Characterization of a yogurt-quality improving exopolysaccharide from Streptococcus thermophilus AR333

Analysis of Pickled Cucumber Products, Based on Microbial Diversity and Flavor Substance Detection

Changes to the microbial community during pickled cucumber fermentation were studied using the 16S rDNA technique. The changes of volatile organic compounds (VOCs) during pickled cucumber fermentation were studied by gas chromatograph-ion mobility spectrometry. At the phylum level, Cyanophyta and Proteobacteria were the dominant flora in the natural fermentation group, and Firmicutes were the dominant flora in the added-bacteria fermentation group. At the generic level, the addition of Lactobacillus led to changes in the community of the bacteria in the added-bacterial fermentation group and decreased the species abundance of other bacteria. In total, 75 volatile organic compounds were identified from naturally fermented pickled cucumber, and 60 volatile organic compounds were identified from fermented pickled cucumber with bacterial addition. The main metabolites were esters, aldehydes, acids, alcohols, ketones, alkanes, nitriles, and alkenes. These metabolites will bring their unique aroma components to the pickled cucumber. Metabolomic analysis of the O2PLS model showed that Weissella and Lactobacillus were closely and positively correlated with nine alcohols, six esters, five aldehydes, four acids, three ketones, and one pyrazine. Pseudomonas and norank_f_Mitochondria show a close positive correlation with four kinds of alcohols, two kinds of esters, one kind of aldehyde, and one kind of nitrile.

The exopolysaccharides produced by Leuconostoc mesenteroides XR1 and its effect on silk drawing phenomenon of yoghurt

Yoghurt fermented by Leuconostoc mesenteroides XR1 from Kefir grains was found to produce a unique silk drawing phenomenon. This property was found to be associated with the exopolysaccharides (EPS), X-EPS, produced by strain XR1. In order to better understand the mechanism that produced this phenomenon, the X-EPS was extracted, purified and characterized. The molecular weight and monosaccharide composition were determined by size exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) and ion chromatography (IC) analysis, respectively. The results showed that its molecular weight was 4.183 × 106 g/mol and its monosaccharide composition was glucose, and glucuronic acid, with the contents of 567.6148 and 0.2096 μg/mg, respectively. FT-IR and NMR analyses showed that X-EPS was an α-pyranose polysaccharide and was composed of 92.22 % α-(1 → 6) linked d-glucopyranose units and 7.77 % α-(1 → 3) branching. Furthermore, it showed a chain-like microstructure with branches in atomic force microscopy (AFM) and scanning electron microscopy (SEM) experiments. These results suggested that the unique structure of X-EPS, gave the yoghurt a strong viscosity and cohesiveness, which resulted in the silk drawing phenomenon. This work suggested that X-EPS holds the potential for food and industrial applications.

Exopolysaccharides of lactic acid bacteria: Structure, biological activity, structure-activity relationship, and application in the food industry: A review

Over the past few decades, researchers have discovered that probiotics play an important role in our daily lives. With the further deepening of research, more and more evidence show that bacterial metabolites have an important role in food and human health, which opens up a new direction for the research of lactic acid bacteria (LAB) in the food and pharmaceutical industry. Many LAB have been widely studied because of the ability of exopolysaccharides (EPS). Lactic acid bacteria exopolysaccharides (LAB EPS) not only have great potential in the treatment of human diseases but also can become natural ingredients in the food industry to provide special qualitative structure and flavor. This paper has organized and summarized the biosynthesis, strain selection, production process parameters, structure, and biological activity of LAB EPS, filling in the monotony and incompleteness of previous articles' descriptions of LAB EPS. Therefore, this paper focuses on the general biosynthetic pathway, structural characterization, structure-activity relationship, biological activity of LAB EPS, and their application in the food industry, which will help to deepen people's understanding of LAB EPS and develop new active drugs from LAB EPS. Although the research results are relatively affluent, the low yield, complex structure, and few clinical trials of EPS are still the reasons that hinder its development. Therefore, future knowledge expansion should focus on the regulation of structure, physicochemical properties, function, higher production of EPS, and clinical trial applications, which can further increase the commercial significance and value of EPS. Furthermore, better understanding the structure-function relationship of EPS in food remains a challenge to date.

