Performance of Lactobacillus sanfranciscensis TMW 1.392 and its levansucrase deletion mutant in wheat dough and comparison of their impact on bread quality

A review of fructosyl-transferases from catalytic characteristics and structural features to reaction mechanisms and product specificity

Carbohydrate-active enzymes are accountable for the synthesis and degradation of glycosidic bonds among diverse carbohydrates. Fructosyl-transferases represent a subclass of these enzymes, employing sucrose as a substrate to generate fructooligosaccharides (FOS) and fructan polymers. This category primarily includes levansucrase (LS, EC 2.4.1.10), inulosucrase (IS, EC 2.4.1.9), and β-fructofuranosidase (Ffase, EC 3.2.1.26). These three enzymes possess a similar five-bladed β-propeller fold and employ an anomer-retaining reaction mechanism mediated by nucleophiles, transition state stabilizers, and general acids/bases. However, they exhibit distinct product profiles, characterized by variations in linkage specificity and molecular mass distribution. Consequently, this article comprehensively explores recent advancements in the catalytic characteristics, structural features, reaction mechanisms, and product specificity of levansucrase, inulosucrase, and β-fructofuranosidase (abbreviated as LS, IS, and Ffase, respectively). Furthermore, it discusses the potential for modifying catalytic properties and product specificity through structure-based design, which enables the rational production of custom fructan and FOS.

The quest for the perfect loaf of sourdough bread continues: Novel developments for selection of sourdough starter cultures

Sourdough fermentation, one of the oldest unit operations in food production, is currently experiencing a revival in bread production at the household, artisanal, and the industrial level. The expanding use of sourdough fermentation in bread production and the adaptation of fermentation to large scale industrial bread production also necessitate the development of novel starter cultures. Developments in the last years also have expanded the tools that are used to assess the metabolic potential of specific strains, species or genera of the Lactobacillaceae and have identified multiple ecological and metabolic traits as clade-specific. This review aims to provide an overview on the clade-specific metabolic potential of members of the Lactobacillaceae for use in sourdough baking, and the impact of these clade-specific traits on bread quality. Emphasis is placed on carbohydrate metabolism, including the conversion of sucrose and starch to soluble polysaccharides, conversion of amino acids, and the metabolism of organic acids. The current state of knowledge to compose multi-strain starter cultures (synthetic microbial communities) that are suitable for back-slopping will also be discussed. Taken together, the communication outlines the current tools for selection of microbes for use in sourdough baking.

Enhancement of Textural and Sensory Characteristics of Wheat Bread Using a Chickpea Sourdough Fermented with a Selected Autochthonous Microorganism

A traditional Greek sourdough, based on the fermentation of chickpea flour by an autochthonous culture, was evaluated as a wheat bread improver. The dominant indigenous microflora (Clostridium perfringens isolates) was identified by 16S rDNA analysis, and a selected strain (C. perfringens CP8) was employed to ferment chickpea flour to obtain a standardized starter culture (sourdough) for breadmaking. In accordance with toxin-typed strain identification, all isolates lacked the cpe gene; thus, there is no concern for a health hazard. Loaf-specific volumes increased with the addition of liquid, freeze-dried, and freeze-dried/maltodextrin sourdoughs compared to control bread leavened by baker's yeast only. Following storage (4 days/25 °C), the amylopectin retrogradation and crumb hardness changes (texture profile analysis) revealed a lower degree of staling for the sourdough-fortified breads. Modifications in the protein secondary structure of fortified doughs and breads were revealed by FTIR analysis. High amounts of organic acids were also found in the sourdough-supplemented breads; butyric and isobutyric acids seemed to be responsible for the characteristic 'butter-like' flavor of these products (sensory analysis). Overall, the addition of liquid or freeze-dried chickpea sourdough in wheat bread formulations can improve the specific volume, textural characteristics, and sensorial properties of loaves, along with extending bread shelf life.

