Microbial ecology of sourdough fermentations: diverse or uniform?

Developing lactic acid bacteria starter cultures for wholemeal rye flour bread with improved functionality, nutritional value, taste, appearance and safety

Starter cultures composed of lactic acid bacteria (LAB) were developed based on the genotypic and phenotypic characterisation of isolates belonging to dominant groups of bacteria in spontaneous rye wholemeal sourdoughs. Combinations of strains have been evaluated on an industrial scale in the sourdough fermentation process. Wholemeal rye bread was prepared using sourdoughs obtained with 3 new starter cultures, and compared to bread made using the commercial culture (LV2). All newly developed cultures used for the preparation of wholemeal rye bread allowed to obtain better quality products as compared to the LV2 based bread. The best results were obtained when the culture containing Lactiplantibacillus plantarum 2MI8 and exopolysaccharide (EPS)-producing Weissella confusa/cibaria 6PI3 strains was applied. The addition of yeast during sourdough breads production, especially the one prepared from mentioned above starter culture, significantly improved their organoleptic properties, their volume and crumb moisture was increased, and also the crumb acidity and hardness was reduced. Fermentation of rye wholemeal dough, especially without the yeast addition, resulted in a significant reduction in the content of higher inositol phosphates as compared to the applied flour, which is associated with improved bioavailability of minerals. The results of this study prove that the investigated new starter cultures can be successfully applied in wholemeal rye bread production.

Phenotypic and genotypic characterisation of Lactobacillus and yeast isolates from a traditional New Zealand Māori potato starter culture

Parāroa Rēwena is a traditional Māori sourdough produced by fermentation using a potato starter culture. The microbial composition of the starter culture is not well characterised, despite the long history of this product. The morphological, physiological, biochemical and genetic tests were conducted to characterise 26 lactic acid bacteria (LAB) and 15 yeast isolates from a Parāroa Rēwena potato starter culture. The results of sugar fermentation tests, API 50 CHL tests, and API ID 32 C tests suggest the presence of four different LAB phenotypes and five different yeast phenotypes. 16S rRNA and 26S rRNA sequencing identified the LAB as Lacticaseibacillus paracasei and the yeast isolates as Saccharomyces cerevisiae, respectively. Multilocus sequence typing (MLST) of the L. paracasei isolates indicated that they had identical genotypes at the MLST loci, to L. paracasei subsp. paracasei IBB 3423 or L. paracasei subsp. paracasei F19. This study provides new insights into the microbial composition of the traditional sourdough Parāroa Rēwena starter culture.

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16S sequencing, Multilocus sequencing typing for LAB in the potato starter culture.

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26S sequencing for yeast in the starter culture.

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Lacticaseibacillus paracasei subsp. paracasei IBB3423.

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Lacticaseibacillus paracasei subsp. paracasei F19.

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Saccharomycescerevisiae.

Optimization of a cultivation procedure to selectively isolate lactic acid bacteria from insects

AIMS

Natural niches and transmission routes of lactic acid bacteria (LAB) are highly versatile. Proposed routes of transmission to food fermentations are from plant material via insects or vice versa. This study aimed to establish a method for the selective isolation of LAB from insects.

METHODS AND RESULTS

Varied parameters that influence growth and selectivity are temperature, type of carbohydrate and atmosphere. Additionally, effects of antibiotics to suppress non-LAB species were evaluated. A model consortium consisting of 12 species representing different lifestyles was inoculated in growth medium to identify conditions for highest diversity and recovery rate. The method was applied to isolate LAB from Drosophila melanogaster, Sitotroga cerealella, Tribolium castaneum and Tenebrio molitor. Isolated species were Leuconostoc mesenteroides, Paucilactobacillus vaccinostercus and Lactiplantibacillus plantarum from D. melanogaster and L. mesenteroides, Pediococcus pentosaceus and Latilactobacillus curvatus from T. molitor. No LAB could be isolated from T. castaneum and S. cerealella. 16S rDNA amplicon sequencing of DNA obtained from insects corroborated part of our results.

CONCLUSION

A combination of different enrichment conditions ensures a high probability to isolate LAB species from insects and can be helpful above already known non-cultivation methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

The novel method allows to selectively isolate LAB from insects and the strategy of the method is of interest to study other niches.

Apple Pomace as a Sustainable Substrate in Sourdough Fermentation

Innovations range from food production, land use, and emissions all the way to improved diets and waste management. Global apple production has amounted to over 87 million tons/year, while 18% are processed, resulting in 20-35% (apple fruit fresh weight) apple pomace (AP). Using modern AP management, integrated knowledge in innovative fermentation demonstrates opportunities for reducing environmental pollution and integration into a circular economy. With this association in view, integrating AP flour during sourdough fermentation increases the nutritional value, highlighting a new approach that could guide innovative fermented foods. In this study, the wheat flour (WF) and AP flour were mixed at different ratios, hydrated with water (1:1 w/v), and fermented using a selective culture of Fructilactobacillus florum DSM 22689 and baker's yeast (single and co-culture). Sourdough fermentation was monitored and analyzed for 72 h. Results suggested that AP may be an important source of organic acids and fermentable sugars that increase nutritional sourdough value. AP flour addition in WF had a positive effect, especially in fermentations with 95% WF and 5% AP, mainly in co-culture fermentation.

