Identification and Population Dynamics of Yeasts in Sourdough Fermentation Processes by PCR-Denaturing Gradient Gel Electrophoresis

Four sourdoughs (A to D) were produced under practical conditions, using a starter obtained from a mixture of three commercially available sourdough starters and baker's yeast. The doughs were continuously propagated until the composition of the microbiota remained stable. A fungi-specific PCR-denaturing gradient gel electrophoresis (DGGE) system was established to monitor the development of the yeast biota. The analysis of the starter mixture revealed the presence of Candida humilis, Debaryomyces hansenii, Saccharomyces cerevisiae, and Saccharomyces uvarum. In sourdough A (traditional process with rye flour), C. humilis dominated under the prevailing fermentation conditions. In rye flour sourdoughs B and C, fermented at 30 and 40°C, respectively, S. cerevisiae became predominant in sourdough B, whereas in sourdough C the yeast counts decreased within a few propagation steps below the detection limit. In sourdough D, which corresponded to sourdough C in temperature but was produced with rye bran, Candida krusei became dominant. Isolates identified as C. humilis and S. cerevisiae were shown by randomly amplified polymorphic DNA-PCR analysis to originate from the commercial starters and the baker's yeast, respectively. The yeast species isolated from the sourdoughs were also detected by PCR-DGGE. However, in the gel, additional bands were visible. Because sequencing of these PCR fragments from the gel failed, cloning experiments with 28S rRNA amplicons obtained from rye flour were performed, which revealed Cladosporium sp., Saccharomyces servazii, S. uvarum, an unculturable ascomycete, Dekkera bruxellensis, Epicoccum nigrum, and S. cerevisiae. The last four species were also detected in sourdoughs A, B, and C.     

Monitoring the bacterial population dynamics in sourdough fermentation processes by using PCR-denaturing gradient gel electrophoresis

Four sourdoughs (A to D) were produced under practical conditions by using a starter mixture of three commercially available sourdough starters and a baker's yeast constitutively containing various species of lactic acid bacteria (LAB). The sourdoughs were continuously propagated until the composition of the LAB flora remained stable. Two LAB-specific PCR-denaturing gradient gel electrophoresis (DGGE) systems were established and used to monitor the development of the microflora. Depending on the prevailing ecological conditions in the different sourdough fermentations, only a few Lactobacillus species were found to be competitive and became dominant. In sourdough A (traditional process with rye flour), Lactobacillus sanfranciscensis and a new species, L. mindensis, were detected. In rye flour sourdoughs B and C, which differed in the process temperature, exclusively L. crispatus and L. pontis became the predominant species in sourdough B and L. crispatus, L. panis, and L. frumenti became the predominant species in sourdough C. On the other hand, in sourdough D (corresponding to sourdough C but produced with rye bran), L. johnsonii and L. reuteri were found. The results of PCR-DGGE were consistent with those obtained by culturing, except for sourdough B, in which L. fermentum was also detected. Isolates of the species L. sanfranciscensis and L. fermentum were shown by randomly amplified polymorphic DNA-PCR analysis to originate from the commercial starters and the baker's yeast, respectively.     

Monitoring the Bacterial Population Dynamics in Sourdough Fermentation Processes by Using PCR-Denaturing Gradient Gel Electrophoresis

Four sourdoughs (A to D) were produced under practical conditions by using a starter mixture of three commercially available sourdough starters and a baker's yeast constitutively containing various species of lactic acid bacteria (LAB). The sourdoughs were continuously propagated until the composition of the LAB flora remained stable. Two LAB-specific PCR-denaturing gradient gel electrophoresis (DGGE) systems were established and used to monitor the development of the microflora. Depending on the prevailing ecological conditions in the different sourdough fermentations, only a few Lactobacillus species were found to be competitive and became dominant. In sourdough A (traditional process with rye flour), Lactobacillus sanfranciscensis and a new species, L. mindensis, were detected. In rye flour sourdoughs B and C, which differed in the process temperature, exclusively L. crispatus and L. pontis became the predominant species in sourdough B and L. crispatus, L. panis, and L. frumenti became the predominant species in sourdough C. On the other hand, in sourdough D (corresponding to sourdough C but produced with rye bran), L. johnsonii and L. reuteri were found. The results of PCR-DGGE were consistent with those obtained by culturing, except for sourdough B, in which L. fermentum was also detected. Isolates of the species L. sanfranciscensis and L. fermentum were shown by randomly amplified polymorphic DNA-PCR analysis to originate from the commercial starters and the baker's yeast, respectively.     

