Exploitation of autochthonous Tuscan sourdough yeasts as potential starters

Postbiotic characterization of a potential probiotic yeast isolate, and its microencapsulation in alginate beads coated layer-by-layer with chitosan

Considering biosafety concerns and survivability limitations of probiotics (PRO) under different stresses, application of postbiotics and encapsulated PRO has received considerable attentions. Accordingly, the objective of the present study was to investigate the postbiotic capabilities of a potential PRO yeast isolate and the effect of encapsulation with alginate (Alg) and chitosan (Ch) on its survival under SGI conditions. Sequencing results of the PCR products led to the identification of Saccharomyces cerevisiae as the selected potential PRO yeast isolated from wheat germ sourdough. High survival of the isolate under simulated gastrointestinal (SGI) conditions (95.74%), its proper adhesion abilities, as well as its potent inhibitory activity against Listeria monocytogenes (75.84%) and Aspergillus niger (77.35%) were approved. Interestingly, the yeast cell-free supernatant (CFS) showed the highest antioxidant (84.35%) and phytate-degrading (56.19%) activities compared to the viable and heat-dead cells of the isolate. According to the results of the HPLC-based assay, anti-ochratoxin A (OTA) capability of the dead cells was also significantly (P < 0.05) higher than that of the viable cell. Meanwhile, the yeast CFS had no anti-OTA and antimicrobial activities against the foodborne bacteria and fungi tested. Further, microencapsulation of the yeast isolate in Alg beads coated layer-by-layer with Ch (with 77.02% encapsulation efficacy and diameter of 1059 μm based on the field emission scanning electron microscopy analysis) significantly enhanced its survivability under SGI conditions in comparison with the free cells. In addition, electrostatic cross-linking between negatively charged carboxylic groups of Alg and positively charged amino groups of Ch was verified in accordance with Fourier transform infrared and zeta potential data. Human and/or industrial food trials in future are needed for practical applications of these emerging ingredients.

Identification and biotechnological characterisation of yeast microbiota involved in spontaneous fermented wholegrain sourdoughs

BACKGROUND

New strategies in the cereal-based industry has brought about the elaboration of new sourdoughs with better microbial stability and safety as well as nutritional value such as those based on wholegrain flours. This has led to an increasing interest in the selection of adapted yeasts for using them as new starters. Therefore, this study aimed to isolate, identify, and characterise diverse yeast strains from wholegrain spontaneous sourdoughs.

RESULTS

Three wholegrain sourdoughs (wheat, rye, and oat) were fermented and monitored for 96 h. Minimum pH values ranged from 3.1 to 3.5 while maximum yeast counts were reached at 72 h. A total of 76 yeast isolates were identified by polymerase chain reaction random amplification of polymorphic DNA (PCR-RAPD) and catalogued in six different species by sequencing the internal transcribed spacer (ITS) region. The major species were Candida glabrata, Saccharomyces cerevisiae, Kazachstania unispora, and Wickerhamomyces anomalus. The studied kinetic parameters of the growth curves (λ, G, ODmax , and μmax ) and the fermentation capacity allowed to ascertain that 12 and 5 strains, respectively, were better than baker's yeast control. The fibre assimilation ability (cellulose, xylose, and β-glucan) was observed in the 27% of the strains and only four strains showed phytase activity.

CONCLUSIONS

The yeast population in the three wholegrain sourdoughs were variable along the fermentation time. Genetic identification showed that strains and species presented a different trend for each sourdough although common species were determined (e.g., W. anomalus). Candida glabrata (4T1) and Saccharomyces cerevisiae (3A6) showed, respectively, better kinetics and impedance results than the positive control, while W. anomalus (C4) was notorious in fibre assimilation and phytase degradation. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Molecular and Technological Characterization of Saccharomyces cerevisiae from Sourdough

