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

Identification of Key Parameters Inducing Microbial Modulation during Backslopped Kombucha Fermentation

The aim of this study was to assess the impact of production parameters on the reproducibility of kombucha fermentation over several production cycles based on backslopping. Six conditions with varying oxygen accessibility (specific interface surface) and initial acidity (through the inoculation rate) of the cultures were carried out and compared to an original kombucha consortium and a synthetic consortium assembled from yeasts and bacteria isolated from the original culture. Output parameters monitored were microbial populations, biofilm weight, key physico-chemical parameters and metabolites. Results highlighted the existence of phases in microbial dynamics as backslopping cycles progressed. The transitions between phases occurred faster for the synthetic consortium compared to the original kombucha. This led to microbial dynamics and fermentative kinetics that were reproducible over several cycles but that could also deviate and shift abruptly to different behaviors. These changes were mainly induced by an increase in the Saccharomyces cerevisiae population, associated with an intensification of sucrose hydrolysis, sugar consumption and an increase in ethanol content, without any significant acceleration in the rate of acidification. The study suggests that the reproducibility of kombucha fermentations relies on high biodiversity to slow down the modulations of microbial dynamics induced by the sustained rhythm of backslopping cycles.

Various cold storage-backslopping cycles show the robustness of Limosilactobacillus fermentum IMDO 130101 as starter culture for Type 3 sourdough production

Type 3 sourdoughs, which are starter culture-initiated and subsequently backslopped, are less studied than other sourdough types. Yet, they can serve as a model to assess how competitive starter culture strains for sourdough production are and how the microbial composition of such sourdoughs may evolve over time. In the present study, Limosilactobacillus fermentum IMDO 130101 was used to produce Type 3 sourdoughs, prepared from wheat and wholemeal wheat flours. Therefore, an initial fermentation of the flour-water mixture was performed at 30 °C for 48 h. This was followed by cold storage-backslopping cycles, consisting of refreshments (50 %, v/v), fermentation steps of 16 h, and storage at 4 °C each week, every three weeks, and every six weeks. The microbial dynamics (culture-dependent and -independent approaches) and metabolite dynamics were measured. In all sourdoughs produced, starter culture strain monitoring, following an amplicon sequence variant approach, showed that Liml. fermentum IMDO 130101 prevailed during one month when the sourdoughs were refreshed each week, during 24 weeks when the sourdoughs were refreshed every three weeks, and during 12 weeks when the sourdoughs were refreshed every six weeks. This suggested the competitiveness and robustness of Liml. fermentum IMDO 130101 for a considerable duration but also showed that the strain is prone to microbial interference. For instance, Levilactobacillus brevis and Pediococcus spp. prevailed upon further cold storage and backslopping. Also, although no yeasts were inoculated into the flour-water mixtures, Kazachstania unispora, Torulaspora delbrueckii, and Wickerhamomyces anomalus were the main yeast species found. They appeared after several weeks of storage and backslopping, which however indicated the importance of an interplay between LAB and yeast species in sourdoughs. The main differences among the mature sourdoughs obtained could be explained by the different flours used, the refreshment conditions applied, and the sampling time (before and after backslopping). Finally, the metabolite quantifications revealed continued metabolite production during the cold storage periods, which may impact the sourdough properties and those of the breads made thereof.

Hierarchical Effects of Lactic Fermentation and Grain Germination on the Microbial and Metabolomic Profile of Rye Doughs

A multi-omics approach was adopted to investigate the impact of lactic acid fermentation and seed germination on the composition and physicochemical properties of rye doughs. Doughs were prepared with either native or germinated rye flour and fermented with Saccharomyces cerevisiae, combined or not with a sourdough starter including Limosilactobacillus fermentum, Weissella confusa and Weissella cibaria. LAB fermentation significantly increased total titrable acidity and dough rise regardless of the flour used. Targeted metagenomics revealed a strong impact of germination on the bacterial community profile of sprouted rye flour. Doughs made with germinated rye displayed higher levels of Latilactobacillus curvatus, while native rye doughs were associated with higher proportions of Lactoplantibacillus plantarum. The oligosaccharide profile of rye doughs indicated a lower carbohydrate content in native doughs as compared to the sprouted counterparts. Mixed fermentation promoted a consistent decrease in both monosaccharides and low-polymerization degree (PD)-oligosaccharides, but not in high-PD carbohydrates. Untargeted metabolomic analysis showed that native and germinated rye doughs differed in the relative abundance of phenolic compounds, terpenoids, and phospholipids. Sourdough fermentation promoted the accumulation of terpenoids, phenolic compounds and proteinogenic and non-proteinogenic amino acids. Present findings offer an integrated perspective on rye dough as a multi-constituent system and on cereal-sourced bioactive compounds potentially affecting the functional properties of derived food products.

