Emerging fermentation technologies: Development of novel sourdoughs

Application of sourdough in gluten-free bakery products

ABSTRACTSIn recent years, the demand for gluten-free (GF) bakery products has grown rapidly due to the remarkable rising number of celiac patients and the increasing health awareness of GF products. However, GF products generally suffer from defects such as poor sensorial level, low nutritional value, high prices and short shelf life. Sourdough is the important starter culture applied in bakery field, and it has been proven to be ideal for enhancing the overall quality of bakery products. This review aims to systematically reviewed the application of sourdough in GF bakery products and its improvement to GF bakery products in terms of texture, shelf life, nutrition and flavor. Its positive effects derive from the complex metabolic activities of sourdough microorganisms, such as acidification, proteolysis, production of exopolysaccharides (EPS), activation of endogenous enzymes, and production of antibacterial substances. Finally, researchers are encouraged to expand the use of sourdough in GF bakery products to increase the variety of GF products. And the technical and nutritional potential of sourdough should be developed more widely.

Improvement on wheat bread quality by in situ produced dextran-A comprehensive review from the viewpoint of starch and gluten

Deterioration of bread quality, characterized by the staling of bread crumb, the softening of bread crust and the loss of aroma, has caused a huge food waste and economic loss, which is a bottleneck restriction to the development of the breadmaking industry. Various bread improvers have been widely used to alleviate the issue. However, it is noteworthy that the sourdough technology has emerged as a pivotal factor in this regard. In sourdough, the metabolic breakdown of carbohydrates, proteins, and lipids leads to the production of exopolysaccharides, organic acids, aroma compounds, or prebiotics, which contributes to the preeminent ability of sourdough to enhance bread attributes. Moreover, sourdough exhibits a "green-label" feature, which satisfies the consumers' increasing demand for additive-free food products. In the past two decades, there has been a significant focus on sourdough with in situ produced dextran due to its exceptional performance. In this review, the behaviors of bread crucial compositions (i.e., starch and gluten) during dough mixing, proofing, baking and bread storing, as well as alterations induced by the acidic environment and the presence of dextran are systemically summarized. From the viewpoint of starch and gluten, results obtained confirm the synergistic amelioration on bread quality by the coadministration of acidity and dextran, and also highlight the central role of acidification. This review contributes to establishing a theoretical foundation for more effectively enhancing the quality of wheat breads through the application of in situ produced dextran.

Weissella cibaria riboflavin-overproducing and dextran-producing strains useful for the development of functional bread

This work describes a method for deriving riboflavin overproducing strains of Weissella cibaria by exposing three strains (BAL3C-5, BAL3C-7, and BAL3C-22) isolated from dough to increasing concentrations of roseoflavin. By this procedure, we selected one mutant overproducing strain from each parental strain (BAL3C-5 B2, BAL3C-7 B2, and BAL3C-22 B2, respectively). Quantification of dextran and riboflavin produced by the parental and mutant strains in a defined medium lacking riboflavin and polysaccharides confirmed that riboflavin was only overproduced by the mutant strains, whereas dextran production was similar in both mutant and parental strains. The molecular basis of the riboflavin overproduction by the mutants was determined by nucleotide sequencing of their rib operons, which encode the enzymes of the riboflavin biosynthetic pathway. We detected a unique mutation in each of the overproducing strains. These mutations, which map in the sensor domain (aptamer) of a regulatory element (the so-called FMN riboswitch) present in the 5' untranslated region of the rib operon mRNA, appear to be responsible for the riboflavin-overproducing phenotype of the BAL3C-5 B2, BAL3C-7 B2, and BAL3C-22 B2 mutant strains. Furthermore, the molecular basis of dextran production by the six W. cibaria strains has been characterized by (i) the sequencing of their dsr genes encoding dextransucrases, which synthesize dextran using sucrose as substrate, and (ii) the detection of active Dsr proteins by zymograms. Finally, the parental and mutant strains were analyzed for in situ production of riboflavin and dextran during experimental bread making. The results indicate that the mutant strains were able to produce experimental wheat breads biofortified with both riboflavin and dextran and, therefore, may be useful for the manufacture of functional commercial breads.

