Effect of Mixed Cultures of Yeast and Lactobacilli on the Quality of Wheat Sourdough Bread

Bioprospecting of sourdough microbial species from artisan bakeries in the city of Valencia

This work describes the characterization of an artisanal sourdough set of bakeries located in the city of Valencia. Culture-dependent and -independent analyses detected Fructilactobacillus sanfranciscensis, Saccharomyces cerevisiae and Kazachstania humilis as dominant species. Nevertheless, specific technological parameters, including backslopping temperature, dough yield, or the addition of salt affected microbial counting, LAB/Yeast ratio, and gassing performance, favouring the appearance of several species of Lactobacillus sp., Limosilactobacillus pontis or Torulaspora delbrueckii as additional players. Sourdough leavening activity was affected positively by yeast counts and negatively by the presence of salt. In addition, the predominance of a particular yeast species appeared to impact the dynamics of CO2 release. Seven important flavour-active compounds (ethyl acetate, 1-hexanol, 2-penthylfuran, 3-ethyl-2-methyl-1,3-hexadiene, 2-octen-1-ol, nonanal and 1-nonanol) were detected in all samples and together with 3-methyl butanol and hexyl acetate represented more than the 53% of volatile abundancy in nine of the ten sourdoughs analysed. Even so, the specific microbial composition of each sample influenced the volatile profile. For example, the occurrence of K. humilis or S. cerevisiae as dominant yeast influenced the composition of major alcohol species, while F. sanfranciscensis and L. pontis positively correlated with aldehydes and octanoic acid content. In addition, relevant correlations could be also found among different technological parameters and between these, volatile compounds and microbial species. Overall, our study emphasises on how differences in technological parameters generate biodiversity in a relatively small set of artisan sourdoughs providing opportunities for excellence and quality baking products.

Microbiome-based precision nutrition: Prebiotics, probiotics and postbiotics

Microorganisms have been used in nutrition and medicine for thousands of years worldwide, long before humanity knew of their existence. It is now known that the gut microbiota plays a key role in regulating inflammatory, metabolic, immune and neurobiological processes. This text discusses the importance of microbiota-based precision nutrition in gut permeability, as well as the main advances and current limitations of traditional probiotics, new-generation probiotics, psychobiotic probiotics with an effect on emotional health, probiotic foods, prebiotics, and postbiotics such as short-chain fatty acids, neurotransmitters and vitamins. The aim is to provide a theoretical context built on current scientific evidence for the practical application of microbiota-based precision nutrition in specific health fields and in improving health, quality of life and physiological performance.

Minimal influence of milling technique in contrast to sourdough on the nutritional and organoleptic quality of bread

A number of studies have shown the effect of cereals and sourdough on bread nutritional and organoleptic quality, but the impact of the milling technique remains little studied. There are two main types of milling technic depending on the bread-making food chain. Industrial bakeries mainly use roller mills while artisanal bakeries may also use stone mill. We set up a participatory experiment with six millers and four bakers to study the impact of these two milling techniques on the quality of flours, sourdough microbiota and the quality of breads. Millers made twenty-two different flours from four different wheat grain varieties using either roller or stone mills. Each baker initiated and maintained sourdoughs with three roller-milled and three stone-milled flours during at least 32 backsloppings and then made bread. The analysis of flours revealed a typical granulometry profile linked to wheat hardness with higher particle sizes for stone-milled flours. Stone-milled flours also had a higher maltose content. However, the milling technic did not drive the composition of the sourdough microbiota. Moreover, the analysis of bread revealed that variation in bread protein fractions and in bread aroma compounds were more related to the specific baker microbial community than to the milling technique. Carbohydrate contents were clearly linked to the main LAB species metabolism. These results revealed that the sourdough microbial community shapes the organoleptic and nutritional quality of bread more than milling techniques.