DNA markers help detect the intraspecific genetic diversity of yeast strains. Eight ISSR (Inter Simple Sequence Repeats) primers were used to assess the intraspecific diversity of Saccharomyces cerevisiae (n = 96) from different populations (n = 3), evaluate the technological characteristics, and investigate trait-loci associations. The primers amplified 154 reproducible and scorable bands, of which 79.87% were polymorphic. The UPGMA (unweighted pair group method with arithmetic mean) dendrogram clustered 96 isolates into two main clusters, supported by STRUCTURE HARVESTER results (ΔK = 2). Analysis of molecular variance (AMOVA) indicated significant genetic differences between (15%) and within the populations (85%) (p < 0.001). Twenty-nine genetically distinct strains were selected for the technological characterization. Principal component analysis (PCA) revealed that five strains with high fermentation capacity, leavening activity, high growth index at 37 °C, and harsh growth conditions were technologically relevant. Trait-loci association analyses indicated that the highest correlation (r = 0.60) was recorded for the fermentation capacity on the 8th and 113th loci, amplified by ISSR-1 and ISSR-6 primers, respectively (p < 0.05). The strains yielding high performances and the associated loci amplified by ISSR markers possess a high potential to generate locus-specific primers to target the strains with high fermentation capacity.

Probiotics in the Sourdough Bread Fermentation: Current Status

Sourdough fermentation is an ancient technique to ferment cereal flour that improves bread quality, bringing nutritional and health benefits. The fermented dough has a complex microbiome composed mainly of lactic acid bacteria and yeasts. During fermentation, the production of metabolites and chemical reactions occur, giving the product unique characteristics and a high sensory quality. Mastery of fermentation allows adjustment of gluten levels, delaying starch digestibility, and increasing the bio-accessibility of vitamins and minerals. This review focuses on the main steps of sourdough fermentation, the microorganisms involved, and advances in bread production with functional properties. The impact of probiotics on human health, the metabolites produced, and the main microbial enzymes used in the bakery industry are also discussed.

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.

Storage time and temperature affect microbial dynamics of yeasts and acetic acid bacteria in a kombucha beverage

Kombucha is a mildly sweet, slightly acidic fermented beverage, commercially available worldwide, that has attracted increasing consumers' interest due to its potential health benefits. Kombucha is commonly prepared using sugared black or green tea, but also other plant substrates are frequently utilised. Kombucha is obtained by fermentation using a symbiotic culture of bacteria and yeasts, whose composition varies depending on inoculum origin, plant substrates and environmental conditions. After fermentation, kombucha drinks are usually refrigerated at 4 °C, in order to maintain their biological and functional properties. There are no reports on the fate of microbial communities of kombucha in relation to long-term storage time and temperature. Here, for the first time, we monitored the diversity and dynamics of the microbial communities of a kombucha beverage fermented with different herbs during storage at 4 °C and at room temperature, for a period of 90 days, utilising culture-dependent and independent approaches. Moreover, cultivable yeasts and acetic acid bacteria (AAB) were isolated from the beverage, inoculated in pure culture, identified by molecular methods, and yeasts assessed for their functional properties. Total yeast counts were not affected by storage temperature and time, although their community composition changed, as Saccharomyces species significantly decreased after 45 days of storage at room temperature, completely disappearing after 90 days. On the other hand, Dekkera anomala (Brettanomyces anomalus), representing 52 % of the yeast isolates, remained viable up to 90 days at both storage temperatures, and was able to produce high levels of organic acids and exopolysaccharides. Data from DGGE (Denaturing Gradient Gel Electrophoresis) band sequencing confirmed that it was the dominant yeast species in all samples across storage. Other yeast isolates were represented by Saccharomyces and Zygosaccharomyces species. Among AAB, Gluconobacter oxydans, Novacetimonas hansenii and Komagataeibacter saccharivorans represented 46, 36 and 18 % of the isolates, whose occurrence remained unchanged across storage at 4 °C and did not vary up to 20 days of storage at room temperature. This work showed that the combination of culture-dependent and independent approaches is important for obtaining a complete picture of the distinctive core microbial community in kombucha beverages during storage, elucidating its diversity and composition, and preliminary characterizing yeast strains with putative functional activities.