Occurrence and dominance of yeast species in sourdough

AIMS: The aim of this work is to identify the dominant yeast species in homemade sourdoughs. METHODS AND RESULTS: PCR/restriction fragment length polymorphism analysis of internal transcribed spacer regions was used for the identification of isolates and the data were confirmed with phenotypic tests. The strains belonging to Saccharomyces cerevisiae were identified to strain level by analysis of inter-delta regions. CONCLUSION: This work shows that the dominant species in homemade sourdoughs can differ from each other. Saccharomyces cerevisiae was found to be the dominant species, followed by the Candida milleri, C. humilis, S. exiguus and Issatchenkia orientalis. The inter-delta regions of S. cerevisiae strains showed high polymorphism. SIGNIFICANCE AND IMPACT OF THE STUDY: Occurrence of single, non-Saccharomyces species and S. cerevisiae polymorphism in the yeast populations of sourdough samples.     

Physiological properties of some yeast strains

Twenty yeast strains have recently been isolated in pure cultures from natural and industrial sources and identified based mainly on physiological properties. The majority of the strains (15) are alcohologenic belonging to the genus Saccharomyces and comprise two brewer's (beer) yeast strains (S. carlsbergensis= S. uvarum A and B), two baker's yeast strains (S. cerevisiae CA and CP), one spirit yeast strain (S. cerevisiae CF) and ten wine yeast strains (S. cerevisiae var. ellipsoideus = S. ellipsoideus 1, 3, 4, 6, 8 and 9; S. oviformis 2, 5 and 7; and S. uvarum 10). The other 5 yeast strains belong to different species: Kloeckera apiculate, Candida mycoderma (Mycoderma vini), Pichia membranaefaciens, Rhodotorula glutinis and Torulopsis holmii, respectively.     

Redox interactions between Saccharomyces cerevisiae and Saccharomyces uvarum in mixed culture under enological conditions

Wine yeast starters that contain a mixture of different industrial yeasts with various properties may soon be introduced to the market. The mechanisms underlying the interactions between the different strains in the starter during alcoholic fermentation have never been investigated. We identified and investigated some of these interactions in a mixed culture containing two yeast strains grown under enological conditions. The inoculum contained the same amount (each) of a strain of Saccharomyces cerevisiae and a natural hybrid strain of S. cerevisiae and Saccharomyces uvarum. We identified interactions that affected biomass, by-product formation, and fermentation kinetics, and compared the redox ratios of monocultures of each strain with that of the mixed culture. The redox status of the mixed culture differed from that of the two monocultures, showing that the interactions between the yeast strains involved the diffusion of metabolite(s) within the mixed culture. Since acetaldehyde is a potential effector of fermentation, we investigated the kinetics of acetaldehyde production by the different cultures. The S. cerevisiae-S. uvarum hybrid strain produced large amounts of acetaldehyde for which the S. cerevisiae strain acted as a receiving strain in the mixed culture. Since yeast response to acetaldehyde involves the same mechanisms that participate in the response to other forms of stress, the acetaldehyde exchange between the two strains could play an important role in inhibiting some yeast strains and allowing the growth of others. Such interactions could be of particular importance in understanding the ecology of the colonization of complex fermentation media by S. cerevisiae.     

The molecular genetic differentiation of cultured Saccharomyces strains

A comparative molecular genetic study of cultured Saccharomyces strains isolated from the surface of berries and various fermentation processes showed that baker's yeast and black-currant isolates contain not only Saccharomyces cerevisiae but also S. cerevisiae and S. bayanus var. uvarum hybrids. The molecular karyotyping of baker's, brewer's, and wine yeasts showed their polyploidy. The restriction enzyme analysis of noncoding rDNA regions (5.8S-ITS and IGS2) makes it possible to differentiate species of the genus Saccharomyces and to identify interspecies hybrids. The microsatellite primer (GTG)5 can be used to study the populations of cultured S. cerevisiae strains.     