Mechanism of carbohydrate and protein conversion during sourdough fermentation: An analysis based on representative Chinese sourdough microbiota

Sourdough fermentation is attracting growing attention because of its positive effects on properties of leavened baked good. However, the changes in dough features and the mechanisms behind them are not well understood, which limits its widespread use. In this study, we assessed the effects of representative lactic acid bacteria in sourdough monoculture or co-culture with yeasts on dough characteristics. Physicochemical analysis identified increased proteolysis and enhanced nutritional properties of co-culture groups. However, a reduction in organic acids contents of co-culture groups compared to monoculture was detected, and this effect was not limited by the yeast species. The RNA sequencing further demonstrated that the presence of yeast enhanced the protein metabolic activity of lactic acid bacteria, while decreased its organic acid biosynthetic activity. Moreover, the proteomic analysis revealed that endogenous metabolic proteins of flour, such as pyruvate kinase, glucosyltransferase and pyruvate dehydrogenase play a key role in carbohydrate metabolism during fermentation. This study uncovered the influence of typical microorganisms and endogenous enzymes on dough characteristics based on different aspects. Bacteria-mediated consumption of proteins and increased proteolysis in co-culture groups may underlie the improved digestibility and nutritional effects of sourdough fermented products, which provides an important basis for nutrient fortified bread making with multi-strain leavening agent.

Comparative Transcriptome Analysis Revealing the Enhanced Volatiles of Cofermentation of Yeast and Lactic Acid Bacteria on Whole Wheat Steamed Bread Dough

To reveal the underlying mechanism of enhanced volatiles of whole wheat steamed bread, the current study screened Saccharomyces cerevisiae Y5 and Lactiplantibacillus plantarum L7 from sourdough and studied the synergetic effect of cofermentation on the volatiles of steamed bread and fermented dough by comparative transcriptome analysis. Cofermentation significantly improved the types and concentration of volatiles in addition to the improved specific volume and texture. Genes involved in galactose, starch, and glucose metabolism and genes encoding pyruvate oxidase and β-galactosidase were significantly upregulated in S. cerevisiae and L. plantarum, respectively. Expression of the OPT2 encoding oligopeptide transporter in S. cerevisiae was upregulated, which facilitated the transmembrane transport of oligopeptide and amino acid into yeast cells. Genes involved in the synthesis and metabolism of amino acids, lipids, and ester compounds in L. plantarum changed significantly, and gene encoding acetic acid kinase was upregulated. Moreover, the quorum sensing-related genes in S. cerevisiae and L. plantarum were upregulated.

Unlocking the potential of low FODMAPs sourdough technology for management of irritable bowel syndrome

Consumption of high FODMAP (Fermentable Oligo-, Di-, and Monosaccharides and Polyols) diet is the leading cause of alteration in the human gut microbiome, thereby, causing irritable bowel syndrome (IBS). Therefore, sourdough technology can be exploited for reduction of FODMAPs in various foods to alleviate the symptoms of IBS. Several microorganisms viz. Pichia fermentans, Lactobacillus fetmentum, Saccharomyces cerevisiae, Torulaspora delbrueckii, Kluyveromyces marxianus etc. have been identified for the production of low FODMAP type II sourdough fermented products. However, more research on regulation of end-product and volatilome profile is required for maximal exploitation of FODMAP-reducing microorganisms. Therefore, the present review is focused on utilisation of lactic acid bacteria and yeasts, alone and in synergy, for the production of low FODMAP sourdough foods. Moreover, the microbial bioprocessing of cereal and non-cereal based low FODMAP fermented sourdough products along with their nutritional and therapeutic benefits have been elaborated. The challenges and future prospects for the production of sourdough fermented low FODMAP foods, thereby, bringing out positive alterations in gut microbiome, have also been discussed.

Microbiota structure of traditional starters from around the Tai-hang mountains and their influence on the fermentation properties, aroma profile and quality of Chinese steamed bread

BACKGROUND

Steamed bread is a popular staple food in China, and the significant regional differences of the microbiota in traditional starters make the flavor and quality of steamed bread highly variable along with long preparation times. Therefore, analyzing the microbial flora of traditional starters and their influences on the flavor and quality may help to solve the problems mentioned earlier, and it may also be conducive to potentially meet consumer needs and permit industrialization of this traditional fermented food.