From Waste to Taste: Application of Fermented Spent Rootlet Ingredients in a Bread System

The process of upcycling and incorporating food by-products into food systems as functional ingredients has become a central focus of research. Barley rootlets (BR) are a by-product of the malting and brewing industries that can be valorised using lactic acid bacteria fermentation. This research investigates the effects of the inclusion of unfermented (BR-UnF), heat-sterilised (BR-Ster), and five fermented BR ingredients (using Weissella cibaria MG1 (BR-MG1), Leuconostoc citreum TR116 (BR-TR116), Lactiplantibacillus plantarum FST1.7 (BR-FST1.7), Lactobacillus amylovorus FST2.11 (BR-FST2.11), and Limosilactobacillus reuteri R29 (BR-R29) in bread. The antifungal compounds in BR ingredients and the impact of BR on dough rheology, gluten development, and dough mixing properties were analysed. Additionally, their effects on the techno-functional characteristics, in vitro starch digestibility, and sensory quality of bread were determined. BR-UnF showed dough viscoelastic properties and bread quality comparable to the baker's flour (BF). BR-MG1 inclusion ameliorated bread specific volume and reduced crumb hardness. Breads containing BR-TR116 had comparable bread quality to BF, while the inclusion of BR-R29 substantially slowed microbial spoilage. Formulations containing BR-FST2.11 and BR-FST1.7 significantly reduced the amounts of sugar released from breads during a simulated digestion and resulted in a sourdough-like flavour profile. This study highlights how BR fermentation can be tailored to achieve desired bread characteristics.

Potential of a Techno-Functional Sourdough and Its Application in Sugar-Reduced Soft Buns

Functional lactic acid bacteria (LAB) as starter cultures used in sourdough fermentation have been researched for years. This study evaluated the LAB strains Leuconostoc citreum DCM65 (mannitol, exopolysaccharide producing, antifungal activity) and Lactiplantibacillus plantarum subsp. plantarum MA418 (amylolytic activity) and their potential as single or co-culture starters in sourdough fermented buns containing different levels of sugar (control 9% and reduced 0, 3, 6%). Cell counts, pH development, and organic acids were determined before and after sourdough fermentation (30 °C, 24 h) and physical properties (color, volume, pore structure, and texture) of buns produced thereof were determined after baking. Sourdoughs started with DCM65 and/or MA418 developed up to log 9.2 CFU/g presumptive LAB after 24 h, assertiveness of the added starter cultures species was confirmed by MALDI-TOF MS. Acetic acid and mannitol were only detected in sourdough fermented with DCM65 (single or co-culture) up to 2.5 mg/g and 9.8 mg/g, respectively. The starter cultures applied influenced physical properties of buns. Sourdough buns started with MA418 had higher volume and slice area, and softer crumb; in contrast, buns fermented with DCM65 had a finer pore structure. In summary, both starter cultures showed high potential in sourdough buns with reduced sugar content.

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.

Strain-specific interaction of Fructilactobacillus sanfranciscensis with yeasts in the sourdough fermentation

Fructilactobacillus (F.) sanfranciscensis is a key bacterium in traditional (type 1) sourdough fermentations. It typically occurs in combination with the sourdough yeast Kazachstania (K.) humilis or the generalist Saccharomyces (S.) cerevisiae. Previous studies revealed intra-species diversity in competitiveness or dominance in sourdoughs of F. sanfranciscensis, as well as preferences for a life with or without a specific yeast. In this study representative, differently behaving strains were studied in media with different sugars and electron acceptors, and in rye sourdough fermentations in the presence and absence of K. humilis or S. cerevisiae. Strain-specific differences were observed in sugar and organic acids spectra in media, and in sourdoughs with F. sanfranciscensis strains in combination with K. humilis or S. cerevisiae. F. sanfranciscensis TMW 1.1150 proved dominant in the presence and absence of any yeast because it most effectively used maltose. Its maltose fermentation was unaffected by electron acceptors. F. sanfranciscensis TMW 1.2138 was the weakest maltose fermenter and incapable of glucose fermentation, and evidently not competitive against the other strains. F. sanfranciscensis TMW 1.392 was the most versatile strain regarding the utilization of different carbohydrates and its ability to exploit electron acceptors like fructose and oxygen. In sourdoughs without yeasts, it outcompeted other strains. The metabolism of F. sanfranciscensis TMW 1.907 was stimulated in combination with S. cerevisiae. In competitive trials, it was assertive only with S. cerevisiae. The intra-species differences in carbohydrate metabolism can widely explain the differences in their behavior in sourdough fermentation. Interaction between F. sanfranciscensis and the yeasts was strain specific and supposedly commensal with K. humilis and rather competitive with S. cerevisiae.

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.