Chinese traditional sourdough steamed bread made by retarded sponge-dough method: Microbial dynamics, metabolites changes and bread quality during continuous propagation

Continuous propagation of Chinese traditional sourdough (CTS) was adopted to simulate the industrial production of sourdough steamed bread made by retarded sponge-dough method (SSB). Establishment of a stable microbial ecosystem occurred in mature sourdough within four days of continuous propagation, as revealed by both microbial and metabolic analyses. Lactobacillus sanfranciscensis and Kazachstania humilis were the predominant bacterial and fungal species in mature sourdoughs. Their relative abundances changed significantly from the first to third day of continuous propagation while exhibited relatively constant from the fourth day onwards despite the use of flour/water for each back-slopping step. Major changes in the metabolites and fermentative characteristics were observed during the initial three days and dough samples showed little temporal metabolic and fermentative variations from the fourth days onwards. Consequently, volumetric and textural properties as well as the volatile flavor compounds of SSB displayed rather high stability from the fourth day onwards.

Nutritional benefits of sourdoughs: A systematic review

Food fermentation using sourdough-i.e., consortia of lactic bacteria and yeasts-is increasingly considered among the public as a natural transformation yielding nutritional benefits; however, it is unclear whether its alleged properties are validated by science. The aim of this study was to systematically review the clinical evidence related to the effect of sourdough bread on health. Bibliographic searches were performed in 2 different databases (The Lens and PubMed) up to February 2022. Eligible studies were randomized controlled trials involving adults, healthy or not, given any type of sourdough bread compared with those given any type of yeast bread. A total of 573 articles were retrieved and investigated, of which 25 clinical trials met the inclusion criteria. The 25 clinical trials included a total of 542 individuals. The main outcomes investigated in the retrieved studies were glucose response (N = 15), appetite (N = 3), gastrointestinal markers (N = 5), and cardiovascular markers (N = 2). Overall, it is currently difficult to establish a clear consensus with regards to the beneficial effects of sourdough per se on health when compared with other types of bread because a variety of factors, such as the microbial composition of sourdough, fermentation parameters, cereals, and flour types potentially influence the nutritional properties of bread. Nonetheless, in studies using specific strains and fermentation conditions, significant improvements were observed in parameters related to glycemic response, satiety, or gastrointestinal comfort after bread ingestion. The reviewed data suggest that sourdough has great potential to produce a variety of functional foods; however, its complex and dynamic ecosystem requires further standardization to conclude its clinical health benefits.

Effects of Lactobacillus plantarum and Saccharomyces cerevisiae co-fermentation on the structure and flavor of wheat noodles

BACKGROUND

Although traditional fermented noodles possess high eating quality, it is difficult to realize large-scale industrialization as a result of the complexity of spontaneous fermentation. In present study, commercial Lactobacillus plantarum and Saccharomyces cerevisiae were applied in the preparation of fermented noodles.

RESULTS

The changes in the structural characteristics and aroma components of noodles after fermentation were investigated via scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), low-field magenetic resonance imaging, electronic nose, and simultaneous distillation and extraction/gas chromatography-mass spectrometry (GC-MS) analysis. SEM images revealed that co-fermentation of the L. plantarum and S. cerevisiae for 10-40 min enhanced the continuity of the gluten network and promoted the formation of pores. FTIR spectra analysis showed that the co-fermentation increased significantly (P < 0.05) the proportion of α-helices of noodles gluten protein, enhancing the orderliness of the molecular structure of protein. After fermentation for 10-40 min, the signal density of hydrogen protons increased from the surface to the core, indicating that the water in the noodles migrated inward during a short fermentation process. The results of multivariate statistical analysis demonstrated that the main aroma differences between unfermented and fermented noodles were mainly in hydrocarbons, aromatic compounds and inorganic sulfides. GC-MS analysis indicated that the main volatile compounds detected were 2, 4-di-tert-butylphenol, bis (2-ethylhexyl) adipate, butyl acetate, dibutyl phthalate, dioctyl terephthalate, bis (2-ethylhexyl) phthalate, pentanol and 2-pentylfuran, etc. CONCLUSION: Co-fermentation with L. plantarum and S. cerevisiae improved the structure of gluten network and imparted more desirable volatile components to wheat noodles. © 2022 Society of Chemical Industry.