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

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

Extraction, purification and characterisation of exopolysaccharides produced by newly isolated lactic acid bacteria strains and the examination of their influence on resistant starch formation

Exopolysaccharides (EPS) were produced by four newly isolated lactic acid bacteria strains, then further extracted, separated and characterised under standardised conditions. Using a sucrose carbon source, these LAB strains belonging to Weissella confusa/cibaria produced EPS with a dextran high molecular weight fraction. The obtained yields of EPS ranged from 3.2 g/L to 47.1 g/L and outstandingly high yields were obtained using Weissella confusa/cibaria 3MI3 isolated from spontaneous spelt sourdough. After purification the influence of EPS-dextran of molar mass 3,244,000 g/mol on resistant starch formation in wheat starch pastes and pasted samples after temperature-cycled storage was examined. Size exclusion chromatography with post-column derivatisation revealed that a 1.5% share of EPS dextran limited formation of high molar mass resistant starch in starch pastes during storage. This work provides new insight on hindering resistant starch formation by using EPS, which could be efficiently produced in sourdough, thus improving the properties of sourdough bread.

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

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

Isolation and characterization of indigenous Weissella confusa for in situ bacterial exopolysaccharides (EPS) production in chickpea sourdough

Legume-based sourdough represents a potential ingredient for the manufacture of novel baked products. However, the lack of gluten of legume flours can restrict their use due to their poor technological properties. To overcome such issue, the in situ production of bacterial exopolysaccharides (EPS) during fermentation has been proposed. In this study, an EPS-producing lactic acid bacteria for in situ production in chickpea sourdough was isolated. After several backsloppings of the spontaneously fermented chickpea flour dough, a dominant strain of Weissella confusa was isolated and identified. W. confusa Ck15 was able to produce linear dextran with 2.6% α-(1 → 3) linked branches, from sucrose. Temperature of 30 °C, dough yield of 333, and 2% of sucrose addition were used to produce fermented chickpea sourdoughs. The acidification and rheology of the sourdoughs inoculated with W. confusa Ck15, Leuconostoc pseudomesenteroides DSM 20193, as positive control, and Lactobacillus plantarum F8, as negative control, were compared. The in situ dextran production by W. confusa Ck15 fermentation led to the highest viscosity increase (5.90 Pa·s) and the highest EPS percentage in the doughs (1.49%), compared to the other doughs. The in situ dextran production represents a potential approach for improving the use of legume flour in bakery products; overall, this experiment represents a first step for the exploitation of microbial EPS for setting up a baking process for chickpea based product.

Structural, thermal and rheological properties of gluten dough: Comparative changes by dextran, weak acidification and their combination

Dextran-containing sourdough has been exploited in breadmaking, obtaining additive-free bread of high quality. Effect of dextran, weak acidification and their association on gluten dough structure, thermal properties and rheology was investigated. Electrophoresis (SDS-PAGE) showed that dextran and acids both lowered the band intensity in the high molecular weight area (Mw > 175 kDa) and size exclusion (SE-HPLC) revealed that weak acidification induced a decrease of 4.73% of the glutenin macropolymer (GMP) content. The higher free thiol (SH) was observed after dextran addition, further suggesting the hindered glutenin polymerization. Fourier transform infrared spectroscopy (FTIR) found that dextran and weak acidity caused increased β-turn and decreased β-sheet structures, suggesting a gluten of lower coherence and resistance to extension. Weakened thermal stability and viscoelasticity were subsequently detected by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic rheology. However, structural, thermal and rheological properties of the weakly acidified group were improved by the associated dextran.

Effect of Amaranth and Quinoa Flours on Exopolysaccharide Production and Protein Profile of Liquid Sourdough Fermented by Weissella cibaria and Lactobacillus plantarum