Characterisation of the microbiota of rice sourdoughs and description of Lactobacillus spicheri sp. nov

The microbiota of two industrially processed rice sourdoughs was characterised by bacteriological culture in combination with PCR-denaturing gradient gel electrophoresis (DGGE) and 16S/28S rDNA sequence analysis. Rice sourdough I was continuously propagated for several years by back-slopping every week, whereas sourdough II was processed by using a commercial starter culture and back-slopping daily for three days. In rice sourdough II Candida krusei and Saccharomyces cerevisiae as well as Lactobacillus fermentum, Lactobacillus gallinarum, Lactobacillus kimchii, Lactobacillus plantarum, and Lactobacillus pontis dominated at the first day of fermentation. RAPD analysis of lactobacilli revealed identical profiles for each of the species except for L. fermentum and L. pontis indicating the presence of different strains. Fluctuations within the LAB community during fermentation were monitored by PCR-DGGE. L. pontis decreased in numbers over time and L. curvatus became dominant after 3 days of fermentation. Rice sourdough I contained S. cerevisiae, Lactobacillus paracasei (present with three different RAPD types), Lactobacillus paralimentarius, and a Lactobacillus strain which could not be allotted to any valid species. Phylogenetic analysis based on 16S rDNA sequences revealed Lactobacillus brevis as the closest relative (97.3% sequence similarity). Differences in some phenotypic characteristics and DNA-DNA relatedness indicated that the strain represents a new Lactobacillus species, for which the name Lactobacillus spicheri is proposed.     

Taxonomic Structure and Monitoring of the Dominant Population of Lactic Acid Bacteria during Wheat Flour Sourdough Type I Propagation Using Lactobacillus sanfranciscensis Starters

The structure and stability of the dominant lactic acid bacterium population were assessed during wheat flour sourdough type I propagation by using singly nine strains of Lactobacillus sanfranciscensis. Under back-slopping propagation with wheat flour type 0 F114, cell numbers of presumptive lactic acid bacteria varied slightly between and within starters. As determined by randomly amplified polymorphic DNA-PCR and restriction endonuclease analysis-pulsed-field gel electrophoresis analyses, only three (LS8, LS14, and LS44) starters dominated throughout 10 days of propagation. The others progressively decreased to less than 3 log CFU g⁻¹. Partial sequence analysis of the 16S rRNA and recA genes and PCR-denaturating gradient gel electrophoresis analysis using the rpoB gene allowed identification of Weissella confusa, Lactobacillus sanfranciscensis, Lactobacillus plantarum, Lactobacillus rossiae, Lactobacillus brevis, Lactococcus lactis subsp. lactis, Pediococcus pentosaceus, and Lactobacillus spp. as the dominant species of the raw wheat flour. At the end of propagation, one autochthonous strain of L. sanfranciscensis was found in all the sourdoughs. Except for L. brevis, strains of the above species were variously found in the mature sourdoughs. Persistent starters were found in association with other biotypes of L. sanfranciscensis and with W. confusa or L. plantarum. Sourdoughs were characterized for acidification, quotient of fermentation, free amino acids, and community-level catabolic profiles by USING Biolog 96-well Eco microplates. In particular, catabolic profiles of sourdoughs containing persistent starters behaved similarly and were clearly differentiated from the others. The three persistent starters were further used for the production of sourdoughs and propagated by using another wheat flour whose lactic acid bacterium population in part differed from the previous one. Also, in this case all three starter strains persisted during propagation.     

Spelt and emmer flours: characterization of the lactic acid bacteria microbiota and selection of mixed starters for bread making

Aims: This study aimed at characterizing the lactic acid bacteria microbiota and selecting mixed endogenous starters to be used for sourdough fermentation of spelt or emmer flours. Methods and Results: Identification of lactic acid bacteria was carried out by partial sequencing of the 16S rRNA, recA, 16S/23S rRNA spacer region and pheS genes. Spelt flour showed the largest biodiversity, while Lactobacillus plantarum dominated in emmer flour. Isolates were subjected to RAPD‐PCR analysis and screened based on the kinetics of growth and acidification, quotient of fermentation and liberation of free amino acids (FAA) during sourdough fermentation. After selection, mixed starters were used according to a two‐step fermentation process. Wheat flour was fermented by the same starters. Spelt and emmer sourdoughs had slightly higher pH than wheat sourdoughs but titratable acidity, concentration of FAA and phytase activity were higher. Specific volume and crumb grain of emmer and, especially, spelt breads approached those of wheat breads. Sensory analysis confirmed the suitability of spelt and emmer for bread making. Conclusions: The sourdough biotechnology was indispensable to completely exploit the potential of spelt and emmer flours. Significance and Impact of the Study: Results filled up the lack of knowledge on the lactic acid bacteria microbiota and technological performances of spelt and emmer flours.     

