Biodiversity of Lactobacillus sanfranciscensis strains isolated from five sourdoughs

AIMS: Five different sourdoughs were investigated for the composition of lactic acid bacteria (LAB) and the biodiversity of Lactobacillus sanfranciscensis strains. METHODS AND RESULTS: A total of 57 strains were isolated from five sourdoughs. Isolated strains were all identified by the 16S rDNA sequence and species-specific primers for L. sanfranciscensis. Results of identification showed that LAB strains were L. sanfranciscensis, Lactobacillus plantarum, Lactobacillus paralimentarius, Lactobacillus fermentum, Lactobacillus pontis, Lactobacillus casei, Weisella confusa and Pediococcus pentosaceus. A total of 21 strains were identified as L. sanfranciscensis and these isolates were detected in all five sourdoughs. Ribotyping was applied to investigate the relationship between intraspecies diversity of L. sanfranciscensis and sourdough. A total of 22 strains of L. sanfranciscensis including L. sanfranciscensis JCM 5668T were compared by ribotyping. The dendrogram of 21 ribotyping patterns showed four clusters, and L. sanfranciscensis JCM 5668T was independent of the others. The different biotypes of L. sanfranciscensis were present in two sourdoughs compared with other three sourdoughs. CONCLUSIONS: The LAB compositions of five sourdoughs were different and the relationship between intraspecies diversity of L. sanfranciscensis strains and five sourdoughs was shown by ribotyping. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated that ribotyping was useful for distinguishing L. sanfranciscensis strains. A further important result is that the intra-species diversity of L. sanfranciscensis strains seems to be related to the sourdough preparation.     

In situ activity of a bacteriocin-producing Lactococcus lactis strain. Influence on the interactions between lactic acid bacteria during sourdough fermentation

AIMS: To biochemically characterize the bacteriocin produced by Lactococcus lactis ssp. lactis M30 and demonstrate its effect on lactic acid bacteria (LAB) during sourdough propagation. METHODS AND RESULTS: A two-peptide bacteriocin produced by L. lactis ssp. lactis M30 was purified by ion exchange, hydrophobic interaction and reversed phase chromatography. Mass spectrometry of the two peptides and sequence analysis of the ltnA2 gene showed that the bacteriocin was almost identical to lacticin 3147. During a 20-day period of sourdough propagation the stability of L. lactis M30 was demonstrated, with concomitant inhibition of the indicator strain Lactobacillus plantarum 20, as well as the non-interference with the growth of the starter strain Lact. sanfranciscensis CB1. CONCLUSIONS: In situ active bacteriocins influence the microbial consortium of sourdough LAB and can "support" the dominance of insensitive strains during sourdough fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The in situ bacteriocinogenic activity of selected lactococci enables the persistence of insensitive Lact. sanfranciscensis strains, useful to confer good characteristics to the dough, at a higher cell concentration with respect to other LAB of the same ecosystem.     

Bacterial population in traditional sourdough evaluated by molecular methods

AIMS: To study the microbial communities in artisanal sourdoughs, manufactured by traditional procedure in different areas of Sicily, and to evaluate the lactic acid bacteria (LAB) population by classical and culture-independent approaches. METHODS AND RESULTS: Forty-five LAB isolates were identified both by phenotypic and molecular methods. The restriction fragment length polymorphism and 16S ribosomal DNA gene sequencing gave evidence of a variety of species with the dominance of Lactobacillus sanfranciscensis and Lactobacillus pentosus, in all sourdoughs tested. Culture-independent method, such as denaturing gradient gel electrophoresis (DGGE) of the V6-V8 regions of the 16S rDNA, was applied for microbial community fingerprint. The DGGE profiles revealed the dominance of L. sanfranciscensis species. In addition, Lactobacillus-specific primers were used to amplify the V1-V3 regions of the 16S rDNA. DGGE profiles flourished the dominance of L. sanfranciscensis and Lactobacillus fermentum in the traditional sourdoughs, and revealed that the closely related species Lactobacillus kimchii and Lactobacillus alimentarius were not discriminated. CONCLUSIONS: Lactobacillus-specific PCR-DGGE analysis is a rapid tool for rapid detection of Lactobacillus species in artisanal sourdough. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reports a characterization of Lactobacillus isolates from artisanal sourdoughs and highlights the value of DGGE approach to detect uncultivable Lactobacillus species.     

