Biodiversity of lactic acid bacteria and yeasts in spontaneously-fermented buckwheat and teff sourdoughs

In this study, four different laboratory scale gluten-free (GF) sourdoughs were developed from buckwheat or teff flours. The fermentations were initiated by the spontaneous biota of the flours and developed under two technological conditions (A and B). Sourdoughs were propagated by continuous back-slopping until the stability was reached. The composition of the stable biota occurring in each sourdough was assessed using both culture-dependent and -independent techniques. Overall, a broad spectrum of lactic acid bacteria (LAB) and yeasts species, belonging mainly to the genera Lactobacillus, Pediococcus, Leuconostoc, Kazachstania and Candida, were identified in the stable sourdoughs. Buckwheat and teff sourdoughs were dominated mainly by obligate or facultative heterofermentative LAB, which are commonly associated with traditional wheat or rye sourdoughs. However, the spontaneous fermentation of the GF flours resulted also in the selection of species which are not consider endemic to traditional sourdoughs, i.e. Pediococcus pentosaceus, Leuconostoc holzapfelii, Lactobacillus gallinarum, Lactobacillus vaginalis, Lactobacillus sakei, Lactobacillus graminis and Weissella cibaria. In general, the composition of the stable biota was strongly affected by the fermentation conditions, whilst Lactobacillus plantarum dominated in all buckwheat sourdoughs. Lactobacillus pontis is described for the first time as dominant species in teff sourdough. Among yeasts, Saccharomyces cerevisiae and Candida glabrata dominated teff sourdoughs, whereas the solely Kazachstania barnetti was isolated in buckwheat sourdough developed under condition A. This study allowed the identification and isolation of LAB and yeasts species which are highly competitive during fermentation of buckwheat or teff flours. Representatives of these species can be selected as starters for the production of sourdough destined to GF bread production.     

Description of the microflora of sourdoughs by culture-dependent and culture-independent methods

Four types of sourdoughs (L, C, B, Q) from artisanal bakeries in Northern Italy were studied using culture-dependent and culture-independent methods. In all samples, the yeast numbers ranged from 160 to 10⁷ cfu/g, and the numbers of lactic acid bacteria (LAB) ranged from 10³ to 10⁹ cfu/g. The isolated LAB were sequenced, and a similarity was noted between two samples (C, Q), both in terms of the species that were present and in terms of the percentage of isolates. In these two samples, Lactobacillus plantarum accounted for 73% and 89% of the bacteria, and Lactobacillus brevis represented 27% and 11%. In the third sample (B), however, the dominant LAB isolate was Lb. brevis (73%), while Lb. plantarum accounted for only 27%. The fourth sourdough (L) was completely different from the others. In this sample, the most prominent isolate was Weisella cibaria (56%), followed by Lb. plantarum (36%) and Pediococcus pentosaceus (8%). In three out of four samples (L, C and Q), all of the yeasts isolated were identified as Saccharomyces cerevisiae, yet only Candida humilis (90%) and Candida milleri (10%) were isolated in the fourth sample (B). The microbial ecology of the sourdoughs was also examined with direct methods. The results obtained by culture-independent methods and DGGE analysis underline a partial correspondence between the DNA and RNA analysis. These results demonstrate the importance of using a combined analytical approach to explore the microbial communities of sourdoughs.     

Microbial re-inoculation reveals differences in the leavening power of sourdough yeast strains

