Reduction of alpha-galactooligosaccharides in soyamilk by Lactobacillus fermentum CRL 722: in vitro and in vivo evaluation of fermented soyamilk

AIMS: Consumption of soya-derived products has been hampered by the presence of alpha-galactooligosaccharides (alpha-GOS) because mammals lack pancreatic alpha-galactosidase (alpha-Gal) which is necessary for their hydrolysis. These sugars thus reach the large intestine causing gastrointestinal disorders in sensitive individuals. The use of lactic acid bacteria (LAB) expressing alpha-Gal is a promising solution for the degradation of alpha-GOS in soyamilk. METHODS AND RESULTS: The capacity of the LAB Lactobacillus fermentum CRL 722 to properly degrade alpha-GOS was studied in vitro using controlled fermentation conditions and in vivo using a rat model. Lactobacillus fermentum CRL 722 was able to grow on commercial soyamilk and completely eliminated stachyose and raffinose during fermentation because of its high alpha-Gal activity. Rats fed soyamilk fermented by this LAB had smaller caecums compared with rats fed unfermented soyamilk. CONCLUSIONS: Soyamilk fermentation by Lact. fermentum CRL 722 results in the reduction of alpha-GOS concentrations in soyamilk, thus eliminating possible undesirable physiological effects normally associated with its consumption. SIGNIFICANCE AND IMPACT OF THE STUDY: Fermentation with Lact. fermentum CRL 722 could prevent gastrointestinal disorders in sensitive individuals normally associated with the consumption of soya-based products. This LAB could thus be used in the elaboration of novel fermented vegetable products which better suit the digestive capacities of consumers.     

Hydrolysis of whey proteins by Lactobacillus acidophilus, Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus grown in a chemically defined medium

AIMS: To evaluate the ability of themophilic lactic acid bacteria (LAB) to hydrolyse the whey proteins beta-lactoglobulin (BLG) and alpha-lactalbumin (ALA) in a chemically defined medium (CDM). METHODS AND RESULTS: The ability of three LAB strains to hydrolyse BLG and ALA was studied in a CDM supplemented with these proteins or whey protein concentrate (WPC). Protein hydrolysis was determined by Tricine/SDS-PAGE and RP-HPLC. Maximum BLG (21%) and ALA (26%) degradation by LAB was observed using WPC. Under starving conditions, BLG degradation was greater for Lactobacillus delbrueckii ssp. bulgaricus CRL 454 than for Lactobacillus acidophilus CRL 636 and Streptococcus thermophilus CRL 804. All three strains showed different peptide profiles and were not able to hydrolyse ALA under starvation. CONCLUSIONS: The assayed LAB strains were able to degrade BLG during growth in a CDM and under starving conditions. The different peptide profiles obtained indicate distinct protease specificities. SIGNIFICANCE AND IMPACT OF THE STUDY: These strains could be used as adjunct cultures to increase BLG digestibility in whey-based or whey-containing foods. To our knowledge, this is the first report on the ability of a Lact. acidophilus strain to degrade BLG.     

Reverse reaction of Aspergillus niger APC-9319 alpha-galactosidase in a supersaturated substrate solution: production of alpha-linked galactooligosaccharide (alpha-GOS)

The alpha-galactosidase that effectively catalyzes a reverse reaction of galactose, Aspergillus niger APC-9319 alpha-galactosidase, was screened from industrial enzyme preparations for food processing containing alpha-galactosidase activity. Reverse reaction of A. niger APC-9319 alpha-galactosidase was performed using a supersaturated solution (90% galactose [w/v]). A. niger APC-9319 alpha-galactosidase was not inhibited even in high substrate concentration, and effectively catalyzed the reverse reaction. The yield of the reaction product, alpha-linked galactooligosaccharide (alpha-GOS), increased greatly as the initial concentration of galactose increased to 90% (w/v), and was more than 50%. Furthermore, the half life of enzyme activity was about three times as long as that using 60% galactose (w/v). alpha-GOS (1.4 g) was prepared from galactose (3.0 g) by reverse reaction of A. niger APC-9319 alpha-galactosidase. The alpha-GOS contained 58% alpha-galactobiose (alpha-Gal2), 28% alpha-galactotriose, and 14% oligosaccharides larger than alpha-galactotriose. The main component of positional isomers in alpha-Gal2 was alpha-1,6Gal2.     

