Sourdough Fermentation Process Research Articles

Adaptive laboratory evolution for acetic acid-tolerance matches sourdough challenges with yeast phenotypes

Acetic acid tolerance of Saccharomyces cerevisiae is an important trait in sourdough fermentation processes, where the accumulation of acid by the growth of lactic acid bacteria reduces the yeast metabolic activity. In this work, we have carried out adaptive laboratory evolution (ALE) experiments in two sourdough isolates of S. cerevisiae exposed to acetic acid, or alternatively to acetic acid and myriocin, an inhibitor of sphingolipid biosynthesis that sped-up the evolutionary adaptation. Evolution approaches resulted in acetic tolerance, and surprisingly, increased lactic susceptibility. Four evolved clones, one from each parental strain and evolutionary scheme, were selected on the basis of their potential for CO2 production in sourdough conditions. Among them, two showed phenotypic instability characterized by strong lactic sensitivity after several rounds of growth under unstressed conditions, while two others, displayed increased constitutive acetic tolerance with no loss of growth in lactic medium. Genome sequencing and ploidy level analysis of all strains revealed aneuploidies, which could account for phenotypic heterogeneity. In addition, copy number variations (CNVs), affecting specially to genes involved in ion transport or flocculation, and single nucleotide polymorphisms (SNPs) were identified. Mutations in several genes, ARG82, KEX1, CTK1, SPT20, IRA2, ASG1 or GIS4, were confirmed as involved in acetic and/or lactic tolerance, and new determinants of these phenotypes, MSN5 and PSP2, identified.

Impacts of Sourdough Technology on the Availability of Celiac Peptides from Wheat α- and γ-Gliadins: In Silico Approach

Celiac peptide-generating α- and γ-gliadins consist of a disordered N-terminal domain extended by an α-helical-folded C-terminal domain. Celiac peptides, primarily located along the disordered part of α- and γ-gliadin molecules, are nicely exposed and directly accessible to proteolytic enzymes occurring in the gastric (pepsin) and intestinal (trypsin, chymotrypsin) fluids. More than half of the potential celiac peptides identified so far in gliadins exhibit cleavage sites for pepsin. However, celiac peptides proteolytically truncated by one or two amino acid residues could apparently retain some activity toward HLA-DQ2 and HLA-DQ8 receptors in docking experiments. Together with the uncleaved peptides, these still active partially degraded CD peptides account for the incapacity of the digestion process to inactivate CD peptides from gluten proteins. In contrast, sourdough fermentation processes involve other proteolytic enzymes susceptible to the deep degradation of celiac peptides. In particular, sourdough supplemented by fungal prolyl endoproteases enhances the degrading capacities of the sourdough fermentation process toward celiac peptides. Nevertheless, since tiny amounts of celiac peptides sufficient to trigger deleterious effects on CD people can persist in sourdough-treated bread and food products, it is advisable to avoid consumption of sourdough-treated food products for people suffering from celiac disease. As an alternative, applying the supplemented sourdough process to genetically modified low gluten or celiac-safe wheat lines should result in food products that are safer for susceptible and CD people.

Exploiting the Native Microorganisms from Different Food Matrices to Formulate Starter Cultures for Sourdough Bread Production.

The use of sourdough for bread production involves fermentation, which is dominated by lactic acid bacteria (LAB) and yeast. Sourdough can be inoculated with a starter culture or through a food matrix containing microorganisms to initiate sourdough fermentation. Sourdough is used as leavening agent for bread making, and metabolites produced by LAB and yeast confer a specific aroma and flavor profile to bread, thus improving its sensory attributes. However, few publications report the effect of microorganisms from different food products and by-products on sourdough fermentation. This review focuses on using different starter cultures from various food sources, from wheat flour to starter cultures. Additionally, included are the types of sourdough, the sourdough fermentation process, and the biochemical transformations that take place during the sourdough fermentation process.

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.

Lifestyles of sourdough lactobacilli – Do they matter for microbial ecology and bread quality?