Molecular characterization of lactic acid bacteria from sourdough breads produced in Sardinia (Italy) and multivariate statistical analyses of results

The objective of this work was to investigate the structure and diversity of lactic acid bacteria (LAB) communities in sourdough used for the production of traditional breads (Carasau, Moddizzosu, Spianata, Zichi) in Sardinia. 16S rDNA sequencing and Randomly Amplified Polymorphic DNA (RAPD-PCR) was applied for the identification and typing of the LAB isolated from 25 samples of sourdoughs. Multivariate statistical techniques were applied to RAPD-PCR pattern to study the biological diversity of sourdough samples. Twelve different species of LAB were identified, and most isolates were classified as facultative heterofermentative lactobacilli. Lactobacillus pentosus dominated the lactic microflora of many samples while Lactobacillus sanfranciscensis was isolated only from a limited number of samples. Although heterofermentative species represented between between 30% and 60% of the isolates in Carasau, Spianata and Zichi sourdoughs, only 2% of the isolates from Moddizzosu sourdoughs were identified as heterofermentative LAB. RAPD-PCR with a single primer followed by cluster analysis did not allow the identification of the isolates at the species level. However, a multidimensional scaling/bootstrapping approach on the RAPD-PCR patterns uncovered the diversity of the LAB communities of LAB showing differences both within and between bread types.     

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.     

Lactic acid bacteria isolated from rye sourdoughs produce bacteriocin-like inhibitory substances active against Bacillus subtilis and fungi

Aim: To screen five strains of lactic acid bacteria (LAB) isolated from rye sourdoughs for the potential production of antimicrobial substances. Methods and Results: Lactobacillus sakei KTU05‐06, Pediococcus acidilactici KTU05‐7, Pediococcus pentosaceus KTU05‐8, KTU05‐9 and KTU05‐10 isolated from rye sourdoughs were investigated for the production of bacteriocin‐like inhibitory substances (BLIS). The supernatants of analysed LAB inhibited growth of up to 15 out of 25 indicator bacteria strains as well as up to 25 out of 56 LAB strains isolated from rye sourdoughs. Moreover, these five LAB were active against ropes‐producing Bacillus subtilis and the main bread mould spoilage causing fungi –Aspergillus, Fusarium, Mucor and Penicillium. Lactobacillus sakei KTU05‐6 demonstrated the best antibacterial properties and is resistant towards heat treatment even at 100°C for 60 min. Conclusions: The use of LAB‐producing antibacterial substances may be a good choice as a co‐starter culture to ensure the stability of sourdoughs and to avoid the bacterial and fungi spoilage of the end product. Significance and Impact of the Study: The antimicrobial compounds designated as sakacin KTU05‐6, pediocin KTU05‐8 KTU05‐9, KTU05‐10 and AcKTU05‐67 were not identical to any other known BLIS, and this finding leads up to the assumption that they might be the novel.     

Lyophilized preparations of bacteriocinogenic Lactobacillus curvatus and Lactococcus lactis subsp. lactis as potential protective adjuncts to control Listeria monocytogenes in dry-fermented sausages