A method based on microbial re-inoculation, or the so-called backslopping and subsequent proofing of rye bread dough simulating commercial one-stage sourdough process, was used for the screening of the leavening capacity of sourdough yeast strains. Two yeast strains were initially tested with seven Lactobacillus strains. Thereafter, 17 yeast strains, mostly of sourdough origin, were tested with a backslopping procedure with heterofermentative Lactobacillus brevis as an acidifying lactic acid bacteria (LAB). The highest leavening capacity was found in sourdoughs containing Candida milleri, in particular when it was accompanied by obligately homofermentative Lactobacillus acidophilus or facultatively heterofermentative Lactobacillus plantarum when it acted homofermentatively. The leavening capacity of the reference strain Saccharomyces cerevisiae was about half that of C. milleri in all sourdoughs tested. The re-inoculation procedure increased the differences found in the leavening capacity of the tested yeast strains during final proofing of rye bread dough. The backslopped sourdoughs containing a heterofermentative Lactobacillus strain were more suppressive than those containing a homofermentative strain. The highest leavening capacity was found in C. milleri strains. The use of one backslopping cycle before assaying the leavening capacity of a laboratory sourdough is recommended since it helps to differentiate between yeast strains to be tested for their leavening power in the final bread dough.     

Molecular identification of the microbiota of French sourdough using temporal temperature gradient gel electrophoresis

The microbiota of four industrial French sourdoughs (BF, GO, VB and RF) was characterized by PCR temporal temperature gel electrophoresis (TTGE). The TTGE technique reveals differences in the 16S rDNA V6–V8 regions of these bacteria. DNA was extracted directly from sourdough samples. A specific TTGE fingerprint was determined for 30 bacterial species, including members of the genera Lactobacillus, Leuconostoc and Weissella, all known to be present in sourdough.These sourdoughs contain different species of lactic acid bacteria (LAB) depending on ecological conditions prevailing in the different sourdough fermentations. Only a few LAB species were found to be competitive and became dominant. Lactobacillus sanfranciscensis was observed as the most frequently found species. In sourdough GO, L. sanfranciscensis, Lactobacillus panis and two new species, Lactobacillus nantensis and Lactobacillus hammesii, were detected. Sourdough BF contain L. sanfranciscensis, Lactobacillus spicheri and Lactobacillus pontis. In sourdough VB, which differed in the process temperature, we identified exclusively L. sanfranciscensis and Leuconostoc mesenteroïdes subsp. mesenteroïdes. Lactobacillus frumenti, L. hammesii and Lacobacillus paralimentarius became the predominant species in sourdough RF. Compared with conventional bacteriological methods, the use of this new molecular approach to analyze the sourdough ecosystem should therefore allow a more complete and rapid assessment of its specific microbiota.     

Adaptability of lactic acid bacteria and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava and use of competitive strains as starters

The adaptability of lactic acid bacteria (LAB) and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava was investigated using PCR-DGGE and bacteriological culture combined with rRNA gene sequence analysis. Sourdoughs were prepared either from flours of the cereals wheat, rye, oat, barley, rice, maize, and millet, or from the pseudocereals amaranth, quinoa, and buckwheat, or from cassava, using a starter consisting of various species of LAB and yeasts. Doughs were propagated until a stable microbiota was established. The dominant LAB and yeast species were Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus paralimentarius, Lactobacillus plantarum, Lactobacillus pontis, Lactobacillus spicheri, Issatchenkia orientalis and Saccharomyces cerevisiae. The proportion of the species within the microbiota varied. L. paralimentarius dominated in the pseudocereal sourdoughs, L. fermentum, L. plantarum and L. spicheri in the cassava sourdough, and L. fermentum, L. helveticus and L. pontis in the cereal sourdoughs. S. cerevisiae constituted the dominating yeast, except for quinoa sourdough, where I. orientalis also reached similar counts, and buckwheat and oat sourdoughs, where no yeasts could be detected. To assess the usefulness of competitive LAB and yeasts as starters, the fermentations were repeated using flours from rice, maize, millet and the pseudocereals, and by starting the dough fermentation with selected dominant strains. At the end of fermentation, most of starter strains belonged to the dominating microbiota. For the rice, millet and quinoa sourdoughs the species composition was similar to that of the prior fermentation, whereas in the other sourdoughs, the composition differed.     

