Structural Analysis of Enzyme-Resistant Isomaltooligosaccharides Reveals the Elongation of α-(1→3)-Linked Branches in Weissella confusa Dextran

Influence of dextrans on the textural, rheological, and microstructural properties of acid-induced faba bean protein gels

Dextrans (DXs) are a group of natural polysaccharides with different branching patterns. Previous studies examining the effects of DXs on plant protein gels have only focused on α-(1 → 3)-branched DXs. Here, we compared the effects of α-(1 → 3)-branched DX L12 with those of two α-(1 → 2)-branched DXs on the properties of glucono-δ-lactone-induced faba bean protein isolate (FPI) gels. DX L12 showed stronger effects in decreasing gel hardness and enhancing gel viscoelasticity than the other two DXs. Moreover, DX L12 decreased the water-holding capacity of FPI gels, whereas the other DXs enhanced it. Microstructural analysis revealed that DX addition promoted phase separation during gel formation. However, FPI/L12 gels exhibited greater phase separation than the other two gels and contained larger void spaces. These differences could be attributed to the varying water adsorption and self-association properties of the DXs. These findings could guide the application of DX in the tailored preparation of plant protein gels.

Dextrans of Weissella cibaria DSM14295: Microbial production, structure and functionality

Lactic acid bacteria of the genus Weissella contribute to spontaneous fermentation in, e.g., sourdough or sauerkraut, but are not registered as starter cultures because of their pending safety assessment. Some strains are able to produce high amounts of exopolysaccharides. This study aims to demonstrate the techno-functionality of five dextrans from W. cibaria DSM14295, produced under varying cultivation conditions, with respect to structural and macromolecular properties. A maximum of 23.1 g/L dextran was achieved by applying the "cold shift" temperature regime. The dextrans differed in molecular mass (9-22∙108 Da, determined by HPSEC-RI/MALLS), intrinsic viscosity (52-73 mL/g), degree of branching (3.8-5.7 % at position O3, determined by methylation analysis) and their side chain length and architecture, determined by HPAEC-PAD after enzymatic hydrolysis. Stiffness of acid gels from milk spiked with these dextrans increased linearly with dextran concentration. Principal component analysis showed that dextrans produced in a semi-defined medium are primarily described by moisture sorption and branching properties, whereas dextrans produced in whey permeate were similar because of their functional and macromolecular properties. Overall, dextrans from W. cibaria DSM14295 have a high potential because of the high production yield and their functionality which can be tailored by the conditions during fermentation.

Gluco-oligosaccharides as potential prebiotics: Synthesis, purification, structural characterization, and evaluation of prebiotic effect

Prebiotics have long been used to modulate the gut microbiota and improve host health. Most established prebiotics are nondigestible carbohydrates, especially short-chain oligosaccharides. Recently, gluco-oligosaccharides (GlcOS) with 2-10 glucose residues and one or more O-glycosidic linkage(s) have been found to exert prebiotic potentials (not fully established prebiotics) because of their selective fermentation by beneficial gut bacteria. However, the prebiotic effects (non-digestibility, selective fermentability, and potential health effects) of GlcOS are highly variable due to their complex structure originating from different synthesis processes. The relationship between GlcOS structure and their potential prebiotic effects has not been fully understood. To date, a comprehensive summary of the knowledge of GlcOS is still missing. Therefore, this review provides an overview of GlcOS as potential prebiotics, covering their synthesis, purification, structural characterization, and prebiotic effect evaluation. First, GlcOS with different structures are introduced. Then, the enzymatic and chemical processes for GlcOS synthesis are critically reviewed, including reaction mechanisms, substrates, catalysts, the structures of resultant GlcOS, and the synthetic performance (yield and selectivity). Industrial separation techniques for GlcOS purification and structural characterization methods are discussed in detail. Finally, in vitro and in vivo studies to evaluate the non-digestibility, selective fermentability, and associated health effects of different GlcOS are extensively reviewed with a special focus on the GlcOS structure-function relationship.

