NMR spectroscopic analysis of exopolysaccharides produced by Leuconostoc citreum and Weissella confusa

Slowly hydrolyzable property of microbial dextrans at the small intestinal α-glucosidase levels leads to the modulated glycemic responses in the mouse model

Dextran-type α-glucans have been known as non-digestible ingredients that can be considered prebiotics to promote colon health. However, recent studies have revealed that various α-linked glucosyl units are hydrolyzed to glucose by small intestinal α-glucosidases. This study analyzed the structural characteristics of exopolysaccharides (EPSs) from Weissella species, and the hydrolysis properties at both in vitro/in vivo levels were investigated. Compared with a previous in vitro digestion model using fungal α-hydrolytic enzymes, dextrans, which mainly consist of α-1,6 linkages with small amounts of α-1,3 linked glucose units, were slowly hydrolyzed to glucose by mammalian mucosal α-glucosidases, resulting in attenuation of the initial glycemic response following administration of EPS samples to mice via oral gavage. The results of this study demonstrate the concept of dextran-type α-glucans as glycemic carbohydrates rather than dietary fibers or prebiotics. Slowly digestible dextrans can be applied as a functional ingredient to regulate postprandial glucose delivery throughout the gastrointestinal tract.

Synthesis of dextran of different molecular weights by recombinant dextransucrase DsrB

Leuconostoc citreum JZ-002 was extracted from artisanal orange wine. This strain was used to synthesize dextran with a purification extraction of 27.9 g/L. The resulting dextran had a molecular weight of 2.45 × 106 Da. A significant portion, amounting to 64 % of the structure, is constituted by the main chain, with α-(1,6) glycosidic bonds acting as the linkages. In contrast, the branched chain, comprising 34 % of the entire molecule, is characterized by the presence of α-(1,3) glycosidic bonds. The dextransucrase DsrB, believed to be accountable for the formation of the dextran backbone, was successfully cloned into the pET-28a-AcmA vector. The recombinant expression of the enzyme was achieved. Purified recombinant enzymes and immobilized in a single go using the gram-positive enhancer matrix (GEM). The maximum yield of dextran produced by suchimmobilized enzyme was 191.9 g/L. The composition featured a dextran connected via α-(1,6) glycosidic linkages. Molecular weight controlled synthesis was achieved with sucrose concentrations of 100-2000 mM and enzyme concentrations of 320-1280 U. The Mw of the synthesized dextran extended from 4680 to 1,320,000 Da. By controlling the ratio between enzyme concentration and sucrose concentration, dextrans with diverse Mw can be enzymatically generated.

Bacteria inhabiting spider webs enhance host silk extensibility

Spider silk is a promising material with great potential in biomedical applications due to its incredible mechanical properties and resistance to degradation of commercially available bacterial strains. However, little is known about the bacterial communities that may inhabit spider webs and how these microorganisms interact with spider silk. In this study, we exposed two exopolysaccharide-secreting bacteria, isolated from webs of an orb spider, to major ampullate (MA) silk from host spiders. The naturally occurring lipid and glycoprotein surface layers of MA silk were experimentally removed to further probe the interaction between bacteria and silk. Extensibility of major ampullate silk produced by Triconephila clavata that was exposed to either Microbacterium sp. or Novosphigobium sp. was significantly higher than that of silk that was not exposed to bacteria (differed by 58.7%). This strain-enhancing effect was not observed when the lipid and glycoprotein surface layers of MA silks were removed. The presence of exopolysaccharides was detected through NMR from MA silks exposed to these two bacteria but not from those without exposure. Here we report for the first time that exopolysaccharide-secreting bacteria inhabiting spider webs can enhance extensibility of host MA silks and silk surface layers play a vital role in mediating such effects.

Physicochemical Characterization of Dextran HE29 Produced by the Leuconostoc citreum HE29 Isolated from Traditional Fermented Pickle

In this study, lactic acid bacteria (LAB) strains were isolated from traditional fermented pickles, and among the identified strains, Leuconostoc citreum HE29 with a strong slimy colony profile was further selected to determine the physicochemical and techno-functional properties of its exopolysaccharide (EPS). Glucose was the only sugar monomer in the core unit of EPS HE29 detected by HPLC analysis, and glucan HE29 revealed 7.3 kDa of molecular weight. Structural characterization of glucan HE29 by 1H and 13C NMR spectroscopy analysis demonstrated that EPS HE29 was a dextran-type EPS containing 5.3% levels of (1 → 3)-linked α-D-glucose units. This structural configuration was also supported by FT-IR analysis, which also demonstrated the functional groups within the dextran HE29 structure. In terms of thermal properties detected by TGA and DSC analysis, dextran HE29 demonstrated a degradation temperature of around 280 °C, showing its strong thermal features. A semi-crystalline nature was observed for dextran HE29 detected by XRD analysis. Finally, AFM and SEM analysis revealed tangled network-like properties and web-like branched structures for dextran HE29, respectively. These findings suggest the importance of plant-based fermented products as LAB sources in obtaining novel EPS structures with potential techno-functional roles.

Microbial exopolysaccharides in the biomedical and pharmaceutical industries

The most significant and renewable class of polymeric materials are extracellular exopolysaccharides (EPSs) produced by microorganisms. Because of their diverse chemical and structural makeup, EPSs play a variety of functions in a variety of industries, including the agricultural industry, dairy industry, biofilms, cosmetics, and others, demonstrating their biotechnological significance. EPSs are typically utilized in high-value applications, and current research has focused heavily on them because of their biocompatibility, biodegradability, and compatibility with both people and the environment. Due to their high production costs, only a few microbial EPSs have been commercially successful. The emergence of financial barriers and the growing significance of microbial EPSs in industrial and medical biotechnology has increased interest in exopolysaccharides. Since exopolysaccharides can be altered in a variety of ways, their use is expected to increase across a wide range of industries in the coming years. This review introduces some significant EPSs and their composites while concentrating on their biomedical uses.