Elaboration of Nanostructured Levan-Based Colloid System as a Biological Alternative with Antimicrobial Activity for Applications in the Management of Pathogenic Microorganisms

Considering the documented health benefits of bacterial exopolysaccharides (EPSs), specifically of bacterial levan (BL), including its intrinsic antimicrobial activity against certain pathogenic species, the current study concentrated on the development of active pharmaceutical ingredients (APIs) in the form of colloid systems (CoSs) containing silver nanoparticles (AgNPs) employing in-house biosynthesized BL as a reducing and capping agent. The established protocol of fermentation conditions implicating two species of lactic acid bacteria (LAB), i.e., Streptococcus salivarius K12 and Leuconostoc mesenteroides DSM 20343, ensured a yield of up to 25.7 and 13.7 g L-1 of BL within 72 h, respectively. An analytical approach accomplished by Fourier-transform infrared (FT-IR) spectroscopy allowed for the verification of structural features attributed to biosynthesized BL. Furthermore, scanning electron microscopy (SEM) revealed the crystalline morphology of biosynthesized BL with a smooth and glossy surface and highly porous structure. Molecular weight (Mw) estimated by multi-detector size-exclusion chromatography (SEC) indicated that BL biosynthesized using S. salivarius K12 has an impressively high Mw, corresponding to 15.435 × 104 kilodaltons (kDa). In turn, BL isolated from L. mesenteroides DSM 20343 was found to have an Mw of only 26.6 kDa. Polydispersity index estimation (PD = Mw/Mn) of produced BL displayed a monodispersed molecule isolated from S. salivarius K12, corresponding to 1.08, while this was 2.17 for L. mesenteroides DSM 20343 isolate. The presence of fructose as the main backbone and, to a lesser extent, glucose and galactose as side chain molecules in EPS hydrolysates was supported by HPLC-RID detection. In producing CoS-BL@AgNPs within green biosynthesis, the presence of nanostructured objects with a size distribution from 12.67 ± 5.56 nm to 46.97 ± 20.23 was confirmed by SEM and energy-dispersive X-ray spectroscopy (EDX). The prominent inhibitory potency of elaborated CoS-BL@AgNPs against both reference test cultures, i.e., Pseudomonas aeruginosa, Escherichia coli, Enterobacter aerogenes, and Staphylococcus aureus and those of clinical origin with multi-drug resistance (MDR), was confirmed by disc and well diffusion tests and supported by the values of the minimum inhibitory and bactericidal concentrations. CoS-BL@AgNPs can be treated as APIs suitable for designing new antimicrobial agents and modifying therapies in controlling MDR pathogens.

Structure characterization and biological activities evaluation of two hetero-polysaccharides from Lepista nuda: Cell antioxidant, anticancer and immune-modulatory activities

Polysaccharides LNP-1 and LNP-2 were extracted and purified from Lepista nuda, and their structural characteristics and biological activities were evaluated. The molecular weights of LNP-1 and LNP-2 were determined to be 16,263 Da and 17,730 Da, respectively. The monosaccharide composition analysis showed that LNP-1 and LNP-2 were composed of fucose, mannose, glucose, and galactose in a molar ratio of 1.00:2.42:1.09:4.04 and 1.00:2.39:1.61:4.23, respectively. The structure analysis revealed that these two polysaccharides were mainly composed of T-Fuc, T-Man, T-Glc, 1,6-Glc 1,6-Gal, and 1,2,6-Man, 1,2,6-Gal. Additionally, LNP-2 contained an additional 1,4-Glc glycosidic linkage in comparison to LNP-1. Both LNP-1 and LNP-2 exhibited anti-proliferation effects on A375 cells, but not on HepG2 cells. Furthermore, LNP-2 showed better cellular antioxidant activity (CAA) than LNP-1. RT-PCR results indicated that LNP-1 and LNP-2 could induce macrophages to secrete immune-modulatory factors NO, IL-6, and TNF-α by regulating their mRNA expression. Overall, this study provides a theoretical basis for the further development of the structure-function relationship of polysaccharides from L. nuda.

Physicochemical and rheological characterizations of a novel exopolysaccharide EPSKar1 and its iron complex EPSKar1-Fe: Towards potential iron-fortification applications