RESULTS

One hundred and thirty-two fungal and 50 bacterial species were identified in five traditional starters, each with a different dominant genus. The fermentation properties of dough showed that total titratable acid, dough volume and gas production increased and the pH decreased with fermentation time. The traditional starters improved the quality of Chinese steamed bread (CSB) including the crumb structure, specific volume and sensory attributes. Thirty-three aroma compounds with a VIP (variable importance for the projection) > 1 were identified as characteristic aroma compounds. The correlations among the microbiota, aroma and qualities of CSB showed a greater contribution from the bacteria, which was consistent with the predictions of metabolic pathways in the sequenced genomes.

CONCLUSION

The quality of CSB fermented with traditional starters was improved induced by their different microbial profiles, and bacteria made a greater contribution than fungus to the aroma and qualities of CSB. © 2023 Society of Chemical Industry.

Does sourdough bread provide clinically relevant health benefits?

During the last decade, scientific interest in and consumer attention to sourdough fermentation in bread making has increased. On the one hand, this technology may favorably impact product quality, including flavor and shelf-life of bakery products; on the other hand, some cereal components, especially in wheat and rye, which are known to cause adverse reactions in a small subset of the population, can be partially modified or degraded. The latter potentially reduces their harmful effects, but depends strongly on the composition of sourdough microbiota, processing conditions and the resulting acidification. Tolerability, nutritional composition, potential health effects and consumer acceptance of sourdough bread are often suggested to be superior compared to yeast-leavened bread. However, the advantages of sourdough fermentation claimed in many publications rely mostly on data from chemical and in vitro analyzes, which raises questions about the actual impact on human nutrition. This review focuses on grain components, which may cause adverse effects in humans and the effect of sourdough microbiota on their structure, quantity and biological properties. Furthermore, presumed benefits of secondary metabolites and reduction of contaminants are discussed. The benefits claimed deriving from in vitro and in vivo experiments will be evaluated across a broader spectrum in terms of clinically relevant effects on human health. Accordingly, this critical review aims to contribute to a better understanding of the extent to which sourdough bread may result in measurable health benefits in humans.

Exploration of microbial profile of traditional starters and its influence on aroma profile and quality of Chinese steamed bread

BACKGROUND

Chinese steamed bread (CSB) is a popular staple food in China with traditional ethnic characteristics. CSB with traditional starters has good flavor and texture but is unstable and requires a long preparation time. Therefore, it is necessary to analyze the traditional starters (ST) and their influence on the flavor and quality of steamed bread to meet people's requirements as a staple food.

RESULTS

The count of yeast, lactic acid bacteria and total microbial population significantly varied in different traditional starters; Saccharomyces and Lactobacillus were the predominant genera. Among the tested samples, fungi were found in ST from Shijiazhuang (SJ), Handan (HD) and Langfang (LF), while bacteria were found in ST from Tangshan (TS) and SJ at sub-predominant levels. In terms of the bread quality, the highest specific volume and porosity were in XT-CSB (Xingtai); the highest height/diameter ratio was in SJ-CSB; and the highest sensory score was in TS-CSB. A total of 26 aroma compounds (VIP > 1; variable importance for predictive components) were identified to discriminate CSB fermented with different starters, which were separated by stepwise canonical discriminant analysis using two functions. The correlation analysis among microbiota, aroma compounds and bread quality showed a higher contribution of bacteria than of fungi.

CONCLUSION

Differences in microbial profiles caused different aroma profiles and quality of CSB; and the CSB fermented with traditional starters were sufficiently separated by stepwise canonical discriminant analysis based on aroma compounds. © 2023 Society of Chemical Industry.

Antioxidant and Functional Features of Pre-Fermented Ingredients Obtained by the Fermentation of Milling By-Products