Genome analysis revealed a repertoire of oligosaccharide utilizing CAZymes in Weissella confusa CCK931 and Weissella cibaria YRK005

Weissella bacteria are gram-positive, anaerobic, fermentative, and have probiotic potential. This study aimed to compare the genomes of W. cibaria YRK005 and W. confusa CCK931 isolated from young radish and kimchi, respectively. The genomic size of W. cibaria YRK005 and W. confusa CCK931 with GC content is 2.36 Mb (45%) and 2.28 Mb (44.67%), respectively. The genome study identified 92 and 83 CAZymes genes, respectively, for W. cibaria YRK005 and W. confusa CCK931, that are responsible for 26 and 27 glycoside hydrolases (GH) and 21 and 27 glycosyl transferases. Both species have one gene for carbohydrate esterases and three genes for carbohydrate-binding modules. The primary CAZymes found in both species that are involved in oligosaccharide utilization are GH1, GH2, GH30, GH13_30, GH13_31, GH42, GH43, and GH65. The study also details the production pathways for glycogen and folate. Both strains include a unique repertoire of genes, including hypothetical proteins, showing adaptability to diverse ecological niches and evolution over time.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01232-7.

The in-situ dextran produced in rice protein yogurt: Effect on viscosity and structural characteristics

Phase separation is one of the primary quality control issues for plant-based beverages during storage. This study applied the in-situ-produced dextran (DX) from Leuconostoc citreum DSM 5577 to solve this problem. Rice flour milled from broken rice was used as the raw material and Ln. citreum DSM 5577 as the starter to prepare rice-protein yogurt (RPY) under different processing conditions. The microbial growth, acidification, viscosity change, and DX content were first analyzed. Then, the proteolysis of rice protein was evaluated, and the role of the in-situ-synthesized DX in viscosity improvement was explored. Finally, the in-situ-synthesized DXs in RPYs under different processing conditions were purified and characterized. The in-situ-produced DX caused a viscosity increase up to 1.84 Pa s in RPY and played a major role in this improvement by forming a new network with high water-binding capacity. The processing conditions affected the content and the molecular features of DXs, with a DX content up to 9.45 mg/100 mg. A low-branched DX (5.79 %) with a high aggregating ability possessed a stronger thickening ability in RPY. This study may guide the application of the in-situ-synthesized DX in plant protein foods and may promote the utilization of broken rice in the food industry.

Characterization and Immunological Activity of Exopolysaccharide from Lacticaseibacillus paracasei GL1 Isolated from Tibetan Kefir Grains

Two exopolysaccharide fractions (GL1-E1 and GL1-E2) of Lacticaseibacillus paracasei GL1 were isolated with the molecular weights of 3.9 × 105 Da and 8.2 × 105 Da, respectively. Both fractions possessed mannose, glucose, and galactose in molar ratios of 1.16:1.00:0.1, and 3.81:1.00:0.12, respectively. A structural arrangement of two fractions was proposed by methylation, one-dimensional and two-dimensional nuclear magnetic resonance experiments. The backbone of GL1-E1 consisted of →4)-α-D-Glcp(1→, →3,4)-α-D-Manp(1→, →3,6)-α-D-Manp(1→, →6)-α-D-Manp(1→, and →6)-α-D-Galp(1→ with α-D-Glcp at branching point. The backbone of GL1-E2 consisted of →4)-α-D-Glcp(1→, →3,4)-α-D-Manp(1→, →3,6)-α-D-Manp(1→, →6)-α-D-Manp(1→, →6)-α-D-Galp(1→, and →4)-β-D-Manp(1→, and the side chain also consisted of α-D-Manp residue. In addition, the differential scanning calorimetry (DSC) analysis indicated that both GL1-E1 and GL1-E2 had good thermal stability. Furthermore, the two fractions could promote the viability of RAW264.7 cells and exert an immunomodulatory role by enhancing phagocytosis, increasing nitric oxide (NO) release and promoting the expression of cytokines.

Characterization of Dextran Produced by the Food-Related Strain Weissella cibaria C43-11 and of the Relevant Dextransucrase Gene

A metabolic feature of lactic acid bacteria (LAB) is the production of exopolysaccharides (EPSs), which have technological and functional properties of interest to the food sector. The present study focused on the characterization of the Weissella cibaria strain C43-11, a high EPS producer in the presence of sucrose, in comparison with a low-producing strain (C2-32), and on possible genetic regulatory elements responsible for the modulation of dextransucrase (dsr) genes expression. NMR analysis of the polymeric material produced by the C43-11 strain indicated the presence of dextran consisting mainly of a linear scaffold formed by α-(1–6) glycosidic linkages and a smaller amounts of branches derived from α-(1–2), α-(1–3), and α-(1–4) linkages. Molecular analysis of the dsr genes and the putative transcriptional promoters of the two strains showed differences in their regulatory regions. Such variations may have a role in the modulation of dsr expression levels in the presence of sucrose. The strong upregulation of the dsr gene in the C43-11 strain resulted in a high accumulation of EPS. This is the first report showing differences in the regulatory elements of the dsr gene in W. cibaria and indicates a new perspective of investigation to identify the regulatory mechanism of EPS production.