Rapid sourdough yeast identification using panfungal PCR combined with high resolution melting analysis

The microbial composition of the sourdough starter affects the sourdough bread properties. Therefore, it is crucial to find a tool for rapid, time-saving, and economical identification of the sourdough microbiota. We focused on the rapid identification of sourdough yeasts. We designed a panfungal real time-PCR targeting the ITS2 region (ITS-amplicon) and a fragment of D1/D2 region of 26S rRNA gene (U-amplicon) and used high resolution melting analysis (HRM) for subsequent species identification. The sensitivity and specificity of our method were tested on the reference yeast cultures. We obtained divergent melting peaks (Tm). The further analysis of melt curves suggests the possibility to discriminate yeasts on the genus- and some on species-specific level in the mixed sample. The applicability of this method in routine practice was evaluated on nine sourdough samples. Revealed melt curves of U-amplicons were predominantly characteristic of the sourdough. The evaluation of the Tm and the shape of the melt curve was used to assess the sourdough yeasts. Additionally, using the HRM-PCR method the contamination with the ergot fungus DNA was revealed. Our data showed HRM-PCR is a simple, rapid, and inexpensive tool useful in identifying sourdough yeasts.

Backslopping Time, Rinsing of the Grains During Backslopping, and Incubation Temperature Influence the Water Kefir Fermentation Process

For eight backslopping steps, eight series of water kefir fermentation processes differing in backslopping time and rinsing of the grains during each backslopping step and eight series of fermentation processes differing in incubation temperature and backslopping time were followed. Short backslopping times resulted in high relative abundances of Liquorilactobacillus nagelii and Saccharomyces cerevisiae, intermediate backslopping times in high relative abundances of Leuconostoc pseudomesenteroides, and long backslopping times in high relative abundances of Oenococcus sicerae and Dekkera bruxellensis. When the grains were rinsed during each backslopping step, the relative abundances of Lentilactobacillus hilgardii and Leuc. pseudomesenteroides increased and those of D. bruxellensis and Liql. nagelii decreased. Furthermore, rinsing of the grains during each backslopping step resulted in a slightly higher water kefir grain growth and lower metabolite concentrations. The relative abundances of Liquorilactobacillus mali were highest at 17°C, those of Leuc. pseudomesenteroides at 21 and 25°C, and those of Liql. nagelii at 29°C. With a kinetic modeling approach, the impact of the temperature and rinsing of the grains during the backslopping step on the volumetric production rates of the metabolites was determined.

In vitro Prebiotic Effect of Bread-Making Process in Inflammatory Bowel Disease Microbiome

Inflammatory bowel disease (IBD), including its two main categories (Crohn's disease and ulcerative colitis), has been linked both to gut microbiota and to diet. Bread is a daily food that has a potential capacity as a prebiotic. Our aim was to evaluate different bread-making processes and their effect on fecal colonic microbiota in IBD patients. The microbial composition of several sourdoughs and dough samples was analyzed by high-throughput sequencing of 16S and 18S rRNA genes. Three types of bread, which followed different bread-making processes, were in vitro digested and incubated with feces from IBD patients. Changes in gut microbiota were assessed by a quantitative polymerase chain reaction using specific bacterial sequence targets. Short-chain fatty acid production was also analyzed by gas chromatography. Lactobacillus sanfranciscensis was the dominant lactic acid bacteria species found in sourdough and bread doughs prepared using sourdough, whereas Saccharomyces cerevisiae was the most dominant yeast in all groups, especially in bread doughs before baking. Differences in microbial composition in raw bread doughs were more related to the type of dough and elaboration than to fermentation time lengths. The analysis of in vitro fecal incubations with bread conditions revealed an increase in most bacterial groups analyzed and short-chain fatty acid production, both in Crohn's disease and ulcerative colitis samples. Most remarkable increases in short-chain fatty acid production mirrored higher abundances of Roseburia species. The potential prebiotic properties observed were mainly obtained when using a high quantity of bread, regardless of bread type. Overall, this study highlights the bacterial dynamics within the bread-making process and the potential prebiotic effect in IBD patients.