Dynamics of microbial communities, flavor, and physicochemical properties of pickled chayote during an industrial-scale natural fermentation: Correlation between microorganisms and metabolites

Pickled chayote is a Chinese fermented vegetable with unique flavors and is favored by local consumers. However, little is known about its quality changes and microbial community succession during fermentation and the relationship between microbes and quality. In the work, the physicochemical quality attributes (pH, acidity, nitrite, texture, and color) and flavor properties (sugars, organic acids, free amino acid [FAA], and volatiles) were investigated. The results revealed that organic acids, FAAs, and key volatiles (esters, terpenes, alcohols, and phenols) significantly increased during fermentation. Lactobacillus was the dominant bacterial genus with Lactobacillus alimentarius being the prevalent species; Kazachstania and Pichia were dominant fungal genera with Kazachstania humilis and Pichia membranifaciens being the prevalent species. The microbial metabolic network found that bacteria (L. alimentarius, L. futsaii, and L. paralimentarius) and fungi (K. humilis and P. membranifaciens) played significant roles in the physicochemical changes and flavor production of pickled chayote.

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.

Assessment of Yeasts as Potential Probiotics: A Review of Gastrointestinal Tract Conditions and Investigation Methods

Probiotics are microorganisms (including bacteria, yeasts and moulds) that confer various health benefits to the host, when consumed in sufficient amounts. Food products containing probiotics, called functional foods, have several health-promoting and therapeutic benefits. The significant role of yeasts in producing functional foods with promoted health benefits is well documented. Hence, there is considerable interest in isolating new yeasts as potential probiotics. Survival in the gastrointestinal tract (GIT), salt tolerance and adherence to epithelial cells are preconditions to classify such microorganisms as probiotics. Clear understanding of how yeasts can overcome GIT and salt stresses and the conditions that support yeasts to grow under such conditions is paramount for identifying, characterising and selecting probiotic yeast strains. This study elaborated the adaptations and mechanisms underlying the survival of probiotic yeasts under GIT and salt stresses. This study also discussed the capability of yeasts to adhere to epithelial cells (hydrophobicity and autoaggregation) and shed light on in vitro methods used to assess the probiotic characteristics of newly isolated yeasts.

Microbial Consortia Involved in Traditional Sicilian Sourdough: Characterization of Lactic Acid Bacteria and Yeast Populations

Sourdough is one of the oldest starters traditionally used for making baked goods, offering several advantages to the sensory, rheology, and shelf life of final products. The present study investigated, for the first time, the microbiota of spontaneously fermented Maiorca dough samples collected from bakeries located in Sicily (Italy). Four sourdough samples (M1, M2, M3, and M4), were produced using Triticum vulgare Host. var. albidum Koern (Maiorca grain) were subjected to LAB and yeasts isolation and identification at the species level. The in-depth characterization of the lactobacilli population revealed that Lactiplantibacillus plantarum and Levilactobacillus brevis unquestionably dominated the Maiorca sourdough ecosystem. Concerning the yeasts community, high species diversity was found. Saccharomyces cerevisiae and Wickerhamomyces anomalus were the most frequently isolated species. In addition, Torulaspora delbrueckii, Pichia kluyveri, Candida boidinii, and Candida diddensiae were also detected. Investigations on both pro-technological and functional traits of the isolated strains could lead to the selection of starters for the production of baked goods.