Production of levan from Bacillus subtilis var. natto and apoptotic effect on SH-SY5Y neuroblastoma cells

Levan is a high-valued polysaccharide of fructose produced by several microbial species. These polysaccharides have been described as effective therapeutic agents in some human disease conditions, such as cancer, heart diseases and diabetes. The objective of this study was to examine the effect of levan (β-(2 → 6)-fructan) produced through sucrose fermentation by B. subtilis var. natto on the proliferation rate, cytotoxicity, and apoptosis of human neuroblastoma SH-SY5Y cells. It was obtained 41.44 g/L of levan in 18 h by biotechnological fermentation and SH-SY5Y cells were exposed to 1000 μg/mL of levan. The treatment with 1000 μg/mL of levan induced apoptosis in SH-SY5Y cancer cells by the significant increase in Annexin V/7-AAD and caspase 3/7 activation, but did not decrease proliferation or triggered a cytotoxic effect. 1000 μg/mL levan treatment is a promising therapeutic strategy for SH-SY5Y neuroblastoma cells.

Proteomic Analysis Explores Interactions between Lactiplantibacillus plantarum and Saccharomyces cerevisiae during Sourdough Fermentation

Sourdough is a fermentation culture which is formed following metabolic activities of a multiple bacterial and fungal species on raw dough. However, little is known about the mechanism of interaction among different species involved in fermentation. In this study, Lactiplantibacillus plantarum Sx3 and Saccharomyces cerevisiae Sq7 were selected. Protein changes in sourdough, fermented with single culture (either Sx3 or Sq7) and mixed culture (both Sx3 and Sq7), were evaluated by proteomics. The results show that carbohydrate metabolism in mixed-culture-based sourdough is the most important metabolic pathway. A greater abundance of L-lactate dehydrogenase and UDP-glucose 4-epimerase that contribute to the quality of sourdough were observed in mixed-culture-based sourdough than those produced by a single culture. Calreticulin, enolase, seryl-tRNA synthetase, ribosomal protein L23, ribosomal protein L16, and ribosomal protein L5 that are needed for the stability of proteins were increased in mixed-culture-based sourdough. The abundance of some compounds which play an important role in enhancing the nutritional characteristics and flavour of sourdough (citrate synthase, aldehyde dehydrogenase, pyruvate decarboxylase, pyruvate dehydrogenase E1 and acetyl-CoA) was decreased. In summary, this approach provided new insights into the interaction between L. plantarum and S. cerevisiae in sourdough, which may serve as a base for further research into the detailed mechanism.

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 Fermentation as a Tool to Improve the Nutritional and Health-Promoting Properties of Its Derived-Products

Cereal products are staple foods highly appreciated and consumed worldwide. Nonetheless, due to the presence of gluten proteins, and other co-existing compounds such as amylase-trypsin inhibitors and fermentable short-chain carbohydrates in those products, their preference by consumers has substantially decreased. Gluten affects the small gut of people with celiac disease, triggering a gut inflammation condition via auto-immune response, causing a cascade of health disorders. Amylase-trypsin inhibitors and fermentable short-chain carbohydrate compounds that co-exists with gluten in the cereal-based foods matrix have been associated with several gastrointestinal symptoms in non-celiac gluten sensitivity. Since the symptoms are somewhat overlapped, the relation between celiac disease and irritable bowel syndrome has recently received marked interest by researchers. Sourdough fermentation is one of the oldest ways of bread leavening, by lactic acid bacteria and yeasts population, converting cereal flour into attractive, tastier, and more digestible end-products. Lactic acid bacteria acidification in situ is a key factor to activate several cereal enzymes as well as the synthesis of microbial active metabolites, to positively influence the nutritional/functional and health-promoting benefits of the derived products. This review aims to explore and highlight the potential of sourdough fermentation in the Food Science and Technology field.

Determination of Technological Parameters and Characterization of Microbiota of the Spontaneous Sourdough Fermentation of Hull-Less Barley

The development of microorganisms of sourdough and biodiversity of microbiota can be influenced by changing the parameters of the technological process such as the ratio of flour and added water, the fermentation temperature and time. The Box-Behnken design methodology was used to determine the optimal parameters for the three-phase spontaneous backslopping fermentation process of hull-less barley sourdough, as well as to characterize the microbiological diversity. The optimized parameters of backslopping fermentation are flour and water ratio 1:1.13, temperature 30 °C, time 24 h in the 1st backslopping; the inoculate, flour and water ratio 1:1:1.3, temperature 31 °C, time 14 h in the 2nd backslopping, and the inoculate, flour and water ratio 1:1:1.5, and temperature 28.5 °C, time 12 h in the 3rd step of backslopping. In the controlled spontaneous fermentation environment in three backslopping steps, the microbiological research of hull-less barley sourdough has confirmed the dominance of species Pediococcus pentosaceus in the 3rd backslopping step of spontaneous fermentation. The developed spontaneous hull-less barley sourdough is consistent with the number of lactic bacteria and yeasts in line with that seen by the active sourdough.

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.