Fundamental study on the effect of hydrostatic pressure treatment on the bread-making performance of oat flour

The use of sourdough in wheat and rye breads has been extensively studied; however, little is known about its potential effect when baking oat bread. Consequently, the impact of sourdough on oat bread quality was investigated. Two different sourdoughs were prepared from wholegrain oat flour without the addition of starter cultures, by continuous propagation at 28 (SD 28) or 37 °C (SD 37) until the composition of the lactic acid bacteria remained stable. The dominant LAB were identified by sequence analysis of the 16S rDNA isolated from pure cultures. LAB from SD 28 belonged to the species Leuconostoc argentinum, Pedicoccus pentosaceus and Weissella cibaria, while Lactobacillus coryniformis dominated SD 37. The isolated LAB were further used as starter cultures for the production of oat sourdoughs. Fundamental rheology revealed softening of the sourdoughs compared to non-acidified and chemically acidified controls, which could not be attributed to proteolytic activity. Incorporation of oat sourdough into an oat bread recipe resulted in significantly increased loaf-specific volume as well as improved texture, independent of addition level or sourdough type. Overall, the results of this study show that sourdoughs containing lactic acid bacteria isolated from oats have the potential to enhance oat bread quality.     

Potential of Lactic Acid Bacteria to Inhibit Rope Spoilage in Wheat Sourdough Bread

The ability of selected lactic acid bacteria to inhibit the growth of rope-forming Bacillus strains in laboratory experiments and in wheat bread was investigated. Growth of Bacillus subtilis and Bacillus licheniformis was inhibited by Lactobacillus plantarum VTT E-78076 and Pediococcus pentosaceus VTT E-90390 in an automated turbidometry assay and in test bakings. Rope spoilage of wheat bread was inhibited by adding 20-30 g of sourdough/100 g of wheat dough if the sourdough was fermented with Lactobacillus plantarum VTT E-78076,Pediococcus pentosaceus VTT E-90390 or Lactobacillus brevis (commercial starter culture) and the pH values of sourdoughs were adjusted below 4.0 and the amount of total titratable acidity value was >12. Addition of lactic acid alone in concentrations comparable with those formed in sourdoughs did not prevent rope spoilage.     

Diversity and screening of lactic acid bacteria in la-baicai made by Korean-Chinese in northeastern China

This study investigated the lactic acid bacteria (LAB) population in la-baicai (spicy cabbage), a traditional fermented food made by the Korean-Chinese community in northeastern China and screened for functional LAB. LAB diversity was analyzed using denaturing gradient gel electrophoresis (DGGE), and 81 LAB strains were isolated and identified based on 16S rDNA sequencing analysis. Polymerase chain reaction DGGE detected 21 LAB species, belonging to the genera Lactobacillus (Lb.), Leuconostoc (Leu.), Pediococcus and Weissella, in 45 la-baicai samples. Lb. plantarum and Lb. sakei were considered to be dominant in the bacterial community. Among 81 LAB isolated by traditional pure culture methods were Lb. plantarum (25 strains), Lb. brevis (two strains), Lb. casei, (four strains), Lb. pentosus (three strains), Enterococcus faecium (45 strains), and E. durans (two strains). The tolerances of these LAB were investigated. Six LAB with high salt (NaCl)-tolerance were screened from the isolates, and 16% (w/v) was the highest salt-tolerance reached. Among the isolates, strain N1, identified as Lb. pentosus, survived well in a simulated digestive environment. Traditional fermented la-baicai from northeastern China is a rich LAB resource. Further study is needed and would be worthwhile to advance the benefits of these LAB.     

Quantitative detection of lactic acid bacteria in dried sourdoughs using real-time PCR