Biological characteristics of strains of lactobacilli, promising for use as eubiotics]

In the course of in vitro studies 3 Lactobacillus strains with pronounced antagonistic activity against some pathogenic and opportunistic bacteria (shigellae, enteropathogenic Escherichia, Proteus, staphylococci) were selected. In experiments on germ-free rats faint colonization by L. plantarum 37 was observed in the small intestine, as well as in the large intestine when low doses of these bacilli were introduced into the gastrointestinal tract of the animals. In vitro experiments demonstrated the decreased growth rate of this strain. The prophylactic administration of two eubiotic strains, L. plantarum 37 and L. fermentum 39, simultaneously with chloramphenicol to primates inhibited the growth of opportunistic bacteria, though L. fermentum 39 excessively suppressed the content of Escherichia coli in the enterobacterial population. The optimum biological effect was achieved with the therapeutic use of these three strains for the correction of dysbiotic disturbances caused by the administration of tetracycline in volunteers.     

Adhesion of probiotic lactobacilli to chick intestinal mucus

In the present work, interactions between three Lactobacillus strains (Lactobacillus fermentum CRL1015, Lactobacillus animalis CRL1014, and Lactobacillus fermentum CRL1016) and chicken small intestinal mucus were determined. Three lactobacilli isolated from chicken and selected by their potentially probiotic properties were able to grow in mucus preparations. Three peaks from gel filtration chromatography of intestinal mucus were obtained. The adhesion to three mucus fractions (I, II, and III), especially fraction III, was higher (P < 0.01) in L. fermentum CRL1015 than L. animalis CRL1014. Pretreatment of this fraction with proteases and metaperiodate showed lower (P < 0.01) adhesion values than that of the control, suggesting that a glycoprotein from the mucus acts as a receptor for L. fermentum CRL1015. Highest adhesion values were obtained at pH 7 and 42 degrees C, and neither the removal of divalent cations with ethylenediaminetetraacetic acid (EDTA) nor the addition of calcium produced significant variation from the adhesion values of the control (P > 0.01). This adhesion was only inhibited by N-acetyl-glucosamine. Salmonella pullorum and Salmonella gallinarum showed high (P < 0.01) values of adhesion to chick intestinal mucus. The results obtained from assays of the inhibition of adherence of Salmonella spp. to mucus, immobilized in polystyrene tissue culture wells, indicated that the pathogen adhesion was not reduced by lactobacilli (P > 0.05) or their spent culture supernatants (P > 0.05), suggesting that these strains did not interfere with the binding sites for Salmonella spp. adhesion to the small intestinal mucus.     

Effect of Lactobacillus fermentum on beta2 toxin production by Clostridium perfringens

Clostridium perfringens, although a member of the normal gut flora, is also an important cause of intestinal disease in animals and, to a lesser extent, in humans. Disease is associated with the production of one or more toxins, and little is known about environmental influences on the production of these toxins. One of the health-promoting effects of lactic acid bacteria (LAB) is the establishment and maintenance of a low pH in the intestine since an acidic environment inhibits the growth of many potentially harmful bacteria. Here, the effect of the LAB Lactobacillus fermentum on beta2 toxin production by C. perfringens is described. Coculturing of C. perfringens with L. fermentum showed that under in vitro conditions, L. fermentum was capable of silencing beta2 toxin production by C. perfringens without influencing bacterial viability. The reduction in toxin production was shown to be most likely a result of the decline in pH. Quantitative PCR showed that the reduction in beta2 toxin production was due to a decrease in cpb2 mRNA. These results suggest that in the intestine, the production of beta2 toxin by C. perfringens might be regulated by other members of the normal intestinal flora.     

Some probiotic properties of chicken lactobacilli

The beneficial effect of lactobacilli has been attributed to their ability to colonize human and animal gastrointestinal tracts. In this work, adhesion assays with three lactobacillus strains and intestinal fragments obtained from chickens were assessed. Lactobacillus animalis and L. fermentum were able to adhere to three kinds of epithelial cells (crop, small and large intestines) with predominance to small intestine. Among the strains considered, L. fermentum subsp. cellobiosus showed the lowest and L. animalis the highest adhesion ability. Scanning electron microphotographs showing L. animalis and L. fermentum adhering to intestinal cells were obtained. The characterization of L. animalis adhesion indicated that lectin-like structure of this strain has glucose/mannose as specific sugars of binding. However, a calcium requirement was not observed. The adhesion of L. fermentum was reduced by addition of sialic acid or mannose (P < 0.01). These carbohydrates can be involved in the interaction between adhesin and epithelial surface. In this case, the dependence on bivalent cations was demonstrated. Lactobacillus fermentum was effective in reducing the attachment of Salmonella pullorum by 77%, while L. animalis was able to inhibit (90%, 88%, and 78%) the adhesion of S. pullorum, S. enteritidis, and S. gallinarum to host-specific epithelial fragments respectively. Our results from this in vitro model suggest that these lactobacilli are able to block the binding sites for Salmonella adhesion.     