Influence of ultrasonication and hydrolysis conditions in methylation analysis of bacterial homoexopolysaccharides

Homoexopolysaccharides (HoEPS) such as α-glucans and β-fructans are synthesized by lactic and acetic acid bacteria. Methylation analysis is an important and well-established tool for the structural analysis of these polysaccharides, however, multiple steps are required for polysaccharide derivatization. Because ultrasonication during methylation and the conditions during acid hydrolysis may influence the results, we investigated their role in the analysis of selected bacterial HoEPS. The results reveal that ultrasonication is crucial for water insoluble α-glucan to swell/disperse and deprotonate prior to methylation whereas it is not necessary for water soluble HoEPS (dextran and levan). Complete hydrolysis of permethylated α-glucans requires 2 M trifluoroacetic acid (TFA) for 60/90 min at 121 °C while levan is hydrolyzed in 1 M TFA for 30 min at 70 °C. Nevertheless, levan was also detectable after hydrolysis in 2 M TFA at 121 °C. Thus, these conditions can be used to analyze a levan/dextran mixture. However, size exclusion chromatography of permethylated and hydrolyzed levan showed degradation and condensation reactions at harsher hydrolysis conditions. Application of reductive hydrolysis with 4-methylmorpholine-borane and TFA did not lead to improved results. Overall, our results demonstrate that conditions used for methylation analysis have to be adjusted for the analysis of different bacterial HoEPS.

Applications of Microbial Exopolysaccharides in the Food Industry

Exopolysaccharides (EPSs) are high molecular weight polysaccharides secreted by microorganisms in the surrounding environment. In addition to the favorable benefits of these compounds for microorganisms, including microbial cell protection, they are used in various food, pharmaceutical, and cosmetic industries. Investigating the functional and health-promoting characteristics of microbial EPS, identifying the isolation method of these valuable compounds, and their applications in the food industry are the objectives of this study. EPS are used in food industries as thickeners, gelling agents, viscosifiers, and film formers. The antioxidative, anticancer, prebiotic, and cholesterol-lowering effects of some of these compounds make it possible to use them in functional food production.

NMR analysis and molecular dynamics conformation of α-1,6-linear and α-1,3-branched isomaltose oligomers as mimetics of α-1,6-linked dextran

The conformational preferences of several α-1,6-linear and α-1,3-branched isomalto-oligosaccharides were investigated by NMR and MD-simulations. Right-handed helical structure contributed to the solution geometry in isomaltotriose and isomaltotetraose with one nearly complete helix turn and stabilizing intramolecular hydrogen bonds in the latter by MD-simulation. Decreased helix contribution was observed in α-1,3-glucopyranosyl- and α-1,3-isomaltosyl-branched saccharide chains. Especially the latter modification was predicted to cause a more compact structure consistent with literature rheology measurements as well as with published dextranase-resistant α-1,3-branched oligosaccharides. The findings presented here are significant because they shed further light on the conformational preference of isomalto-oligosaccharides and provide possible help for the design of dextran-based drug delivery systems or for the targeted degradation of capsular polysaccharides by dextranases in multi-drug resistant bacteria.

Products Released from Structurally Different Dextrans by Bacterial and Fungal Dextranases

Dextran hydrolysis by dextranases is applied in the sugar industry and the medical sector, but it also has a high potential for use in structural analysis of dextrans. However, dextranases are produced by several organisms and thus differ in their properties. The aim of this study was to comparatively investigate the product patterns obtained from the incubation of linear as well as O3- and O4-branched dextrans with different dextranases. For this purpose, genes encoding for dextranases from Bacteroides thetaiotaomicron and Streptococcus salivarius were cloned and heterologously expressed in Escherichia coli. The two recombinant enzymes as well as two commercial dextranases from Chaetomium sp. and Penicillium sp. were subsequently used to hydrolyze structurally different dextrans. The hydrolysis products were investigated in detail by HPAEC-PAD. For dextranases from Chaetomium sp., Penicillium sp., and Bacteroides thetaiotaomicron, isomaltose was the end product of the hydrolysis from linear dextrans, whereas Penicillium sp. dextranase led to isomaltose and isomaltotetraose. In addition, the latter enzyme also catalyzed a disproportionation reaction when incubated with isomaltotriose. For O3- and O4-branched dextrans, the fungal dextranases yielded significantly different oligosaccharide patterns than the bacterial enzymes. Overall, the product patterns can be adjusted by choosing the correct enzyme as well as a defined enzyme activity.