Novel Yeasts Producing High Levels of Conjugated Linoleic Acid and Organic Acids in Fermented Doughs

Traditional fermented foods are obtained by a complex consortium of autochthonous microorganisms producing a wide variety of bioactive compounds, thus representing a reservoir of strains with new functional properties. Here, doughs obtained using five different wholegrain flours were singly fermented with selected yeast strains, which were evaluated for their functional traits. Lactate, volatile fatty acids and conjugated linoleic acid isomers produced by fermented doughs were detected by HPLC, while dough anti-inflammatory capacity was measured on human peripheral blood mononuclear cells by flow cytometry. Yeast potential probiotic activity was assessed by evaluating their resistance to simulated gastric and intestinal fluids. For the first time we report evidence of yeast strains producing high levels of the conjugated linoleic acid (CLA) isomer CLA 10-12tc and propionic acid, which are known for their specific health benefits. Moreover, such yeast strains showed an anti-inflammatory capacity, as revealed by a significantly decreased production of the strongly pro-inflammatory cytokine IL-1β. All our Saccharomyces cerevisiae strains were remarkably resistant to simulated gastric and intestinal fluids, as compared to the commercial probiotic strain. The two strains S. cerevisiae IMA D18Y and L10Y showed the best survival percentage. Our novel yeast strains may be exploited as valuable functional starters for the industrial production of cereal-based innovative and health-promoting fermented foods.

Bioactive Properties of Breads Made with Sourdough of Hull-Less Barley or Conventional and Pigmented Wheat Flours

Functional and nutritional properties of baked goods can be enhanced by the use of sourdough fermentation, which is defined as a mixture of water and flour fermented by lactobacilli (LAB) and yeasts. Previous data highlighted the ability of sourdoughs obtained with selected LAB strains and commercial flour to produce bioactive peptides equipped with antioxidant and anti-inflammatory properties. More recently, it has been proven that choosing the most suitable combination of selected LAB and high-functional-value flours greatly increase the amount of low-molecular-weight antioxidant compounds responsible for improving the nutritional value of the products. This work aimed to isolate bioactive peptides both from sourdoughs and baked breads obtained with pigmented wheat and barley and a selected combination of LABs. Soluble water extracts were obtained, and low-molecular-weight peptides were isolated. Antioxidant activity was detected by assaying the intracellular ROS production in stressed cultured macrophages, treated with peptides. Moreover, anti-inflammatory activity, highlighted by NFkB pathway inhibition and by COX2 reduction in stressed cells, was demonstrated for peptides obtained from breads. The results allowed the conclusion that the combination of flours and LAB used in the present manuscript led to the production of bakery products with beneficial effects on oxidative and inflammatory status.

Technological and Safety Attributes of Lactic Acid Bacteria and Yeasts Isolated from Spontaneously Fermented Greek Wheat Sourdoughs

The aim of the present study was to assess the technological and safety potential of 207 lactic acid bacteria (LAB) and 195 yeast strains isolated from spontaneously fermented Greek wheat sourdoughs. More accurately, the amylolytic, proteolytic, lipolytic, phytase and amino acid decarboxylase activities, along with the production of exopolysaccharides and antimicrobial compounds by the LAB and yeast isolates, were assessed. A well diffusion assay revealed seven proteolytic LAB and eight yeast strains; hydrolysis of tributyrin was evident only in 11 LAB strains. A further Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) indicated partial hydrolysis of gluten. Lipolysis kinetics over 21 days was applied, exhibiting that lipolytic activity ranged from 6.25 to 65.50 AU/mL. Thirteen LAB inhibited Penicillium olsonii and Aspergillus niger growth and 12 yeast strains inhibited Pe. chrysogenum growth. Twenty-one Lactiplantibacillus plantarum strains exhibited inhibitory activity against Listeria monocytogenes, as well as several sourdough-associated isolates. The structural gene encoding plantaricin 423 was detected in 19 Lcb. plantarum strains, while the structural genes encoding plantaricins NC8, PlnE/F, PlnJ/K, and S were detected in two Lcb. plantarum strains. None of the microbial strains tested exhibited exopolysaccharide (EPS) production, amino acid decarboxylase, amylolytic or phytase activity. The technological and safety potential of the Lcb. plantarum and Wickerhamomyces anomalus strains was highlighted, since some of them exhibited proteolytic, lipolytic, antibacterial and antimould activities.