Sourdough is used in production of (steamed) bread as leavening agent (type I sourdoughs) or as baking improver to enhance flavour, texture, and shelf life of bread (type II sourdoughs). The long-term propagation of sourdoughs eliminates dispersal limitation and consistently leads to sourdough microbiota that are composed of host adapted lactobacilli. In contrast, community assembly in spontaneous cereal fermentations is limited by dispersal and nomadic or environmental lactic acid bacteria are the first colonizers of these sourdoughs.Propagation of sourdoughs for use as sole leavening agent (type I sourdoughs) dictates fermentation conditions that select for rapid growth. Type I wheat- and rye sourdoughs are consistently populated by insect-adapted lactobacilli, particularly Lactobacillus sanfranciscensis, which is characterized by a small genome size and a restricted metabolic potential. The diverse fermentation conditions employed in industrial or artisanal Type II sourdough fermentation processes also result in a more diverse microbiota. Nevertheless, type II sourdoughs are typically populated by vertebrate host adapted lactobacilli of the L. delbrueckii and L. reuteri groups. Metabolic traits of host-adapted lactobacilli that enhance competitiveness in intestinal ecosystems also provide technological functionality in bread making. Examples include formation of exopolysaccharides, arginine-, glutamine- and glutamate based mechanisms of acid resistance, and glycosyl hydrolases that reduce FODMAP levels in sourdough and sourdough bread. In conclusion, consideration of the lifestyle of sourdough lactobacilli facilitates the selection of competitive and functional sourdough starter cultures.

Omics approaches to understand sourdough fermentation processes

The application of omics methodologies helps to further unravel sourdough fermentation processes. Of all methodologies applied, metagenetics is the most used one to analyse sourdoughs, allowing to elucidate their microbial structure, albeit that it is based on the sequencing of a very small part of whole-community DNA. Although shotgun metagenomics, metatranscriptomics, metaproteomics, and meta-metabolomics are very promising to analyse sourdough fermentations and the terminology is often used in a confusing way, they have not been fully used sensu stricto yet. For instance, up to now, metatranscriptomics is restricted to the use of a functional gene microarray for lactic acid bacteria. Further, meta-metabolomics often deals with metabolite target analysis of sourdough fermentation samples to determine the actual concentrations of residual substrates and metabolites produced as well as to list their volatilome solely. In contrast, genomics has been applied several times, albeit that the whole-genome sequence of only one yeast strain and of 41 lactic acid bacterial strains, originally isolated from sourdoughs, is available. However, the genomics data accessible in public databases should be considered with caution because of inaccurate gene annotations, due to automated annotation pipelines, thereby possibly overruling original, high-quality, well-curated gene annotations.

Microbial Ecology and Process Technology of Sourdough Fermentation.

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

Process analytical technologies in food industry - challenges and benefits: A status report and recommendations.

Process analytical technologies in food industry - challenges and benefits: A status report and recommendations.

Використання борошна з пшениці ваксі в технології кексів на дріжджах

In this article, based on the analysis of cakes production features and waxy wheat flour (amylose-free) technological properties, shown the practicability of its use in the preparation of these products made from yeast dough. It has been determined the influence of waxy wheat flour mass fraction and method of its introduction on the course of the yeast cakes production technological process, namely, gas formation, acid accumulation and raising power of cakes' semi-products, the specific volume of the dough. The obtained results show that the addition of amylose-free flour in the recipe is accompanied by an intensification of the process of alcoholic and lactic acid fermentation, the formation of more loosened structure of sourdough and dough during their maturation, as evidenced by the improvement of their raising power and an increase in the specific volume. Comparative characteristics of methods for introduction flour with modified carbohydrate composition shows that the use of a mixture of baking and amylose-free flour promotes greater intensification of the sourdough fermentation process and by adding the maximum amount of waxy wheat flour in dough kneading - more rapid maturation of dough. It is shown that the use of amylose-free flour will allow to intensify fermentation of cakes' semi-products and to reduce the duration of the yeast cakes production process.

Selected ion flow tube-mass spectrometry for online monitoring of submerged fermentations: a case study of sourdough fermentation.

Selected ion flow tube-mass spectrometry (SIFT-MS) has recently gained interest as an alternative method to traditional GC-MS for the detection of targeted volatile sample compounds, due to its ease of use, its speed and sensitivity, and its potential for real-time quantification. The feasibility of this technique was demonstrated using the case of the production of ethanol during sourdough fermentation. The potential of SIFT-MS as an online monitoring device for food fermentations was further demonstrated by the detection of acetoin in certain sourdough fermentations. This allowed discrimination between sourdough fermentation processes and illustrated the importance of real-time monitoring of food fermentations.

