Impact of baker’s practices, terroir and wheat varieties on sourdough microbial taxonomic and functional diversity
Résumé
Using sourdough bread ecosystems as a model and a participatory research approach, we have analysed
human impact on the dispersion and selection of lactic acid bacteria and yeasts. In France, microbial
diversity associated with bread-making practises has recently been documented. In order to better
understand the origin of the sourdough microbial diversity, we analyzed the effect of (i) terroir (ii) wheat
varieties, (iii) bakers on sourdough microbial taxonomic and functional diversity. Three populations of
old wheat and three varieties of commercial wheat were each grown on three terroirs. For each terroir,
grains from the three old populations were mixed and so were grains from the three modern varieties.
The flours of the six seeds lots were sent to four different bakers, who initiated and maintained six
sourdoughs for three weeks. The sourdoughs were then analyzed by cultural and non-cultural methods.
Total yeast counts varied from 5.6 log10 to 8.49 log10 CFU/g while LAB counts varied from 7 log10 to
10.6 log10 CFU/g. By culture-dependent methods, five yeasts species were identified and fifteen acid
lactic bacteria species. The composition of the sourdough dominant species varies according to the
bakers but does not appear to change according to the origin of the flour. The sourdoughs impact the
rising of the dough but the rate of total CO2 release depends mainly on the type of wheat varieties. The
nutritional quality of the bread results from the interaction between the sourdough, the type of wheat
varieties and the terroir. Overall, house microbiota appears to be the main factor driving sourdough
ecosystem microbial diversity but the origin of wheat also impacts bread quality. Our results highlight
the role of human and socio-cultural practices in maintaining taxonomic and functional diversity of
microbial species.