AIM: Study of the effectiveness of in situ bacteriocin production by lactic acid bacteria (LAB) to control Listeria monocytogenes in dry-fermented sausages. METHODS AND RESULTS: Two bacteriocin-producing strains: Lactococcus lactis subsp. lactis LMG21206 and Lactobacillus curvatus LBPE were grown in a pilot scale fermentor and lyophilized to be directly used in dry sausage fermentation. A commercial starter culture (Bel'meat SL-25) not inhibitory to L. monocytogenes (Bac- starter) was mixed (1 : 1) with each of the two lyophilized bacteriocin-producing strains to obtain starters active against the pathogen (Bac+ starter). Anti-Listeria effectiveness of the Bac+ starters was studied in dry-fermented sausages. The meat batter was experimentally contaminated with a mixture of four different strains of L. monocytogenes (10(2)-10(3) CFU g(-1)). The results showed that L. monocytogenes did not grow in any of the contaminated batches, but no significant decrease (P > 0.05) was observed either in the positive control (no added starter culture) or in samples fermented with the Bac- starter culture during the fermentation period and up to 15 days of drying. When the Bac+ starter contained Lb. curvatus LBPE, cell counts of L. monocytogenes decreased to below the detectable limit (<10 CFU g(-1)) after 4 h of fermentation and no survivors could be recovered by enrichment beyond day 8 of drying. When the Bac+ starter culture containing Lc. lactis LMG21206 was used, a decrease in Listeria counts to below the detectable limit was achieved after 15 days of drying. CONCLUSIONS: The bacteriocin-producing strains studied may be used as adjunct cultures for sausage fermentations to control the occurrence and survival of L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: Addition of the Bac+ strains, especially the Lb. curvatus strain would provide an additional hurdle to enhance the control of L. monocytogenes in fermented meat products.     

Influence of baking enzymes on antimicrobial activity of five bacteriocin‐like inhibitory substances produced by lactic acid bacteria isolated from Lithuanian sourdoughs

Aim: To evaluate the effect of four different baking enzymes on the inhibitory activity of five bacteriocin‐like inhibitory substances (BLIS) produced by lactic acid bacteria (LAB) isolated from Lithuanian sourdoughs. Methods and Results: The overlay assay and the Bioscreen methods revealed that the five BLIS exhibited an inhibitory effect against spore germination and vegetative outgrowth of Bacillus subtilis, the predominant species causing ropiness in bread. The possibility that the observed antibacterial activity of BLIS might be lost after treatment with enzymes used for baking purposes was also examined. Conclusions: The enzymes tested; hemicellulase, lipase, amyloglucosidase and amylase had little or no effect on the majority of the antimicrobial activities associated with the five BLIS studied. Significance and Impact of the Study: This study suggests a potential application in the sourdough baking industry for these antimicrobial producing LAB strains in the control of B. subtilis spore germination and vegetative outgrowth.     

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.     

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.     

Characterization of sourdough lactic acid bacteria based on genotypic and cell-wall protein analyses

AIMS: To evaluate the effectiveness of two independent methods in differentiating a large population of lactic acid bacteria (LAB) isolated from wheat flours and sourdoughs and to correlate eventual differences/similarities among strains with their geographical origin and/or process parameters. METHODS AND RESULTS: One hundred fifty strains belonging to Lactobacillus spp. and Weissella spp., plus eight type strains, one for each species, and two unidentified isolates, were characterized by randomly amplified polymorphic DNA (RAPD) and SDS-PAGE of cell-wall proteins. The RAPD analysis separated the eight type strains but did not always assign all the strains of a species to the same group, while SDS-PAGE cell-wall protein profiles were species-specific. Frequently, strains isolated from sourdoughs of the same geographical origin or produced by similar raw material/process parameters showed similar RAPD and/or cell-wall profiles. CONCLUSIONS: The combined use of the RAPD and cell-wall protein analysis represents a useful tool to classify large adventitious microbial populations and to discriminate the diversity of the strains. SIGNIFICANCE AND IMPACT OF THE STUDY: This study represents a typing of a large collection of flour/sourdough LAB and provides evidence of the advantage of using two independent methods in the classification and traceability of microorganisms.     

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.     

Differentiation of Lactobacillus sanfranciscensis strains by randomly amplified polymorphic DNA and pulsed-field gel electrophoresis

Genetic diversity of Lactobacillus sanfranciscensis strains isolated from naturally fermented sourdoughs of different origin was evaluated by using randomly amplified polymorphic DNA (RAPD). Computer-assisted comparison of the RAPD patterns revealed a clear separation of L. sanfranciscensis from other obligately heterofermentative Lactobacillus species closely related or normally present in sourdough. Six clusters, five of them constituted by strains of the same origin, were recognized at a similarity level of 63%. Pulsed-field gel electrophoresis (PFGE) results on strains chosen as representative were generally in good agreement with the grouping obtained by RAPD. Both techniques showed a high degree of discriminatory power and indicated the existence of a remarkable genetic polymorphism within the species. Furthermore, the chromosome size of L. sanfranciscensis was estimated by PFGE to be about 1.4 Mb.     