Evolution of Bacterial Consortia in Spontaneously Started Rye Sourdoughs during Two Months of Daily Propagation

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.     

Evidence of different fermentation behaviours of two indigenous strains of Saccharomyces cerevisiae and Saccharomyces uvarum isolated from Amarone wine

Aims:  To explain the role of Saccharomyces cerevisiae and Saccharomyces uvarum strains (formerly Saccharomyces bayanus var. uvarum ) in wine fermentation.
Methods and Results:  Indigenous Saccharomyces spp. yeasts were isolated from Amarone wine (Italy) and analysed. Genotypes were correlated to phenotypes: Melibiose⁻ and Melibiose⁺ strains displayed a karyotype characterized by three and two bands between 225 and 365 kb, respectively. Two strains were identified by karyotype analysis (one as S. cerevisiae and the other as S. uvarum ). The technological characterization of these two strains was conducted by microvinifications of Amarone wine. Wines differed by the contents of ethanol, residual sugars, acetic acid, glycerol, total polysaccharides, ethyl acetate, 2-phenylethanol and anthocyanins. Esterase and β-glucosidase activities were assayed on whole cells during fermentation at 13° and 20°C. Saccharomyces uvarum displayed higher esterase activity at 13°C, while S. cerevisiae displayed higher β-glucosidase activity at both temperatures.
Conclusions:  The strains differed by important technological and qualitative traits affecting the fermentation kinetics and important aroma components of the wine.
Significance and Impact of the Study:  The contribution of indigenous strains of S. cerevisiae and S. uvarum to wine fermentation was ascertained under specific winemaking conditions. The use of these strains as starters in a winemaking process could differently modulate the wine sensory characteristics.     

Characterization of natural hybrids of Saccharomyces cerevisiae and Saccharomyces bayanus var. uvarum

Nine yeast strains were isolated from spontaneous fermentations in the Alsace area of France, during the 1997, 1998 and 1999 grape harvests. Strains were characterized by pulsed-field gel electrophoresis, PCR-restriction fragment length polymorphism (RFLP) of the MET2 gene, delta-PCR, and microsatellite patterns. Karyotypes and MET2 fragments of the nine strains corresponded to mixed chromosomal bands and restriction patterns for both Saccharomyces cerevisiae and Saccharomyces bayanus var. uvarum. They also responded positively to amplification with microsatellite primers specific to both species and were demonstrated to be diploid. However, meiosis led to absolute nonviability of their spores on complete medium. All the results demonstrated that the nine yeast strains isolated were S. cerevisiaexS. bayanus var. uvarum diploid hybrids. Moreover, microsatellite DNA analysis identified strains isolated in the same cellar as potential parents belonging to S. bayanus var. uvarum and S. cerevisiae.     

Molecular source tracking of predominant lactic acid bacteria in traditional Belgian sourdoughs and their production environments

Aims:  To investigate the circulation of predominant sourdough lactic acid bacteria (LAB) species in the production environment of two Belgian artisan sourdough bakeries.
Methods and Results:  Isolates were collected from sourdoughs, flour, hands of the baker and air in the bakery setting and taxonomically characterized using repetitive element sequence-based PCR fingerprinting, pheS and/or 16S rRNA gene sequencing and amplified fragment length polymorphism (AFLP) analysis. In parallel, PCR-DGGE (denaturing gradient gel electrophoresis) analysis of V3-16S rDNA amplicons was applied to visualize the predominant bacterial population in the sourdoughs and the corresponding bakery environment (flour, hands of the baker, air and bakery equipment). Both approaches revealed that sourdoughs produced at D01 and D10 were mainly dominated by Lactobacillus spicheri and L. plantarum and by L. sanfranciscensis , respectively, and that these LAB species also circulated in the corresponding bakery environment. Furthermore, AFLP fingerprinting demonstrated that sourdough and bakery environment isolates of these species were genetically indistinguishable. For more sensitive source-tracking, SYBR Green-based real-time PCR assays were developed using species-specific primers targeting the pheS gene of L. plantarum and L. sanfranciscensis, detected in air samples from D01 and D10, respectively.
Conclusions:  The results obtained in this study indicate that specific strains of LAB persist in artisan doughs over years and circulate in the bakery environment. Furthermore, the importance of air as a potential carrier of LAB in artisan bakery environments was demonstrated.
Significance and Impact of the Study:  PheS -based real-time PCR can be used to detect, quantify and/or monitor specific LAB species (e.g. starter cultures) in sourdough and bakery environment samples.     

