Influences of Ingredients and Bakers on the Bacteria and Fungi in Sourdough Starters and Bread.

Sourdough starters are naturally occurring microbial communities in which the environment, ingredients, and bakers are potential sources of microorganisms. The relative importance of these pools remains unknown. Here, bakers from two continents used a standardized recipe and ingredients to make starters that were then baked into breads. We characterized the fungi and bacteria associated with the starters, bakers' hands, and ingredients using 16S and internal transcribed spacer (ITS) rRNA gene amplicon sequencing and then measured dough acidity and bread flavor. Starter communities were much less uniform than expected, and this variation manifested in the flavor of the bread. Starter communities were most similar to those found in flour but shared some species with the bakers' skin. While humans likely contribute microorganisms to the starters, the reverse also appears to be true. This bidirectional exchange of microorganisms between starters and bakers highlights the importance of microbial diversity on bodies and in our environments as it relates to foods.IMPORTANCE Sourdough starters are complex communities of yeast and bacteria which confer characteristic flavor and texture to sourdough bread. The microbes present in starters can be sourced from ingredients or the baking environment and are typically consistent over time. Herein, we show that even when the recipe and ingredients for starter and bread are identical, different bakers around the globe produce highly diverse starters which then alter bread acidity and flavor. Much of the starter microbial community comes from bread flour, but the diversity is also associated with differences in the microbial community on the hands of bakers. These results indicate that bakers may be a source for yeast and bacteria in their breads and/or that bakers' jobs are reflected in their skin microbiome.

Reese AT ，Madden AA ，Joossens M ，Lacaze G ，Dunn RR ... -  《mSphere》

The diversity and function of sourdough starter microbiomes.

Humans have relied on sourdough starter microbial communities to make leavened bread for thousands of years, but only a small fraction of global sourdough biodiversity has been characterized. Working with a community-scientist network of bread bakers, we determined the microbial diversity of 500 sourdough starters from four continents. In sharp contrast with widespread assumptions, we found little evidence for biogeographic patterns in starter communities. Strong co-occurrence patterns observed in situ and recreated in vitro demonstrate that microbial interactions shape sourdough community structure. Variation in dough rise rates and aromas were largely explained by acetic acid bacteria, a mostly overlooked group of sourdough microbes. Our study reveals the extent of microbial diversity in an ancient fermented food across diverse cultural and geographic backgrounds.

Landis EA ，Oliverio AM ，McKenney EA ，Nichols LM ，Kfoury N ，Biango-Daniels M ，Shell LK ，Madden AA ，Shapiro L ，Sakunala S ，Drake K ，Robbat A ，Booker M ，Dunn RR ，Fierer N ，Wolfe BE ... -  《eLife》

Sourdough starter culture microbiomes influence physical and chemical properties of wheat bread.

Sourdough fermentation is an ancient leavening method that uses wild yeasts to produce carbon dioxide, contributing to bread rise, and bacteria which produce organic acids. Sourdough starter cultures are known to be diverse in terms of the microorganisms they comprise and while specific genera and species of microorganisms have been identified from starters and associated with specific attributes, overarching relationships between sourdough starter culture microbiomes and bread quality are not well understood. The objective of this study was to characterize differences in the physical and chemical properties of breads produced with sourdough starter cultures with unique microbiomes. Sourdough starter cultures (n = 20) of known microbial populations were used to produce wheat-based dough and bread, which were analyzed for chemical and physical properties then compared to their microbial populations in order to identify relationships between microbial profiles and dough/bread qualities. All samples were also compared to bread produced only with Saccharomyces cerevisiae (baker's yeast). Significant differences among pH, titratable acidity, loaf volume, crumb firmness, crust color, free amino acids, and organic acids were observed when comparing sourdough breads to the yeast-only control (p ≤ 0.05). Furthermore, bacterial diversity of sourdough starter cultures was correlated with lactic acid and free amino acid in the dough and loaf volume and crumb firmness of baked breads. No significant correlations were found between fungal diversity and measured outcomes. These data demonstrate the importance of considering sourdough starter microbiomes as an ingredient in baked goods and they contribute to quality and safety outcomes in bread production. PRACTICAL APPLICATION: Sourdough starter cultures have diverse and dynamic populations of bacteria and yeasts, which contribute to the production of bread products. These populations can influence the physical and chemical properties of sourdough fermentation and final breads. Understanding of the relationship between sourdough starter microbiomes and bread quality parameters can lead to targeted development of sourdough bread products with specific physical and chemical properties.