β-Glucan Production by Levilactobacillus brevis and Pediococcus claussenii for In Situ Enriched Rye and Wheat Sourdough Breads

Sourdough fermentation is a common practice spread across the globe due to quality and shelf life improvement of baked goods. Above the widely studied exopolysaccharide (EPS) formation, which is exploited for structural improvements of foods including baked goods, β-glucan formation, by using lactic acid bacteria (LAB), offers additional values. Through renunciation of sucrose addition for bacterial β-d-glucan formation, which is required for the production of other homopolysaccharides, residual sweetness of baked goods can be avoided, and predicted prebiotic properties can be exploited. As promising starter cultures Levilactobacillus (L.) brevis TMW (Technische Mikrobiologie Weihenstephan) 1.2112 and Pediococcus (P.) claussenii TMW 2.340 produce O2-substituted (1,3)-β-d-glucan upon fermenting wheat and rye doughs. In this study, we have evaluated methods for bacterial β-glucan quantification, identified parameters influencing the β-glucan yield in fermented sourdoughs, and evaluated the sourdough breads by an untrained sensory panel. An immunological method for the specific detection of β-glucan proved to be suitable for its quantification, and changes in the fermentation temperature were related to higher β-glucan yields in sourdoughs. The sensory analysis resulted in an overall acceptance of the wheat and rye sourdough breads fermented by L.brevis and P.claussenii with a preference of the L. brevis fermented wheat sourdough bread and tart-flavored rye sourdough bread.

Design of a "Clean-Label" Gluten-Free Bread to Meet Consumers Demand

The market of gluten-free (GF) products has been steadily increasing in last few years. Due to the technological importance of gluten, the GF food production is still a challenge for the industry. Indeed, large quantities of fat, sugars, structuring agents, and flavor enhancers are added to GF formulations to make textural and sensorial characteristics comparable to conventional products, leading to nutritional and caloric intake imbalances. The formulation of the novel "clean-label" GF bread included a commonly used mixture of maize and rice flour (ratio 1:1) fortified with selected protein-rich flours. Naturally hydrocolloids-containing flours (psyllium, flaxseed, chia) were included in the bread formulation as structuring agents. A type-II sourdough was obtained by using a selected Weissella cibaria P9 and a GF sucrose-containing flour as substrate for fermentation to promote the exo-polysaccharides synthesis by the starter lactic acid bacterium. A two-step protocol for bread-making was set-up: first, the GF sourdough was fermented (24 h at 30 °C); then, it was mixed with the other ingredients (30% of the final dough) and leavened with baker's yeast before baking. Overall, the novel GF bread was characterized by good textural properties, high protein content (8.9% of dry matter) and in vitro protein digestibility (76.9%), low sugar (1.0% of dry matter) and fat (3.1% of dry matter) content, and an in vitro predicted glycemic index of 85.

Usage of in situ exopolysaccharide-forming lactic acid bacteria in food production: Meat products-A new field of application?

In the meat industry, hydrocolloids and phosphates are used to improve the quality attributes of meat products. However, latest research results revealed that the usage of exopolysaccharide (EPS)-forming lactic acid bacteria (LAB), which are able to produce EPS in situ during processing could be an interesting alternative. The current review aims to give a better understanding of bacterial EPS production in food matrices with a special focus on meat products. This includes an introduction to microbial EPS production (homopolysaccharides as well as heteropolysaccharides) and an overview of parameters affecting EPS formation and yield depending on LAB used. This is followed by a summary of methods to detect and characterize EPS to facilitate a rational selection of starter cultures and fermentation conditions based on desired structure-function relationships in different food matrices. The mechanism of action of in situ generated EPS is then highlighted with an emphasis on different meat products. In the process, this review also highlights food additives currently used in meat production that could in the future be replaced by in situ EPS-forming LAB.

Leuconostoc citreum TR116 as a Microbial Cell Factory to Functionalise High-Protein Faba Bean Ingredients for Bakery Applications