The use of milling by-products as ingredients in food formulations has increased gradually over the past years, due to their well-recognized health properties. Fermentation performed with selected microbial strains or microbial consortia is the most promising way to reduce antinutritional factors of cereals and bran, while increasing their nutritional and functional properties. This work, developed within the BBI project INGREEN, was aimed to study the functional, nutritional and technological features of a pre-fermented ingredient obtained from the fermentation of a mixture of rye bran and wheat germ by a selected microbial consortium composed of yeasts (Kazachstania unispora and Kazachstania servazii) and lactic acid bacteria (Latilactobacillus curvatus) using as reference the unfermented mixture and the same mixture fermented by a baker’s yeast. The selected microbial consortium improved the complexity of the volatile molecules such as acids, alcohols and esters. A better retention of color parameters was maintained compared to the product fermented by a baker’s yeast. In addition, the fermentation by the selected consortium showed a significant increase in short chain fatty acids (more than 5-fold), antioxidant activity (22–24%), total phenol content (53–71%), bioactive peptides (39–52%), a reduction of 20–28% in phytic acid content and an increase in prebiotic activity not only compared to the unfermented product but also compared to the preferment obtained with a baker’s yeast. Overall, the fermentation by the selected microbial consortium can be considered a valuable way to valorize milling by-products and promote their exploitation as food ingredients.

Impact of Leavening Agent and Wheat Variety on Bread Organoleptic and Nutritional Quality

Leavened bread can be made with different wheat varieties and leavening agents. Several studies have now demonstrated that each of these factors can play a role in bread quality. However, their relative impact in artisanal bread making remains to be elucidated. Here, we assessed the impact of two wheat varieties as well as the impact of sourdoughs and yeasts on multiple components of bread organoleptic and nutritional quality. Using a participatory research approach including scientists and bakers, we compared breads leavened with three different sourdoughs and three different commercial yeasts as well as a mix of sourdough and yeast. Breads were made from two wheat varieties commonly used in organic farming: the variety “Renan” and the landrace “Barbu”. Except for bread minerals contents that mostly depended on wheat variety, bread quality was mostly driven by the fermenting agent. Sourdough breads had lower sugar and organic acids contents. These differences were mostly attributable to lower amounts of maltose and malate. They also had a higher proportion of soluble proteins than yeast breads, with specific aroma profiles. Finally, their aroma profiles were specific and more diverse compared to yeast breads. Interestingly, we also found significant nutritional and organoleptic quality differences between sourdough breads. These results highlight the value of sourdough bread and the role of sourdough microbial diversity in bread nutritional and organoleptic quality.

Improvement of Sourdough and Bread Qualities by Fermented Water of Asian Pears and Assam Tea Leaves with Co-Cultures of Lactiplantibacillus plantarum and Saccharomyces cerevisiae

Qualities of sourdough and sourdough bread using fermented water from Asian pears and Assam tea leaves with Lactiplantibacillus plantarum 299v and Saccharomyces cerevisiae TISTR 5059 as starter cultures were evaluated. Changes in the growth of lactic acid bacteria and yeast, pH, sourdough height, total phenolic contents (TPCs) and antioxidant activities detected by ORAC, FRAP and DPPH radical scavenging assays were monitored during sourdough production. Mature sourdough was achieved within 4 h after 18 h retard fermentation and used for bread production. The bread was then analyzed to determine chemical and physical properties, nutritional compositions, TPCs, antioxidant activities and sensory properties as well as shelf-life stability. Results showed that fermented water significantly promoted the growth of yeast and increased TPCs and antioxidant activities of sourdough. Compared to common sourdough bread, fermented water sourdough bread resulted in 10% lower sugar and 12% higher dietary fiber with improved consumer acceptability; TPCs and antioxidant activities also increased by 2–3 times. The fermented water sourdough bread maintained microbial quality within the standard range, with adequate TPCs after storage at room temperature for 7 days. Fermented water from Asian pears and Assam tea leaves with L. plantarum 299v and S. cerevisiae TISTR 5059 as starter cultures improved dough fermentation and bread quality.