A real-time PCR system with 16S rRNA gene-targeted group-specific primers was developed to quantitatively detect lactic acid bacteria (LAB) of the genera Lactobacillus, Leuconostoc, Pediococcus, and Weissella in different types of commercially available dried sourdoughs. Despite a high degree of degradation in the DNA isolated from the doughs, the 341-bp 16S rRNA gene fragment of the sourdough LAB biota could specifically be amplified. For dried sourdoughs, the resulting calculated LAB cell counts were determined to be up to 3.7 × 10⁷ cells/g fresh dough, whereas in non-fermented dough acidifiers, used as a control, the calculated LAB cell counts did not exceed 3.6 × 10⁴ cells/g fresh dough. Moreover, the effect of low pH and/or high lactic acid concentrations prevailing in the doughs on the detectability of LAB cells in spray- and roller-dried sourdoughs by PCR was investigated. Drying of non-acidified sourdoughs still permitted to detect the LAB cells by PCR, whereas drying of acidified doughs reduced the detectable cell counts by approximately 5 (spray dried) and 2 (roller dried) orders of magnitudes. Incubation of acidified doughs for 24 h did not affect the detectability of LAB cells in spray-dried doughs but further reduced the detectable cell counts in roller-dried doughs by additional 2 orders of magnitude.     

Identification of lactic acid bacteria isolated from oat sourdoughs and investigation into their potential for the improvement of oat bread quality

The use of sourdough in wheat and rye breads has been extensively studied; however, little is known about its potential effect when baking oat bread. Consequently, the impact of sourdough on oat bread quality was investigated. Two different sourdoughs were prepared from wholegrain oat flour without the addition of starter cultures, by continuous propagation at 28 (SD 28) or 37 °C (SD 37) until the composition of the lactic acid bacteria remained stable. The dominant LAB were identified by sequence analysis of the 16S rDNA isolated from pure cultures. LAB from SD 28 belonged to the species Leuconostoc argentinum, Pedicoccus pentosaceus and Weissella cibaria, while Lactobacillus coryniformis dominated SD 37. The isolated LAB were further used as starter cultures for the production of oat sourdoughs. Fundamental rheology revealed softening of the sourdoughs compared to non-acidified and chemically acidified controls, which could not be attributed to proteolytic activity. Incorporation of oat sourdough into an oat bread recipe resulted in significantly increased loaf-specific volume as well as improved texture, independent of addition level or sourdough type. Overall, the results of this study show that sourdoughs containing lactic acid bacteria isolated from oats have the potential to enhance oat bread quality.     

Sourdough-isolated<Emphasis Type="Italic"> Lactobacillus fermentum</Emphasis> as a potent anti-mould preservative of a traditional Iranian bread

Sourdough bread is an ancient method for making long microbial shelf life and strongly flavoured breads. Traditional sourdough bread-making has been practised for centuries in Iran. Although rural bread-making is still highly reliant on sourdough, urban bakeries usually use bakers yeast and also sodium bicarbonate instead. In this study the anti-mould preservative effects of three lactic acid bacteria isolates were investigated on one of the popular traditional Iranian bread (Lavash). Starter cultures were prepared using 20 h cultures of three sourdough-isolated strains, Lactobacillus casei, Lactobacillus plantarum and Lactobacillus fermentum. Different concentrations (0.5%, 1%, 2%, 4% and 8%) of lactobacillus starter cultures were used to prepare a variety of sourdoughs. Lavash doughs were inoculated with 20% of each lactobacilli-fermented sourdough. After a 20 h incubation at 30 °C, a decrease in pH was observed in the different lactobacilli sourdoughs. However an 8% inoculum of L. fermentum resulted in a significant decrease in pH (3.87 to 2.70). Concentrations of 2% and higher of the three lactobacilli used in Lavash sourdough delayed mould growth during storage. However this preservative effect was more significant when an 8% inoculum of L. fermentum was used. These results tend to suggest that selected strains of lactobacilli have a beneficial role in prevention of bread waste by mould spoilage, and hence could extend bread shelf life.     

