Abstract
Sourdough bread is the result of a process which, from the field to the oven, involves farmers, millers and bakers. In France, this chain was initially built with sustainability in mind. Social sustainability with the valorization of knowledge and practices, economic sustainability with a territorial anchor and environmental sustainability with a low use of inputs and energy and the maintenance of biodiversity. My thesis was part of a participatory research approach that aimed to support and develop this sustainable sector by addressing the issues of flour supply, maintenance of microbial biodiversity and dissemination of knowledge. First, my thesis focused on the study of the impact of the leavening agent (sourdough/yeast) and the wheat variety on the nutritional and organoleptic quality of breads. Through a collective bread-making experiment, I showed that, compared to yeast, sourdoughs produce breads with a lower carbohydrate content, a higher relative soluble protein content and a more complex aromatic profile. Wheat varieties mainly influence the mineral content of breads.In a second step, I studied the effect of flour milling techniques on the dynamics of microbial communities' installation in sourdoughs and on bread quality. This part, co-constructed in all its scientific steps by all the actors of the sector and the academic researchers, revealed that with equivalent rate of ash, the milling technique, either using stone or roller mills, had a low impact on the biochemical composition of the wheat flour, with a higher content of sugars in the flours produced with stone mills. Whatever the milling technique and the bakery, the succession of microbial communities after the initiation of new sourdoughs followed a very similar dynamic. It is characterized by a rapid microbial colonization and by the invasion of the medium in five backsloppings by one species of yeast and between 10 and 20 backsloppings by two to three species of lactic acid bacteria. The microbial species that settled varied according to the baker but did not depend on the milling technique or the type of wheat population. The quality of the breads was mainly impacted by the sourdough. The milling technique had a lesser effect with a lower fructose content and a higher soluble protein content in sourdough breads made with stone-milled flours compared to rolled-milled ones. In the last part of my dissertation, I combined experimental notes, social network exchanges and semi-structured interviews with stakeholders, to report and analyze the design, the steps, the different roles of each participant in our participatory research approach. The interviews showed that millers and bakers embraced the results and were willing to enlarge their knowledge and that the researchers wanted to frame their research in a social and environmental context. In conclusion, my thesis showed that the milling technique had little influence on the sourdough microbial community and the quality of the bread, while the bakery house with its own practices played a major role. My work showed the interest of participatory research for knowledge sharing and the development of local farming and artisanal sector.