The biodiversity of lactic acid bacteria in Greek traditional wheat sourdoughs is reflected in both composition and metabolite formation

Lactic acid bacteria (LAB) were isolated from Greek traditional wheat sourdoughs manufactured without the addition of baker's yeast. Application of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cell protein, randomly amplified polymorphic DNA-PCR, DNA-DNA hybridization, and 16S ribosomal DNA sequence analysis, in combination with physiological traits such as fructose fermentation and mannitol production, allowed us to classify the isolated bacteria into the species Lactobacillus sanfranciscensis, Lactobacillus brevis, Lactobacillus paralimentarius, and Weissella cibaria. This consortium seems to be unique for the Greek traditional wheat sourdoughs studied. Strains of the species W. cibaria have not been isolated from sourdoughs previously. No Lactobacillus pontis or Lactobacillus panis strains were found. An L. brevis-like isolate (ACA-DC 3411 t1) could not be identified properly and might be a new sourdough LAB species. In addition, fermentation capabilities associated with the LAB detected have been studied. During laboratory fermentations, all heterofermentative sourdough LAB strains produced lactic acid, acetic acid, and ethanol. Mannitol was produced from fructose that served as an additional electron acceptor. In addition to glucose, almost all of the LAB isolates fermented maltose, while fructose as the sole carbohydrate source was fermented by all sourdough LAB tested except L. sanfranciscensis. Two of the L. paralimentarius isolates tested did not ferment maltose; all strains were homofermentative. In the presence of both maltose and fructose in the medium, induction of hexokinase activity occurred in all sourdough LAB species mentioned above, explaining why no glucose accumulation was found extracellularly. No maltose phosphorylase activity was found either. These data produced a variable fermentation coefficient and a unique sourdough metabolite composition.     

Yeast biodiversity and dynamics during sweet wine production as determined by molecular methods

In this study we investigated yeast biodiversity and dynamics during the production of a sweet wine obtained from dried grapes. Two wineries were selected in the Collio region and grapes, grape juices and wines during fermentations were analyzed by culture-dependent methods (plating on WLN medium) and culture-independent methods (PCR-DGGE). Moreover, the capability of the Saccharomyces cerevisiae starter cultures to take over the fermentation was assessed by RAPD-PCR. On WLN agar several species of non-Saccharomyces yeasts (Hanseniaspora, Metschnikowia, Pichia, Candida, Torulaspora and Debaryomyces), but also strains of S. cerevisiae, were isolated. After inoculation of the starter cultures, only colonies typical of S. cerevisiae were observed. Using PCR-DGGE, the great biodiversity of moulds on the grapes was underlined, both at the DNA and RNA level, while the yeast contribution started to become important only in the musts. Here, bands belonging to species of Candida zemplinina and Hanseniaspora uvarum were visible. Lastly, when the S. cerevisiae isolates were compared by RAPD-PCR, it was determined that only in one of the fermentations followed, the inoculated strain conducted the alcoholic fermentation. In the second fermentation, the starter culture was not able to promptly implant and other populations of S. cerevisiae could be isolated, most likely contributing to the final characteristics of the sweet wine produced.     

Influence of geographical origin and flour type on diversity of lactic acid bacteria in traditional Belgian sourdoughs

A culture-based approach was used to investigate the diversity of lactic acid bacteria (LAB) in Belgian traditional sourdoughs and to assess the influence of flour type, bakery environment, geographical origin, and technological characteristics on the taxonomic composition of these LAB communities. For this purpose, a total of 714 LAB from 21 sourdoughs sampled at 11 artisan bakeries throughout Belgium were subjected to a polyphasic identification approach. The microbial composition of the traditional sourdoughs was characterized by bacteriological culture in combination with genotypic identification methods, including repetitive element sequence-based PCR fingerprinting and phenylalanyl-tRNA synthase (pheS) gene sequence analysis. LAB from Belgian sourdoughs belonged to the genera Lactobacillus, Pediococcus, Leuconostoc, Weissella, and Enterococcus, with the heterofermentative species Lactobacillus paralimentarius, Lactobacillus sanfranciscensis, Lactobacillus plantarum, and Lactobacillus pontis as the most frequently isolated taxa. Statistical analysis of the identification data indicated that the microbial composition of the sourdoughs is mainly affected by the bakery environment rather than the flour type (wheat, rye, spelt, or a mixture of these) used. In conclusion, the polyphasic approach, based on rapid genotypic screening and high-resolution, sequence-dependent identification, proved to be a powerful tool for studying the LAB diversity in traditional fermented foods such as sourdough.     