Sourdough production: fermentation strategies, microbial ecology, and use of non-flour ingredients

Sourdough production is an ancient method to ferment flour from cereals for the manufacturing of baked goods. This review deals with the state-of-the-art of current fermentation strategies for sourdough production and the microbial ecology of mature sourdoughs, with a particular focus on the use of non-flour ingredients. Flour fermentation processes for sourdough production are typically carried out by heterogeneous communities of lactic acid bacteria and yeasts. Acetic acid bacteria may also occur, although their presence and role in sourdough production can be criticized. Based on the inoculum used, sourdough productions can be distinguished in fermentation processes using backslopping procedures, originating from a spontaneously fermented flour-water mixture (Type 1), starter culture-initiated fermentation processes (Type 2), and starter culture-initiated fermentation processes that are followed by backslopping (Type 3). In traditional recipes for the initiation and/or propagation of Type 1 sourdough productions, non-flour ingredients are often added to the flour-water mixture. These ingredients may be the source of an additional microbial inoculum and/or serve as (co-)substrates for fermentation. An example of the former is the addition of yoghurt; an example of the latter is the use of fruit juices. The survival of microorganisms transferred from the ingredients to the fermenting flour-water mixture depends on the competitiveness toward particular strains of the microbial species present under the harsh conditions of the sourdough ecosystem. Their survival and growth is also determined by the presence of the appropriate substrates, whether or not carried over by the ingredients added.

Sourdough Microbiome Comparison and Benefits

Sourdough is the oldest form of leavened bread used as early as 2000 BC by the ancient Egyptians. It may have been discovered by accident when wild yeast drifted into dough that had been left out resulting in fermentation of good microorganisms, which made bread with better flavour and texture. The discovery was continued where sourdough was produced as a means of reducing wastage with little known (at that point of time) beneficial effects to health. With the progress and advent of science and technology in nutrition, sourdough fermentation is now known to possess many desirable attributes in terms of health benefits. It has become the focus of attention and practice in modern healthy eating lifestyles when linked to the secret of good health. The sourdough starter is an excellent habitat where natural and wild yeast plus beneficial bacteria grow by ingesting only water and flour. As each sourdough starter is unique, with different activities, populations and interactions of yeast and bacteria due to different ingredients, environment, fermentation time and its carbohydrate fermentation pattern, there is no exact elucidation on the complete make-up of the sourdough microbiome. Some lactic acid bacteria (LAB) strains that are part of the sourdough starter are considered as probiotics which have great potential for improving gastrointestinal health. Hence, from a wide literature surveyed, this paper gives an overview of microbial communities found in different sourdough starters. This review also provides a systematic analysis that identifies, categorises and compares these microbes in the effort of linking them to specific functions, particularly to unlock their health benefits.

Investigating the growth kinetics in sourdough microbial associations

In this study we investigated the effect of the single strain in stabilization of type I sourdough microbial associations by crossing six different Fructilactobacillus sanfranciscensis with five Kazachstania humilis strains. Furthermore, we compared three predictive models, Zwitwering based on Gompertz's equation, Baranyi and Roberts' function and Schiraldi's function to evaluate which one best fitted the experimental data in determining the behaviour of co-cultivated microorganisms. Specific growth rates (μ_m) and lag time (λ) values for each mixed population were assessed. Results showed that the different F. sanfranciscensis strains significantly steer the growth kinetics within the pair and affect the ratio bacterial/yeast cells, as data analysis confirmed, whereas K. humilis accommodates to the bacterial strain. To compare the growth models, Root Mean Square (RMS) values were calculated for each predicted curve by implementing an algorithm based on an iterative process to minimize the deviation among observed and calculated data. Schiraldi's function performed better than the others, revealing, on average, the smallest RMS values and providing the best fitting for over 70% of co-cultivation experiments. Models prove to be consistent in predicting growth kinetics of microbial consortia too.

Overcoming bread quality decay concerns: main issues for bread shelf life as a function of biological leavening agents and different extra ingredients used in formulation. A review

As is widely accepted, the quality decay of freshly baked bread that affects product shelf life is the result of a complex multifactorial process that involves physical staling, together with microbiological, chemical and sensorial spoilage. In this context, this paper provides a critical review of the recent literature about the main factors affecting shelf life of bread during post-baking. An overview of the recent findings about the mechanism of bread staling is firstly provided. Afterwards, the effect on staling induced by baker's yeasts and sourdough as well as by the extra ingredients commonly utilized for bread fortification is also addressed and discussed. As inclusion/exclusion criteria, only papers dealing with wheat bread and not with long-life bread or gluten-free bakery products are taken into consideration. Despite recent developments in international scientific literature, the whole mechanism that induces bread staling is far from being completely understood and the best analytical methods to be adopted to measure and/or describe in depth this process appear still debated. In this topic, the effects induced on bread shelf life by the use of biological leavening agents (baker's yeasts and sourdough) as well as by some extra ingredients included in the bread recipe have been individuated as two key issues to be addressed and discussed in terms of their influence on the kinetics of bread staling. © 2020 Society of Chemical Industry.

