus, Streptococcus and Weissella are associated with sourdough production [177,178]. In the above micro-ecological niche, the genus Lactobacillus is dominant.…”

“…However, several non-Saccharomyces yeasts occur in the fungal consortia in sourdough fermentation, such as Candida, Rhodotorula, Pichia, Trichosporon, Sporobolomyces and Yarrowia [184][185][186]. [177,178,187].…”

Evidence for two main domestication trajectories inSaccharomyces cerevisiaelinked to distinct bread-making processes

“…Worldwide, S. cerevisiae is the most widespread species found in sourdoughs [40] made by bakers, but also in sourdough made by farmersbakers [41,42]. It can be found as the dominant species in sourdough, even in bakeries where no industrial starter is used, suggesting that the species may colonize a sourdough from the bakery's environment or the baker's hands [43]. Therefore, bakery strains of S. cerevisiae may have undergone different domestication processes.…”

Campaign-Based Citizen Science for Environmental Mycology: The Science Solstice and Summer Soil-Stice Projects to Assess Drug Resistance in Air- and Soil-Borne <i>Aspergillus fumigatus</i>

“…Although the majority of citizen science microbiology projects focus on bacteria, there are several related to mycology. Kew's Lost and Found Fungi project asks volunteers to hunt for 100 mushrooms in the UK that are rare or potentially extinct (fungi.myspecies.info/content/ lost-and-found-fungi-project), the Mushroomfinder app developed by the University of Vienna records mushroom observations across Austria (www.univie.ac.at/oemykges/ pilzfinder-at/), and the Global Sourdough Project identified bacteria and yeasts in sourdough starters sent in by bakers from around the world (Reese 2020). Both Slovenia (www.invazivke.si) and the UK (www.livingashproject.org.…”