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.     

Conjugal transfer of plasmid pIP501 from Lactococcus lactis to Lactobacillus delbruckii subsp. bulgaricus and Lactobacillus helveticus

Abstract Plasmid pIP501 was transferred by conjugation from Lactococcus lactis to Lactobacillus delbrückii subsp. bulgaricus and Lactobacillus helveticus . Only Lb. delbrückii subsp. bulgaricus transconjugants could act as a donor in crosses with Lc. lactis . No Lactobacillus transconjugants were detected after inter- or intra-species Lactobacillus crosses. Plasmid pIP501 has undergone no detectable deletion or rearrangement during transfer from Lc. lactis to Lactobacillus strains.     

Application of a novel polyphasic approach to study the lactobacilli composition of sourdoughs from the Abruzzo region (central Italy)

AIMS: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approach. METHODS AND RESULTS: A polyphasic approach, consisting of a two-step multiplex polymerase chain reaction (PCR) system, 16S rRNA gene sequence analysis and physiological features, was applied to identify 127 isolates, representing about 37% of the presumptive lactobacilli collected from sourdough samples. Multiplex PCR successfully identified 111 isolates, while 16S rRNA gene sequencing was applied for the other 16 isolates, two of which could not be associated with any previously described lactic acid bacteria (LAB) species. Strain diversity was evaluated by phenotypic and random amplified polymorphic DNA-PCR analysis. Molecular detection of Lactobacillus group species was also performed on total DNA extracted from the doughs. CONCLUSIONS: Abruzzo region sourdough lactobacilli biodiversity, reflected in both Lactobacillus species composition and strain polymorphism, is similar to that of other Italian regions and is a source of novel LAB species. SIGNIFICANCE AND IMPACT OF THE STUDY: Within culture-independent methods, multiplex PCR is a rapid tool to study the lactobacilli population of sourdoughs.     

Glutamine deamidation by cereal-associated lactic acid bacteria

AIMS: It was the aim of our work to investigate glutamine deamidation by lactic acid bacteria isolated from cereal fermentations and to elucidate the ecological and technological relevance in baking of the conversion of glutamine to glutamate. METHODS AND RESULTS: Lactobacillus sanfranciscensis and Lact. reuteri were found to display glutaminase activity. The addition of glutamine to modified Man, Rogosa and Sharp medium increased the cell yields of Lact. sanfranciscensis, as well as the production of lactic and acetic acid. The final pH; however, was increased in the glutamine-containing medium. The addition of 47 mmol kg(-1) glutamate to chemically acidified doughs significantly changed the bread flavour. In sourdoughs with enhanced proteolytic activity, strain-dependent production of 27-120 mmol glutamate per kilogram sourdough was observed. CONCLUSIONS: Lactobacillus sanfranciscensis and Lact. reuteri converted glutamine into glutamate; this conversion improves the acid tolerance of lactobacilli and significantly influences wheat bread flavour. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper illustrates the complex interaction of sourdough-lactobacilli with their environment: the flour provides substrates for metabolic activities that enable the lactobacilli to reach higher cell counts, and the produced metabolite may be one of the reasons why the flavour of fermented breads is different to the flavour of chemically acidified breads.     