The effects of dynamic bacterial succession on the flavor metabolites during Baijiu fermentation

The succession of microbial community significantly affect the flavor formation of traditional fermented foods and beverages. Chinese liquor (Baijiu) fermentation is a typical spontaneous solid-state fermentation process driven by natural microbiota. The type of process used to make liquor-craft or industrial-alters the operational environment and the aromatic qualities of the product contributed by various microbial consortia. But differences in microbial community assembly and temporal succession are often overlooked. In this study, we investigated bacterial community dynamics, substrate consumption, and metabolite production during both craft and industrial liquor-making processes (CLP and ILP, respectively). We found that the compositions of bacterial communities were different, even though no significant difference (p > 0.05) was observed in bacterial species between CLP and ILP at the beginning of fermentation. During ILP, glucose was used more rapidly by microflora, leading in turn to a higher ethanol production rate during the early stage of fermentation. The higher rate of ethanol production in ILP shortened the lifetime of bacteria such as Weissella, Pediococcus, Leuconostoc, and Bacillus during the early stage of fermentation. Lactobacillus sp. became dominant earlier in ILP than in CLP. Finally, the change in bacterial community dynamics led to changes in aroma compounds. Using CLP and ILP as a model system, our results illustrate the dynamic nature of Baijiu fermentations and microbial succession patterns therein. This can be applied to optimize the fermentation processes and flavors attributes of this and other fermented foods.

Reducing FODMAPs and improving bread quality using type II sourdough with selected starter cultures

This study focussed on lactic acid bacteria (LAB) screening for sourdough type II elaboration and evaluating the effects of sourdough fermentation in bread making, focussing mainly on reducing FODMAPs. After a technological performance screening, six strains (Levilactobacillus brevis, Weissella minor, Lactiplantibacillus plantarum, Leuconostoc citreum, Limosilactobacillus fermentum, and Companilactobacillus farciminis) were selected for sourdough preparation. Total titratable acidity, pH, specific volume, and enumeration of microorganisms were carried out on sourdoughs, doughs, and breads. Breads were subjected to texture profile and colour analysis, moulds and yeast enumeration, and total fructans (main group of FODMAPs) quantification. Breads produced with sourdough showed a significant reduction of fructans, greater acidity, volume, and better performance during storage when compared to fermentation using only baker's yeast. Including specific cultures as starters in sourdough reduced fructans content by >92%, thereby producing a low FODMAP bread suitable for Irritable Bowel Syndrome patients with improved nutritional and technological properties.

Diversity and dynamics of sourdough lactic acid bacteriota created by a slow food fermentation system

Sourdough is a naturally fermented dough that is used worldwide to produce a variety of baked foods. Various lactic acid bacteria (LAB), which can determine the quality of sourdough baked foods by producing metabolites, have been found in the sourdough ecosystem. However, spontaneous fermentation of sourdough leads to unpredictable growth of various micro-organisms, which result in unstable product quality. From an ecological perspective, many researchers have recently studied sourdough LAB diversity, particularly the elucidation of LAB community interactions and the dynamic mechanisms during the fermentation process, in response to requests for the control and design of a desired sourdough microbial community. This article reviews recent advances in the study of sourdough LAB diversity and its dynamics in association with unique characteristics of the fermentation system; it also discusses future perspectives for better understanding of the complex sourdough microbial ecosystem, which can be attained efficiently by both in vitro and in situ experimental approaches.