Exopolysaccharides (EPSs) are known for their positive contribute to the technological properties of many foods, including bakery products. These molecules can be obtained performing piloted fermentation with lactic acid bacteria (LAB). In order to select strains able to produce EPS, a screening test in agar medium containing sucrose, fructose or glucose as carbohydrate source was performed on 21 LAB strains. Results allowed to select 8 Weissella cibaria, 2 Weissella confusa, and 2 Leuconostoc spp. strains as EPS producers only in the presence of sucrose. A further screening in liquid medium enriched with sucrose (10%) (mMRS_S) indicated the W. cibaria strain C43-11 as the higher EPS producer. The selected strain was used to develop liquid sourdoughs (LSs) with dough yield (DY) 500, fermented for 15 h and based on wheat flour and wheat gluten or pseudocereals (quinoa or amaranth) in ratio 1:1, in the presence or not of sucrose at 3% (w/w, LS weight), in comparison to Lactobacillus plantarum ITM21B, a strain not producing EPS in mMRS_S. Results indicated that the use of pseudocereals favored the EPS production. Formulations were optimized by modifying DY (500 or 250), sucrose concentration (3 or 6%) and flour ratio. LSs were characterized for the content of organic acids (lactic, acetic, phenyllactic, OH-phenyllactic), pH, TTA, EPS, viscosity, total protein degradation and protein pattern. The highest EPS production (20.79 g/kg) and viscosity (1168 mPa s) were obtained in LS (DY 250, sucrose 6%) based on quinoa flour and started with C43-11 strain. The LS was characterized by the presence of phenyllactic and OH-phenyllactic acids, protein degradation by 51.7% and proteins in the range 14-80 kDa. In these conditions, also strain ITM21B was able to produce EPS at level of 4.61 g/kg and to degrade proteins by 53.8% in LS based on wheat and quinoa flours (1:1) (DY250 and sucrose 3%). Therefore, results demonstrated that the use of selected conditions (flour type, DY, sucrose) can stimulate specific attributes of strains making them suitable for production of short fermented (15 h) LSs which can be used as bread improvers.

Molecular analysis of the dominant lactic acid bacteria of chickpea liquid starters and doughs and propagation of chickpea sourdoughs with selected Weissella confusa

Fermented chickpea liquid is used as a leavening agent in chickpea bread production. In the present study, traditional chickpea liquid starter and dough samples were collected from bakeries in Turkey and microbiologically investigated. Culture-independent analysis for microbiota diversity, performed by MiSeq Illumina, identified Clostridium perfringens as major group in all samples, while Weissella spp. Dominated LAB community. A culture-dependent methodology was applied and 141 isolates were confirmed to be members of the LAB group based on 16s rRNA gene sequence analysis. In particular, 11 different LAB species were identified confirming the high frequency of isolation of weissellas, since Weissella confusa and Weissella cibaria constituted 47.8 and 12.4%, respectively, of total LAB isolated. The other species were Enterococcus faecium, Enterococcus lactis, Lactobacillus brevis, Lactobacillus plantarum, Leuconostoc mesenteroides, Leuconostoc mesenteroides subsp. Dextranium, Pediococcus acidilactici, Pediococcus pentosaceus and Streptococcus lutetiensis. Due to high frequency of isolation, W. confusa strains were investigated at technological level and W. confusa RL1139 was used as mono-culture starter in the experimental chickpea sourdough production. Chemical and microbiological properties, as well as volatile organic compounds (VOCs) of the chickpea liquid starters and doughs were subjected to a multivariate analysis. Control and W. confusa inoculated chickpea liquid starter and dough samples were close to each other in terms of some characteristics related to chemical, microbiological and VOCs profile, but the inoculated sourdough showed a higher generation of certain VOCs, like butanoic acid (81.52%) and ethyl acetate (8.15%) than control sourdough. This is important in order to maintain typical characteristics of the traditional chickpea dough, but at the same time improving the aroma profile. This work demonstrated that W. confusa RL1139 can be applied at large scale production level without compromising the typical characteristics of the final product.

Effect of microbial exopolysaccharide on wheat bran sourdough: Rheological, thermal and microstructural characteristics

Rheological, thermal and microstructural properties of wheat bran sourdough (WBS) containing different levels of microbial exopolysaccharide (EPS) extracted from Lactobacillus plantarum were investigated. All sourdough samples showed pseudoplastic behavior and the highest apparent viscosity was achieved at 1.5% EPS. The values of consistency coefficient of 1 and 2.5% EPS were significantly lower than for the dough without EPS. Increasing EPS in WBS produced a decrease in the storage, loss, and complex moduli of the sourdough, except that made with 1.5% EPS. This can be attributed to the microbial EPS structure and its ability to bind with water. It can be concluded, due to high hygroscopicity of EPS, WBS containing EPS had a lower access to water and other dough constituents. Thermal and microstructural results showed that EPS strongly modified starch gelatinization by prohibiting water access to amorphous parts of the granules and stabilized crystalline regions of starch causing an increase of end set temperature.