Relationship between Microbial Composition of Sourdough and Texture, Volatile Compounds of Chinese Steamed Bread

The objective of this work was to explore the relationship between the microbial communities of sourdoughs collected from the Xinjiang and Gansu areas of China and the quality of steamed bread. Compared to yeast-based steamed bread, sourdough-based steamed bread is superior in terms of its hardness, adhesiveness, flexibility, and chewiness. It is rich in flavor compounds, but a significant difference in volatile flavor substances was observed between the two sourdoughs. A total of 19 strains of lactic acid bacteria (LAB) were isolated from the Gansu sourdough sample, in which Lactiplantibacillus plantarum and Pediococcus pentosaceus were the dominant species, accounting for 42.11% and 36.84%, respectively. A total of 16 strains of LAB were isolated from the Xinjiang sourdough sample, in which Lactiplantibacillus plantarum was the dominant species, accounting for 75%. High-throughput sequencing further confirmed these results. Clearly, the species diversity of Gansu sourdough was higher. The volatile profiles of the sourdoughs were similar, but differences in the individual volatile compounds were detected between the sourdoughs of the Gansu and Xinjiang regions. These results point out that the differences in the microbiota and the dominant strains lead to differences in the quality of sourdoughs from region to region. This investigation offers promising guidance on improving the quality of traditional steamed bread by adjusting the microorganisms in sourdough.

Improving accessibility and bioactivity of raw, germinated and enzymatic-treated spelt (Triticum spelta L.) seed antioxidants by fermentation

Lactic acid, alcoholic, combined and spontaneous fermentation of raw, germinated and enzymatic-treated spelt seeds significantly improved the content of extractable and bound phenolics and considerably increased the extractable:bound ratio, and therefore positively affected the accessibility of the spelt antioxidants. The highest extractable and bound individual phenolic contents and in vitro antioxidant activities of extracts were obtained following fermentation of germinated spelt seeds with Saccharomyces cerevisiae, while for enzymatic-treated seeds, Lactobacillus plantarum (alone or with S. cerevisiae) was the most effective. For extractable phenolics, trans-ferulic acid increased the most in yeast-fermented germinated seeds (2922%); for bound phenolics, cis-ferulic acid showed the greatest relative increase in yeast-fermented raw spelt seeds (466%). Spontaneous fermentation of germinated and enzymatic-treated samples decreased intracellular oxidation most effectively, probably due to apigenin derivatives. Cellular uptake of bound hydroxycinnamic acids was significantly higher than that of extractable hydroxycinnamic acids; however, the latter were more efficient in vivo antioxidants.

Date Seeds Flour Used as Value-Added Ingredient for Wheat Sourdough Bread: An Example of Sustainable Bio-Recycling

Our study proposed date seeds flour (DSF) as an innovative ingredient for sourdough bread production through sustainable bio-recycling. We isolated autochthonous lactic acid bacteria and yeasts from DSF and DSF-derived doughs to build up a reservoir of strains from which to select starters ensuring rapid adaptation and high ecological fitness. The screening based on pro-technological criteria led to the formulation of a mixed starter consisting of Leuconostoc mesenteroides, Lactiplantibacillus plantarum, and Saccharomyces cerevisiae strains, which allowed obtaining a mature type I sourdough after consecutive refreshments, in which an aliquot of the durum wheat flour (DWF) was replaced by DSF. The resulting DSF sourdough and bread underwent an integrated characterization. Sourdough biotechnology was confirmed as a suitable procedure to improve some functional and sensory properties of DWF/DSF mixture formulation. The radical scavenging activity increased due to the consistent release of free phenolics. Perceived bitterness and astringency were considerably diminished, likely because of tannin degradation.

Lactic acid bacteria synergistic fermentation affects the flavor and texture of bread

Fermentation strains play a key role in the quality of bread. The combination of yeast and lactic acid bacteria (LAB) may effectively improve the function and nutritional properties of bread. In this study, the dough was fermented to make bread by using single strain (Saccharomyces cerevisiae, mode A), the combination of two strains (S. cerevisiae and Lactiplantibacillus plantarum, mode B; S. cerevisiae and Lactobacillus delbrueckii, mode C), or three strains (S. cerevisiae, L. plantarum, and L. delbrueckii, mode D). The specific volume, texture, and aroma substances of bread were evaluated. The possibility of mixed fermentation of selected yeast and LAB to replace natural fermentation dough was evaluated. The results showed that the specific volume of bread in mode B was 15.2% higher than that of mode A. The structure was softer and the taste was more vigorous in mode B bread. The content of volatile compounds was highest in mode B bread among the four mode bread. The characteristic flavors were ethyl 2-hydroxypropionate and z-3-hexenol. The cofermentation in mode B made the bread aroma richer and gave better aroma characteristics to bread. Therefore, the fermentation of S. cerevisiae and L. plantarum can be recommended to replace naturally fermented dough to improve the quality of bread. PRACTICAL APPLICATION: L. plantarum and L. delbrueckii, separately or together, assisted in yeast fermentation to make bread. The specific volume, texture, and aroma substances of bread were evaluated to replace natural fermented dough with mixed fermentation. L. plantarum-assisted yeast fermentation improved the specific volume, texture, and aroma of bread. The characteristic flavors were ethyl 2-hydroxypropionate and z-3-hexenol in bread. Therefore, the fermentation of S. cerevisiae and L. plantarum could replace naturally fermented dough to improve the quality of bread.