Lactic Acid Bacteria in Raw-Milk Cheeses: From Starter Cultures to Probiotic Functions

Traditional cheeses produced from raw milk exhibit a complex microbiota, characterized by a sequence of different microorganisms from milk coagulation and throughout maturation. Lactic acid bacteria (LAB) play an essential role in traditional cheese making, either as starter cultures that cause the rapid acidification of milk or as secondary microbiota that play an important role during cheese ripening. The enzymes produced by such dynamic LAB communities in raw milk are crucial, since they support proteolysis and lipolysis as chief drivers of flavor and texture of cheese. Recently, several LAB species have been characterized and used as probiotics that successfully promote human health. This review highlights the latest trends encompassing LAB acting in traditional raw milk cheeses (from cow, sheep, and goat milk), and their potential as probiotics and producers of bioactive compounds with health-promoting effects.

Effects of Fly Maggot Protein Replacement of Fish Meal on Growth Performance, Immune Level, Antioxidant Level, and Fecal Flora of Blue Foxes at Weaning Stage

Simple Summary

Given the shortage of fish meal, other animal protein replacements are actively being researched. One such alternative is fly maggot protein—a highly nutritious insect protein containing chitin, lysozyme, and other biologically active substances. The purpose of this study was to examine how the replacement of fish meal with fly maggot protein affects growth, immune indexes, antioxidant levels, and fecal microflora in blue foxes (Alopex lagopus) during weaning. The results showed that fly maggot protein replacement had no adverse effects on the growth, immune indexes, and antioxidant levels of blue foxes at weaning. Further, it could modulate the fecal microflora. This indicates that fly maggot protein can serve as a novel animal protein alternative to fish meal for feeding blue foxes.

Abstract

Dietary protein is a key nutritional parameter and warrants special attention in animal husbandry. This study aimed to evaluate the effect of replacing fish meal (F) with fly maggot protein (M) on the growth performance, antioxidant levels, immune indexes, and fecal microflora in weaned blue foxes (Alopex lagopus). Twenty weaned blue foxes were randomly assigned to the control (F diet; 6% of F) or experimental (M diet; F substituted by M) group (10 blue foxes per group). The duration of the trial was 28 days. The results showed that there was no significant difference in average daily gain between group M and group F during the experiment (p = 0.473). Moreover, the diarrhea index was similar between group M and group F during the entire experimental period (p = 0.112). At the end of the experiment, the levels of IL-6 and IgG in group M at 28 d were significantly higher than that in group F (p = 0.004, p = 0.025, respectively), but not IL-1β, IL-2, SIgA, IgM, and TNF-α. The levels of SOD in group M at 28 d were significantly higher than those in group F (p = 0.001), and no difference of MDA and T-AOC was found between group F and M (p = 0.073, p = 0.196, respectively). In both groups, the diversity of fecal microbes first increased and then decreased with the progress of the experimental period. Initially, there were differences in the composition of microbial communities between the two groups. However, this difference was attenuated at later stages of the experimental period. In conclusion, fly maggot protein can replace fish meal as a source of animal protein in feed material for blue foxes during the weaning period.

Structural Characterization of Exopolysaccharide Produced by Leuconostoccitreum B-2 Cultured in Molasses Medium and Its Application in Set Yogurt

Sugarcane molasses is an agricultural by-product containing sucrose. In this study, the exopolysaccharide (M-EPS) produced by Leuconostoc citreum B-2 in molasses-based medium was characterized, optimized, and its application in set yogurt was investigated. The structure analysis, including gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance, revealed that the M-EPS was a linear dextran composed of D-glucose units, which were linked by α-(1→6) glycosidic bonds with 19.3% α-(1→3) branches. The M-EPS showed a lower molecular weight than that produced from sucrose. The M-EPS was added into the set yogurt, and then the water holding capacity, pH, and microstructure of set yogurt were evaluated. Compared with the controls, the addition of M-EPS improved the water holding capacity and reduced the pH of set yogurt. Meanwhile, the structure of the three-dimensional network was also observed in the set yogurt containing M-EPS, indicating that M-EPS had a positive effect on the stability of set yogurt. The results provide a theoretical basis for the cost-effective utilization of sugarcane molasses.

Minimalist Design of an Intrinsically Disordered Protein-Mimicking Scaffold for an Artificial Membraneless Organelle

Liquid-liquid phase separation (LLPS) is an emerging and universal mechanism for intracellular organization, particularly, by forming membraneless organelles (MLOs) hosting intrinsically disordered proteins (IDPs) as scaffolds. Genetic engineering is generally applied to reconstruct IDPs harboring over 100 amino acid residues. Here, we report the first design of synthetic hybrids consisting of short oligopeptides of fewer than 10 residues as "stickers" and dextran as a "spacer" to recapitulate the characteristics of IDPs, as exemplified by the multivalent FUS protein. Hybrids undergo LLPS into micron-sized liquid droplets resembling LLPS in vitro and in living cells. Moreover, the droplets formed are capable of recruiting proteins and RNAs and providing a favorable environment for a biochemical reaction with highly enriched components, thereby mimicking the function of natural MLOs. This simple yet versatile model system can help elucidate the molecular interactions implicated in MLOs and pave ways to a new type of biomimetic materials.

Prebiotic activities of dextran from Leuconostoc mesenteroides SPCL742 analyzed in the aspect of the human gut microbial ecosystem

The aim of this study was to investigate the prebiotic activities of dextran (LM742) produced by Leuconostoc mesenteroides SPCL742 in the aspect of the human gut microbial ecosystem focusing on microbiome and metabolome changes in in vitro colonic fermentation. LM742 dextran had a medium-chain structure with the molecular weight of 1394.87 kDa (DP = 7759.22) and α-1,6 and α-1,3 linkages with a 26.11 : 1 ratio. The LM742 dextran was resistent to digestive enzymes in the human gastrointestinal conditions. The individual cultivation of 30 intestinal bacteria with LM742 dextran showed the growth of Bacteroides spp., whereas in vitro human fecal fermentation with LM742 exhibited the symbiotic growth of Bacteroides spp. and beneficial bacteria such as Bifidobacterium spp. Further co-cultivation of Bacteroides xylanisolvens and several probiotics indicated that B. xylanisolvens provides a cross-feeding of dextran to probiotics. In fecal fermentation, LM742 dextran resulted in increased concentrations of short-chain fatty acids, valerate and pantothenate, but it rarely affected the conversion of betaine to trimethylamine. Lastly, LM742 dextran inhibited the adhesion of pathogenic E. coli to human epithelial cells. Taken together, these results demonstrate the prebiotic potential of LM742 dextran as a health-beneficial polysaccharide in the human intestine.