Se-enriched sprouted seeds as functional additives in sourdough fermentation

Sprouted seeds possess potential to stimulate the growth and acidifying activity of lactic acid bacteria. Simultaneous enrichment of the sprouted seeds in deficient selenium may create a multifunctional additive to sourdough fermentation with consequent supplementation of human diet. Bread being a staple diet seems to be a perfect carrier of this micronutrient.In the study germinating seeds revealed high ability to accumulate selenium from watering solution, up to 188 mg Se/kg of dried sprouts in the case of lentil. The process of selenium accumulation strongly depended on the plant species resulting in total Se content in soy and lentil biomass twice as high as in rye or wheat sprouts. A high correlation (R2 = 0.97) between selenium concentration in water and Se accumulation in biomass was observed. Raising of pH from 7.0 to 8.0 increased 2.5 times selenium uptake.The addition of Se-enriched plant biomass had stimulating effect on the sourdough fermentation process allowing to shorten it by 8–16 h, depending on the dose and temperature. Se fortified rye sprouts used in amounts 2.5 g/100 g of flour did not deteriorate sensory quality of bread and raised five times selenium content in it.

2D-fluorescence and multivariate data analysis for monitoring of sourdough fermentation process

Sourdough is used for the manufacture of bakery products, especially rye bread and vital for the development of its typical flavor. Although the process of sourdough fermentation is known thousands of years, still it is not understood in detail. Despite, in modern bread fabrication quality requirements are very high and demand a consequent control not only for the final baking process, but also for the production of intermediates. Characteristic process variables like pH-value and the degree of acidity are typically measured off-line to receive information about the state of the fermentation process. A new approach for monitoring the actual process state is the employment of 2D-fluorescence spectroscopy. As a non-invasive, optical method it is widely used for monitoring various types of bioprocesses, e.g. yeast or bacterial cultivations. In this contribution the application of partial least squares (PLS) regression and principal component regression (PCR) models for prediction of process variables of rye sourdough fermentations are compared to an evaluation where principal component analysis (PCA) is combined with artificial neural networks (ANN) for prediction of pH-value and acidity. For the pH-value PLS regression proved as good as PCR models and the combination of PCA and ANN. The average percentage root mean square error of prediction (pRMSEP) was between 2.5 and 5.1%. For the prediction of the acidity level, the best results were obtained using PLS regression models (pRMSEP: 6.0–8.1%). Smoothing the noisy 2D-fluorescence spectra slightly decreased the errors about 0.6%. Predictions with data sets of varying dough yield and constant temperature led to about 2% better results than data sets with different temperatures and constant dough yield. These results indicate a higher sensitivity of the prediction quality with respect to varying temperature compared to varying dough yield.

Gliadin Degradation Ability of Artisanal Lactic Acid Bacteria, The Potential Probiotics from Dairy Products

Selected Lactobacillus spp. with high protease and acid producing capacity was explored for effective gliadin degradation in wheat sourdough environment. The total titratable acidity (TTA), pH and lactic acid bacteria (LAB) counts were evaluated. At the end of fermentation, the acidity and pH of the sourdough samples reached to 13.49-17.34 and 3.84-3.52 range, respectively. LAB population was enumerated as 107-109 colony forming unit (CFU)/g dough. Gliadin profiles were examined qualitatively using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and reverse phase-high performance liquid chromatography (RP-HPLC) techniques. Especially RP-HPLC could be considered as a sensitive technique and is useful to determine the biochemical changes in gliadin fragmentation throughout sourdough fermentation process. LAB inoculated sourdoughs and chemically acidified sourdoughs generally represent similar gliadin degradation patterns. Although the total removal of gliadin toxicity could not be achieved in all dough formulations, it may be beneficial to use LAB to improve the dough and bread quality through the exploration of its bioconversion by-products.

Microbial ecology of sourdough fermentations: Diverse or uniform?