The influence of backslopping on lactic acid bacteria diversity in tarhana fermentation

Tarhana is produced at batch systems in which the microbiota has changed accordingly to the microbial load from ingredients. In order to stabilize the microbiota, the effects of backslopping carried out under different temperature regimes (25 and 30 °C), pH (3.70 and 4.00) and inoculation rates (5, 10 and 15%) on lactic acid bacteria (LAB) diversity were determined in tarhana dough. LAB and Total Aerobic Mesophilic Bacteria (TAMB) numbers increased in all tarhana dough samples subjected to backslopping. Temperature and pH significantly affected the microbiological diversity of tarhana whereas the different inoculation rates did not. Tarhana dough showed complex tarhana microbiota following backslopping at pH 4.00 independently on the temperature applied. When backslopping was carried out at pH 3.70 and 25 °C, tarhana microbiota stabilized and became steady after several cycles. The LAB species found in all dough samples after the final backslopping were Lactobacillus plantarum, Lactobacillus alimentarius and Lactobacillus brevis which were able to carry out the fermentation in all conditions tested. In order to obtain a stable presence of LAB populations at industrial level for tarhana production, this work showed that backslopping is recommended at pH 3.70 and 25 °C with any inoculation ratios.

Comparison of backslopping and two-stage fermentation methods for koumiss powder production based on chemical composition and nutritional properties

BACKGROUND

Koumiss is a traditional fermented beverage made from mare's milk. The traditional backslopping method for koumiss production has shortcomings in terms of microbiological diversity and nutritional characteristics. In this study, a two-stage fermentation method was established to scale up the production of koumiss powder. The chemical composition and nutritional properties of a novel two-stage fermentation koumiss powder (TKP) were compared with backslopping koumiss powder (BKP).

RESULTS

The TKP exhibited important nutritional and functional properties, including a high percentage of essential amino acids, and high polyunsaturated fatty acid, vitamin, and mineral content. The essential amino acid content of TKP was not significantly different from that of BKP. The oleic acid, linoleic acid, linolenic acid, and water-soluble vitamin content of TKP was higher than that of BKP. The Ca:P ratio of TKP was also close to the optimal Ca:P ratio in humans.

CONCLUSION

The novel method could be applied for the scaled-up production of koumiss powder with similar nutritional properties to traditional backslopping koumiss powder. The successful production of koumiss powder could also promote the development of the koumiss industry. © 2019 Society of Chemical Industry.

Bacterial community dynamics in spontaneous sourdoughs made from wheat, spelt, and rye wholemeal flour

Sourdough fermentation is a traditional process that is used to improve bread quality. A spontaneous sourdough ecosystem consists of a mixture of flour and water that is fermented by endogenous lactic acid bacteria (LAB) and yeasts. The aim of this study was to identify bacterial diversity during backslopping of spontaneous sourdoughs prepared from wheat, spelt, or rye wholemeal flour. Culture-dependent analyses showed that the number of LAB (10⁹  CFU/ml) was higher by three orders of magnitude than the number of yeasts (10⁶  CFU/ml), irrespective of the flour type. These results were complemented by next-generation sequencing of the 16S rDNA V3 and V4 variable regions. The dominant phylum in all sourdough samples was Firmicutes, which was represented exclusively by the Lactobacillales order. The two remaining and less abundant phyla were Proteobacteria and Bacteroidetes. The culture-independent approach allowed us to detect changes in microbial ecology during the 72-hr fermentation period. Weissella sp. was the most abundant genus after 24 hr of fermentation of the rye sourdough, but as the process progressed, its abundance decreased in favor of the Lactobacillus genus similarly as in wheat and spelt sourdoughs. The Lactobacillus genus was dominant in all sourdoughs after 72 hr, which was consistent with our results obtained using culture-dependent analyses. This work was carried out to determine the microbial biodiversity of sourdoughs that are made from wheat, spelt, and rye wholemeal flour and can be used as a source of strains for specific starter cultures to produce functional bread.

Relation Between Gut Microbiota Composition and Traditional Spontaneous Fermented Dairy Foods Among Kazakh Nomads in Xinjiang, China

The human gastrointestinal tract represents one of the most densely populated microbial ecosystems studied to date. Although this microbial consortium has been recognized to have a crucial impact on human health, its precise composition is still subject to intense investigation, as people from different regions have different gut microbiota structures. The Kazakh nomads in Xinjiang, China still retain their nomadic lifestyle and traditional diet. Their specific diet style and ancient genetic background shaped their gut microbiota to contain unique characteristics. In present study, the compositions of the gut microbiota and fermented dairy foods were assessed by high-throughput sequencing of the 16S rRNA gene. Twenty-nine Kazakh nomads were recruited, and 33 traditional fermented dairy foods were collected from five pasturing areas (Buerjin, Zhaosu, Nilka, Tekes, and Fuhai) in northern Xinjiang, China. The correlation of the physical index with the gut microbiota was also analyzed. The unique diet style of Kazakh may be a critical factor in keeping their gut microbiota in a balanced state and help them to remain in good health. PRACTICAL APPLICATION: This research shows that the consumption of spontaneous fermented dairy food plays an important role in increasing gut microbial diversity. Some probiotics in fermented dairy food, such as Bifidobacterium and Lactobacillus, have positive correlation with human body health index such as body mass index and blood glucose. These may provide some theoretical supports to adjuvant therapy of obesity and diabetes through scientific dietary intervention.