Exopolysaccharides Produced by Lactic Acid Bacteria: From Biosynthesis to Health-Promoting Properties

The production of exopolysaccharides (EPS) by lactic acid bacteria (LAB) has attracted particular interest in the food industry. EPS can be considered as natural biothickeners as they are produced in situ by LAB and improve the rheological properties of fermented foods. Moreover, much research has been conducted on the beneficial effects of EPS produced by LAB on modulating the gut microbiome and promoting health. The EPS, which varies widely in composition and structure, may have diverse health effects, such as glycemic control, calcium and magnesium absorption, cholesterol-lowering, anticarcinogenic, immunomodulatory, and antioxidant effects. In this article, the latest advances on structure, biosynthesis, and physicochemical properties of LAB-derived EPS are described in detail. This is followed by a summary of up-to-date methods used to detect, characterize and elucidate the structure of EPS produced by LAB. In addition, current strategies on the use of LAB-produced EPS in food products have been discussed, focusing on beneficial applications in dairy products, gluten-free bakery products, and low-fat meat products, as they positively influence the consistency, stability, and quality of the final product. Highlighting is also placed on reports of health-promoting effects, with particular emphasis on prebiotic, immunomodulatory, antioxidant, cholesterol-lowering, anti-biofilm, antimicrobial, anticancer, and drug-delivery activities.

A comprehensive review on mutan (a mixed linkage of α-1-3 and α-1-6 glucans) from bacterial sources

Mutan is an extracellular sticky polymer having α-1-3 and α-1-6 glycosidic linkages with a large diversity in molecular weights and structures depending on the source. These compounds are reported to be highly thermostable and also have potential physiochemical and biological applications. The main aim of this review is to provide an overview of glucosyltransferases and their role in mutan synthesis. The production strategies and structural properties of bacterial mutans are discussed with a goal to improve production efficiency. The physicochemical features, chemical modifications, potential industrial applications and future prospects are also discussed. According to data, mutan and its derivatives will play a larger role in medicinal sectors and as thermoplastics in the near future.Abbreviations: ABTS: 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid; BHI: Brain heart infusion broth; ¹³C (HSQC) NMR: Heteronuclear Single Quantum Coherence NMR; CBMs: Carbohydrate binding modules; DPPH: 2,2-diphenyl-1-picrylhydrazyl; FTIR: Fourier-transform infrared spectroscopy; GC-MS: Gas chromatography-mass spectrometry; GPC: Gel permeation chromatography; Gtfs: Glucosyltransferases; ¹H (DQF-COSY): Double-quantum filtered correlation spectroscopy; HPAEC-PAD: High-performance anion exchange chromatography with pulsed amperometric detection; HPLC: High performance liquid chromatography; HPSEC-RI: High-performance size exclusive chromatography coupled with refractive index; HPSEC-MALLS: High-performance size exclusive chromatography with multi-angle laser light scattering detection; MALDI-TOF: Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry; M_w: Weight-average molecular weight; MWD: Molecular weight distribution; NMR: Nuclear magnetic resonance spectroscopy; TEM: Transmission electron microscopy; THB: Todd Hewitt Broth; TTY: Tryticase tryptose yeast extract broth.

Factorial Design to Optimize Dextran Production by the Native Strain Leuconostoc mesenteroides SF3

Dextran is an extracellular bacterial polysaccharide for which industrial applications have been found in different areas. Several researchers have optimized the fermentation conditions to maximize dextran production. This study aimed to characterize the dextran of Leuconostoc mesenteroides SF3, which was isolated from the aguamiel of Agave salmiana. To maximize the yield of dextran, the effects of sucrose concentration, temperature, and incubation time were studied. The experiments were conducted using a factorial design and a response surface methodology. L. mesenteroides SF3 produced a maximum yield of dextran (23.8 g/L ± 4) after 16 h of incubation at 25 °C with 10% sucrose. The functional properties such as water absorption capacity, oil absorption capacity, and emulsion activity of this unique dextran were 361.8% ± 3.1, 212.0% ± 6.7, and 58.3% ± 0.7, respectively. These properties indicate that the dextran produced by L. mesenteroides SF3 is a high-quality polysaccharide with potential applications in the food industry, and the optimized conditions for its production could be used for the commercial production of this dextran, which have significant industrial perspectives.

Microbial Exopolysaccharides in Traditional Mexican Fermented Beverages

Exopolysaccharides (EPS) are biopolymers produced by many microorganisms, including some species of the genus Acetobacter, Bacillus, Fructobacillus, Leuconostoc, Lactobacillus, Lactiplantibacillus, Pediococcus, Pichia, Rhodotorula, Saccharomycodes, Schizosaccharomyces, and Sphingomonas, which have been reported in the microbiota of traditional fermented beverages. Dextran, levan, glucan, gellan, and cellulose, among others, are EPS produced by these genera. Extracellular biopolymers are responsible for contributing to specific characteristics to fermented products, such as modifying their organoleptic properties or contributing to biological activities. However, EPS can be easily found in the dairy industry, where they affect rheological properties in products such as yogurt or cheese, among others. Over the years, LAB has been recognized as good starter strains in spontaneous fermentation, as they can contribute beneficial properties to the final product in conjunction with yeasts. To the best our knowledge, several articles have reported that the EPS produced by LAB and yeasts possess many both biological and technological properties that can be influenced by many factors in which fermentation occurs. Therefore, this review presents traditional Mexican fermented beverages (tavern, tuba, sotol, and aguamiel) and relates them to the microbial EPS, which affect biological and techno-functional activities.