Multiple Techno-Functional Characteristics of Leuconostoc and Their Potential in Sourdough Fermentations

In this study, the potential of Leuconostoc as non-conventional sourdough starter cultures was investigated. A screening for antifungal activities of 99 lactic acid bacteria (LAB) strains revealed high suppression of bakery-relevant moulds in nine strains of Leuconostoc with activities against Penicillium sp., Aspergillus sp., and Cladosporium sp. Mannitol production was determined in 49 Leuconostoc strains with >30 g/L mannitol in fructose (50 g/L)-enriched MRS. Further, exopolysaccharides (EPS) production was qualitatively determined on sucrose (40 g/L)-enriched MRS agar and revealed 59 EPS positive Leuconostoc strains that harboured dextransucrase genes, as confirmed by PCR. Four multifunctional Lc. citreum strains (DCM49, DCM65, MA079, and MA113) were finally applied in lab-scale sourdough fermentations (30 °C, 24 h). Lc. citreum was confirmed by MALDI-TOF MS up to 9 log CFU/g and pH dropped to 4.0 and TTA increased to 12.4. Antifungal compounds such as acetic acid, phenyllactic and hydroxyphenyllactic acids were determined up to 1.7 mg/g, 2.1 µg/g, and 1.3 µg/g, respectively, mannitol up to 8.6 mg/g, and EPS up to 0.62 g/100 g. Due to the observed multifunctionalities and the competitiveness in the natural flour microbiota present in sourdoughs, non-conventional LAB genera such as Leuconostoc seem promising for application in sourdough-based bakery products.

Commercial Organic Versus Conventional Whole Rye and Wheat Flours for Making Sourdough Bread: Safety, Nutritional, and Sensory Implications

Organic farming is gaining a broad recognition as sustainable system, and consumer demand for organic products has increased dramatically in the recent past. Whether organic agriculture delivers overall advantages over conventional agriculture is, however, contentious. Here, the safety, nutritional, and sensory implications of using commercial organic rye, soft, and durum wheat flours rather than conventional-made sourdough bread have been investigated. Culture-dependent and culture-independent approaches were used to explore the microbial architecture of flours and to study their dynamics during sourdough propagation. Besides biochemical features, the main nutritional (amino acid content, asparagine level, and antioxidant activity) characteristics of sourdoughs were investigated, and their effect on the structural, nutritional, and sensory profiles of breads assessed. Overall, the organic farming system led to flours characterized by lower content of asparagine and cell density of Enterobacteriaceae while showing higher concentration of total free amino acids. Differences of the flours mirrored those of sourdoughs and breads. The use of sourdough fermentation guaranteed a further improvement of the flour characteristics; however, a microbial and sensory profile simplification as well as a slight decrease of the biochemical parameters was observed between breads with sourdough after one-cycle fermentation and 10 days of propagation.

Sourdough Biotechnology Applied to Gluten-Free Baked Goods: Rescuing the Tradition

Recent studies suggest that the beneficial properties provided by sourdough fermentation may be translated to the development of new GF products that could improve their technological and nutritional properties. The main objective of this manuscript is to review the current evidence regarding the elaboration of GF baked goods, and to present the latest knowledge about the so-called sourdough biotechnology. A bibliographic search of articles published in the last 12 years has been carried out. It is common to use additives, such as hydrocolloids, proteins, enzymes, and emulsifiers, to technologically improve GF products. Sourdough is a mixture of flour and water fermented by an ecosystem of lactic acid bacteria (LAB) and yeasts that provide technological and nutritional improvements to the bakery products. LAB-synthesized biopolymers can mimic gluten molecules. Sourdough biotechnology is an ecological and cost-effective technology with great potential in the field of GF products. Further research is necessary to optimize the process and select species of microorganisms robust enough to be competitive in any circumstance.

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.

Isolation and Characterization of Lactic Acid Bacteria and Yeasts from Typical Bulgarian Sourdoughs

Traditional sourdoughs in Bulgaria were almost extinct during the centralized food production system. However, a rapidly developing trend of sourdough revival in the country is setting the demand for increased production and use of commercial starter cultures. The selection of strains for such cultures is based on geographical specificity and beneficial technological properties. In this connection, the aim of this study was to isolate, identify and characterize lactic acid bacteria (LAB) and yeasts from typical Bulgarian sourdoughs for the selection of strains for commercial sourdough starter cultures. Twelve samples of typical Bulgarian sourdoughs were collected from different geographical locations. All samples were analyzed for pH, total titratable acidity and dry matter content. Enumeration of LAB and yeast was also carried out. Molecular identification by 16S rDNA sequence analysis was performed for 167 LAB isolates, and 106 yeast strains were identified by ITS1-5.8S-ITS2 rRNA gene partial sequence analysis. The LAB strains were characterized according to their amylolytic and proteolytic activity and acidification capacity, and 11 strains were selected for further testing of their antimicrobial properties. The strains with the most pronounced antibacterial and antifungal activity are listed as recommended candidates for the development of starter cultures for sourdoughs or other food products.

A review of sourdough starters: ecology, practices, and sensory quality with applications for baking and recommendations for future research

The practice of sourdough bread-making is an ancient science that involves the development, maintenance, and use of a diverse and complex starter culture. The sourdough starter culture comes in many different forms and is used in bread-making at both artisanal and commercial scales, in countries all over the world. While there is ample scientific research related to sourdough, there is no standardized approach to using sourdough starters in science or the bread industry; and there are few recommendations on future directions for sourdough research. Our review highlights what is currently known about the microbial ecosystem of sourdough (including microbial succession within the starter culture), methods of maintaining sourdough (analogous to land management) on the path to bread production, and factors that influence the sensory qualities of the final baked product. We present new hypotheses for the successful management of sourdough starters and propose future directions for sourdough research and application to better support and engage the sourdough baking community.