Lactic acid bacteria isolated from canine faeces

AIMS: Lactic acid bacteria (LAB) were isolated and sequenced from the faeces of healthy dogs. Five of these strains were selected and further characterized to clarify the potential of these strains as probiotics for canine. METHODS AND RESULTS: LAB were found in 67% (14/21) of the canine faeces samples when plated on Lactobacilli Selective Media without acetic acid. Out of 13 species identified with partial 16S rRNA gene sequencing, Lactobacillus fermentum LAB8, L. mucosae LAB12, L. rhamnosus LAB11, L. salivarius LAB9 and Weissella confusa LAB10 were selected as candidate probiotic strains based on their frequency, quantity in faeces, growth density, acid tolerance and antimicrobial activity. The minimal inhibitory concentration values of these isolates were determined for 14 antibiotics. L. salivarius LAB9, W. confusa LAB10 and L. mucosae LAB12 were viable in pH 2 for 4 h (mLBS), indicating tolerance to acidity and thus the potential to survive in gastrointestinal tract of the canine. The LAB8-LAB12 strains showed antimicrobial activity against Micrococcus luteus A1 NCIMB86166. CONCLUSIONS: Thirteen different LAB species were found from the faecal microbiota of the healthy canines. Five acid tolerant and antimicrobially active LAB strains with the capacity to grow to high densities both aerobically and anaerobically were chosen to serve as candidate probiotics. SIGNIFICANCE AND IMPACT OF THE STUDY: The selected LAB strains are among the first host-specific LAB with antimicrobial activity isolated from canines that could serve as potential probiotics for canine use.     

Competitive selection of lactic acid bacteria that persist in the human oral cavity

Lactic acid bacteria (LAB) might offer opportunities as oral probiotics provided candidate strains persist in the mouth. After intake of a mixture of 69 LAB, strains of Lactobacillus fermentum and Lactobacillus salivarius were especially recovered. Coaggregation with other microbes is likely not a prerequisite for persistence since L. salivarius strongly coaggregated with typical oral cavity isolates, whereas L. fermentum failed to display this phenotype.     

Diversity and technological properties of predominant lactic acid bacteria from fermented cassava used for the preparation of Gari, a traditional African food

Traditional fermentation of cassava is dominated by a lactic acid bacteria (LAB) population. Fermentation is important for improving product flavour and aroma as well as safety, especially by reduction of its toxic cyanogenic glucosides. The production of Gari from cassava in Benin typically occurs on a household or small industrial scale, and consequently suffers from inconsistent product quality and may not always be safe for consumption. Therefore, the diversity of LAB from a typical cassava fermentation for the preparation of Gari, and their technologically relevant characteristics were investigated with a view towards selection of appropriate starter cultures. A total of 139 predominant strains isolated from fermenting cassava were identified using phenotypic tests and genotypic methods such as rep-PCR and RAPD-PCR. DNA-DNA hybridisation and sequencing of the 16S rRNA genes were done for selected strains. Lactobacillus plantarum was the most abundantly isolated species (54.6% of isolates), followed by Leuconostoc fallax (22.3%) and Lactobacillus fermentum (18.0%). Lactobacillus brevis, Leuconostoc pseudomesenteroides and Weissella paramesenteroides were sporadically isolated. The L. plantarum strains were shown to be better acid producers and capable of faster acid production than the L. fallax or L. fermentum strains. The incidence of beta-glucosidase (linamarase) activity was also highest among strains of this species. Production of antagonistic substances such as H2O2 and bacteriocins, however, was more common among L. fallax and L. fermentum strains. Strains of all three species were capable of utilising the indigestible sugars raffinose and stachyose. Therefore, a starter culture containing a mixture of strains from all three species was recommended.     

Distribution of indigenous Lactobacilli in the digestive tract of conventional and gnotobiotic rats.