Application of antifungal lactobacilli in combination with coatings based on apple processing by-products as a bio-preservative in wheat bread production

In this study various coatings from apple press cake (AP) with immobilized antifungal bacterial cells were used for bread surface treatment to increase anti-moulding effect. The antifungal effect and technological properties of newly isolated Lactobacillus coryniformis LUHS71, L. curvatus LUHS51, L. farraginis LUHS206 and Leuconostoc mesenteroides LUHS225 strains. Then, the lactobacilli were tested for the effects of incorporation of sourdough on acrylamide formation in bread and antifungal effect against moulds commonly associated with bread spoilage. The addition of 15-20% of sourdoughs significantly (p = 0.0001) improved bread volume and crumb porosity depending on LAB strain, and reduced acrylamide formation on average by 23% (for LUHS51 and LUHS206) by 54% (for LUHS71 and LUHS225) compared to control bread. Additionally, the use of AP-LAB coatings prolonged shelf life from 3 to 6 days for control bread, and up to 9 days for sourdough breads. The combination of antifungal LAB sourdough and the AP-LAB coating leads to produce high quality bread with extended shelf life and would be a new and promising environmentally-friendly technological alternative.

Lactic Acid Bacterium Population Dynamics in Artisan Sourdoughs Over One Year of Daily Propagations Is Mainly Driven by Flour Microbiota and Nutrients

This study aimed to: (i) assess at what extent traditional, daily propagated, sourdough can be considered a stable microbial ecosystem; (ii) ascertain the drivers of stability/variability. For this purpose, samples of sourdough, flour and environment were collected over 1 year from three different bakeries located in Altamura, Castellana Grotte, and Matera. Culture-dependent and –independent analyses were carried out on all the samples. In addition, sourdough and flour were subjected to biochemical characterization. In all the sourdoughs sampled at the same bakery, cell density of lactic acid bacteria fluctuated of one-two log cycles. However, 16S metagenetic analysis showed that sourdough bacterial microbiota was remarkably stable, in terms of species. Yet, some differences were found during time at intra-specific level. Indeed, bacterial strains succeeded in a 1-year lapse of time or even in 6-months, such as in the case of strains isolated from Altamura sourdough samples. Residual carbohydrates, lactic acid, ethanol and free amino acids varied in the same sourdough collected at different sampling times. These variations could be attributed to combination of various factors, such as fermentation temperature and strain succession. In addition, concentration of flour nutrients varied over 1 year and, in some cases, in a shorter time lapse. This may have favored certain strains over others. For this reason and also because of its inherent contamination by lactic acid bacteria, we found flour as the major driver of strains succession.

Impact of process conditions on the microbial community dynamics and metabolite production kinetics of teff sourdough fermentations under bakery and laboratory conditions

Teff and teff sourdoughs are promising ingredients for bread production. Therefore, this study aimed at the characterization of spontaneous and flour-native starter culture-initiated teff sourdough productions under bakery and laboratory conditions. Backslopped laboratory and bakery teff sourdough productions were characterized by different lactic acid bacteria (LAB) and yeast species, but were both characterized by a pH below 4.0 after five backslopping steps. The sourdough-associated Lactobacillus sanfranciscensis was isolated for the first time from backslopped spontaneous teff sourdoughs. The autochthonous strain L. sanfranciscensis IMDO 150101 was tested as starter culture during laboratory teff sourdough fermentations. Its prevalence could be related to the process conditions applied, in particular the ambient temperature (below 30°C). Breads made with 20% teff sourdough (on flour basis) displayed interesting features compared with all-wheat-based reference breads. Teff sourdoughs were characterized as to their pH evolution, microbial community dynamics, and microbial species composition. Representative strains of the LAB species isolated from these sourdoughs, in particular L. sanfranciscensis, may be selected as starter cultures for the production of stable teff sourdoughs and flavorful breads, provided they are adapted to the environmental conditions applied.