Lactobacillus-fermented sourdoughs improve the quality of gluten-free bread made from pearl millet flour

The study investigated the effect of sourdough made from combinations of four Lactobacillus spp. on the physicochemical properties, consumer acceptability, and shelf life of bread made from pearl millet flour. Fermentation based on both single and multiple species reduced the pH of the dough and increased its titratable acidity and H₂O₂ content. The addition of sourdough increased the elasticity and reduced the stiffness of the pearl millet dough. Sourdough fermented with L. brevis had the greatest effect on loaf height, specific volume, porosity, and moisture content. During storage, the moisture content of the bread crumb decreased, but that of their crust increased. Sourdough-based loaves retained their moisture better than conventional loaves and the sourdough suppressed the development of mold for a longer period. An organoleptic assessment showed that the sourdough-based bread was more palatable than either conventional or chemically acidified ones. The tissue softness, chewiness, and flavor of the pearl millet bread decreased during storage. The use of sourdough based on either L. brevis, L. paralimentarius, or L. brevis + L. paralimentarius is recommended to produce high-quality pearl millet-based bread.

Exploiting synergies of sourdough and antifungal organic acids to delay fungal spoilage of bread

Fungal spoilage of bread remains an unsolved issue in bread making. This work aims to identify alternative strategies to conventional preservatives in order to prevent or delay fungal spoilage of bread. The minimum inhibitory concentration (MIC) of bacterial metabolites and chemical preservatives was evaluated in vitro, and compared to their in situ activity in baking trials. Calcium propionate, sorbic acid, 3-phenyllactic acid, ricinoleic acid, and acetic acid were tested both individually and in combination at their MIC values against Aspergillus niger and Penicillium roqueforti. The combination of acetic acid with propionate and sorbate displayed additive effects against the two fungi. For these reasons, we introduced sourdough fermentation with specific strains of lactobacilli, using wheat or flaxseed, in order to generate acetate in bread. A combination of Lactobacillus hammesii and propionate reduced propionate concentration required for shelf life extension of wheat bread 7-fold. Flaxseed sourdough bread fermented with L. hammesii, excluding any preservative, showed a shelf life 2 days longer than the control bread. The organic acid quantification indicated a higher production of acetic acid (33.8 ± 4.4 mM) when compared to other sourdough breads. Addition of 4% of sucrose to sourdough fermentation with L. brevis increased the mould free shelf-life of bread challenged with A. niger by 6 days. The combination of L. hammesii sourdough and the addition of ricinoleic acid (0.15% or 0.08%) prolonged the mould free shelf-life by 7-8 days for breads produced with wheat sourdoughs. In conclusion, the in vitro MIC of bacterial metabolites and preservatives matched the in situ antifungal effect. Of the different bacterial metabolites evaluated, acetic acid had the most prominent and consistent antifungal activity. The use of sourdough fermentation with selected strains able to produce acetic acid allowed reducing the use of chemical preservatives.

Industrial production of sourdoughs for the baking branch - An overview

Sourdoughs are produced both in artisanal and industrial size. Sourdough manufacturers deliver the baking branch either with starters for production of in-house sourdoughs or with fully fermented sourdough products. In the latter case sourdough production is separated in time and space from the bread production. A big part of this convenience products are dried sourdoughs, which are mainly produced from rye and wheat flour, but also from other starch containing plants, like pseudocereals or legumes. The requirements regarding the raw materials used differ from that used for baking bread. The most applied drying techniques for sourdoughs are drum and spray-drying. Compared with other foods, sourdough and sourdough products have only a low risk regarding food safety due to pH < 4.2, however formation of biogenic amines or acrylamide has taken into account. More tools for sourdough authentication are needed but, before developing and validating methods, it would be necessary to include different sourdough products in a clear regulatory framework.