Distribution of indigenous lactobacilli in the gastrointestinal tracts of rats was investigated at the species level. The indigenous lactobacilli isolated from conventional rats were divided into three groups, Lactobacillus acidophilus and its related strains, L. fermentum, and L. murini. Localization of the Lactobacillus groups in the gastrointestinal tracts could be distinguished clearly based on arabinose and glucose fermentation reaction of isolates from each part of the gastrointestinal tract. Group I (L. acidophilus and the related strains) and Group II (L. fermentum) were the major populations of lactobacilli on the walls of the non-glandular part and in the contents of the stomachs of both conventional and gnotobiotic rats. Group I predominated in all the parts of the digestive tract of conventional rats, whereas Group II was in the minority in the lower part of the gastrointestinal tracts of both groups of rats. Group III (L. murini) was the predominant population of Lactobacillus in the lower part of small intestine of conventional rats and in all parts of the gastrointestinal tracts of gnotobiotic rats except for the wall of the non-glandular part of the stomach.     

Complete glutathione system in probiotic Lactobacillus fermentum ME-3

There is much information about glutathione (GSH) in eukaryotic cells, but relatively little is known about GSH in prokaryotes. Without GSH and glutathione redox cycle lactic acid bacteria (LAB) cannot protect themselves against reactive oxygen species. Previously we have shown the presence of GSH in Lactobacillus fermentum ME-3 (DSM14241). Results of this study show that probiotic L. fermentum ME-3 contains both glutathione peroxidase and glutathione reductase. We also present that L. fermentum ME-3 can transport GSH from environment and synthesize GSH. This means that it is characterized by a complete glutathione system: synthesis, uptake and redox turnover ability that makes L. fermentum ME-3 a perfect protector against oxidative stress. To our best knowledge studies on existence of the complete glutathione system in probiotic LAB strains are still absent and glutathione synthesis in them has not been demonstrated.     

Lactic acid bacteria fermentation of human milk oligosaccharide components, human milk oligosaccharides and galactooligosaccharides

Human milk contains about 7% lactose and 1% human milk oligosaccharides (HMOs) consisting of lactose with linked fucose, N-acetylglucosamine and sialic acid. In infant formula, galactooligosaccharides (GOSs) are added to replace HMOs. This study investigated the ability of six strains of lactic acid bacteria (LAB), Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus reuteri, Streptococcus thermophilus and Leuconostoc mesenteroides subsp. cremoris, to digest HMO components, defined HMOs, and GOSs. All strains grew on lactose and glucose. N-acetylglucosamine utilization varied between strains and was maximal in L. plantarum; fucose utilization was low or absent in all strains. Both hetero- and homofermentative LAB utilized N-acetylglucosamine via the Embden-Meyerhof pathway. Lactobacillus acidophilus and L. plantarum were the most versatile in hydrolysing pNP analogues and the only strains releasing mono- and disaccharides from defined HMOs. Whole cells of all six LAB hydrolysed oNP-galactoside and pNP-galactoside indicating β-galactosidase activity. High β-galactosidase activity of L. reuteri, L. fermentum, S. thermophilus and L. mesenteroides subsp. cremoris whole cells correlated to lactose and GOS hydrolysis. Hydrolysis of lactose and GOSs by heterologously expressed β-galactosidases confirmed that LAB β-galactosidases are involved in GOS digestion. In summary, the strains of LAB used were not capable of utilizing complex HMOs but metabolized HMO components and GOSs.     

Reduction of non-digestible oligosaccharides in soymilk: application of engineered lactic acid bacteria that produce alpha-galactosidase

Human consumption of soy-derived products has been limited by the presence of non-digestible oligosaccharides (NDO), such as the alpha-galactooligosaccharides raffinose and stachyose. Most mammals, including man, lack pancreatic alpha-galactosidase (alpha-Gal), which is necessary for the hydrolysis of these sugars. However, such NDO can be fermented by gas-producing microorganisms present in the cecum and large intestine, which in turn can induce flatulence and other gastrointestinal disorders in sensitive individuals. The use of microorganisms expressing alpha-Gal is a promising solution to the elimination of NDO before they reach the large intestine. In the present study, lactic acid bacteria engineered to degrade NDO have been constructed and are being used as a tool to evaluate this solution. The alpha-Gal structural genes from Lactobacillus plantarum ATCC8014 (previously characterized in our laboratory) and from guar have been cloned and expressed in Lactococcus lactis. The gene products were directed to different bacterial compartments to optimize their possible applications. The alpha-Gal-producing strains are being evaluated for their efficiency in degrading raffinose and stachyose: i) in soymilk fermentation when used as starters and ii) in situ in the upper gastrointestinal tract when administered to animals orally, as probiotic preparations. The expected outcomes and possible complications of this project are discussed.     