Characterization of a nanoparticulate exopolysaccharide from Leuconostoc holzapfelii KM01 and its potential application in drug encapsulation

Fermentation of Lactic Acid Bacteria (LAB) is considered to be a sustainable approach for polysaccharide production. Herein, exopolysaccharide (EPS)-producing LAB strain KM01 was isolated from Thai fermented dessert, Khao Mak, which was then identified as Leuconostoc holzapfelii. High-performance anion-exchange chromatography, nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy suggested that the KM01 EPS comprises α-1,6-linked glucosides. The molecular weight of KM01 EPS was around 500 kDa, but it can form large aggregates formation (MW > 2000 kDa) in an aqueous solution, judged by transmission electron microscopy and dynamic light scattering to be around 150 nm in size. Furthermore, this KM01 EPS form highly viscous hydrogels at concentrations above 5% (w/v). The formation of hydrogels and nanoparticle of KM01 EPS was found to be reversible. Finally, the suitability of KM01 EPS for biomedical applications was demonstrated by its lack of cytotoxicity and its ability to form complexes with quercetin. Unlike the common α-1,6-linked dextran, KM01 EPS can enhance the solubility of quercetin significantly.

Green Silver Nanoparticles Embedded in Cellulosic Network for Fresh Food Packaging

The demand for increasing the shelf life of fresh food as well as the need for protecting the food against foodborne infections warrant the demand for increasing the shelf life of fresh food. The incorporation of nanoparticles into the packaging material can enhance the preservation of perishable foods. Silver nanoparticles (AgNPs), in particular, have antibacterial, anti-mold, anti-yeast, and anti-viral activities can be embedded into the biodegradable packaging materials for this purpose. This study focuses on antimicrobial packaging materials for food by mixing the extracts of different plants with silver nitrate and depositing this mixture as a layer on the blotting papers, which are thick sheets of paper made of cellulose. Because the blotting papers are highly absorbent and porous, silver nitrate solution along with the plant extracts can be easily applied and allowed for in situ synthesis of AgNPs. Subsequently, these papers were analyzed and characterized using scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, and energy dispersive X-ray analysis. The coated paper exhibited good antibacterial activity against Escherichia coli and Staphylococcus aureus. Furthermore, the coated paper when used as a packaging material for tomatoes and coriander leaf, the shelf life was extended to about 30 days and 15 days respectively. The prepared cost-effective silver packing material can be used in food packaging for various perishable foods.

Lactic Acid Bacteria Isolated from Fermented Doughs in Spain Produce Dextrans and Riboflavin

Many lactic acid bacteria (LAB) produce metabolites with applications in the food industry, such as dextran-type exopolysaccharides (EPS) and riboflavin (vitamin B₂). Here, 72 bacteria were isolated from sourdoughs made by Spanish bread-makers. In the presence of sucrose, colonies of 22 isolates showed a ropy phenotype, and NMR analysis of their EPS supported that 21 of them were dextran producers. These isolates were identified by their random amplified polymorphic DNA (RAPD) patterns and their rrs and pheS gene sequences as LAB belonging to four species (Weissella cibaria, Leuconostoc citreum, Leuconostoc falkenbergense and Leuconostoc mesenteroides). Six selected strains from the Leuconostoc (3) and Weissella (3) genera grew in the absence of riboflavin and synthesized vitamin B₂. The EPS produced by these strains were characterized as dextrans by physicochemical analysis, and the L. citreum polymer showed an unusually high degree of branching. Quantification of the riboflavin and the EPS productions showed that the W. cibaria strains produce the highest levels (585–685 μg/and 6.5–7.4 g/L, respectively). Therefore, these new LAB strains would be good candidates for the development of fermented foods bio-fortified with both dextrans and riboflavin. Moreover, this is the first report of riboflavin and dextran production by L. falkenbergense.

Structures and anti-melanoma activities of two polysaccharides from Angelica sinensis (Oliv.) Diels

Polysaccharide is one of the necessary macromolecules in life activities, and it is also a very promising natural product for tumor prevention and treatment. In this study, two homogeneous polysaccharides (APS-4I and APS-4II) were isolated from Angelica sinensis (Oliv.) Diels. APS-4I was a linear glucan with molecular weight of 16.1 kDa, which was composed of 88.4% α-1,6-Glcp, 4.1% α-1,2-Glcp, 3.9% α-1,3-Glcp, and 2.8% α-T-Glcp. APS-4II was a novel polysaccharide with molecular weight of 11.1 kDa, which consisted of 55.4% α-1,6-Glcp, 10.4% α-1,3,5-Araf, 8.7% α-T-Araf, 9.2% α-1,5-Araf, 4.0% α-1,3-Araf, 3.6% α-1,4-Galp, and 9.1% β-1,3-Galp. NMR results demonstrated that APS-4II has a backbone composed of →6)-α-Glcp-(1 → 6)-α-Glcp-(1 → 5)-α-Araf-. (1 → 5)-α-Araf-(1 → 3,5)-α-Araf-(1 → 3)-β-Galp-(1 → 3)-β-Galp-(1 → 4)-α-Galp-(1 → 3)-α-Araf-(1 → 3,5)-α-Araf-(1→. Both APS-4I and APS-4II inhibited the tumor growth of B16-bearing mice, and the suppressive effect of APS-4II reached 64.7 ± 7.3%. Meanwhile, there were higher lymphocyte numbers and the levels of IL-2, IFN-γ, and TNF-α in peripheral blood of APS-4II-treated mice than those in APS-4I-treated mice. Furthermore, APS-4II showed a higher inhibitory effect on the proliferation of B16 cells and stronger promoting effects on the proliferation of splenocytes, the phagocytosis of peritoneal macrophages, and the cytotoxicity of NK cells. These results demonstrated that APS-4II could be a promising therapeutic agent for melanoma.