Identification and Characterization of Lactic Acid Bacteria Involved in Natural and Lactic Acid Bacterial Fermentations of Pastes of Soybeans and Soybean-Maize Blends Using Culture-Dependent Techniques and Denaturing Gradient Gel Electrophoresis

Pastes of soybeans and soybean-maize blends were fermented with inoculum through back-slopping using lactic acid bacteria (LAB) fermented cereal gruel, thobwa and without inoculum (naturally). LAB involved in the fermentations were characterized using culture-dependent and culture-independent analyses. Decreases in pH from 6.4 to 3.9–4.2 and from 6.9 to 5.4–5.8 after 72 h were observed in LAB fermented pastes (LFP) and in naturally fermented pastes (NFP), respectively. LAB increased from 5.0 to 8.7–9.6 log₁₀ cfu/g in NFP and from 8.1 to 9.3 log₁₀ cfu/g in LFP. LAB in both fermentations were heterofermentative lactobacilli (82.4%) and homofermentative cocci (17.6%), of which 44.7% and 42.9% were exopolysaccharide producers, respectively. Principal component analysis based on carbohydrate fermentation, CO₂ production and arginine hydrolysis showed four clusters dominated by Lactobacillus fermentum, Weissella confusa, Lactobacillus brevis 1 and Pediococcus pentosaceus, respectively. Sequencing of 16S rDNA gene confirmed Lb. fermentum, W. confusa/W. cibaria, and P. pentosaceus as identities of species in three clusters. Denaturing gradient gel electrophoresis (DGGE) confirmed these species as the dominant microbiota. DGGE showed higher similarity in microbial profiles of LFP throughout fermentation and low similarity in NFP during early and late stages of fermentation.     

Microbiological and technological characterization of sourdoughs destined for bread-making with barley flour

The aim of the present study was the microbiological and technological characterization of laboratory- made sourdoughs for use in barley-flour-based bread-making. A defined multi-strain starter culture consisting of selected lactic acid bacteria (LAB) and yeasts from wheat sourdoughs was inoculated into three flour–water mixtures, composed of: (i) 100% wheat flour (ii) 50% wheat flour and 50% hull-less barley flour (composite flour); (iii) 100% hull-less barley flour. After two months of continuous propagation, the chemical characteristics of the three sourdoughs were investigated by measuring: pH, total titratable acidity and concentrations of various microbial metabolites by HPLC (i.e. lactic, acetic, phenyllactic and butyric acids and diacetyl). The microbial traits were studied through viable counts, isolation and typing of LAB and yeasts and PCR-DGGE analyses. Only Saccharomyces cerevisiae and Lactobacillus plantarum were detectable in the sourdoughs together with other lactobacilli species which were different depending on the type of flour blend used. The molecular typing of the isolates highlighted that only a few strains among those initially inoculated prevailed. The volume increases of the three types of sourdough were also investigated and a correlation was seen between an increase in the barley flour content and a reduction in the dough volume.     

Bacterial community dynamics,lactic acid bacteria species diversity and metabolite kinetics of traditional Romanian vegetable fermentations

BACKGROUND: Artisanal vegetable fermentations are very popular in Eastern European countries. Fresh vegetables undergo a spontaneous fermentation in the presence of salt, which is mainly carried out by lactic acid bacteria (LAB). RESULTS: Culture‐dependent and culture‐independent analyses of end‐samples of various spontaneous vegetable fermentations carried out in houses of the Chiodju region (central Romania) revealed Lactobacillus plantarum and Lactobacillus brevis as the most frequently isolated LAB species. Leuconostoc mesenteroides and Leuconostoc citreum were also found. Furthermore, the community dynamics of spontaneous cauliflower and mixed‐vegetable (green tomatoes, carrots and cauliflower) fermentations revealed three steps: an initial phase characterised by the presence of Enterobacteriaceae and a wide LAB species diversity, encompassing Weissella species; a second phase from day 3 onwards wherein L. citreum and Lb. brevis occurred; and a final phase characterised by the prevalence of Lb. brevis and Lb. plantarum. Metabolite target analysis revealed that glucose and fructose were mostly depleted at the end of fermentation. The main products of carbohydrate metabolism were lactic acid, acetic acid, ethanol and small amounts of mannitol, indicating heterolactate fermentation. CONCLUSION: Given their prevalence at the end of vegetable fermentations, Lb. brevis and Lb. plantarum appear to be good candidate starter cultures for controlled vegetable fermentation processes. © 2012 Society of Chemical Industry     