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.

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.

Characterization and selection of functional yeast strains during sourdough fermentation of different cereal wholegrain flours

The increasing demand for healthy baked goods boosted studies on sourdough microbiota with beneficial metabolic traits, to be used as potential functional starters. Here, 139 yeasts isolated from cereal-based fermented foods were in vitro characterized for their phytase and antioxidant activities. The molecular characterization at strain level of the best 39 performing isolates showed that they did not derive from cross contamination by baker’s yeast. Afterwards, the 39 isolates were in vivo analyzed for their leavening ability, phytase activity and polyphenols content using five different wholegrain flours, obtained from conventional and pigmented common wheat, emmer and hull-less barley. Combining these findings, through multivariate permutation analysis, we identified the 2 best performing strains, which resulted diverse for each flour. Doughs singly inoculated with the selected strains were further analyzed for their antioxidant capacity, phenolic acids, xanthophylls and anthocyanins content. All the selected yeasts significantly increased the total antioxidant activity, the soluble, free and conjugated, forms of phenolic acids and anthocyanins of fermented doughs. This study revealed the importance of a specific selection of yeast strains for wholegrain flours obtained from different cereals or cultivars, in order to enhance the pro-technological, nutritional and nutraceutical traits of fermented doughs.

Large Genetic Intraspecific Diversity of Autochthonous Lactic Acid Bacteria and Yeasts Isolated from PDO Tuscan Bread Sourdough

The diverse metabolites, positively affecting the nutritional, organoleptic and technological traits of leavened baked goods, are produced by different sourdough lactic acid bacteria (LAB) and yeast strains, as the result of their genetic intraspecific diversity. Therefore, the molecular and functional strain-level characterization of sourdough microbiota is crucial to valorize traditional or origin protected baked end-products, develop innovative starter cultures and design functional cereal-based foods. To this aim, the genetic intraspecific diversity of 96 Lactobacillus sanfranciscensis, 65 Kazachstania humilis and three Saccharomyces cerevisiae characterizing Protected Designation of Origin (PDO) Tuscan bread sourdough, was investigated, using P4, P7 and M13 random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), (GTG)5 repetitive element sequence-based (rep)-PCR and inter-delta region analyses, respectively. Regarding LAB, the combination of P4, P7 and M13 RAPD-PCR analyses revealed a huge degree of intraspecific variability, discriminating 43 biotypes out of 96 isolates of L. sanfranciscensis. (GTG)5 rep-PCR showed a discriminatory index of 0.95, grouping the 65 K. humilis isolated from PDO Tuscan bread sourdough in 9 biotypes. The high polymorphism among both LAB and yeast isolates of PDO Tuscan bread sourdough outlines a highly complex microbial community structure, whose relative composition and specific physiological characteristics could be responsible for the peculiar organoleptic, rheological, nutritional and potentially nutraceutical features of PDO Tuscan bread.

Comparison of bacterial communities in gliadin-degraded sourdough (Khamir) sample and non-degraded sample

The study was undertaken to investigate the comparison lying between bacterial communities in autochthonous gliadin-degraded sourdough sample (D13) and non-degraded sample (D50). Degree of gliadin degradation in various samples was determined by Fourier transform infrared spectroscopy and represented samples were selected for 16 S rDNA sequence analysis by Illumina Miseq platform. It was observed, that Proteobacteria (50.65%) and Actinobacteria (6.70%) phyla were more abundant as compared with Firmicutes (42.53%) in D13, however, Firmicutes (83.44) were more abundant, comparatively, in D50 than Proteobacteria (14.97%). Lower taxonomic levels surfaced its more prominent effects. It had been also observed that Lactobacillus genera was the core genera (50.37%) followed by Weissella (27.15%) and Psychrobacter (21.53%) in D50 and D13, respectively. Shannon and Simpson indices indicated that degraded sample had more bacterial diversity and richness compared with non-degraded sample.