Sourdough is a specific and stressful ecosystem inhabited by yeasts and lactic acid bacteria (LAB), mainly heterofermentative lactobacilli. On the basis of their inocula, three types of sourdough fermentation processes can be distinguished, namely backslopped ones, those initiated with starter cultures, and those initiated with a starter culture followed by backslopping. Typical sourdough LAB species are Lactobacillus fermentum, Lactobacillus paralimentarius, Lactobacillus plantarum, and Lactobacillus sanfranciscensis. Typical sourdough yeast species are Candida humilis, Kazachstania exigua, and Saccharomyces cerevisiae. Whereas region specificity is claimed in the case of artisan backslopped sourdoughs, no clear-cut relationship between a typical sourdough and its associated microbiota can be found, as this is dependent on the sampling, isolation, and identification procedures. Both simple and very complex consortia may occur. Moreover, a series of intrinsic and extrinsic factors may influence the composition of the sourdough microbiota. For instance, an influence of the flour (type, quality status, etc.) and the process parameters (temperature, pH, dough yield, backslopping practices, etc.) occurs. In this way, the presence of Lb. sanfranciscensis during sourdough fermentation depends on specific environmental and technological factors. Also, Triticum durum seems to select for obligately heterofermentative LAB species. Finally, there are indications that the sourdough LAB are of intestinal origin.

Growth characterization of individual rye sourdough bacteria by isothermal microcalorimetry

The present work tests the feasibility of the isothermal microcalorimetry method to study the performance of individual lactic acid bacteria during solid-state fermentation in rye sourdough. Another aim was to elucidate the key factors leading to the formation of different microbial consortia in laboratory and industrial sourdough during continuous backslopping propagation. Strains of the individual LAB isolated from industrial and laboratory sourdough cycle were grown in 10 kGy irradiated rye dough in vials of an isothermal calorimeter and the power-time curves were obtained. Sugars, organic acids and free amino acids in the sourdough were measured. The OD-time curves of the LAB strains during growth in flour extract or MRS (De Man, Rogosa and Sharpe) broth were also determined. The maximum specific growth rates of Lactobacillus sakei, Lactobacillus brevis, Lactobacillus curvatus and Leuconostoc citreum strains that dominated in backslopped laboratory sourdough were higher than those of Lactobacillus helveticus, Lactobacillus panis, Lactobacillus vaginalis, Lactobacillus casei and Lactobacillus pontis strains originating from industrial sourdough. Industrial strains had higher specific growth rates below pH 4·8. It was supposed that during long-run industrial backslopping processes, the oxygen sensitive species start to dominate because of the O(2) protective effect of rye sourdough. Measurements of the power-time curves revealed that the LAB strains dominating in the industrial sourdough cycle had better acid tolerance but lower maximum growth rate and oxygen tolerance than species isolated from a laboratory sourdough cycle. Isothermal microcalorimetry combined with chemical analysis is a powerful method for characterization of sourdough fermentation process and determination of growth characteristics of individual bacteria in sourdough.

Monitoring the bacterial population dynamics in sourdough fermentation processes by using PCR-denaturing gradient gel electrophoresis.

Four sourdoughs (A to D) were produced under practical conditions by using a starter mixture of three commercially available sourdough starters and a baker's yeast constitutively containing various species of lactic acid bacteria (LAB). The sourdoughs were continuously propagated until the composition of the LAB flora remained stable. Two LAB-specific PCR-denaturing gradient gel electrophoresis (DGGE) systems were established and used to monitor the development of the microflora. Depending on the prevailing ecological conditions in the different sourdough fermentations, only a few Lactobacillus species were found to be competitive and became dominant. In sourdough A (traditional process with rye flour), Lactobacillus sanfranciscensis and a new species, L. mindensis, were detected. In rye flour sourdoughs B and C, which differed in the process temperature, exclusively L. crispatus and L. pontis became the predominant species in sourdough B and L. crispatus, L. panis, and L. frumenti became the predominant species in sourdough C. On the other hand, in sourdough D (corresponding to sourdough C but produced with rye bran), L. johnsonii and L. reuteri were found. The results of PCR-DGGE were consistent with those obtained by culturing, except for sourdough B, in which L. fermentum was also detected. Isolates of the species L. sanfranciscensis and L. fermentum were shown by randomly amplified polymorphic DNA-PCR analysis to originate from the commercial starters and the baker's yeast, respectively.