Dynamics and biodiversity of populations of lactic acid bacteria and acetic acid bacteria involved in spontaneous heap fermentation of cocoa beans in Ghana

The Ghanaian cocoa bean heap fermentation process was studied through a multiphasic approach, encompassing both microbiological and metabolite target analyses. A culture-dependent (plating and incubation, followed by repetitive-sequence-based PCR analyses of picked-up colonies) and culture-independent (denaturing gradient gel electrophoresis [DGGE] of 16S rRNA gene amplicons, PCR-DGGE) approach revealed a limited biodiversity and targeted population dynamics of both lactic acid bacteria (LAB) and acetic acid bacteria (AAB) during fermentation. Four main clusters were identified among the LAB isolated: Lactobacillus plantarum, Lactobacillus fermentum, Leuconostoc pseudomesenteroides, and Enterococcus casseliflavus. Other taxa encompassed, for instance, Weissella. Only four clusters were found among the AAB identified: Acetobacter pasteurianus, Acetobacter syzygii-like bacteria, and two small clusters of Acetobacter tropicalis-like bacteria. Particular strains of L. plantarum, L. fermentum, and A. pasteurianus, originating from the environment, were well adapted to the environmental conditions prevailing during Ghanaian cocoa bean heap fermentation and apparently played a significant role in the cocoa bean fermentation process. Yeasts produced ethanol from sugars, and LAB produced lactic acid, acetic acid, ethanol, and mannitol from sugars and/or citrate. Whereas L. plantarum strains were abundant in the beginning of the fermentation, L. fermentum strains converted fructose into mannitol upon prolonged fermentation. A. pasteurianus grew on ethanol, mannitol, and lactate and converted ethanol into acetic acid. A newly proposed Weissella sp., referred to as "Weissella ghanaensis," was detected through PCR-DGGE analysis in some of the fermentations and was only occasionally picked up through culture-based isolation. Two new species of Acetobacter were found as well, namely, the species tentatively named "Acetobacter senegalensis" (A. tropicalis-like) and "Acetobacter ghanaensis" (A. syzygii-like).     

Production of natural folates by lactic acid bacteria starter cultures isolated from artisanal Argentinean yogurts

Folate is a B-group vitamin that cannot be synthesized by humans and must be obtained exogenously. Although some species of lactic acid bacteria (LAB) can produce folates, little is known about the production of this vitamin by yogurt starter cultures. Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains were isolated from artisanal Argentinean yogurts and were grown in folate-free culture medium (FACM) and nonfat milk after which intracellular and extracellular folate production were evaluated. From the initial 92 isolated LAB strains, 4 L. delbrueckii subsp. bulgaricus and 32 S. thermophilus were able to grow in the absence of folate. Lactobacillus delbrueckii subsp. bulgaricus CRL 863 and S.?thermophilus CRL 415 and CRL 803 produced the highest extracellular folate levels (from 22.3 to 135?μg/L) in FACM. In nonfat milk, these strains were able to increase the initial folate concentrations by almost 190%. This is the first report where native strains of L. delbrueckii subsp. bulgaricus were shown to produce natural folate. The LAB strains identified in this study could be used in developing novel fermented products bio-enriched in natural folates that could in turn be used as an alternative to fortification with the controversial synthetic chemical folic acid.     

Genetic screening of functional properties of lactic acid bacteria in a fermented pearl millet slurry and in the metagenome of fermented starchy foods

Lactic acid bacteria (LAB) (n = 152) in African pearl millet slurries and in the metagenomes of amylaceous fermented foods were investigated by screening 33 genes involved in probiotic and nutritional functions. All isolates belonged to six species of the genera Pediococcus and Lactobacillus, and Lactobacillus fermentum was the dominant species. We screened the isolates for the abilities to survive passage through the gastrointestinal tract and to synthesize folate and riboflavin. The isolates were also tested in vitro for their abilities to survive exposure to bile salts and to survive at pH 2. Because the ability to hydrolyze starch confers an ecological advantage on LAB that grow in starchy matrixes as well as improving the nutritional properties of the gruels, we screened for genes involved in starch metabolism. The results showed that genes with the potential ability to survive passage through the gastrointestinal tract were widely distributed among isolates and metagenomes, whereas in vitro tests showed that only a limited set of isolates, mainly those belonging to L. fermentum, could tolerate a low pH. In contrast, the wide distribution of genes associated with bile salt tolerance, in particular bsh, is consistent with the high frequency of tolerance to bile salts observed. Genetic screening revealed a potential for folate and riboflavin synthesis in both isolates and metagenomes, as well as high variability among genes related to starch metabolism. Genetic screening of isolates and metagenomes from fermented foods is thus a promising approach for assessing the functional potential of food microbiotas.     