Iron is a micronutrient essential for human health and physiology. Iron-deficiency anemia, the most common form of anemia, may occur from an iron homeostasis imbalance. Iron fortification is a promising and most sustainable and affordable solution to tackle the global prevalence of this anemia. Herein, we investigate physicochemical, rheological and stability characteristics of a novel exopolysaccharide 'EPSKar1' (derived from Lacticaseibacillus rhamnosus strain Kar1) and its iron complex 'EPSKar1-Fe (II)'. Our findings demonstrate that EPSKar1 is a high molecular-weight (7.8 × 10⁵ Da) branched-chain heteropolysaccharide composed of galactose, N-acetylglucosamine, and mannose in a molar ratio of 8:4:1, respectively, and exhibits strong emulsifying and water-holding capacities. We find that EPSKar1 forms strong complexes with Fe, wherein the interactions between EPSKar1-Fe (II) complexes are mediated by sulfate, carboxyl, and hydroxyl groups. The rheological analyses reveal that the EPSKar1 and EPSKar1-Fe (II) complexes exhibited shear thickening and thinning properties in skim milk and water, respectively; however, the suspension of EPSKar1 in skim milk is viscoelastic with predominantly elastic response (G'>G" and tan δ < 1). In comparison, EPSKar1-Fe (II) complex exhibits remarkable stability under various processing conditions, highlighting its usefulness for the development of fortified dairy products. Together, these findings underpin considerable prospects of EPSKar1-Fe (II) complex as a novel iron-fortifier possessing multifarious rheological benefits for food applications.

Extracellular Polysaccharide Extraction from Streptococcus thermophilus in Fermented Milk

Lactic acid bacteria such as Streptococcus thermophilus are known to produce extracellular polysaccharide (EPS) in fermented foods that enhance the creaminess and mouthfeel of the product, such as yogurt. Strains producing larger amounts of EPS are highly sought-after, and therefore, robust and accurate quantification methodologies are important. This study found that two commonly used methodologies significantly underestimated the amount of EPS produced as measured using a milk matrix. To this end, a proteolytic step was implemented prior to EPS extraction (Method C). An initial proteolytic step using xanthan gum-spiked milk significantly increased recovery yield to 64%, compared to 27.8% for Method A and 34.3% for Method B. Method C showed no improvement when assessed using a chemically defined medium. Method C was further validated using three strains of S. thermophilus with varying EPS-production capabilities (ST^LOW, ST^MID, ST^HIGH). Overall, Method C demonstrated significant improvements in the EPS extraction yield for all three S. thermophilus strains in fermented milk. On average, Method C improved isolation yield by ∼3- to 6-fold compared with Method A and by ∼2- to 3-fold compared with method B. There were no significant differences between samples when they were grown in a chemically defined medium, highlighting the importance of a proteolytic step specifically for fermented milk samples. In commercial applications, accurate quantification of EPS-production is an important aspect when finding new strains. IMPORTANCE Extracellular polysaccharide (EPS) production by milk-fermenting microorganisms is a highly sought-after trait in improving the perceived thickness, creaminess, and mouthfeel of yogurt. Streptococcus thermophilus are commonly isolated and their EPS production is quantified in the search for higher-producing strains. In this study, we demonstrated that two commonly used methods for isolating EPS from milk samples significantly underestimated the true amount of EPS present. We demonstrated that the addition of a proteolytic step prior to EPS extraction isolated over 2-fold more EPS than identical samples processed using the traditional protocols. We further validated this method in fermented milk samples from three strains of S. thermophilus that included a low-, mid-, and high-EPS producing strain. Again, we showed significant improvements in EPS isolation using a proteolytic step. In the search for new S. thermophilus strains with enhanced EPS production, accurate quantification in an optimal medium is essential.

Rapid isolation of exopolysaccharide-producing Streptococcus thermophilus based on molecular marker screening

BACKGROUND

As a natural food additive, exopolysaccharide (EPS) produced by Streptococcus thermophilus can improve product viscosity and texture. The protein EpsA is a putative pathway-specific transcriptional regulator for EPS biosynthesis in S. thermophilus.

RESULTS

According to comparative analysis of EPS biosynthetic gene clusters, a conserved region of epsA (609 bp) was employed to design primer pair epsA-F/R as a molecular marker for the isolation of EPS-producing (EPS⁺ ) S. thermophilus. Two EPS⁺ S. thermophiles strains, AR333 and S-3, were band-positive, whereas Lactococcus lactis NZ9000 (non-EPS-producing, EPS^- ), Lactobacillus casei LC2W (EPS⁺ ) and L. plantarum AR113 (EPS⁺ ) were negative by polymerase chain reaction (PCR) amplicon bands using the epsA probe. This indicated good specificity of the epsA probe to EPS⁺ S. thermophilus. Moreover, based on PCR screening with the epsA probe, 23 positive strains were isolated and identified as S. thermophilus from our microbial library and natural fermented milk with 141.3-309.2 mg L^-1 of EPS production, demonstrating the validity of our molecular marker screening method.

CONCLUSION

The designed molecular marker of epsA can rapidly screen EPS⁺ S. thermophilus, which has potential application in the dairy and other food industries. © 2021 Society of Chemical Industry.

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.