The role of dextran production in the metabolic context of Leuconostoc and Weissella Tunisian strains

High molecular weight dextrans improve the rheological properties of fermented products and have immunomodulatory and antiviral activity. We report on 5.84 × 10⁷-2.61 × 10⁸ Da dextrans produced by Leuconostoc lactis AV1n, Weissella cibaria AV2ou and Weissella confusa V30 and FS54 strains. Dextransucrases catalyze dextran synthesis by sucrose hydrolysis concomitant with fructose generation. The four bacteria have dextransucrases with molecular weight of about 160 kDa detected by zymograms. Each bacterium showed different interplay of dextran production and metabolic fluxes. All bacteria produced lactate, and AV2ou apart, synthesized mannitol from fructose. FS54 hydrolyzed dextran blue and the concentration of dextran produced by this bacterium decreased during the stationary phase. The AV1n binding to Caco-2 cells and polystyrene plates was higher under conditions for dextran synthesis. Thus, this is the first instance of a Weissella dextranase, associated with a dextransucrase ability, and of a positive influence of dextran on adhesion and aggregation properties of a bacterium.

Structural and physicochemical characterisation and antioxidant activity of an α-D-glucan produced by sourdough isolate Weissella cibaria MED17

An exopolysaccharide (EPS) producer slimy-mucoid type colony was isolated from sourdough and identified as Weissella cibaria MED17. The ¹H and ¹³C NMR spectra of EPS MED17 demonstrated that this EPS was a dextran type glucan ((1 → 6)-linked α-D-glucose core structure) containing (1 → 3)-linked α-D-glucose branches and proportion of (1 → 6)-linked α-D-glucose units to (1 → 3)-linked α-D-glucose units was 94.3:5.7%. The FTIR analysis also confirmed the (1 → 6)-linked α-D-glucose linkage. A high level of thermal stability was observed for glucan MED17 as no degradation up to 300 °C was observed by TGA and DSC analysis. The XRD analysis of glucan MED17 showed its semi- crystalline nature and its compact sheet-like morphology was observed by SEM analysis. Finally, antioxidant characteristics of glucan MED17 were determined by ABTS and DPPH radical scavenging activity tests that revealed a moderate antioxidant activity of glucan MED17. These findings show potential techno-functional characteristics of glucan MED17.

Structural characterization of mixed-linkage α-glucans produced by mutants of Lactobacillus reuteri TMW 1.106 dextransucrase

Dextrans and other bacterial α-glucans are versatile and structurally diverse polysaccharides which can be enzymatically synthesized by using glucansucrases. By substituting certain amino acids in the active site of these enzymes, the structure of the synthesized polysaccharides can be modified. In this study, such amino acid substitutions were applied (single and combined) to the dextransucrase from Lactobacillus reuteri TMW 1.106 and the structures of the synthesized polysaccharides were subsequently characterized in detail. Besides methylation analysis, α-glucans were hydrolyzed by several glycoside hydrolases and the liberated oligosaccharides were identified by comparison to standard compounds or by isolation and NMR spectroscopic characterization. Furthermore, two-dimensional NMR spectroscopy was used to analyze the untreated polysaccharides. The results demonstrated that structurally different α-glucans were formed, for example different highly O4-branched dextrans or several reuteran-like polymers with varying fine structures. Consequently, mutant Lactobacillus reuteri TMW 1.106 dextransucrases can be used to form structurally unique polysaccharides.

Enzymatic Synthesis and Characterization of Mono-, Oligo-, and Polyglucosylated Conjugates of Caffeic Acid and Gallic Acid

Glucansucrases can be used to glucosylate various plant-derived phenolic compounds by using sucrose as donor substrate. We applied Lactobacillus reuteri TMW 1.106 dextransucrase to glucosylate the acceptor substrates caffeic acid and gallic acid. Subsequently, monoglucosylated and in particular oligo- and polyglucosylated conjugates were characterized by using different chromatographic techniques and two-dimensional NMR spectroscopy. Both acceptors were substituted at positions O3 and O4. Under the conditions used, two monoglucosylated products were formed for caffeic acid, whereas only one O3-monosubstituted conjugate was detected for gallic acid. However, both acceptors resulted in O4-substituted oligo- and polyglucosylated conjugates, the amount of which was higher from gallic acid than from caffeic acid. Profile analysis tensiometry suggested that, in contrast to unmodified dextrans, oligo- and polymeric glucoconjugates of gallic acid are highly interfacially active. Overall, we provide the first detailed characterization of enzymatically conjugated oligo- and polymeric dextrans, which may have further potential as functional ingredients.

