Artisanal and farmer bread making practices differently shape fungal species community composition in French sourdoughs

Abstract

Preserving microbial diversity in food systems is one of the many challenges to be met to achieve food security and quality. However, there is still a lack of knowledge about the factors that may influence food microbial diversity, notably in fermented foods. Although industrialization led to the selection and spread of specific fermenting microbial strains, there are still ongoing artisanal processes that may allow the conservation of a wider diversity of microbial species. We examined whether the diversity of artisanal practices could lead to an increased level in fungal species diversity for bread making. We used an interdisciplinary participatory research approach including bakers, psycho-sociologists and microbiologists to analyse French bread making practices and describe fungal communities in naturally fermented sourdough. Bread making practices were clustered in a farmer practices’ group and an artisanal practices’ group. Surprisingly, the well-known bakery yeast, Saccharomyces cerevisiae, was dominant (i.e. with a relative abundance over 50%) in only 24% of sourdoughs and other yeast species of the closely related Kazachstania genus were frequent. Bread making practices were found to drive the distribution of these species. The differences in fungal communities were associated with variation in sourdough acidity, maltose concentration and hydration. Overall, our results showed that preserving bread making practices diversity allows the preservation of a higher taxonomic and functional diversity in microbial communities.

Interactions between Kazachstania humilis Yeast Species and Lactic Acid Bacteria in Sourdough

“…These microbial communities are quite simple, usually harboring one effective yeast species and two effective LAB species [6]. However, a rather high microbial diversity has been described when considering different sourdoughs all over the world; more than 60 LAB species and 30 yeast species have been described so far [7][8][9][10][11][12][13][14][15][16]. Most described LAB species belong to the genus Lactobacillus, and most yeast species to the genera Saccharomyces, Kazachstania, Wickerhamomyces, Torulaspora, and Pichia.…”

“…Pentose may be fermented by the phosphogluconate pathway [17,18]. The most widespread yeast species in sourdough are Saccharomyces cerevisiae, Kazachstania humilis (previously named Candida humilis), Kazachstania exigua, Pichia kudriavzevii, and Torulaspora delbrueckii [6,14,16]. These yeast species all ferment hexoses in the absence and presence of oxygen, and thus, convert carbohydrates into ethanol, carbon dioxide, and acetic acid.…”

“…In the presence of oxygen, they are able to ferment hexoses if enough glucose is present, i.e., they are Crabtree-positive [19]. In addition to producing organic acids and ethanol, LAB and yeast are responsible for bread aroma compounds, and are involved in bread texture and mineral bioavailability.Sourdough microbial communities can be maintained through backslopping (i.e., the repeated inoculation of water and flour with a former chief sourdough), for more than 30 years [16]. The stability of these communities relies on the association and interaction between community members.…”

“…Sourdough microbial communities can be maintained through backslopping (i.e., the repeated inoculation of water and flour with a former chief sourdough), for more than 30 years [16]. The stability of these communities relies on the association and interaction between community members.…”

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

“…The yeast species found in sourdough mainly belong to the genera Saccharomyces sensus stricto, Kazachstania, Pichia, Torulaspora. 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].…”