Undesirable Microorganisms in Cereal Flours and Their Impact on the Stability of Sourdough Microbiome

Sourdough is the result of fermentation of a mixture of cereal flour and water by metacommunities consisting mainly of lactic acid bacteria and yeast. The microorganisms inhabit sourdough bakery products are responsible for their unique organoleptic properties, high nutritional value, and long shelf-life. Sometimes, apart from typical microbiota, the sourdough is contaminated with undesirable microorganisms from the production environment or raw ingredients. This may cause instability of the sourdough ecosystem, even in a very short time. The use of constant and specific technological parameters is a condition for guaranteeing the microbiological stability of the leaven. In this chapter, we describe the current state of knowledge on pathways for microbial contamination from cereal flours (wheat and rye) into bread produced by sourdough fermentation. We focus on: (i) the occurrence of microbiota in wheat and rye flours; (ii) factors influencing microbial contamination of flours; (iii) undesirable microorganisms in sourdough.