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. 2021 May 25;10(6):1189.
doi: 10.3390/foods10061189.

Metagenetic Analysis for Microbial Characterization of Focaccia Doughs Obtained by Using Two Different Starters: Traditional Baker's Yeast and a Selected Leuconostoc citreum Strain

Massimo Ferrara  1 , Angelo Sisto  1 , Giuseppina Mulè  1 , Paola Lavermicocca  1 , Palmira De Bellis  1
Affiliations

Metagenetic Analysis for Microbial Characterization of Focaccia Doughs Obtained by Using Two Different Starters: Traditional Baker's Yeast and a Selected Leuconostoc citreum Strain

Massimo Ferrara et al. Foods. .

Abstract

Lactic acid bacteria (LAB) decisively influence the technological, nutritional, organoleptic and preservation properties of bakery products. Therefore, their use has long been considered an excellent strategy to improve the characteristics of those goods. The aim of this study was the evaluation of microbial diversity in different doughs used for the production of a typical Apulian flatbread, named focaccia. Leavening of the analyzed doughs was obtained with baker's yeast or by applying an innovative "yeast-free" protocol based on a liquid sourdough obtained by using Leuconostoc citreum strain C2.27 as a starter. The microbial populations of the doughs were studied by both a culture-dependent approach and metagenetic analyses. The flours used for dough preparation were also subjected to the same analyses. The metagenetic analyses were performed by sequencing the V5-V6 hypervariable regions of the 16S rRNA gene and the V9 hypervariable region of the 18S rRNA gene. The results indicate that these hypervariable regions were suitable for studying the microbiota of doughs, highlighting a significant difference between the microbial community of focaccia dough with baker's yeast and that of the dough inoculated with the bacterial starter. In particular, the dough made with baker's yeast contained a microbiota with a high abundance of Proteobacteria (82% of the bacterial population), known to be negatively correlated with the biochemical properties of the doughs, while the Proteobacteria in dough produced with the L. citreum starter were about 43.5% lower than those in flour and dough prepared using baker's yeast. Moreover, the results show that the L. citreum C2.27 starter was able to dominate the microbial environment and also reveal the absence of the genus Saccharomyces in the dough used for the production of the "yeast-free" focaccia. This result is particularly important because it highlights the suitability of the starter strain for obtaining an innovative "yeast-free" product.

Keywords: baker’s yeast; lactic acid bacteria; liquid sourdough; metagenetic analysis; microbiota; yeast-free dough.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic representation of the production of two different doughs: (A) dough with the liquid sourdough started with L. citreum C2.27 (DS), and (B) dough with baker’s yeast (DB).
Figure 2
Figure 2
Alpha diversity indexes (Chao1, ACE, Shannon, Simpson) of bacterial (A) and fungal (B) microbiota in dough with baker’s yeast (DB), dough with sourdough (DS) and flour (F) samples.
Figure 3
Figure 3
Principal coordinate analysis (PCoA) as 2D (right) and 3D (left) plots of bacterial (A) and fungal (B) communities of dough with baker’s yeast (DB), dough with sourdough (DS) and flour (F) samples. PCoA was calculated using the Bray–Curtis index to compute dissimilarities among different samples. Hypothesis testing was conducted by analysis of molecular variance (AMOVA) test (p < 0.05).
Figure 4
Figure 4
Relative abundance and taxonomic assignments of microbial flora at genus level of dough with baker’s yeast (DB), dough with sourdough (DS) and flour (F) samples. Minor genera with <0.1% relative abundance are represented as “Other”.
Figure 5
Figure 5
Genera with a significantly different abundance between dough with sourdough (DS) and dough with baker’s yeast (DB) samples. The statistical cutoffs of p < 0.05 (Welch test) and q-value < 0.05 (FDR) were set as the significance threshold.
Figure 6
Figure 6
Genera with a significantly different abundance between dough with baker’s yeast (DB) and flour (F) samples (A) and dough with sourdough (DS) and flour (F) samples (B). The statistical cutoffs of p < 0.05 (Welch test) and q-value < 0.05 (FDR) were set as the significance threshold.
Figure 7
Figure 7
Absolute number of assigned reads to genera belonging to Ascomycota and Basidiomycota phyla for dough with baker’s yeast (DB), dough with sourdough (DS) and flour (F) samples.
Figure 8
Figure 8
Relative abundance of genera belonging to Ascomycota and Basidiomycota phyla for dough with baker’s yeast (DB), dough with sourdough (DS) and flour (F) samples. Data are represented as a normalized percentage of the assigned genera.
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