Grain legumes, such as faba beans, have been investigated as promising ingredients to enhance the nutritional value of wheat bread. However, a detrimental effect on technological bread quality was often reported. Furthermore, considerable amounts of antinutritional compounds present in faba beans are a subject of concern. Sourdough-like fermentation can positively affect baking performance and nutritional attributes of faba bean flours. The multifunctional lactic acid bacteria strain Leuconostoc citreum TR116 was employed to ferment two faba bean flours with different protein contents (dehulled flour (DF); high-protein flour (PR)). The strain’s fermentation profile (growth, acidification, carbohydrate metabolism and antifungal phenolic acids) was monitored in both substrates. The fermentates were applied in regular wheat bread by replacing 15% of wheat flour. Water absorption, gluten aggregation behaviour, bread quality characteristics and in vitro starch digestibility were compared to formulations containing unfermented DF and PR and to a control wheat bread. Similar microbial growth, carbohydrate consumption as well as production of lactic and acetic acid were observed in both faba bean ingredients. A less pronounced pH drop as well as a slightly higher amount of antifungal phenolic acids were measured in the PR fermentate. Fermentation caused a striking improvement of the ingredients’ baking performance. GlutoPeak measurements allowed for an association of this observation with an improved gluten aggregation. Given its higher potential to improve protein quality in cereal products, the PR fermentate seemed generally more promising as functional ingredient due to its positive impact on bread quality and only moderately increased starch digestibility in bread.

Screening for gum-producing Lactic acid bacteria in Oil palm (Elaeis guineensis) and raphia palm (Raphia regalis) sap from South-West Nigeria

Lactic acid bacteria have wide applications in food processing. Lactic acid bacteria produced exopolysaccharides (EPS) which could be used as possible replacer for commercial stabilizer and thickeners produced by nonfood grade bacteria. Seventy-two samples of Oil and Raphia palm sap were collected in eighteen locations across South-Western Nigeria and screened for exopolysaccharide production in 6% sucrose agar using streaked plate method. Four hundred EPS-producing bacteria (EPB) isolated were clustered based on morphological characteristics into two broad groups and preliminary screened for EPS-producing capacity. Twenty representative of EPB were selected from the broad groups for tentative identification by API 50CHL and 10 high yielding EPB were selected for large-scale EPS production. Each strain was inoculated into 6% sucrose broth with 3% (v/v) preculture grown overnight in a 1.5 ml flask and incubated at 37°C for 72 hr. The EPSs were purified and freeze-dried prior to quantification of yields. EPS-producing bacteria were identified as Leuconostoc lactis, Lactobacillus fermentum, Lactobacillus delbrueckii ssp. lactis, L. delbrueckii ssp. delbrueckii, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus crispatus, and Leuconostoc mesenteroides ssp. mesenteroides/dextranicum. EPS yield ranged from 132-810.75 mg/L and EPS-producing potential of lactic acid bacteria (LAB) strains ranged; 36% (132-245 mg/L), 36% (250-460 mg/L), and 28% (461-820 mg/L). L. plantarum had the highest EPS yield of 810.75 mg/L whereas L. crispatus had the least yield 242.5 mg/L. These results suggest that majority of LAB in palm wine saps are gum-producing bacteria. Leuconostoc and Lactobacillus were the most abundant LAB found in this study while L. plantarum could have applications as potential starter cultures for the production of exopolysaccharides (EPS) at industrial level.

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.

Flavoring Production in Kamut®, Quinoa and Wheat Doughs Fermented by Lactobacillus paracasei, Lactobacillus plantarum, and Lactobacillus brevis: A SPME-GC/MS Study

This study identified the odor-active compounds and the qualitative characteristics of doughs from “ancient” grains flours fermented by lactic acid bacteria. For this purpose doughs made with quinoa and Kamut® flours have been produced and inoculated with strains belonging to the species Lactobacillus paracasei, Lactobacillus plantarum and Lactobacillus brevis and compared with fermented doughs made from 100% wheat flour. The quality of the doughs was determined by assessment of pH, total titratable acidity, lactic acid bacteria growth and flavor compounds. The results showed that lactic acid bacteria used were able to grow in the different substrates reaching more than 9.0 log CFU/g after 24 h fermentation, although the best microbial growth was recorded in the doughs made with quinoa flour fermented with Lactobacillus paracasei I1. Good acidification and heterogeneous aromatic profile were recognized in all the doughs even if the volatile composition mainly derived from microbial specie. Among all the used strains, mostly Lactobacillus paracasei I1 positively contributed to the aromatic profile of the doughs, independently from flour type, producing the highest amount of different ketones such as, diacetyl, acetoin, 2,6-dimethyl-4-heptanone, 5-methyl-3-hexanone, 4-methyl-3-penten-2-one, volatile compounds highly appreciated in the bakery products for their buttery, fatty and fruity notes. So, the positive characteristic of Lactobacillus paracasei I1 to enhance the production of desired volatile compounds could make it suitable as adjunct culture starter in the bakery industry. Many differences in volatile organic compounds derived also by the type of flour used. Quinoa fermented doughs were characterized for specific nutty, roasted, acid and buttery tones derived from pyrazines, ketones and acid compounds whereas Kamut® fermented doughs were characterized for fruity, rose, green and sweet tones derived from aldehydes and ketones production. So, the use of quinoa and Kamut® flours opportunely fermented, as partial or complete substitution of wheat flour, may be interesting for producing more balanced bakery products with respect to nutritional aspects and to unique aromatic profile. Furthermore, the supplementation of these flours, rich in protein content and free amino acids, could represent an optimal substrate to enhance the growth of lactic acid bacteria used as starter culture in leavened bakery products.