Metagenetic Analysis for Microbial Characterization of Focaccia Doughs Obtained by Using Two Different Starters: Traditional Baker's Yeast and a Selected Leuconostoc citreum Strain

Lactic acid bacteria (LAB) decisively influence the technological, nutritional, organoleptic and preservation properties of bakery products. Therefore, their use has long been considered an excellent strategy to improve the characteristics of those goods. The aim of this study was the evaluation of microbial diversity in different doughs used for the production of a typical Apulian flatbread, named focaccia. Leavening of the analyzed doughs was obtained with baker’s yeast or by applying an innovative “yeast-free” protocol based on a liquid sourdough obtained by using Leuconostoc citreum strain C2.27 as a starter. The microbial populations of the doughs were studied by both a culture-dependent approach and metagenetic analyses. The flours used for dough preparation were also subjected to the same analyses. The metagenetic analyses were performed by sequencing the V5–V6 hypervariable regions of the 16S rRNA gene and the V9 hypervariable region of the 18S rRNA gene. The results indicate that these hypervariable regions were suitable for studying the microbiota of doughs, highlighting a significant difference between the microbial community of focaccia dough with baker’s yeast and that of the dough inoculated with the bacterial starter. In particular, the dough made with baker’s yeast contained a microbiota with a high abundance of Proteobacteria (82% of the bacterial population), known to be negatively correlated with the biochemical properties of the doughs, while the Proteobacteria in dough produced with the L. citreum starter were about 43.5% lower than those in flour and dough prepared using baker’s yeast. Moreover, the results show that the L. citreum C2.27 starter was able to dominate the microbial environment and also reveal the absence of the genus Saccharomyces in the dough used for the production of the “yeast-free” focaccia. This result is particularly important because it highlights the suitability of the starter strain for obtaining an innovative “yeast-free” product.

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.

Yeasts and Lactic Acid Bacteria for Panettone Production: An Assessment of Candidate Strains

The recovery of yeasts and lactic acid bacteria (LAB) involved in sourdough fermentation is the first step in the selection of starters with suitable technological aptitude and capable of producing desired aromas and/or aromatic precursors. In this work, two sourdoughs samples (MA and MB) and the derived doughs (samples A and B) were collected from a bakery during artisanal Panettone manufacture. Yeasts and bacteria were isolated at different fermentation steps on selective agar media. A total of 77 isolates were obtained and characterized. Representative strains of yeasts and LAB were identified by sequencing the D1/D2 domain of the 26S rRNA and the 16S rRNA genes, respectively. Moreover, the volatile organic compounds (VOCs) produced in the collected samples were detected and correlated to the species found in the same samples. The results highlighted the occurrence of Kazachstania humilis in both samples A and B, while Saccharomyces cerevisiae strains were detected only in samples B. Among LAB, Fructilactobacillus sanfranciscensis was the main species detected in both sourdoughs. Furthermore, strains belonging to the species Lactiplantibacillus plantarum, Furfurilactobacillus rossiae, Lactobacillus parabuchneri, Leuconostoc citreum, and Leuconostoc mesenteroides were assessed in the dough samples.

Functional and Healthy Features of Conventional and Non-Conventional Sourdoughs

Sourdough is a composite ecosystem largely characterized by yeasts and lactic acid bacteria which are the main players in the fermentation process. The specific strains involved are influenced by several factors including the chemical and enzyme composition of the flour and the sourdough production technology. For many decades the scientific community has explored the microbiological, biochemical, technological and nutritional potential of sourdoughs. Traditionally, sourdoughs have been used to improve the organoleptic properties, texture, digestibility, palatability, and safety of bread and other kinds of baked products. Recently, novel sourdough-based biotechnological applications have been proposed to meet the demand of consumers for healthier and more natural food and offer new inputs for the food industry. Many researchers have focused on the beneficial effects of specific enzymatic activities or compounds, such as exopolysaccharides, with both technological and functional roles. Additionally, many studies have explored the ability of sourdough lactic acid bacteria to produce antifungal compounds for use as bio-preservatives. This review provides an overview of the fundamental features of sourdoughs and their exploitation to develop high value-added products with beneficial microorganisms and/or their metabolites, which can positively impact human health.

Sourdough yeast-bacteria interactions can change ferulic acid metabolism during fermentation

The metabolism of ferulic acid (FA) was studied during fermentation with different species and strains of lactic acid bacteria (LAB) and yeasts, in synthetic sourdough medium. Yeast strains of Kazachstania humilis, Kazachstania bulderi, and Saccharomyces cerevisiae, as well as lactic acid bacteria strains of Fructilactobacillus sanfranciscensis, Lactiplantibacillus plantarum, Lactiplantibacillus xiangfangensis, Levilactobacillus hammesii, Latilactobacillus curvatus and Latilactobacillus sakei were selected from French natural sourdoughs. Fermentation in presence or absence of FA was carried out in LAB and yeasts monocultures, as well as in LAB/yeast co-cultures. Our results indicated that FA was mainly metabolized into 4-vinylguaiacol (4-VG) by S. cerevisiae strains, and into dihydroferulic acid (DHFA) and 4-VG in the case of LAB. Interactions of LAB and yeasts led to the modification of FA metabolism, with a major formation of DHFA, even by the strains that do not produce it in monoculture. Interestingly, FA was almost completely consumed by the F. sanfranciscensis bFs17 and K. humilis yKh17 pair and converted into DHFA in 89.5 ± 19.6% yield, while neither bFs17, nor yKh17 strains assimilated FA in monoculture.