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.

A new Leuconostoc citreum strain discovered in the traditional sweet potato sour liquid fermentation as a novel bioflocculant for highly efficient starch production

Sour liquid fermentation is commonly used in the sedimentation process of traditional starch production, where bacteria play a critical role in starch flocculation. In this study, the dynamic changes of bacterial compositions during sweet potato sour liquid (SPSL) fermentation were profiled using the single-molecule real-time (SMRT) sequencing, unveiling that Leuconostoc citreum, Leuconostoc pseudomesenteroides, Lactococcus lactis, and Lactobacillus plantarum were the dominant microorganisms in the process, and Leuconostoc citreum exhibited a strong positive correlation with starch flocculation rate (FR). In total, 75 lactic acid bacterial (LAB) strains were isolated from the SPSL, but only 7 of them caused starch flocculation. For the first time, Leuconostoc citreum strains were reported with excellent starch-flocculating abilities (up to 55.56% FR in 20 min), which might be attributed to their ability to connect starch granules through the cell surface to form large aggregation. This study provides a comprehensive understanding of the bacterial dynamics in SPSL fermentation at the species level. A starch flocculation yield of 93.63% was achieved within 1 h by using the newly discovered Leuconostoc citreum SJ-57. The time required for total starch sedimentation was reduced from 10 h to 4 h, compared with the traditional process. These results suggest that this novel bioflocculant is more suitable for modernizing the traditional SPSL fermentation process and achieving rapid and highly efficient starch sedimentation.

An update on water kefir: Microbiology, composition and production

Water kefir is a sparkling, slightly acidic fermented beverage produced by fermenting a solution of sucrose, to which dried fruits have been added, with water kefir grains. These gelatinous grains are a symbiotic culture of bacteria and yeast embedded in a polysaccharide matrix. Lactic acid bacteria, yeast and acetic acid bacteria are the primary microbial members of the sugary kefir grain. Amongst other contributions, species of lactic acid bacteria produce the exopolysaccharide matrix from which the kefir grain is formed, while yeast assists the bacteria by a nitrogen source that can be assimilated. Exactly which species predominate within the grain microbiota, however, appears to be dependent on the geographical origin of the grains and the fermentation substrate and conditions. These factors ultimately affect the characteristics of the beverage produced in terms of aroma, flavour, and acidity, for example, but can also be controlled and exploited in the production of a beverage of desired characteristics. The production of water kefir has traditionally occurred on a small scale and the use of defined starter cultures is not commonly practiced. However, as water kefir increases in popularity as a beverage - in part because of consumer lifestyle trends and in part due to water kefir being viewed as a health drink with its purported health benefits - the need for a thorough understanding of the biology and dynamics of water kefir, and for defined and controlled production processes, will ultimately increase. The aim of this review is to provide an update into the current knowledge of water kefir.

Characterization of exopolysaccharides produced by Weissella confusa XG-3 and their potential biotechnological applications

In this study, exopolysaccharides (EPSs) produced by Weissella confusa XG-3 were characterized. The monosaccharide composition of XG-3 EPS was determined to include glucose according to GC data, and its molecular weight was 3.19 × 10⁶ Da, as determined by HPLC. Scanning electron microscopy (SEM) revealed a smooth, porous, and branched structure, and atomic force microscopy (AFM) confirmed the presence of round lumps and chains on irregular surfaces of XG-3 EPS. The results of the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) analyses suggested that XG-3 EPS is a linear α-(1,6)-linked dextran. X-ray diffraction (XRD) data confirmed the noncrystalline amorphous structure, and the results of the Congo red assay corresponded to the random coiled chain conformation of XG-3 dextran. XG-3 dextran exhibited good radical scavenging activity and reducing power and possessed high thermal stability, with a degradation temperature (Td) of 306.8 °C. The absolute value of the zeta potential and particle size of XG-3 dextran continually increased with increasing dextran concentration. The water contact angle showed that XG-3 dextran had relatively high hydrophobicity in the presence of sucrose. XG-3 dextran stimulated the growth of Lactobacillus spp. and Bifidobacterium spp. These findings indicate that XG-3 dextran has unique characteristics and can be potentially applied as a food additive and an antioxidant.

Levan from Leuconostoc citreum BD1707: production optimization and changes in molecular weight distribution during cultivation

Background

Levan is a well-known homopolymer of fructose composed predominantly of β-(2, 6) fructofuranosyl linkages in the backbone with occasional β-(2, 1) linkages in the branch chains with varied applications. However, high production cost due to low yield of microbial levan has become a bottleneck for its practical applications. Furthermore, factors affecting the molecular mass of the synthesized levan by Leuconostoc spp. during prolonged cultivation is not fully elucidated.

Methods

The cultivation condition for Leuconostoc citreum BD1707 to synthesize levan was optimized by single-factor experiments and subsequently with response surface methodology (RSM). The average molecular weight (Mw) of levan synthesized by the strain L.citreum BD1707 under the optimized cultivation conditions was monitored by high-performance size exclusion chromatography (HPSEC). Finally, the enzyme with levan-degrading activity was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).