Arginine catabolism by sourdough lactic acid bacteria: purification and characterization of the arginine deiminase pathway enzymes from Lactobacillus sanfranciscensis CB1

The cytoplasmic extracts of 70 strains of the most frequently isolated sourdough lactic acid bacteria were screened initially for arginine deiminase (ADI), ornithine transcarbamoylase (OTC), and carbamate kinase (CK) activities, which comprise the ADI (or arginine dihydrolase) pathway. Only obligately heterofermentative strains such as Lactobacillus sanfranciscensis CB1; Lactobacillus brevis AM1, AM8, and 10A; Lactobacillus hilgardii 51B; and Lactobacillus fructivorans DD3 and DA106 showed all three enzyme activities. Lactobacillus plantarum B14 did not show CK activity. L. sanfranciscensis CB1 showed the highest activities, and the three enzymes were purified from this microorganism to homogeneity by several chromatographic steps. ADI, OTC, and CK had apparent molecular masses of ca. 46, 39, and 37 kDa, respectively, and the pIs were in the range of 5.07 to 5.2. The OTCs, CKs, and especially ADIs were well adapted to pH (acidic, pH 3.5 to 4.5) and temperature (30 to 37 degrees C) conditions which are usually found during sourdough fermentation. Internal peptide sequences of the three enzymes had the highest level of homology with ADI, OTC, and CK of Lactobacillus sakei. L. sanfranciscensis CB1 expressed the ADI pathway either on MAM broth containing 17 mM arginine or during sourdough fermentation with 1 to 43 mM added arginine. Two-dimensional electrophoresis showed that ADI, OTC, and CK were induced by factors of ca. 10, 4, and 2 in the whole-cell extract of cells grown in MAM broth containing 17 mM arginine compared to cells cultivated without arginine. Arginine catabolism in L. sanfranciscensis CB1 depended on the presence of a carbon source and arginine; glucose at up to ca. 54 mM did not exert an inhibitory effect, and the pH was not relevant for induction. The pH of sourdoughs fermented by L. sanfranciscensis CB1 was dependent on the amount of arginine added to the dough. A low supply of arginine (6 mM) during sourdough fermentation by L. sanfranciscensis CB1 enhanced cell growth, cell survival during storage at 7 degrees C, and tolerance to acid environmental stress and favored the production of ornithine, which is an important precursor of crust aroma compounds.     

Isolation and characterization of bacteriocin-like inhibitory substances from lactic acid bacteria isolated from Azerbaijan cheeses

The search for lactic acid bacteria (LAB) producing bacteriocin-like inhibitory substances (BLISs) was performed in traditional Azerbaijan cheeses. Eight strains have been isolated and identified, four of which (S1a, S2, Q2b, and M1b) were identified as Lactobacillus buchneri. The remaining four strains (M3a, A4b, Q4a, and A3) were identified as L. pentosus, L. brevis, L. fermentum, and L. collinoides, respectively. Antimicrobial agents of all isolated LAB strains suppressed the growth of Lactobacillus bulgaricus 340, Escherichia coli, Enterococcus durans, and Listeria innocua. Saccharomyces cerevisiae and Candida pseudotropicalis were resistant to these BLISs. Proteinase K and trypsin completely inactivated BLIS whereas lipase and amylase partially inactivated BLIS.     

PCR-DGGE analysis of lactic acid bacteria and yeast dynamics during the production processes of three varieties of Panettone

Aims:  To study lactic acid bacteria (LAB) and yeast dynamics during the production processes of sweet-leavened goods manufactured with type I sourdoughs.
Methods and Results:  Fourteen sourdough and dough samples were taken from a baking company in central Italy during the production lines of three varieties of Panettone. The samples underwent pH measurements and plating analysis on three solid media. The microbial DNA was extracted from both the (sour)doughs and the viable LAB and yeast cells collected in bulk, and subjected to PCR-denaturing gradient gel electrophoresis (DGGE) analysis. The molecular fingerprinting of the cultivable plus noncultivable microbial populations provide evidence of the dominance of Lactobacillus sanfranciscensis , Lactobacillus brevis and Candida humilis in the three fermentation processes. The DGGE profiles of the cultivable communities reveal a bacterial shift in the final stages of two of the production processes, suggesting an effect of technological parameters on the selection of the dough microflora.
Conclusions:  Our findings confirm the importance of using a combined analytical approach to explore microbial communities that develop during the leavening process of sweet-leavened goods.
Significance and Impact of the Study:  In-depth studies of sourdough biodiversity and population dynamics occurring during sourdough fermentation are fundamental for the control of the leavening process and the manufacture of standardized, high-quality products.