Identification of some chromosomes of the brewing yeast Saccharomyces uvarum

Abstract Chromosomal DNA molecules of Saccharomyces uvarum and Saccharomyces cerevisiae were separated using Orthogonal Field Alteration Gel Electrophoresis (OFAGE). Hybridization with specific probes of S. cerevisiae chromosomes allowed the identification of seven chromosomes of S. uvarum . The majority of the studied chromosomal DNA molecules show the same OFAGE mobility as the corresponding molecules of S. cerevisiae , with some minor differences.
Hybridizations with two distinct bands of S. uvarum were observed with each URA1 (marker of chromosome XI) and ARG80 (marker of chromosome XIII) probes, demonstrating the presence of at least two copies of these genes in the brewing yeast.     

Microbial Ecology Dynamics during Rye and Wheat Sourdough Preparation

The bacterial ecology during rye and wheat sourdough preparation was described by 16S rRNA gene pyrosequencing. Viable plate counts of presumptive lactic acid bacteria, the ratio between lactic acid bacteria and yeasts, the rate of acidification, a permutation analysis based on biochemical and microbial features, the number of operational taxonomic units (OTUs), and diversity indices all together demonstrated the maturity of the sourdoughs during 5 to 7 days of propagation. Flours were mainly contaminated by metabolically active genera (Acinetobacter, Pantoea, Pseudomonas, Comamonas, Enterobacter, Erwinia, and Sphingomonas) belonging to the phylum Proteobacteria or Bacteroidetes (genus Chryseobacterium). Their relative abundances varied with the flour. Soon after 1 day of propagation, this population was almost completely inhibited except for the Enterobacteriaceae. Although members of the phylum Firmicutes were present at very low or intermediate relative abundances in the flours, they became dominant soon after 1 day of propagation. Lactic acid bacteria were almost exclusively representative of the Firmicutes by this time. Weissella spp. were already dominant in rye flour and stably persisted, though they were later flanked by the Lactobacillus sakei group. There was a succession of species during 10 days of propagation of wheat sourdoughs. The fluctuation between dominating and subdominating populations of L. sakei group, Leuconostoc spp., Weissella spp., and Lactococcus lactis was demonstrated. Other subdominant species such as Lactobacillus plantarum were detectable throughout propagation. As shown by PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis, Saccharomyces cerevisiae dominated throughout the sourdough propagation. Notwithstanding variations due to environmental and technology determinants, the results of this study represent a clear example of how the microbial ecology evolves during sourdough preparation.     

Influence of artisan bakery- or laboratory-propagated sourdoughs on the diversity of lactic Acid bacterium and yeast microbiotas

Seven mature type I sourdoughs were comparatively back-slopped (80 days) at artisan bakery and laboratory levels under constant technology parameters. The cell density of presumptive lactic acid bacteria and related biochemical features were not affected by the environment of propagation. On the contrary, the number of yeasts markedly decreased from artisan bakery to laboratory propagation. During late laboratory propagation, denaturing gradient gel electrophoresis (DGGE) showed that the DNA band corresponding to Saccharomyces cerevisiae was no longer detectable in several sourdoughs. Twelve species of lactic acid bacteria were variously identified through a culture-dependent approach. All sourdoughs harbored a certain number of species and strains, which were dominant throughout time and, in several cases, varied depending on the environment of propagation. As shown by statistical permutation analysis, the lactic acid bacterium populations differed among sourdoughs propagated at artisan bakery and laboratory levels. Lactobacillus plantarum, Lactobacillus sakei, and Weissella cibaria dominated in only some sourdoughs back-slopped at artisan bakeries, and Leuconostoc citreum seemed to be more persistent under laboratory conditions. Strains of Lactobacillus sanfranciscensis were indifferently found in some sourdoughs. Together with the other stable species and strains, other lactic acid bacteria temporarily contaminated the sourdoughs and largely differed between artisan bakery and laboratory levels. The environment of propagation has an undoubted influence on the composition of sourdough yeast and lactic acid bacterium microbiotas.