Detailed Structural Characterization of Glucans Produced by Glucansucrases from Leuconostoc citreum TMW 2.1194

The water kefir organism Leuconostoc citreum TMW 2.1194 forms highly branched dextrans with O3- and O4-bound side chains. To obtain detailed information on the enzymatic synthesis of these polymers, the four glucansucrases encoded by Leuconostoc citreum TMW 2.1194 were cloned, heterologously expressed, and used for polysaccharide production. Molecular and macromolecular structure of the synthesized glucans were analyzed by methylation analysis, two-dimensional NMR spectroscopy, oligosaccharide analysis after partial hydrolysis, and asymmetric flow field-flow fractionation. It was demonstrated that two glucansucrases form insoluble glucans with variously branched dextran sections and varying portions of consecutive, 1,3-linked glucose units. In contrast, the other two glucansucrases synthesized O3- (Lc6255) and O4-branched (Lc1785) soluble dextrans. Analysis, isolation, and characterization of enzymatically liberated oligosaccharides showed that monomeric and elongated side chains are abundant in both polysaccharides. From the structures and size distributions it was concluded that Lc1785 is mainly responsible for synthesis of fermentatively produced soluble dextrans.

Techno-Functional Role of Exopolysaccharides in Cereal-Based, Yogurt-Like Beverages

This review describes the technical and functional role of exopolysaccharides (EPSs) in cereal-based, yogurt-like beverages. Many microorganisms produce EPSs as a strategy for growing, adhering to solid surfaces, and surviving under adverse conditions. In several food and beverages, EPSs play technical and functional roles. Therefore, EPSs can be isolated, purified, and added to the product, or appropriate bacteria can be employed as starter cultures to produce the EPSs in situ within the matrix. The exploitation of in situ production of EPSs is of particular interest to manufacturers of cereal-base beverages aiming to mimic dairy products. In this review, traditional and innovative or experimental cereal-based beverages, and in particular, yogurt-like beverages are described with a particular focus in lactic acid bacteria (LAB’s) EPS production. The aim of this review is to present an overview of the current knowledge of exopolysaccharides produced by lactic acid bacteria, and their presence in cereal-based, yogurt-like beverages.

Synthesis of novel α-glucans with potential health benefits through controlled glucose release in the human gastrointestinal tract

The glycemic carbohydrates we consume are currently viewed in an unfavorable light in both the consumer and medical research worlds. In significant part, these carbohydrates, mainly starch and sucrose, are looked upon negatively due to their rapid and abrupt glucose delivery to the body which causes a high glycemic response. However, dietary carbohydrates which are digested and release glucose in a slow manner are recognized as providing health benefits. Slow digestion of glycemic carbohydrates can be caused by several factors, including food matrix effect which impedes α-amylase access to substrate, or partial inhibition by plant secondary metabolites such as phenolic compounds. Differences in digestion rate of these carbohydrates may also be due to their specific structures (e.g. variations in degree of branching and/or glycosidic linkages present). In recent years, much has been learned about the synthesis and digestion kinetics of novel α-glucans (i.e. small oligosaccharides or larger polysaccharides based on glucose units linked in different positions by α-bonds). It is the synthesis and digestion of such structures that is the subject of this review.