Results

The levan yield of BD1707 reached 34.86 g/L with a corresponding productivity of 7.47 g/L/d under the optimal cultivation conditions deduced by RSM, i.e., cultivation at 26 °C and 200 rpm for 112 h in tomato juice supplemented with 172 g/L sucrose with an initial pH value of 6.12. The Mw of levan reached a peak value of 2.320 × 10⁷ Da at 6 h of cultivation under the optimized cultivation conditions and then gradually decreased to 8.809 × 10⁶ Da after 120 h of cultivation.

Conclusion

The levan yield of the strain L.citreum BD1707 could be sufficiently enhanced via cultivation condition optimization. The decrease in molecular mass of the synthesized levan was attributed predominantly to the hydrolytic activity of levansucrase secreted by L.citreum BD1707 during cultivation, with an estimated Mw of 130 KD by SDS-PAGE, while the effect of acid hydrolysis could be nearly neglected.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00673-y.

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.

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.

Overview of exopolysaccharides produced by Weissella genus - A review

Exopolysaccharides (EPS) from lactic acid bacteria (LAB) are much diversed in structure, composition and applications which also adding a great commercial potential due to its generally recognized as safe (GRAS) status. LAB genus such as Lactobacillus, Leuconostoc, Streptococcus, Weissella, Lactococcus are known to produce EPS. Among this genus, Weissella is enormously reported for diversity and high production of EPS with wide range of industrial applications and bio-functional properties. This review summarize in detail about the Weissella EPS from genus to functional application. Physico-chemical characterization from production, purification step to structural elucidation of Weissella EPS is comprehensively discussed along with their properties. Weissella genus has revealed various EPS with significant functional potentials, making massive application in food and pharma industries as viscosifiers, biothickener, emulsifiers and stabilizers. In addition to this, biological properties of these EPS revealed multiple health promoting properties which can be explored for further applications in food and pharmaceutical sectors.

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.

Identification of Genes Required for Glucan Exopolysaccharide Production in Lactobacillus johnsonii Suggests a Novel Biosynthesis Mechanism

Exopolysaccharides are key components of the surfaces of their bacterial producers, contributing to protection, microbial and host interactions, and even virulence. They also have significant applications in industry, and understanding their biosynthetic mechanisms may allow improved production of novel and valuable polymers. Four categories of bacterial exopolysaccharide biosynthesis have been described in detail, but novel enzymes and glycosylation mechanisms are still being described. Our findings that a putative bactoprenol glycosyltransferase and flippase are essential to homopolysaccharide biosynthesis in Lactobacillus johnsonii FI9785 indicate that there may be an alternative mechanism of glucan biosynthesis to the glucansucrase pathway. Disturbance of this synthesis leads to a slow-growth phenotype. Further elucidation of this biosynthesis may give insight into exopolysaccharide production and its impact on the bacterial cell.

Lactobacillus johnsonii FI9785 makes two capsular exopolysaccharides—a heteropolysaccharide (EPS2) encoded by the eps operon and a branched glucan homopolysaccharide (EPS1). The homopolysaccharide is synthesized in the absence of sucrose, and there are no typical glucansucrase genes in the genome. Quantitative proteomics was used to compare the wild type to a mutant where EPS production was reduced to attempt to identify proteins associated with EPS1 biosynthesis. A putative bactoprenol glycosyltransferase, FI9785_242 (242), was less abundant in the Δeps_cluster mutant strain than in the wild type. Nuclear magnetic resonance (NMR) analysis of isolated EPS showed that deletion of the FI9785_242 gene (242) prevented the accumulation of EPS1, without affecting EPS2 synthesis, while plasmid complementation restored EPS1 production. The deletion of 242 also produced a slow-growth phenotype, which could be rescued by complementation. 242 shows amino acid homology to bactoprenol glycosyltransferase GtrB, involved in O-antigen glycosylation, while in silico analysis of the neighboring gene 241 suggested that it encodes a putative flippase with homology to the GtrA superfamily. Deletion of 241 also prevented production of EPS1 and again caused a slow-growth phenotype, while plasmid complementation reinstated EPS1 synthesis. Both genes are highly conserved in L. johnsonii strains isolated from different environments. These results suggest that there may be a novel mechanism for homopolysaccharide synthesis in the Gram-positive L. johnsonii.

IMPORTANCE Exopolysaccharides are key components of the surfaces of their bacterial producers, contributing to protection, microbial and host interactions, and even virulence. They also have significant applications in industry, and understanding their biosynthetic mechanisms may allow improved production of novel and valuable polymers. Four categories of bacterial exopolysaccharide biosynthesis have been described in detail, but novel enzymes and glycosylation mechanisms are still being described. Our findings that a putative bactoprenol glycosyltransferase and flippase are essential to homopolysaccharide biosynthesis in Lactobacillus johnsonii FI9785 indicate that there may be an alternative mechanism of glucan biosynthesis to the glucansucrase pathway. Disturbance of this synthesis leads to a slow-growth phenotype. Further elucidation of this biosynthesis may give insight into exopolysaccharide production and its impact on the bacterial cell.

Potential prebiotic effect of a long-chain dextran produced by Weissella cibaria: an in vitro evaluation

Dextrans are homopolysaccharides of D-glucose units produced by lactic acid bacteria. They have several technological applications and potential utilisation in positively modulating gut microbiota is attracting increasing attention. Whereas the prebiotic activity of low polymerisation degree (DP) dextrans has been established, high DP dextrans still deserve deeper investigation. In the present study, a long linear chain dextran produced by Weissella cibaria was compared to inulin with regards to the growth of specific health-related taxa and to the production of organic acids in pH-controlled batch cultures of intestinal microbiota. qPCR quantification of Lactobacillus, Bifidobacterium, Prevotella, Bacteroides fragilis, and Faecalibacterium prausnitzii revealed differences in their relative abundance, depending on the carbon source, that reflected the pattern of fermentation products determined by HPLC. Dextran mainly enhanced the relative amount of Prevotella and Bacteroides, consistently with a favourable acetate-propionate ratio suggesting a promising utilisation as functional ingredient in the food industry.