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

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

Effect of temperature on production of oligosaccharides and dextran by Weissella cibaria 10 M

The formation of HoPS and oligosaccharides in sourdough fermentation improves bread quality but is dependent on the expression of glycansucrases by lactic acid bacteria. Data on the expression of dextransucrases by Weissella spp., however, are limited. This study therefore aimed to assess dextansucrase expression in W. cibaria 10 M, focusing on the effect of temperature. The effect of temperature on growth, oligosaccharide and dextran synthesis by W. cibaria 10 M was determined and the expression and activity of cell-associated dextransucrase from W. cibaria 10 M were investigated. The oligosaccharides profiles were measured by thin layer chromatography and high performance anion exchange chromatography coupled to pulsed amperometric detection. Dextran formation was quantified by size exclusion chromatography. W. cibaria grew fastest at 30 °C but oligosaccharide formation was highest at 20 °C or less. Dextransucrase expression as measured by reverse transcription quantitative PCR, SDS-PAGE, and activity of cell-associated dextransucrase were maximal at 15 °C. Cold shift incubation, characterized by incubation at 30 °C to obtain biomass, followed by shift to 6 °C to induce dextransucrase expression, supported high dextransucrase activity in laboratory media. Cold shift fermentation of wheat and sorghum sourdoughs supplemented with 15 or 30% sucrose increased the yields of oligosaccharides, and resulted in formation of 16 and 12 g/kg dextran in wheat and sorghum sourdoughs, respectively. Dextran formation was decreased in favour of oligosaccharide formation when doughs were supplemented with maltose. In conclusion, cold shift fermentation of sourdough with W. cibaria supports high dextran yields or formation of oligosaccharides without excess acidification.

Isolation of lactic acid bacteria starters from Jeung-pyun for sourdough fermentation

Lactic acid bacteria (LAB) are key for the fermentation of sourdoughs to improve the quality and nutritive value of bread. The aim of this study was to isolate the LAB starter for sourdough fermentation from Jeung-pyun, a Korean traditional rice cake. Among the twenty two LAB screened, five isolates were selected based on exo-polysaccharide production. Among them, three isolates showed cell growth greater than 8.5 Log CFU/g, maximum increase in the volume of dough, and dextran concentration up to 0.16%. During the sourdough fermentation, pH and total titratable acidity (TTA) were changed, as the three isolates synthesized lactic acid and acetic acid with fermentation quotients less than 2.0. They were identified as Leuconostoc lactis EFEL005, Lactobacillus brevis EFEL004, and Le. citreum EFEL006. They displayed good fermentation properties (growth, dextran production, pH, and TTA) in dough and they are regarded as potential starters to be used in sourdough fermentation.

Sugar Beet Pulp as Leuconostoc mesenteroides T3 Support for Enhanced Dextransucrase Production on Molasses

Sugar beet pulp (SBP) and molasses, as an agro industrial waste material, are produced in large amounts annually. Thus, a major challenge nowadays is to develop procedures that could increase the value of the generated waste. In this study, SBP as a support for cell immobilization and molasses as a source of nutrients were used for a dextransucrase (DS) production by Leuconostoc mesenteroides T3. The influence of SBP in native form (SBP-N) and after treatment with NaOH (SBP-NaOH) on DS production was investigated. The optimal medium composition for the maximum DS production was determined by varying the concentration of molasses, SBP, and sucrose. The maximum DS yield of 2.02 U/ml was obtained in the medium with 2.5 % of molasses, 2.5 % SBP-NaOH, and 4 % of sucrose concentration. Scanning electron microscopy (SEM) showed immobilization of Lc. mesenteroides T3 cells onto SBP-NaOH. According to the obtained results, the production of DS on molasses could be improved by using NaOH-treated SBP as a carrier for whole-cell immobilization. Our study reveals the basis for the development of process for DS production with additional reduction of expenses by using waste materials for obtaining the valuable biotechnological product.

Production, properties, and industrial food application of lactic acid bacteria-derived exopolysaccharides

Exopolysaccharides (EPS)-producing lactic acid bacteria (LAB) are industrially important microorganisms in the development of functional food products and are used as starter cultures or coadjutants to develop fermented foods. There is large variability in EPS production by LAB in terms of chemical composition, quantity, molecular size, charge, presence of side chains, and rigidity of the molecules. The main body of the review will cover practical aspects concerning the structural diversity structure of EPS, and their concrete application in food industries is reported in details. To strengthen the food application and process feasibility of LAB EPS at industrial level, a future academic research should be combined with industrial input to understand the technical shortfalls that EPS can address.