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.

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.

Non-Conventional Yeasts as Alternatives in Modern Baking for Improved Performance and Aroma Enhancement

Saccharomyces cerevisiae remains the baker’s yeast of choice in the baking industry. However, its ability to ferment cereal flour sugars and accumulate CO2 as a principal role of yeast in baking is not as unique as previously thought decades ago. The widely conserved fermentative lifestyle among the Saccharomycotina has increased our interest in the search for non-conventional yeast strains to either augment conventional baker’s yeast or develop robust strains to cater for the now diverse consumer-driven markets. A decade of research on alternative baker’s yeasts has shown that non-conventional yeasts are increasingly becoming important due to their wide carbon fermentation ranges, their novel aromatic flavour generation, and their robust stress tolerance. This review presents the credentials of non-conventional yeasts as attractive yeasts for modern baking. The evolution of the fermentative trait and tolerance to baking-associated stresses as two important attributes of baker’s yeast are discussed besides their contribution to aroma enhancement. The review further discusses the approaches to obtain new strains suitable for baking applications.

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.

Co-culture fermentation of Pediococcus acidilactici XZ31 and yeast for enhanced degradation of wheat allergens

Previous researchers have shown the potential of sourdough and isolated lactic acid bacteria in reducing wheat allergens. As the interactions of lactic acid bacteria with yeast is a key event in sourdough fermentation, we wished to investigate how yeast affects metabolism of lactic acid bacteria, thereby affecting protein degradation and antigenic response. In this study, three strains isolated from sourdough were selected for dough fermentation, namely Pediococcus acidilactici XZ31, Saccharomyces cerevisiae JM1 and Torulaspora delbrueckii JM4. The changes in dough protein during the fermentation process were studied. Protein degradation and antigenic response in dough inoculated with Pediococcus acidilactici XZ31 monoculture and co-culture with yeast were mainly evaluated by SDS-PAGE, immunoblotting, ELISA and Liquid chromatography-tandem mass spectrometry assay. The whole-genome transcriptomic changes in Pediococcus acidilactici XZ31 were also investigated by RNA sequencing. The results showed that water/salt soluble protein and Tri a 28/19 allergens content significantly decreased after 24 h fermentation. Co-culture fermentation accelerated the degradation of protein, and reduced the allergen content to a greater extent. RNA-sequencing analysis further demonstrated that the presence of yeast could promote protein metabolism in Pediococcus acidilactici XZ31 for a certain period of time. These results revealed a synergistic effect between Pediococcus acidilactici XZ31 and yeast degrading wheat allergens, and suggested the potential use of the multi-strain leavening agent for producing hypoallergenic wheat products.

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.

Characterization of Microbial Dynamics and Volatile Metabolome Changes During Fermentation of Chambourcin Hybrid Grapes From Two Pennsylvania Regions