Distribution and genetic diversity of lactic acid bacteria from traditional fermented sausage

This study was conducted to investigate the distribution and genetic diversity of the native lactic acid bacteria (LAB) population in nem chua, a popular traditional Vietnamese uncooked fermented sausage. A total of 74 LAB isolates were identified and their molecular fingerprints were obtained using repetitive-PCR (rep-PCR) and pulse-field gel electrophoresis (PFGE). The results revealed that the majority of LAB isolates were Lactobacillus plantarum (67.6%), followed by Pediococcus pentosaceus (21.6%). A minority of LAB (9.5%) were Lactobacillus brevis and Lactobacillus farciminis (1.4%). A large genetic plasticity within the same species was also observed. Both rep-PCR and PFGE methods were found to be acceptable regarding reproducibility and reliability. However, this study demonstrated the higher discriminatory power of PFGE compared to rep-PCR, as observed by the higher number of clusters generated (17 and 12 clusters of L. plantarum respectively, seven and six clusters of P. pentosaceus respectively and four and two clusters of L. brevis respectively), and lower percentage of similarity among clusters in PFGE data analysis. These results also revealed that there was not a single LAB strain that was found to predominate in the product. To our knowledge, this is the first detailed analysis of the native LAB population in nem chua. As this traditional sausage is fermented naturally or only with back-slop, knowledge about the native LAB population in the product is very important to understand the microflora that has been active in fermenting the nem chua and to ensure the safety of this uncooked sausage.     

Free D- and L-Amino Acid Evolution During Sourdough Fermentation and Baking

The evolution of free D- and L-amino acids in sourdoughs started with various lactic acid bacteria (LAB) and yeasts was studied. Lactobacillus brevis subsp. lindneri CB1 and Lactobacillus plantrum DC400 had high proteolytic activity. During sourdough fermentation, Saccharomyces cerevisiae 141 and Saccharomyces exiguus M14 sequentially utilized free amino acids produced by bacterial activity. Due to increased cell yeast autolysis, more S. exiguus M14 inocula caused more free amino acids which were partially utilized by LAB without causing hydrolysis of wheat flour protein. D-alanine, D-glutamic acid and traces of other D-isomers were observed in sourdoughs fermented with L. brevis subsp. lindneri CB1 and S. cerevisiae 141. Free total D- and L-amino acid content decreased by more than 44% after baking the sourdoughs. No abiotic generation of new D-amino acid isomers was detected in the baked sourdoughs.     

Robustness of Lactobacillus plantarum starters during daily propagation of wheat flour sourdough type I

This study aimed at investigating the robustness of selected sourdough strains of Lactobacillus plantarum. Seven strains were singly used as sourdough type I starters under daily back-slopping propagation (ten days) using wheat flour. Cell numbers of presumptive lactic acid bacteria varied slightly (median values of 9.13–9.46 log cfu g⁻¹) between and within started sourdoughs, as well as the acidifying activity (median values of 1.24–1.33). After three days also the control sourdough (unstarted) had the same values. As shown by RAPD-PCR analysis, five (DB200, 3DM, G10C3, 12H1 and LP20) out of seven strains maintained elevated cell numbers (ca. 9 log cfu g⁻¹) throughout ten days. The other two strains progressively decreased to less than 5 log cfu g⁻¹. As identified by partial sequencing of 16S rRNA and recA genes, L. plantarum (11 isolates), pediococci (7), Lactobacillus casei (3) and Lactobacillus rossiae (2) dominated the flour microbiota. Monitoring of lactic acid bacteria during sourdough propagation was carried out by culture dependent approach and using PCR-DGGE (Denaturing Gradient Gel Electrophoresis). Except for the sourdough started with L. plantarum LP20, in all other sourdoughs at least one autochthonous strain of L. plantarum emerged. All emerging strains of L. plantarum showed different RAPD-PCR profiles. L. rossiae and Pediococcus pentosaceus were only found in the control and sourdough started with strain 12H1. The characterization of the catabolic profiles of sourdoughs (Biolog System) showed that sourdoughs containing persistent starters behaved similarly and their profiles were clearly differentiated from the others. One persistent strain (DB200) of L. plantarum and Lactobacillus sanfranciscensis LS44, previously shown to be persistent ( Siragusa et al., 2009), were used as the mixed starter to produce a wheat flour sourdough. Both strains cohabited and dominated during ten days of propagation.     

