Evolution of bacterial consortia in spontaneously started rye sourdoughs during two months of daily propagation.

Marianna Bessmeltseva,Toomas Paalme,Inga Sarand,Ene Viiard,Jaak Simm,Jonathan H Badger

doi:10.1371/journal.pone.0095449

Marianna Bessmeltseva, Toomas Paalme + Show 4 more

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https://doi.org/10.1371/journal.pone.0095449

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Abstract

The evolution of bacterial consortia was studied in six semi-solid rye sourdoughs during long-term backslopping at different temperatures. Each rye sourdough was started spontaneously in a laboratory (dough yield 200), propagated at either 20°C or 30°C, and renewed daily at an inoculation rate of 1∶10 for 56 days. The changes in bacterial diversity over time were followed by both DGGE coupled with partial 16S rRNA gene sequencing and pyrosequencing of bar-coded 16S rRNA gene amplicons. Four species from the genus Lactobacillus (brevis, crustorum, plantarum, and paralimentarius) were detected in different combinations in all sourdoughs after 56 propagation cycles. Facultative heterofermentative lactic acid bacteria dominated in sourdoughs fermented at 30°C, while both obligate and facultative heterofermentative LAB were found to dominate in sourdoughs fermented at 20°C. After 56 propagation cycles, Kazachstania unispora (formerly Saccharomyces unisporus) was identified as the only yeast species that dominated in sourdoughs fermented at 20°C, while different combinations of strains from four yeast species (Kazachstania unispora, Saccharomyces cerevisiae, Candida krusei and Candida glabrata) were detected in sourdoughs propagated at 30°C. The evolution of bacterial communities in sourdoughs fermented at the same temperature did not follow the same time course and changes in the composition of dominant and subdominant bacterial communities occurred even after six weeks of backslopping.

Highlights

Sourdough is a mixture of flour and water fermented with a microbial community mainly consisting of lactic acid bacteria (LAB) and yeasts
Because the water content and fermentation temperature are the main factors that affect the composition of the bacterial community [2], we evaluated the establishment of microbial consortia in spontaneously fermented rye sourdoughs with a low dough yield at two different temperatures (20 and 30uC) backslopped daily for 56 days
After 24 hours of fermentation at 20uC the average viable count of bacteria increased from 2.06105 Colony forming units (CFU)/g in the raw flour to 5.76108 while the first fermentation cycle at 30uC resulted in 7.26108 CFU/g (Table 1)

Summary

Introduction

Sourdough is a mixture of flour and water fermented with a microbial community mainly consisting of lactic acid bacteria (LAB) and yeasts. LAB dominate the microbial community and are responsible for acid production while yeasts work to leaven the dough [1,2]. Lactic acid fermentation plays an important role in the production of rye bread by both decreasing the activity of aamylase and improving dough texture [3]. Lactobacillus amylovorus, Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus panis, Lactobacillus pontis, and Lactobacillus reuteri have been identified as dominant species in rye sourdoughs [4,6,7,8,9]. The same LAB species are able to dominate the microbial communities within mature sourdoughs made with different types of flour under otherwise identical conditions [8,10,11]. It has been shown that initial differences in the microbial communities found in spontaneously started rye and wheat sourdoughs decreases during backslopping propagations and that a common core microbiota is established [11]

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