Clark CS ，Ohstrom A ，Rolon ML ，Smith M ，Wolfe BE ，Wee J ，Van Buiten CB ... -  《-》

Microbial community dispersal from wheat grains to sourdoughs: A contribution of participatory research.

Understanding microbial dispersal is critical to understand the dynamics and evolution of microbial communities. However, microbial dispersal is difficult to study because of uncertainty about their vectors of migration. This applies to both microbial communities in natural and human-associated environments. Here, we studied microbial dispersal along the sourdoughs bread-making chain using a participatory research approach. Sourdough is a naturally fermented mixture of flour and water. It hosts a community of bacteria and yeasts whose origins are only partially known. We analysed the potential of wheat grains and flour to serve as an inoculum for sourdough microbial communities using 16S rDNA and ITS1 metabarcoding. First, in an experiment involving farmers, a miller and bakers, we followed the microbiota from grains to newly initiated and propagated sourdoughs. Second, we compared the microbiota of 46 sourdough samples collected everywhere in France, and of the flour used for their back-slopping. The core microbiota detected on the seeds, in the flour and in the sourdough was composed mainly of microbes known to be associated with plants and not living in sourdoughs. No sourdough yeast species were detected on grains and flours. Sourdough lactic acid bacteria were rarely found in flour. When they were, they did not have the same amplicon sequence variant (ASV) as found in the corresponding sourdough. However, the low sequencing depth for bacteria in flour did not allow us to draw definitive conclusion. Thus, our results showed that sourdough yeasts did not come from flour, and suggest that neither do sourdough LAB.

von Gastrow L ，Michel E ，Legrand J ，Amelot R ，Segond D ，Guezenec S ，Rué O ，Chable V ，Goldringer I ，Dousset X ，Serpolay-Bessoni E ，Taupier-Letage B ，Vindras-Fouillet C ，Onno B ，Valence F ，Sicard D ... -  《-》

Sourdough starters exhibit similar succession patterns but develop flour-specific climax communities.

The microbial fermentation behind sourdough bread is among our oldest technologies, yet there are many opportunities for sourdough science to learn from traditional bakers. We analyzed 16S rRNA sequences in R to assess the bacterial community structure and performance of 40 starters grown from 10 types of flour over 14 days, and identified six distinct stages of succession. At each stage, bacterial taxa correlate with determinants of bread quality including pH, rise, and aromatic profile. Day 1 starter cultures were dominated by microorganisms commonly associated with plants and flour, and by aromas similar to toasted grain/cereal. Bacterial diversity peaked from days 2-6 as taxa shifted from opportunistic/generalist bacteria associated with flour inputs, toward specialized climax bacterial communities (days 10-14) characterized by acid-tolerant taxa and fruity (p < 3.03e-03), sour (p < 1.60e-01), and fermented (p < 1.47e-05) aromas. This collection of traits changes predictably through time, regardless of flour type, highlighting patterns of bacterial constraints and dynamics that are conserved across systems and scales. Yet, while sourdough climax communities exhibit similar markers of maturity (i.e., pH ≤ 4 and enriched in Lactobacillus (mean abundance 48.1%), Pediococcus (mean abundance 22.7%), and/or Gluconobacter (mean abundance 19.1%)), we also detected specific taxa and aromas associated with each type of flour. Our results address important ecological questions about the relationship between community structure and starter performance, and may enable bakers to deliberately select for specific sourdough starter and bread characteristics.

McKenney EA ，Nichols LM ，Alvarado S ，Hardy S ，Kemp K ，Polmanteer R ，Shoemaker A ，Dunn RR ... -  《PeerJ》