Crystal structure of thermophilic dextranase from Thermoanaerobacter pseudethanolicus

The crystal structures of the wild type and catalytic mutant Asp-312→Gly in complex with isomaltohexaose of endo-1,6-dextranase from the thermophilic bacterium Thermoanaerobacter pseudethanolicus (TpDex), belonging to the glycoside hydrolase family 66, were determined. TpDex consists of three structural domains, a catalytic domain comprising an (β/α)8-barrel and two β-domains located at both N- and C-terminal ends. The isomaltohexaose-complex structure demonstrated that the isomaltohexaose molecule was bound across the catalytic site, showing that TpDex had six subsites (-4 to +2) in the catalytic cleft. Marked movement of the Trp-376 side-chain along with loop 6, which was the side wall component of the cleft at subsite +1, was observed to occupy subsite +1, indicating that it might expel the cleaved aglycone subsite after the hydrolysis reaction. Structural comparison with other mesophilic enzymes indicated that several structural features of TpDex, loop deletion, salt bridge and surface-exposed charged residue, may contribute to thermostability.

Biopolymers from lactic acid bacteria. Novel applications in foods and beverages

Lactic acid bacteria (LAB) are microorganisms widely used in the fermented food industry worldwide. Certain LAB are able to produce exopolysaccharides (EPS) either attached to the cell wall (capsular EPS) or released to the extracellular environment (EPS). According to their composition, LAB may synthesize heteropolysaccharides or homopolysaccharides. A wide diversity of EPS are produced by LAB concerning their monomer composition, molecular mass, and structure. Although EPS-producing LAB strains have been traditionally applied in the manufacture of dairy products such as fermented milks and yogurts, their use in the elaboration of low-fat cheeses, diverse type of sourdough breads, and certain beverages are some of the novel applications of these polymers. This work aims to collect the most relevant issues of the former reviews concerning the monomer composition, structure, and yields and biosynthetic enzymes of EPS from LAB; to describe the recently characterized EPS and to present the application of both EPS-producing strains and their polymers in the fermented (specifically beverages and cereal-based) food industry.

Cloning and characterization of a Weissella confusa dextransucrase and its application in high fibre baking

Wheat bran offers health benefits as a baking ingredient, but is detrimental to bread textural quality. Dextran production by microbial fermentation improves sourdough bread volume and freshness, but extensive acid production during fermentation may negate this effect. Enzymatic production of dextran in wheat bran was tested to determine if dextran-containing bran could be used in baking without disrupting bread texture. The Weissella confusa VTT E-90392 dextransucrase gene was sequenced and His-tagged dextransucrase Wc392-rDSR was produced in Lactococcus lactis. Purified enzyme was characterized using ¹⁴C-sucrose radioisotope and reducing value-based assays, the former yielding K_m and V_max values of 14.7 mM and 8.2 μmol/(mg∙min), respectively, at the pH optimum of 5.4. The structure and size of in vitro dextran product was similar to dextran produced in vivo. Dextran (8.1% dry weight) was produced in wheat bran in 6 h using Wc392-rDSR. Bran with and without dextran was used in wheat baking at 20% supplementation level. Dextran presence improved bread softness and neutralized bran-induced volume loss, clearly demonstrating the potential of using dextransucrases in bran bioprocessing for use in baking.

Exopolysaccharides from sourdough lactic acid bacteria

The use of sourdough improves the quality and increases the shelf life of bread. The positive effects are associated with metabolites produced by lactic acid bacteria (LAB) during sourdough fermentation, including organic acids, exopolysaccharides (EPS), and enzymes. EPS formed during sourdough fermentation by glycansucrase activity from sucrose influence the viscoelastic properties of the dough and beneficially affect the texture and shelf life (in particular, starch retrogradation) of bread. Accordingly, EPS have the potential to replace hydrocolloids currently used as bread improvers and meet so the consumer demands for a reduced use of food additives. In this review, the current knowledge about the functional aspects of EPS formation by sourdough LAB especially in baking applications is summarized.