Characterization of Artisanal Spontaneous Sourdough Wheat Bread from Central Greece: Evaluation of Physico-Chemical, Microbiological, and Sensory Properties in Relation to Conventional Yeast Leavened Wheat Bread

In the present study, both yeast leavened bread (YLB) and artisanal sourdough wheat bread (SDB) were prepared. The physico-chemical, microbiological, and sensory properties of breads were monitored as a function of storage time (T = 25 °C). As expected, the titratable acidity (TA) values of SDB were higher than those of YLB. The aroma profile of SDB was similar to that of YLB, including classes of compounds such as alcohols, aldehydes, ketones, esters, organic acids, terpenes, and sulfur compounds; however, the concentrations between the two were different. Aroma deterioration of bread during storage was partly related to the loss of several volatiles. Texture and sensory analysis showed that SDB was harder, less elastic, but richer in aroma and light sour taste than YLB. Mold growth was apparent when the population of yeasts/molds reached approximately 4 log cfu/g. This yeast/mold count was reached on days 4–5 for YLB and day 18 + for SDB. A 16S amplicon meta-barcoding analysis showed that the bacterial profile of SDB was dominated by a single genus, (Lactobacillus). Analysis of the eukaryotic load showed that at the genus level, Saccharomyces and Alternaria were the most abundant genera, independently of the gene sequenced (18S or ITS). Based primarily on mold growth and texture data, which proved to be the most sensitive quality parameters, the shelf life was ca. 4–5 days for YLB and 10 days for SDB.

Innovations in Sourdough Bread Making

The application of sourdough is considered to be a key tool for the production of high-quality bread. Several advantages have been presented through the application of sourdough in bread making, such as increased shelf life, improved aromatic profiles and sensory characteristics, increased nutritional value, and health benefits. Technological benefits have also been recorded, such as the successful application of sourdough in gluten-free breads. Likewise, an upsurge of interest in sourdough applications in bread making as well as in other foodstuffs (pasta) has been witnessed in recent years. Many factors are considered important for sourdough preparations; however, the proper selection of the starter cultures is considered the most central. This Special Issue of Fermentation aims to disseminate recent innovative research regarding sourdough bread making, as well as authoritative reviews that compile information from previously published material.

Volatile Organic Compounds in Breads Prepared with Different Sourdoughs

Sourdough is an old example of a natural starter composed of a mixture of flour, water, and metabolites and is produced by naturally occurring lactic acid bacteria and yeasts that influence bread aroma. In this work, four types of sourdough were used to prepare bread: one sourdough with yeast beer and three with bacteria and yeasts. The physicochemical parameters (pH, moisture, water activity, and organic acids) of the bread and sourdoughs were assessed. Lactic, acetic, and succinic acids were found in considerable amounts in sourdoughs and the corresponding breads. The fermentation quotient (molar ratio between lactic and acetic acid) ranged from 0.39 to 3.4 in sourdoughs. Lactic acid was prevalent in all types of bread and showed the highest value in bread made from sourdough with a 1.5 bacteria/yeast ratio (8722.24 mg/kg). Moreover, volatile organic compounds were identified in bread samples. Alcohols, aldehydes, and acetic acid were mainly found. The alcohol concentration ranged from 140.88 to 401.20 ng/g. Aldehydes ranged from 185.01 to 454.95 ng/g, and acetic acid ranged from 91.40 to 173.81 ng/g. Bread prepared from sourdough with a 1.5 bacteria/yeast ratio showed a considerable amount of alcohols and acetic acid.

The diversity and function of sourdough starter microbiomes

Humans have relied on sourdough starter microbial communities to make leavened bread for thousands of years, but only a small fraction of global sourdough biodiversity has been characterized. Working with a community-scientist network of bread bakers, we determined the microbial diversity of 500 sourdough starters from four continents. In sharp contrast with widespread assumptions, we found little evidence for biogeographic patterns in starter communities. Strong co-occurrence patterns observed in situ and recreated in vitro demonstrate that microbial interactions shape sourdough community structure. Variation in dough rise rates and aromas were largely explained by acetic acid bacteria, a mostly overlooked group of sourdough microbes. Our study reveals the extent of microbial diversity in an ancient fermented food across diverse cultural and geographic backgrounds.

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.

Fermentative Foods: Microbiology, Biochemistry, Potential Human Health Benefits and Public Health Issues

Fermented foods identify cultures and civilizations. History, climate and the particulars of local production of raw materials have urged humanity to exploit various pathways of fermentation to produce a wide variety of traditional edible products which represent adaptations to specific conditions. Nowadays, industrial-scale production has flooded the markets with ferments. According to recent estimates, the current size of the global market of fermented foods is in the vicinity of USD 30 billion, with increasing trends. Modern challenges include tailor-made fermented foods for people with special dietary needs, such as patients suffering from Crohn's disease or other ailments. Another major challenge concerns the safety of artisan fermented products, an issue that could be tackled with the aid of molecular biology and concerns not only the presence of pathogens but also the foodborne microbial resistance. The basis of all these is, of course, the microbiome, an aggregation of different species of bacteria and yeasts that thrives on the carbohydrates of the raw materials. In this review, the microbiology of fermented foods is discussed with a special reference to groups of products and to specific products indicative of the diversity that a fermentation process can take. Their impact is also discussed with emphasis on health and oral health status. From Hippocrates until modern approaches to disease therapy, diet was thought to be of the most important factors for health stability of the human natural microbiome. After all, to quote Pasteur, "Gentlemen, the microbes will have the last word for human health." In that sense, it is the microbiomes of fermented foods that will acquire a leading role in future nutrition and therapeutics.