Sensory analysis of juice blend containing isomalto-oligosaccharides produced by fermentation with Weissella cibaria

This study aimed at producing isomaltooligosaccharides in juice blends using orange juice and malt extract and assessing their acceptability. Different blend formulations were prepared and fermented, varying the concentration of orange juice, sucrose and malt extract. Dextransucrase from Weissella cibaria 10 M was used to enzymatically synthesize α(1-6) linked glucan-oligosaccharides by transglycosylation reactions, with maltose as acceptor carbohydrate and sucrose as donor. The optimal yield of oligosaccharides was after 24 h, producing 19.4 g/L of oligosaccharides (degree of polymerization 3) from 36 g/L maltose and 19 g/L sucrose. All the blend proved to be good alternatives for synthesizing isomalto-oligosaccharides with different degrees of polymerization. Sensory analysis showed good average acceptability compared to natural orange juice, achieving scores of around 6 on a 9-point hedonic scale. In a comprehensive analysis, juice blends containing orange juice and malt extract with Weissella cibaria to produce oligosaccharides exhibited good sensory indicators as an innovative prebiotic beverage. A prebiotic oligosaccharide beverage can be produced by enzymatic synthesis of oligosaccharides with different degrees of polymerization.

Starch biotransformation into isomaltooligosaccharides using thermostable alpha-glucosidase from Geobacillus stearothermophilus

The present study first identified the biotransformation of starch as a novel preparation method was investigated using the alpha-transglucosidase-producing Geobacillus stearothermophilus U2. Subsequently, 5 L- and 20 L-scale fermentations were performed. After isolation and purification, liquid alpha-glucosidase preparations were obtained. Through covalent cross-linking and adsorption cross-linking using chitosan as the carrier and glutaraldehyde as the crosslinking agent, the conditions for immobilization of alpha-glucosidase on chitosan were determined. Moreover, Isomaltooligosaccharides (IMOs) were then prepared using chitosan membrane-immobilized alpha-glucosidase, beta-amylase, pullulanase, fungal alpha-amylase and starch as substrate. The mixed syrup that contained IMOs was evaluated and analyzed by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). In addition, small-scale preparation of IMOs was performed. These results are a strong indication that the alpha-transglucosidase-producing G. stearothermophilus as a potential application technique can be successfully used to prepare industrial IMOs.

Structural characterization of the exopolysaccharides from water kefir

Water kefir is a beverage which is produced by initiating fermentation of a fruit extract/sucrose solution with insoluble kefir grains. Exopolysaccharides that are formed from sucrose play a major role in the kefir grain formation, but the exopolysaccharides in the kefir beverage and the detailed structural composition of the whole kefir grains have not been studied yet. Therefore, kefir grains and the corresponding kefir beverage were analyzed for exopolysaccharides by multiple chromatographic approaches and two-dimensional NMR spectroscopy. Furthermore, different fractionation techniques were applied to obtain further information about the exopolysaccharides. The exopolysaccharide-fraction of the investigated kefir beverage was predominantly composed of O3- and O2-branched dextrans as well as lower amounts of levans. The insoluble dextrans from the kefir grains were mostly O3-branched and contained an elevated portion of 1,3-linked glucose units compared to the soluble dextrans. The structurally different exopolysaccharides in water kefir suggest the involvement of multiple bacteria.

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.

UP-HILIC-MS/MS to Determine the Action Pattern of Penicillium sp. Dextranase

Investigation of the action pattern of enzymes acting on carbohydrates is challenging, as both the substrate and the digestion products are complex mixtures. Dextran and its enzyme-derived oligosaccharides are widely used for many industrial applications. In this work, a new method relying on ultra-performance hydrophilic interaction liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UP-HILIC-Q/TOF-MS/MS) was developed to analyze a complex mixture of dextran oligosaccharide products to determine the action pattern of dextranase. No derivatization of oligosaccharides was required and the impact of the α- and β-configurations of the native oligosaccharides on the chromatographic separation was eliminated. The 1→6, 1→3, 1→4 backbone linkages and the branch linkages of these oligosaccharides were all distinguished from diagnostic ions in their MS/MS spectra, including fragments corresponding to (0,2)A, (0,3)A, (0,4)A, B-H2O, (2,5)A, and (3,5)A. The sequences of the oligosaccharide products were similarly established. Thus, the complex oligosaccharide mixtures in dextran digestion products were profiled and identified using this method. The more enzyme-resistant structures in dextran were established using much less sample, labor, time, and uncertainty than in previous studies. This method provides an efficient, sensitive, and straightforward way to monitor the entire process of digestion, establish the action pattern of the dextranase from Penicillium sp., and to support the proper industrial application of dextranase.