Fermentation pH Modulates the Size Distributions and Functional Properties of Gluconobacter albidus TMW 2.1191 Levan

Bacterial levan has gained an increasing interest over the last decades due to its unique characteristics and multiple possible applications. Levan and other exopolysaccharides (EPSs) production are usually optimized to obtain the highest concentration or yield while a possible change of the molecular size and mass during the production process is mostly neglected. In this study, the molar mass and radius of levan samples were monitored during fermentations with the food-grade, levan-producing acetic acid bacterium Gluconobacter (G.) albidus TMW 2.1191 in shake flasks (without pH control) and bioreactors (with pH control at 4.5, 5.5 and 6.5, respectively). In uncontrolled fermentations, the levan size/molar mass continuously decreased concomitantly with the continuous acidification of the nutrient medium. On the contrary, the amount, molar mass and size of levan could be directly influenced by controlling the pH during fermentation. Using equal initial substrate amounts, the largest weight average molar mass and geometric radius of levan were observed at constant pH 6.5, while the highest levan concentration was obtained at constant pH 4.5. Since there is a special demand to find suitable hydrocolloids from food-grade bacteria to develop novel gluten-free (GF) products, these differently produced levans were used for baking of GF breads, and the best quality improvement was obtained by addition of levan with the highest mass and radius. This work, therefore, demonstrates for the first time that one bacterial strain can produce specific high molecular weight fractions of one EPS type, which differ in properties and sizes among each other in dependence of the controllable production conditions.

The Impact of Different Lactic Acid Bacteria Sourdoughs on the Quality Characteristics of Toast Bread

The effect of sourdough inoculated with three novel single strains of lactic acid bacteria (LAB) (Lactobacillus casei jQ412732, Lactobacillus plantarum jQ301799, and Lactobacillus brevis IBRC-M10790) as well as mixed strains was evaluated on the quality characteristics of Toast bread. Antifungal properties of sourdoughs due to organic acid production were measured by HPLC, and storability was evaluated by thermal and textural analysis in days 1, 3, and 6. Despite the impact of sourdough concentration on microbial preservation, no significant effect was observed in the case of enthalpy reduction. Mixed LAB strains showed the best results in reducing the enthalpy and hardness of bread as well as better microbial preservation by producing the highest amount of organic acids, justified by sensory panelists. Among single strains, L. casei gave better results in reducing hardness and staling rate of bread. Scanning Electron Microscopy micrographs of bread also showed the differences.

Purification and characterization of an intracellular levansucrase derived from Bacillus methylotrophicus SK 21.002

An intracellular levansucrase from Bacillus methylotrophicus SK 21.002 was isolated, purified, and characterized. The final specific levansucrase activity was 135.40 U/mg protein with an 11.78-fold enrichment and a 9.28% recovery rate. The molecular weight of the enzyme was approximately 60,000 Da as evaluated by gel filtration and SDS-PAGE. Both the maximum transfructosylation and hydrolytic activities were observed at pH 6.5. The enzyme exhibited optimum transfructosylation activity at 40 °C, whereas the optimum temperature of hydrolytic activity was 45 °C. Cu(2+), Fe(2+), Zn(2+), and Ni(2+) inhibited both the transfructosylation and hydrolytic activities up to 100%, whereas Mn(2+) inhibited only hydrolytic activity. Ca(2+) and Mg(2+) stimulated both transfructosylation and hydrolytic activities. The chemical modifiers (n-bromosuccinimide and phenylmethanesulfonyl fluoride) strongly inhibited hydrolytic and transfructosylation activity of the levansucrase. The Km and Vmax values of the purified levansucrase were 117.2 mM and 33.23 μmol/mg·Min, respectively. When the fructose concentration was below 0.2 M, higher fructose concentrations promoted the transfructosylation and inhibited the hydrolytic activity.

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.