Yeast Biodiversity in Fermented Doughs and Raw Cereal Matrices and the Study of Technological Traits of Selected Strains Isolated in Spain

Bakers use pure microorganisms and/or traditional sourdoughs as the leavening agent for making bread. The performance of each starter and the substances produced by the microorganisms greatly affect the dough rheology and features of breads. Modern sourdoughs inoculated with selected lactic acid bacteria and yeasts are microbiologically stable, safer than traditional sourdoughs, and easy to use. However, the commercial repertoire of baker’s yeasts is still limited. Therefore, there is a demand for new strains of yeast species, capable of conferring distinctive traits to breads made from a variety of agri-food matrices, in the design of innovative starters. In this context, we report the first comprehensive study on yeasts isolated from a wide range of fermented doughs, cereal flours, and grains of Spain. Nine yeast species were identified from 433 isolates, which were distributed among separate clades. Moreover, phenotypic traits of potential technological relevance were identified in selected yeast strains. Mother doughs (MDs) showed the greatest yeast biodiversity, whereas commercial Saccharomyces starters or related and wild strains often dominated the bakery doughs. A metataxonomic analysis of wheat and tritordeum MDs revealed a greater richness of yeast species and percentage variations related to the consistency, flour type, and fermentation time of MDs.

Lemon juice and apple juice used as source of citrate and malate, respectively, enhance the formation of buttery aroma compounds and/or organic acids during Type 2 and Type 3 sourdough productions performed with Companilactobacillus crustorum LMG 23699

Extra ingredients are often used in traditional sourdough production recipes by artisan bakeries. These ingredients may be the source of microorganisms or stimulate the growth and/or the metabolic activities of the microorganisms added to or naturally present in the flour-water mixture. The present study examined the influence of the addition of lemon juice or apple juice as source of citrate or malate, respectively, on the growth and activity of the citrate- and malate-positive Companilactobacillus crustorum LMG 23699 strain (formerly known as Lactobacillus crustorum LMG 23699), used to initiate firm (dough yield of 200) wheat sourdough productions, and on the flavour of the baked goods produced. Three fermentation strategies were applied, namely one-step long fermentation sourdough production processes with the addition of juice at the start (Type 2) and backslopped fermentations with the addition of juice either only at the start of the sourdough productions or at the start of the sourdough productions and at the beginning of each subsequent refreshment step during the whole backslopping process (both Type 3). It turned out that the starter culture strain used prevailed during all sourdough productions performed. Yeasts were particularly present in Type 3 sourdough productions, although lemon juice retarded their growth. Due to high yeast activity, high concentrations of ethanol and glycerol were produced toward the end of the sourdough productions. Addition of lemon juice stimulated the production of lactic acid, acetic acid, and the buttery flavour compounds acetoin and diacetyl, because of citrate conversion, during the Type 2 and Type 3 sourdough productions. In Type 3 sourdough productions, these compounds were found in higher concentrations only when lemon juice was added at each backslopping step. Alternatively, the addition of apple juice led to high concentrations of lactic acid because of malolactic fermentation in both Type 2 and Type 3 sourdough productions. Moreover, the addition of apple juice increased the initial concentrations of the carbohydrates (fructose, glucose, and sucrose) and sugar alcohols (mannitol and sorbitol), which were exhausted upon backslopping or accumulated in the sourdough matrix, respectively. Baked goods produced using sourdoughs obtained from the Type 2 and Type 3 sourdough productions with the addition of juice at each backslopping step were significantly different in flavour from doughs supplemented with the respective juices and lactic acid and/or Type 3 sourdough productions with the addition of juice only at the start.

History and Domestication of Saccharomyces cerevisiae in Bread Baking

The yeast Saccharomyces cerevisiae has been instrumental in the fermentation of foods and beverages for millennia. In addition to fermentations like wine, beer, cider, sake, and bread, S. cerevisiae has been isolated from environments ranging from soil and trees, to human clinical isolates. Each of these environments has unique selection pressures that S. cerevisiae must adapt to. Bread dough, for example, requires S. cerevisiae to efficiently utilize the complex sugar maltose; tolerate osmotic stress due to the semi-solid state of dough, high salt, and high sugar content of some doughs; withstand various processing conditions, including freezing and drying; and produce desirable aromas and flavors. In this review, we explore the history of bread that gave rise to modern commercial baking yeast, and the genetic and genomic changes that accompanied this. We illustrate the genetic and phenotypic variation that has been documented in baking strains and wild strains, and how this variation might be used for baking strain improvement. While we continue to improve our understanding of how baking strains have adapted to bread dough, we conclude by highlighting some of the remaining open questions in the field.

