Microbial species diversity in French traditional organic bread doughs C. Urien*, E. Lhomme+, C. Aulard, Y. Mouffok, B. Onno +, J. Legrand *, X. Dousset +, D. Sicard* *UMR
de Génétique Végétale, INRA - Université Paris-Sud, France + ONIRIS, Nantes, France e-mail :
[email protected]
Global context Prokaryotic and eukaryotic microorganisms dominate life on Earth with respect to the numbers of individuals and biomass. Yet, the diversity of microbial communities are unknown in most ecosystems. Here, we studied the microbial communities in bread leavened doughs and sourdoughs. Two kinds of microorganisms are involved in the bread making process: Lactic Acid Bacteria (LAB) and yeasts. These organisms play a role in the color, flavor, taste and fermentation of the bread. Despite the cultural significance of bread in France, the diversity of microbial communities has never been studied in French traditional bakeries. The aim of the present work was to describe the diversity of microbial communities in 14 bakeries using organic wheat flour.
Materials and Methods Microbial diversity was studied during the bread making process in 14 bakeries located in different French regions (Fig. 1). Samples were taken just before the sourdough was used as leaven agent in the bread dough.
Yeast diversity
Seven out of the eight yeast species found in the sampled sourdoughs belong to the “Saccharomyces complex” (green crosses on Fig 2).
Densities of yeasts and LAB were evaluated and species identified at three polymorphic loci (D1D2 of rDNA, ActI gene and NTS).
Fig 1: Localisation of bakeries studied
Microorganism densities The yeast density was included between 5.5 and 7.8 log10 CFU by gram of dough. The LAB density was included between 7.8 and 10.8 log10 CFU by gram of dough. The mean LAB density was close to 9 log10 CFU by gram in nine of the 14 cases.
Fig 2: Taken from Kurtzman and Robnett, 2003. Phylogenetic tree of the ‘Saccharomyces complex’ into 14 clades as represented by one of three most parsimonious trees derived from MP analysis of a dataset comprised of nucleotide sequences from 18S, 5.8S/alignable ITS, and 26S (three regions) rDNAs, EF-1K, mitochondrial small-subunit rDNA and COX II. Tree length=5135, CI=0.329, RI=0.631, RC=0.208. Bootstrap valuess 50% are given. P.anomala is the outgroup species, and all species are analyzed from type strains. Green crosses correspond to the species found during our study.
Except for the Bakery 2, yeast and LAB densities did not vary or varied faintly between the heart and the surface samples.
Fig 3: Densities of yeasts (in red) and LAB (in blue) in log 10 during the bread making process for 14 bakeries. Samples were taken in the heart (circle) and the surface (triangle) of the sourdough. Standard deviation is introduced for each mean (arrows).
Specific richness
Most species were affiliated to the Kazachstania clade (K. unispora, K. exigua, K. bulderi, K. barnettii and Candida humilis). To the best of our knowledge, two species were never found in a bakery product before: K. bulderi and Candida carpophila. This latter also belongs to the Saccharomycotina subphylum.
Conclusion
Eight and seven species of yeast and LAB respectively were identified (Fig. 4). A maximum of six species were detected in each sourdough.
This study shown that except for C. carpophila, yeast species found in 14 French organic bread sourdoughs were genetically close. Among them, two species were never already described in bakery products. S. cerevisiae, used in industrial bakery as leaven agent, was found in only five of all the bakeries. Microbial communities described were dimly complex but generally differed between two sourdoughs. Contrary to LAB, there was no yeast species shared by all the bread sourdoughs. Densities of LAB and yeast differed between two sourdoughs. The LAB density was higher than the yeast density in all the sourdoughs. Variation between densities was 10 times more for LAB than for yeasts.
The same major or exclusive LAB species Lactobacillus sanfranciscensis was found:in all the samples. This species was found in all the sourdoughs and was the major species in most 11 of the 14 sourdoughs.
In the light of these results we would like to know if the microbial communities and microbial densities also vary in non organic French sourdoughs.
Species names \ Baker ID
9
1
14
2
6
7
8
11
10
5
13
12
3
4
Saccharomyces cerevisiae
YEASTS
Kazachstania unispora
0,75
Candida humilis Torulaspora delbrueckii
LAB
Candida carpophila Lactobacillus sanfranciscensis
0,75
Lactobacillus pentosus Lactobacillus kimchii Lactobacillus hamessii no Lactobacillus
Fig 4: Specific richness of yeasts and LAB from final leavened doughs used for the bread making process in 14 organical bakeries.
A larger richness of yeast species was detected. Six different major yeast species were found in the sourdoughs. C. humilis is the most frequent major yeast species.
Thanks a lot to the bakers who shared with us their bread making knowledge and pleasure of good bread: Jean-François Bertellot, Christian Dalmasso, La Boulangeoise, Pain Virgule and Michel Perrin.