Microbial diversity present on grapes in wineries, and throughout fermentation has been associated with important metabolites for final wine quality. Although microbiome-metabolome associations have been well characterized and could be used as indicators of wine quality, the impact of regionality on the microbiome and metabolome is not well known. Additionally, studies between microbiome and metabolome have been conducted on single species grape such as Vitis vinifera instead of other species and interspecific hybrids. Although the Pennsylvania wine industry is relatively young compared to California, the industry has been experiencing rapid growth over the past decade and is expected to continue to grow in the future. Pennsylvania's climate of cold winters and high levels of rainfall throughout the growing season favors cultivation of interspecific hybrid grapes such as Vitis ssp. Chambourcin, one of the most commonly grown hybrid varieties in the state. Chambourcin is a prime candidate for studying the impact of regionality on microbiome-metabolome interactions as interspecific hybrid varieties could shape the future of winemaking. Here, we identify for the first time the regional distribution of microbial communities and their interactions with volatile metabolome during fermentation (0-20 days) by integrating high throughput Illumina sequencing (16S and ITS) and headspace-solid phase microextraction-gas chromatography-mass spectrometry. Analyzing 88 samples from nine wineries in the Central and East Pennsylvania regions, we observed high microbial diversity during early stages of fermentation (1-4 days) where non-Saccharomyces yeasts such as Starmerella and Aureobasidium and non-Oenococcus bacteria, Sphingomonas, likely contribute to microbial terroir to the resulting wines. Furthermore, key differentiators between two regions in Pennsylvania, as identified by LEfSe analysis, include the fungal genera Cladosporium and Kazachstania and the bacterial genera Lactococcus and Microbacterium. Moreover, 29 volatile fermentation metabolites were discriminated significantly (variable importance in projection > 1) between the two regions as shown by Partial Least Squares-Discriminant Analysis. Finally, Spearman's correlation identified regional differences of microbial-metabolite associations throughout fermentation that could be used for targeted microbiome manipulation to improve wine quality and preserve regionality. In summary, these results demonstrate the microbial signatures during fermentation and differential microorganisms and metabolites further support impact of regionality on Chambourcin wines in Pennsylvania.

Screening of Lactic Acid Bacteria and Yeasts from Sourdough as Starter Cultures for Reduced Allergenicity Wheat Products

Previous researchers have shown the potential of sourdough or related lactic acid bacteria in reducing wheat allergens. However, there are no mixed or single cultures for producing reduced allergenicity wheat products. In this study, twelve strains of lactic acid bacteria and yeast isolated from sourdough were evaluated for their ability to hydrolyze proteins and ferment dough. Strain Pediococcus acidilacticiXZ31 showed higher proteolytic activity on both casein and wheat protein substrates, and had strong ability to reduce wheat protein allergenicity. The tested Saccharomyces and non-Saccharomyces showed limited proteolysis. Strains Torulaspora delbrueckii JM1 and Saccharomyces cerevisiae JM4 demonstrated a higher capacity to ferment dough compared to other yeasts. These strains may be applied as starters for the preparation of reduced allergenicity wheat products.

Interactions between Kazachstania humilis Yeast Species and Lactic Acid Bacteria in Sourdough

Sourdoughs harbor simple microbial communities usually composed of a few prevailing lactic acid bacteria species (LAB) and yeast species. However, yeast and LAB found in sourdough have been described as highly diverse. Even if LAB and yeast associations have been widely documented, the nature of the interactions between them has been poorly described. These interactions define the composition and structure of sourdough communities, and therefore, the characteristics of the final bread product. In this study, the nature of the interactions between strains of two commonly found sourdough yeast species, Kazachstania humilis and Saccharomyces cerevisiae, and lactic acid bacteria isolated from sourdoughs has been analyzed. Population density analysis showed no evidence of positive interactions, but instead revealed neutral or negative asymmetric interaction outcomes. When in coculture, the yeasts´ population size decreased in the presence of LAB regardless of the strain, while the LAB´s population size was rarely influenced by the presence of yeasts. However, a higher maltose depletion was shown in maltose-negative K. humilis and maltose-positive obligately heterofermentative LAB cocultures compared to monocultures. In addition, tested pairs of obligately heterofermentative LAB and K. humilis strains leavened dough as much as couples of LAB and S. cerevisiae strains, while K. humilis strains never leavened dough as much as S. cerevisiae when in monoculture. Taken together, our results demonstrate that even if higher fermentation levels with increased maltose depletion were detected for K. humilis and obligately heterofermentative LAB pairs, these interactions cannot be ecologically classified as positive, leading us to rethink the established hypothesis of coexistence by facilitation in sourdoughs.