Microbial Ecology of Greek Wheat Sourdoughs, Identified by a Culture-Dependent and a Culture-Independent Approach

The aim of the present study was to assess the microecosystem of 13 homemade spontaneously fermented wheat sourdoughs from different regions of Greece, through the combined use of culture-dependent (classical approach; clustering by Random Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) and identification by PCR species-specific for Lactiplantibacillus plantarum, and sequencing of the 16S-rRNA and 26S-rRNA gene, for Lactic Acid Bacteria (LAB) and yeasts, respectively) and independent approaches [DNA- and RNA-based PCR-Denaturing Gradient Gel Electrophoresis (DGGE)]. The pH and Total Titratable Acidity (TTA) values ranged from 3.64–5.05 and from 0.50–1.59% lactic acid, respectively. Yeast and lactic acid bacteria populations ranged within 4.60–6.32 and 6.28–9.20 log CFU/g, respectively. The yeast: LAB ratio varied from 1:23–1:10,000. A total of 207 bacterial and 195 yeast isolates were obtained and a culture-dependent assessment of their taxonomic affiliation revealed dominance of Lb. plantarum in three sourdoughs, Levilactobacillus brevis in four sourdoughs and co-dominance of these species in two sourdoughs. In addition, Companilactobacillusparalimentarius dominated in two sourdoughs and Fructilactobacillussanfranciscensis and Latilactobacillus sakei in one sourdough each. Lactococcus lactis, Lb. curvatus, Leuconostoc citreum, Ln. mesenteroides and Lb. zymae were also recovered from some samples. Regarding the yeast microbiota, it was dominated by Saccharomyces cerevisiae in 11 sourdoughs and Pichia membranifaciens and P. fermentans in one sourdough each. Wickerhamomyces anomalus and Kazachstania humilis were also recovered from one sample. RNA-based PCR-DGGE provided with nearly identical results with DNA-based one; in only one sample the latter provided an additional band. In general, the limitations of this approach, namely co-migration of amplicons from different species to the same electrophoretic position and multiband profile of specific isolates, greatly reduced resolution capacity, which resulted in only partial verification of the microbial ecology detected by culture-dependent approach in the majority of sourdough samples. Our knowledge regarding the microecosystem of spontaneously fermented Greek wheat-based sourdoughs was expanded, through the study of sourdoughs originating from regions of Greece that were not previously assessed.

Technological Performance and Selection of Lactic Acid Bacteria Isolated from Argentinian Grains as Starters for Wheat Sourdough

The selection of lactic acid bacteria strains is interesting for the development of sourdough to obtain wheat bread with improved technological and nutritional properties. In this work, the performance of ten different LAB strains isolated from diverse cereals in wheat sourdough was evaluated. Five facultative heterofermentative (Lactobacillus pentosus ES124, Lactobacillus paralimentarius ES259, Lactobacillus plantarum ES137, Lactobacillus plantarum ATCC8014 and Lactobacillus plantarum ES147), three obligately heterofermentative (Lactobacillus brevis ES253, Lactobacillus fermentum ES142 and Lactobacillus fermentum ES148) and two homofermentative (Pediococcus acidilactici ES22 and Enterococcus faecium ES74) lactic acid bacteria strains were evaluated in ten single strain fermentations. Sugar profile, volatile compounds and proteolytic ability of sourdoughs were analyzed. The microbiological counts showed that facultative heterofermentative strains presented higher counts than homofermentative sourdoughs. Monosaccharides (glucose and fructose), maltose and sucrose, isomaltose and dextrin were detected in fermentations with homofermentative strains whilst in those with heterofermentative strains maltose/sucrose, isomaltose and dextrin were found. L. paralimentarius ES259 and L. pentosus ES124 showed the highest diversity of volatile compounds. L. plantarum ES137 and P. acidilactici ES22 were the strains with the highest proteolytic activity. The technological performance allowed us to select LAB as starters to develop breads with specific rheological properties and final quality.

Ecology of yeasts associated with kernels of several durum wheat genotypes and their role in co-culture with Saccharomyces cerevisiae during dough leavening

This work was performed to investigate on the yeast ecology of durum wheat to evaluate the interaction between kernel yeasts and the commercial baker's yeast Saccharomyces cerevisiae during dough leavening. Yeast populations were studied in 39 genotypes of durum wheat cultivated in Sicily. The highest level of kernel yeasts was 2.9 Log CFU/g. A total of 413 isolates was collected and subjected to phenotypic and genotypic characterization. Twenty-three yeast species belonging to 11 genera have been identified. Filobasidium oeirense, Sporobolomyces roseus and Aureobasidium pullulans were the species most commonly found in durum wheat kernels. Doughs were co-inoculated with yeasts isolated from wheat kernels and commercial Saccharomyces cerevisiae, in order to evaluate the interactions between yeasts and the leavening performance. Yeast populations of all doughs have been monitored as well as dough volume increase and weight loss (as CO₂) measured after 2 h of fermentation. The doughs whose final volume was higher than control dough (inoculated exclusively with S. cerevisiae) were those inoculated with Naganishia albida, Vishniacozyma dimennae (118 mL each), and Candida parapsilosis (102 mL). The weight losses were variable, depending on the co-culture used with S. cerevisiae and the values were in the range of 0.08-1.00 g CO₂/100 g. The kernel yeasts species C. parapsilosis, N. albida, P. terrestris, R. mucilaginosa and V. dimennae deserves future attention to be co-inoculated with the commercial starter S. cerevisiae in order to improve the sensory characteristics of bread.