The effect of structure and texture on the breakdown pattern during mastication and impacts on in vitro starch digestibility of high fibre rye extrudates

The snack product category is lacking palatable, high dietary fiber containing products. This study explored how the addition of native or fermented rye bran influences the texture and sensory properties of endosperm rye flour based extrudates. In addition, mastication and bolus properties (n = 26), and in vitro starch digestibility were assessed. Three high fiber extrudates based on endosperm rye flour (EF) were produced with addition of either 40% native rye bran (NBE) or 40% fermented rye bran (FBE), and with no added bran (EFE) to achieve two pairs of extrudates to compare. EFE and FBE had different composition but resembled each other regarding macrostructure and the second pair (NBE vs. FBE) had similar core composition but different structure due to bran fermentation. The fermentation of bran was performed using exopolysaccharide (EPS)-producing strain Weissella confusa, which led to 3% (3 g per 100 g bran; dry weight) in situ dextran production. The compositionally similar extrudates (NBE vs. FBE) varied in both structure and instrumental texture: FBE were less dense, less hard and crispier than NBE. The extrudates with different composition (EFE vs. FBE) varied regarding instrumental texture: FBE were less hard and crispier than EFE. There were also subtle structural differences FBE being somewhat denser than EFE. NBE and FBE differed regarding sensory texture while textures of EFE and FBE were perceived similar. Mastication properties of the different products did not exhibit remarkable differences. There was a large number of smaller particles in both NBE and FBE bolus samples. The fragile structure of FBE, and its lower bolus viscosity, led to high in vitro starch digestibility. The results demonstrate that the structural attributes of the extrudates, rather than the core composition, dictate the breakdown pattern during mastication and in vitro starch digestibility. The extrudates with similar composition may be digested at different rates depending on their structural attributes. Although FBE had higher in vitro starch digestibility, its high DF content, palatable texture and improved sensory properties were important determinants underlying eating quality and therefore it could be a promising product to snack food category.

Isolation and characterization of high exopolysaccharide-producing Weissella confusa VP30 from young children's feces

Background

Lactic acid bacteria (LAB) are known to have a significant ability to colonize the human intestinal tract and adhere to the surface of intestinal epithelial cells. Among the various lactic acid bacteria, exopolysaccharide (EPS) producing strains are known to provide a variety of health benefits for their hosts (e.g. anti-inflammatory, antioxidant, antitumor and stress tolerant effects). Recently, EPSs and EPS-producing lactic acid cultures have gained interest within the food industry and are playing important roles as biothickeners and texturizing agents due to their hydrocolloidal nature. In this study, 156 lactic acid bacterial strains isolated from fecal samples of healthy young children were screened and evaluated for active EPS-production capability.

Results

Among the various human origin lactic acid flora isolated, Weissella confusa VP30 showed the highest EPS productivity and its EPS producing properties were characterized under various cultural conditions in this research. To document the safety of W. confusa VP30, antibiotic resistance, hemolytic, and ammonia production properties were evaluated in addition. No significant negative results were observed. The maximum EPS production by W. confusa VP30 was 59.99 ± 0.91 g/l after 48 h of cultivation in media containing 10% sucrose, far exceeding EPS production by other bacterial strains reported elsewhere. Based on gel permeation chromatography (GPC), the molecular weight of EPS produced by W. confusa VP30 was 3.8 × 10⁶ Da. Structural analysis of the released EPS fraction by ¹³C and ¹H nuclear magnetic resonance (NMR) spectroscopy revealed that W. confusa VP30 can produce dextran with glucose units linked with 96.5% α (1 → 6) glycosidic bonds and 3.5% α (1 → 3) branches.

Conclusion

The high EPS production capability and safety of W. confusa VP30 justify food industry consideration of this cell strain for further evaluation and potential industrial use.

Genetic and technological characterization of lactic acid bacteria isolated from tropically grown fruits and vegetables

Phyllosphere microorganisms are common contaminants of fruit or vegetable containing foods. The aim of this study was to identify and characterize lactic acid bacteria isolated from fruits and vegetables from Reunion Island, regarding possible application in food. Among 77 isolates, a large diversity of species was observed, with isolates belonging to Lactobacillus plantarum (3 isolates), other species of Lactobacillus (3), Lactococcus lactis (13), Leuconostoc pseudomesenteroides (25), Leuconostoc lactis (1), Leuconostoc mesenteroides (7), Leuconostoc citreum (14), Weissella cibaria (4), Weissella confusa (4), other species of Weissella (2) and Fructobacillus tropaeoli (1). Several of these species, although belonging to lactic acid bacteria, are poorly characterized, because of their low occurrence in dairy products. Lactobacillus, Lactococcus, Leuconostoc and Weissella isolates were classified by (GTG)₅ fingerprinting in 3, 6, 21 and 10 genetic groups, respectively, suggesting a large intra-species diversity. Several Weissella and Lactobacillus isolates were particularly tolerant to acid and osmotic stress, whereas Lc. pseudomesenteroides 60 was highly tolerant to oxidative stress. Isolates of Weissella 30, 64 and 58, Leuconostoc 60 and 12b, Lactobacillus 75 and Fructobacillus 77 present relevant characteristics for their use as starters or as preservative cultures for fruits and vegetables.