Performance of Leuconostoc citreum FDR241 during wheat flour sourdough type I propagation and transcriptional analysis of exopolysaccharides biosynthesis genes

This study focused on the performance of the dextran producer Leuconostoc citreum as starter culture during 30 days of wheat flour type I sourdough propagation (back-slopping). As confirmed by RAPD-PCR analysis, the strain dominated throughout the propagation procedure, consisting of daily fermentations at 20 °C. The sourdoughs were characterized by consistent lactic acid bacteria cell density and acidification parameters, reaching pH values of 4.0 and mild titratable acidity. Carbohydrates consumption remained consistent during the propagation procedure, leading to formation of mannitol and almost equimolar amount of lactic and acetic acid. The addition of sucrose enabled the formation of dextran, inducing an increase in viscosity of the sourdough of 2-2.6 fold, as well as oligosaccharides. The transcriptional analysis based on glucosyltransferases genes (GH70) showed the existence in L. citreum FDR241 of at least five different dextransucrases. Among these, only one gene, previously identified as forming only α-(1-6) glycosidic bonds, was significantly upregulated in sourdough fermentation conditions, and the main responsible of dextran formation. A successful application of a starter culture during long sourdough back-slopping procedure will depend on the strain robustness and fermentation conditions. Transcriptional regulation of EPS-synthetizing genes might contribute to increase the efficiency of industrial processes.

Genotyping of Lactobacillus sanfranciscensis isolates from Chinese traditional sourdoughs by multilocus sequence typing and multiplex RAPD-PCR

Lactobacillus sanfranciscensis is the predominant lactic acid bacteria (LAB) species in Chinese traditional sourdoughs and conduces to the flavor and rheology properties of Chinese steamed bread, a staple food originated in China over 1500years ago. The aim of this study is to describe the intraspecific diversity of 98 L. sanfranciscensis isolates from 11 Chinese traditional sourdoughs in different regions by multilocus sequence typing (MLST) and multiplex random amplified polymorphic DNA-polymerase chain reaction (multiplex RAPD-PCR). MLST scheme was reduced from six gene fragments (gdh, gyrA, mapA, nox, pgmA and pta) to five (gdh, gyrA, mapA, nox and pta) since the fragment of pgmA displayed only one allele. 10 different sequence types (STs) were revealed by MLST and 6 of them containing 79.8% of the isolates were classified into one clonal complex, demonstrating a close relationship among them. The multiplex-RAPD analysis was performed by employing the combined primers OPL-05+RD1 and divided the 98 L. sanfranciscensis isolates into 6 types with the similarity level of 70%. According to the result, it seems that the genotypic variations of L. sanfranciscensis strains showed by MLST have no relations to geographical origin. MLST seems to have a higher discriminatory power compared with multiplex-RAPD since it produced more groups, but multiplex-RAPD could help to distinguish some strains in the same ST. Hence, an optimal genotypic characterization of L. sanfranciscensis was obtained under the combination of MLST and multiplex-RAPD analysis, targeting different genetic variations.

Microbial Ecology and Process Technology of Sourdough Fermentation

From a microbiological perspective, sourdough is to be considered as a specific and stressful ecosystem, harboring yeasts and lactic acid bacteria (LAB), that is used for the production of baked goods. With respect to the metabolic impact of the sourdough microbiota, acidification (LAB), flavor formation (LAB and yeasts), and leavening (yeasts and heterofermentative LAB species) are most noticeable. Three distinct types of sourdough fermentation processes can be discerned based on the inocula applied, namely backslopped ones (type 1), those initiated with starter cultures (type 2), and those initiated with a starter culture followed by backslopping (type 3). A sourdough-characteristic LAB species is Lactobacillus sanfranciscensis. A sourdough-characteristic yeast species is Candida humilis. Although it has been suggested that the microbiota of a specific sourdough may be influenced by its geographical origin, region specificity often seems to be an artefact resulting from interpretation of the research data, as those are dependent on sampling, isolation, and identification procedures. It is however clear that sourdough-adapted microorganisms are able to withstand stress conditions encountered during their growth. Based on the technological setup, type 0 (predoughs), type I (artisan bakery firm sourdoughs), type II (industrial liquid sourdoughs), and type III sourdoughs (industrial dried sourdoughs) can be distinguished. The production of all sourdoughs, independent of their classification, depends on several intrinsic and extrinsic factors. Both the flour (type, quality status, etc.) and the process parameters (fermentation temperature, pH and pH evolution, dough yield, water activity, oxygen tension, backslopping procedure and fermentation duration, etc.) determine the dynamics and outcome of (backslopped) sourdough fermentation processes.