Intraspecies diversity and genome-phenotype-associations in Fructilactobacillus sanfranciscensis

In this study the intraspecies diversity of Fructilactobacillus (F.) sanfranciscensis (formerly Lactobacillus sanfranciscensis) was characterized by comparative genomics supported by physiological data. Twenty-four strains of F. sanfranciscensis were analyzed and sorted into six different genomic clusters. The core genome comprised only 43,14 % of the pan genome, i.e. 0.87 Mbp of 2.04 Mbp. The main annotated genomic differences reside in maltose, fructose and sucrose as well as nucleotide metabolism, use of electron acceptors, and exopolysacchride formation. Furthermore, all strains are well equipped to cope with oxidative stress via NADH oxidase and a distinct thiol metabolism. Only ten of 24 genomes contain two maltose phosphorylase genes (mapA and mapB). In F. sanfranciscensis TMW 1.897 only mapA was found. All strains except those from genomic cluster 2 contained the mannitol dehydrogenase and should therefore be able to use fructose as external electron acceptor. Moreover, six strains were able to grow on fructose as sole carbon source, as they contained a functional fructokinase gene. No growth was observed on pentoses, i.e. xylose, arabinose or ribose, as sole carbon source. This can be referred to the absence of ribose pyranase rbsD in all genomes, and absence of or mutations in numerous other genes, which are essential for arabinose and xylose metabolism. Seven strains were able to produce exopolysaccharides (EPS) from sucrose. In addition, the strains containing levS were able to grow on sucrose as sole carbon source. Strains of one cluster exhibit auxotrophies for purine nucleotides. The physiological and genomic analyses suggest that the biodiversity of F. sanfranciscensis is larger than anticipated. Consequently, "original" habitats and lifestyles of F. sanfranciscensis may vary but can generally be referred to an adaptation to sugary (maltose/sucrose/fructose-rich) and aerobic environments as found in plants and insects. It can dominate sourdoughs as a result of reductive evolution and cooperation with fructose-delivering, acetate-tolerant yeasts.

Potential of Bacteria from Alternative Fermented Foods as Starter Cultures for the Production of Wheat Sourdoughs

Microbial strains for starter culture-initiated sourdough productions are commonly isolated from a fermenting flour-water mixture. Yet, starter culture strains isolated from matrices other than sourdoughs could provide the dough with interesting metabolic properties and hence change the organoleptic properties of the concomitant breads. Furthermore, the selection of sourdough starter cultures does not need to be limited to lactic acid bacteria (LAB), as other food-grade microorganisms are sometimes found in sourdoughs. Therefore, different strains belonging to LAB, acetic acid bacteria (AAB), and coagulase-negative staphylococci (CNS) that originated from different fermented food matrices (fermenting cocoa pulp-bean mass, fermented sausage, and water kefir), were examined as to their prevalence in a wheat sourdough ecosystem during 72-h fermentations. Limosilactobacillus fermentum IMDO 222 (fermented cocoa pulp-bean mass isolate) and Latilactobacillus sakei CTC 494 (fermented sausage isolate) seemed to be promising candidates as sourdough starter culture strains, as were the AAB strains Acetobacter pasteurianus IMDO 386B and Gluconobacter oxydans IMDO A845 (both isolated from fermented cocoa pulp-bean mass), due to their competitiveness in the wheat flour-water mixtures. Wheat breads made with G. oxydans IMDO A845 sourdoughs were significantly darker than reference wheat breads.

Proteomic characterization of extracellular vesicles produced by several wine yeast species

In winemaking, the use of alternative yeast starters is becoming increasingly popular. They contribute to the diversity and complexity of wine sensory features and are typically used in combination with Saccharomyces cerevisiae, to ensure complete fermentation. This practice has drawn the interest on interactions between different oenological yeasts, which are also relevant in spontaneous and conventional fermentations, or in the vineyard. Although several interactions have been described and some mechanisms have been suggested, the possible involvement of extracellular vesicles (EVs) has not yet been considered. This work describes the production of EVs by six wine yeast species (S. cerevisiae, Torulaspora delbrueckii, Lachancea thermotolerans, Hanseniaspora uvarum, Candida sake and Metschnikowia pulcherrima) in synthetic grape must. Proteomic analysis of EV-enriched fractions from S. cerevisiae and T. delbrueckii showed enrichment in glycolytic enzymes and cell-wall-related proteins. The most abundant protein found in S. cerevisiae, T. delbrueckii and L. thermotolerans EV-enriched fractions was the enzyme exo-1,3-β-glucanase. However, this protein was not involved in the here-observed negative impact of T. delbrueckii extracellular fractions on the growth of other yeast species. These findings suggest that EVs may play a role in fungal interactions during wine fermentation and other aspects of wine yeast biology.

A study revealing volatile aroma produced by Pediococcus pentosaceus in dough fermentation

Pediococcus pentosaceus is important probiotics in Chinese Laomian. Its role in meat and fermented vegetable has been largely demonstrated, but few studies have investigated the role of P. pentosaceus in Chinese Laomian. For this purpose, we simulated Laomian fermentation using Saccharomyces cerevisiae and P. pentosaceus. Volatile aroma was detected by headspace solid-phase microextraction gas-chromatography-mass spectrometry. Real-time fluorescent quantitative polymerase chain reaction was used to determine dynamic growth of S. cerevisiae and P. pentosaceus in fermentation. Extracellular proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Folin-Ciocalteu method was used to detect extracellular protease activity in different pH values. Owing to addition of P. pentosaceus, the types and contents of esters increase, the relative contents of acetic acid hexyl ester, formic acid octyl ester, and heptanoic acid ethyl ester rise obliviously; especially, the relative content of hexanoic acid ethyl ester was highly correlated with P. pentosaceus by increasing 20.61%. As the gel electrophoresis results display, due to mixed fermentation of S. cerevisiae and P. pentosaceus, the 25k Da and 51k Da proteins expression quantity of P. pentosaceus clearly increased. Under neutral and alkaline culture conditions, the extracellular protease activity of P. pentosaceus is higher. This research benefits to gain insight into the fermentation actions of P. pentosaceus in Chinese Laomian.