Composition and function of sourdough microbiota: From ecological theory to bread quality.

Sourdough has traditionally been used as leavening agent in artisanal baking. The production of baked and steamed cereal products increasingly employs sourdough as baking improver to achieve improved bread quality, or to obtain "clean label" products. Sourdoughs are maintained in bakeries by continuous propagation; composition and metabolic activity of sourdough microbiota and their impact on bread quality are therefore shaped by processing parameters and fermentation substrates. The diversity of fermentation processes leads to diverse compositions of sourdough microbiota. This communication explores whether concepts in community assembly support an improved understanding of the microbial ecology of sourdough. Community assembly is determined by diversification, drift, dispersal, and selection. Evidence for diversification in sourdoughs is inconclusive. Drift has been shown to shape sourdough microbiota only in specific cases. Increasing knowledge on the primary habitat of sourdough lactobacilli indicates that dispersal (limitation) is an important determinant in sourdoughs that are propagated only for short periods of time. In contrast, selection of adapted organisms mainly determines the microbiota of sourdoughs that are propagated for a long time. Bacterial metabolic traits that determine competitiveness in sourdough fermentation, i.e. effective use of maltose, exopolysaccharide formation from sucrose, the use of electron acceptors by heterofermentative lactic acid bacteria, and acid resistance mediated by arginine and glutamine conversion, also determine bread quality. The concepts in community assembly thus provide a valuable tool to understand the influence of the technology of sourdough fermentation on microbial ecology and on bread quality.