The genus Weissella: taxonomy, ecology and biotechnological potential

Bacteria assigned to the genus Weissella are Gram-positive, catalase-negative, non-endospore forming cells with coccoid or rod-shaped morphology (Collins et al., 1993; Björkroth et al., 2009, 2014) and belong to the group of bacteria generally known as lactic acid bacteria. Phylogenetically, the Weissella belong to the Firmicutes, class Bacilli, order Lactobacillales and family Leuconostocaceae (Collins et al., 1993). They are obligately heterofermentative, producing CO2 from carbohydrate metabolism with either d(-)-, or a mixture of d(-)- and l(+)- lactic acid and acetic acid as major end products from sugar metabolism. To date, there are 19 validly described Weissella species known. Weissella spp. have been isolated from and occur in a wide range of habitats, e.g., on the skin and in the milk and feces of animals, from saliva, breast milk, feces and vagina of humans, from plants and vegetables, as well as from a variety of fermented foods such as European sourdoughs and Asian and African traditional fermented foods. Thus, apart from a perceived technical role of certain Weissella species involved in such traditional fermentations, specific Weissella strains are also receiving attention as potential probiotics, and strain development of particularly W. cibaria strains is receiving attention because of their high probiotic potential for controlling periodontal disease. Moreover, W. confusa and W. cibaria strains are known to produce copius amounts of novel, non-digestible oligosaccharides and extracellular polysaccharides, mainly dextran. These polymers are receiving increased attention for their potential application as prebiotics and for a wide range of industrial applications, predominantly for bakeries and for the production of cereal-based fermented functional beverages. On the detrimental side, strains of certain Weissella species, e.g., of W. viridescens, W. cibaria and W. confusa, are known as opportunistic pathogens involved in human infections while strains of W. ceti have been recently recongnized as etiological agent of "weissellosis," which is a disease affecting farmed rainbow trouts. Bacteria belonging to this species thus are important both from a technological, as well as from a medical point of view, and both aspects should be taken into account in any envisaged biotechnological applications.

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.

Weissella confusa Cab3 dextransucrase: properties and in vitro synthesis of dextran and glucooligosaccharides

Food-derived Weissella spp. have gained attention during recent years as efficient dextran producers. Weissella confusa Cab3 dextransucrase (WcCab3-DSR) was isolated applying PEG fractionation and used for in vitro synthesis of dextran and glucooligosaccharides. WcCab3-DSR had a molar mass of 178 kDa and was activated by Co(2+) and Ca(2+) ions. Glycerol and Tween 80 enhanced enzyme stability, and its half-life at 30°C increased from 10h to 74 h and 59 h, respectively. The (1)H and (13)C NMR spectral analysis of the produced dextran confirmed the presence of main chain α-(1→6) linkages with only 3.0% of α-(1→3) branching, of which some were elongated. An HPSEC analysis in DMSO revealed a high molecular weight of 1.8 × 10(7)g/mol. Glucooligosaccarides produced through the acceptor reaction with maltose, were analyzed with HPAEC-PAD and ESI-MS/MS. They were a homologous series of isomaltooligosaccharides with reducing end maltose units. To the best of our knowledge, this is a first report on native W. confusa dextransucrase.

Glucansucrases: three-dimensional structures, reactions, mechanism, α-glucan analysis and their implications in biotechnology and food applications

Glucansucrases are extracellular enzymes that synthesize a wide variety of α-glucan polymers and oligosaccharides, such as dextran. These carbohydrates have found numerous applications in food and health industries, and can be used as pure compounds or even be produced in situ by generally regarded as safe (GRAS) lactic acid bacteria in food applications. Research in the recent years has resulted in big steps forward in the understanding and exploitation of the biocatalytic potential of glucansucrases. This paper provides an overview of glucansucrase enzymes, their recently elucidated crystal structures, their reaction and product specificity, and the structural analysis and applications of α-glucan polymers. Furthermore, we discuss key developments in the understanding of α-glucan polymer formation based on the recently elucidated three-dimensional structures of glucansucrase proteins. Finally we discuss the (potential) applications of α-glucans produced by lactic acid bacteria in food and health related industries.