Abstract
Bread has a historical and cultural importance in France. However, the diversity of the French bakers' practices was never described and linked to the biodiversity. During the 20th century, industrialization promoted the use of yeast starters and standardized processes. However, becoming more aware of global changes, some farmers-bakers and bakers now use sourdough as a fermenting agent, a naturally fermented dough composed of flour, water, bacteria and yeasts. The goal of my PhD was a) to characterize their sourdough microbial species diversity and to analyse its structuring factors, b) to follow the microbial species dispersion and selection from seed to bread, and c) to test the terroir, wheat variety type and sourdough effects on bread's nutritional and organoleptic properties. This research emerged from a participatory co-construction by bakers, farmers and scientists. We showed that France hosts a wide species diversity in sourdough. Two main groups of practices, the baker and farmer-baker like practices, structured the yeast species diversity. The dominant bacterium seems to come from the flour while yeast dominant species seems to come from the house microbiota. The dynamic of selection over backsloppings differed for bacteria and yeasts. The bread quality results from the interaction between the sourdough, the wheat varieties and the wheat terroir. Overall, our results highlight the role of agronomic and bakery practices on each step of the chain and documented the role of domestication in the dispersion and selection of microbial species diversity.