Effect of Select Parameters of the Sourdough Rye Fermentation on the Activity of Some Mixed Starter Cultures

The effect of select parameters (i.e., rye flour ash content, temperature, and dough yield) of the sourdough fermentation on the fermentation activity of different starter cultures (lactic acid bacteria Lactococcus lactis ssp. Lactis, Weissella confusa, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus helveticus, and yeast Kluyveromyces marxianus subsp. Marxianus) was determined. The major metabolic end products of fermentation (D, L-lactic acid, acetic acid, ethanol and glycerol) and the evolution of total phenolic content and folic acid during bread making were measured. Lactobacillus helveticus and Kluyveromyces marxianus allowed obtaining sourdoughs with the highest lactic acid/acetic acid ratios. The mixed starter culture with Lactococcus lactis and Saccharomyces cerevisiae generated the most important quantities of D/L lactic acid. The maximum values of ethanol concentration were obtained in case of the sourdoughs from whole rye flour fermented at lower temperature (30°C) with mixed starter cultures containing Sacchomyces cerevisiae. The fermentation process and type of starter culture are also tools to increase the bioactive compounds, enabling the increase of the phenolic content of the sourdough.     

In situ production and analysis of Weissella confusa dextran in wheat sourdough

Several lactic acid bacteria belonging to the genera Leuconostoc, Lactobacillus, and Weissella have been introduced to wheat sourdough baking for in situ production of exopolysaccharides. This is considered a novel method for improving the shelf-life, volume and nutritional value of bread without additives. However, in situ production of exopolysaccharides during sourdough fermentation is challenged by simultaneous acidification due to metabolic activities of the bacteria, which may significantly diminish the positive technological impact of exopolysaccharides. In this study, the growth, activity and in situ production of dextran by Weissella confusa VTT E-90392 in wheat sourdoughs were investigated. Furthermore, the influence of dextran-enriched sourdoughs, at the addition level of 43%, on the subsequent bread quality was established. W. confusa efficiently produced dextran from the added sucrose in wheat sourdough without strong acid production. A new specific enzyme-assisted method for in situ analysis of dextran in sourdoughs was developed. With this method, we could for the first time proof significant (11–16 g/kg DW) production of polymeric dextran in sourdoughs. Concomitant formation of shorter isomaltooligosaccharides by W. confusa was also detected. The produced dextran significantly increased the viscosity of the sourdoughs. Application of dextran-enriched sourdoughs in bread baking provided mildly acidic wheat bread with improved volume (up to 10%) and crumb softness (25–40%) during 6 days of storage. Hence, W. confusa is a promising new strain for efficient in situ production of dextrans and isomaltooligosaccharides in sourdoughs without strong acidification.     

Comparative study of spontaneously fermented sourdoughs originating from two regions of Greece: Peloponnesus and Thessaly

A total of 167 yeast and 136 lactic acid bacteria strains were isolated from spontaneously fermented wheat sourdoughs from two regions of Greece, namely Thessaly and Peloponnesus. Identification of the isolates exhibited dominance of Torulaspora delbrueckii with sporadic presence of Saccharomyces cerevisiae and, regarding the lactic acid bacteria, dominance of Lactobacillus sanfranciscensis in the sourdoughs from Thessaly and Lb. plantarum subsp. plantarum in the sourdoughs from Peloponnesus. The latter was accompanied by Pediococcus pentosaceus as secondary microbiota. None of the above mentioned strains exhibited amylolytic, lipolytic or proteolytic activities, and none of the lactic acid bacteria strains produced antimicrobial compounds.