Abstract
Hundreds of sourdoughs have been investigated in the last decades. However, many studies used a culture-dependent and/or culture-independent microbiological approach [mainly based on denaturing gradient gel electrophoresis (DGGE) of PCR amplicons], seldomly combined with a metabolite target analysis, to characterize the microbial species communities of the sourdoughs examined. Moreover, attention was mainly paid on lactic acid bacteria (LAB) and yeast species. In the present study, distinct household-scale (including an artisan lambic brewery) and artisan bakery-scale backslopped sourdoughs (17 in total), obtained from different regions (Belgium, France, United Kingdom, and USA), were examined through a multiphasic approach, encompassing a culture-dependent analysis [targeting LAB, acetic acid bacteria (AAB), and yeasts], different culture-independent techniques [rRNA-PCR-DGGE, metagenetics, and metagenomics (four bakery sourdoughs)], and metabolite target analysis. It turned out that the microbial species diversity of the sourdoughs was influenced by the house microbiota of the producer. Further, when the producer made use of different flours, the sourdoughs harbored similar microbial communities, independent of the flour used. AAB were only present in the Belgian sourdoughs, which might again be related to the processing environment. Fructilactobacillus sanfranciscensis (formerly known as Lactobacillus sanfranciscensis) was the prevalent LAB species of the eight sourdoughs produced by two of the three bakeries of different countries analyzed. These sourdoughs were characterized by the presence of either Saccharomyces cerevisiae or Kazachstania humilis. Moreover, the presence of Fl. sanfranciscensis was positively correlated with the production of mannitol and negatively correlated with the presence of other LAB or AAB species. Sourdoughs produced in an artisan lambic brewery were characterized by the presence of the yeast species Dekkera anomala and Pichia membranifaciens. One household sourdough was characterized by the presence of uncommon species, such as Pediococcus parvulus and Pichia fermentans. Metagenomic sequencing allowed the detection of many more LAB and AAB species than the other methods applied, which opened new frontiers for the understanding of the microbial communities involved during sourdough production processes.
Highlights
Sourdoughs are matrices of mainly cereal flour and water that are fermented by means of lactic acid bacteria (LAB; mainly heterofermentative LAB species) and yeasts (De Vuyst et al, 2016, 2017; Settanni, 2017; Van Kerrebroeck et al, 2017; Gobbetti et al, 2019)
San Francisco sourdough harbors a microbial consortium of Fructilactobacillus sanfranciscensis and Kazachstania humilis that is the result of a nutritional mutualism and thanks to mutual stress responses (Gänzle et al, 1998; Vogel, 2015; Jacques et al, 2016; De Vuyst et al, 2017)
The numbers of the presumptive acetic acid bacteria (AAB) were highest in the samples from the sourdoughs made in the lambic brewery and varied between 6.2 log (CFU/g) (GB-WL) and 7.9 log (CFU/g) (G-B-W)
Summary
Sourdoughs are matrices of mainly cereal flour and water that are fermented by means of lactic acid bacteria (LAB; mainly heterofermentative LAB species) and yeasts (De Vuyst et al, 2016, 2017; Settanni, 2017; Van Kerrebroeck et al, 2017; Gobbetti et al, 2019). San Francisco sourdough harbors a microbial consortium of Fructilactobacillus sanfranciscensis (formerly known as Lactobacillus sanfranciscensis; Zheng et al, 2020) and Kazachstania humilis (formerly Candida humilis) that is the result of a nutritional mutualism and thanks to mutual stress responses (Gänzle et al, 1998; Vogel, 2015; Jacques et al, 2016; De Vuyst et al, 2017). Other consortia of maltose-positive LAB and maltose-negative yeasts occur (e.g., Fl. sanfranciscensis and other Kazachstania species) as well as consortia of LAB species with a glucoserepressed maltose metabolism and maltose-positive yeasts [e.g., Lactiplantibacillus plantarum (formerly known as Lactobacillus plantarum) and Saccharomyces cerevisiae], supporting on mutual relationships (Guerzoni et al, 2007; De Vuyst et al, 2017; Sieuwerts et al, 2018)
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