Phenotypic and genotypic characteristics of lactic acid bacteria isolated from sour congee in Inner Mongolia of China

Sour congee is a popular food in the western regions of Inner Mongolia in China. It has a complex microbial population, which contributes to its unique flavor and functional properties. In this study, we chose 28 sour congee samples that were collected from different areas in Inner Mongolia for analysis of the microbial community of lactic acid bacteria (LAB) by classical biochemical tests, 16S rRNA gene sequencing, multiplex PCR assay of recA gene and restriction fragment length polymorphism (RFLP) analysis of the tuf gene (encoding elongation factor Tu). The results revealed that all the isolates were identified as Lactobacillus (L.) paracasei (38 strains), L. fermentum (28 strains), L. plantarum (7 strains), L. brevis (4 strains), L. reuteri (2 strains), L. amylolyticus (1 strain), Enterococcus (E.) faecalis (3 strains), E. italicus (2 strains) or Lactococcus lactis subsp. lactis (1 strain). The predominant LAB were L. casei and L. fermentum in sour congee samples. The diversity of LAB derived from sour congee could offer useful information for further research on sour congee, and the results demonstrated that the combination of tuf gene and RFLP patterns can be considered as a useful tool for differentiation of the L. casei group.     

Functionality of lactic acid bacteria peptidase activities in the hydrolysis of gliadin‐like fragments

Aims: To evaluate the role of the peptidase activities from sourdough lactic acid bacteria (LAB) in the degradation of α‐gliadin fragments. Methods and Results: Different proline‐containing substrates were hydrolysed by LAB indicating pro‐specific peptidase activities. Lactobacillus plantarum CRL 775 and Pediococcus pentosaceus CRL 792 displayed the highest tri‐ and di‐peptidase activities, respectively. Lactobacillus plantarum strains hydrolysed more than 60%α‐gliadin fragments corresponding to the 31–43 and 62–75 amino acids in the protein after 2 h. None of the LAB strains alone could hydrolyse 57–89 α‐gliadin peptide; however, the combination of L. plantarum CRL 775 and P. pentosaceus CRL 792 led to hydrolysis (57%) of this peptide in 8 h. Conclusions: The capacity of LAB strains to degrade α‐gliadin fragments was not correlated to individual peptidase activities. Several strains separately degraded the 31–43 and 62–75 α‐gliadin fragments, while the 57–89 peptide degradation was associated with the combination of peptidase profiles from pooled LAB strains. This is the first report on the peptide hydrolase system of sourdough pediococci and its ability to reduce α‐gliadin fragments. Significance and Impact of the Study: This study contributes to a better knowledge of sourdough LAB proteolytic system and its role in the degradation of proline‐rich α‐gliadin peptides involved in celiac disease.     

Influence of temperature and backslopping time on the microbiota of a type I propagated laboratory wheat sourdough fermentation

Sourdough fermentation is a cereal fermentation that is characterized by the formation of stable yeast/lactic acid bacteria (LAB) associations. It is a unique process among food fermentations in that the LAB that mostly dominate these fermentations are heterofermentative. In the present study, four wheat sourdough fermentations were carried out under different conditions of temperature and backslopping time to determine their effect on the composition of the microbiota of the final sourdoughs. A substantial effect of temperature was observed. A fermentation with 10 backsloppings (once every 24 h) at 23°C resulted in a microbiota composed of Leuconostoc citreum as the dominant species, whereas fermentations at 30 and 37°C with backslopping every 24 h resulted in ecosystems dominated by Lactobacillus fermentum. Longer backslopping times (every 48 h at 30°C) resulted in a combination of Lactobacillus fermentum and Lactobacillus plantarum. Residual maltose remained present in all fermentations, except those with longer backslopping times, and ornithine was found in almost all fermentations, indicating enhanced sourdough-typical LAB activity. The sourdough-typical species Lactobacillus sanfranciscensis was not found. Finally, a nonflour origin for this species was hypothesized.