Structure, physicochemical characterization, and antioxidant activity of the highly arabinose-branched exopolysaccharide EPS-M2 from Streptococcus thermophilus CS6

Streptococcus thermophilus CS6 could produce the high exopolysaccharide (EPS) level in optimized skimmed milk medium. However, physicochemical properties and structure of these polymers have not been fully characterized. In this study, two purified fractions (EPS-M1 and EPS-M2) exhibited good rheology, thermostability and antioxidant activity. Further monosaccharide composition, molecular weight and NMR analysis indicated EPS-M2 was composed of galactose, arabinose and glucose (5:2.5:1) with an average molecular weight of 2.22 × 10⁴ Da and its suggested repeating unit was →6)-[α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 4)-β-D-Galp-(1 → 6)-[α-L-Araf-(1 → 5)-{α-L-Araf-(1 → 3)}-α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 4)-β-D-Galp-(1 → 6)-[β-D-Galp-(1 → 5)-α-L-Araf-(1 → 5)-α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 6)-[β-D-Galp-(1 → 5)-α-L-Araf-(1 → 5)-{α-L-Araf-(1 → 3)}-α-L-Araf-(1 → 3)]-β-D-Galp-(1→. High EPS production relied on the expression of eps gene cluster and key enzymes of nucleotide sugar metabolism. Overall, EPS-M2 from a potential functional starter S. thermophilus CS6 provided opportunities for natural thickener, stabilizer, and antioxidant agent exploration in the food industry.

Recent Advances in the Production of Exopolysaccharide (EPS) from Lactobacillus spp. and Its Application in the Food Industry: A Review

Exopolysaccharide (EPS) show remarkable properties in various food applications. In this review paper, EPS composition, structural characterization, biosynthesis pathways, and recent advancements in the context of application of EPS-producing Lactobacillus spp. in different food industries are discussed. Various chemical and physical properties of Lactobacillus EPS, such as the structural, rheological, and shelf-life enhancement of different food products, are mentioned. Moreover, EPSs play a characteristic role in starter culture techniques, yogurt production, immunomodulation, and potential prebiotics. It has been seen that the wastes of fermented and non-fermented products are used as biological food for EPS extraction. The main capabilities of probiotics are the use of EPS for technological properties such as texture and flavor enhancement, juiciness, and water holding capacities of specific food products. For these reasons, EPSs are used in functional and fermented food products to enhance the healthy activity of the human digestive system as well as for the benefit of the food industry to lower product damage and increase consumer demand. Additionally, some pseudocereals such as amaranth and quinoa that produce EPS also play an important role in improving the organoleptic properties of food-grade products. In conclusion, more attention should be given to sustainable extraction techniques of LAB EPS to enhance structural and functional use in the developmental process of food products to meet consumer preferences.

Physico-Chemical and Antioxidant Properties of Skimmed Varenets (Slavic Baked Milk Yogurt) Mixed with Enzyme-Modified Potato Starches

The present studies have examined the effect of potato starches treated with amylase B.licheformis (Bl) (laboratory sample) or Amylosubtilin® (AM) (Berdsk Factory of Biological Preparations (now: Sibbiofarm), Russia) in different concentrations on the quality of Slavic skim milk drink Varenets made from baked milk. The baked milk is milk heated to 98 °C for 3 hours, it has a sweet aroma and taste and creamy hue. The presence of enzyme-modified potato starches (Bl or AM) has been found to promote the activation of lactic acid fermentation, the accumulation of exopolysaccharides, and such stabilized products have a higher viscosity, a lower percentage of syneresis compared to the control sample. The antioxidant capacity of the Varents samples after fermentation was evaluated by two assays: analysis of radical capture activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH •); and the ability to restore Fe + 3 (Iron Reduction Antioxidant Ability Assay, FRAP). All Varentz samples showed different values for DPPH, FRAP assays depending on the starches used. The Introduction of pre-fermented starches into defatted jam promotes formation of enhanced antioxidant properties of milk product. The use of starches modified with enzymes improves sensory characteristics, in particular, as a fat imitator, formsfull taste of the drink.

Microbial exopolysaccharide production of Streptococcus thermophilus and its antiquorum sensing activity

Interest in the production of exopolysaccharides by microorganisms has increased in the recent years. Using low-cost product is the main step of microbial production to reduce cost and compete with chemical production. In this work, EPS production of Streptococcus thermophilus isolates from yogurt (S2), kefir (S3), and S. thermophilus ATCC 19258 (S1) isolate which was used as control strains were investigated by using different fruit pulps. S. thermophilus isolates were identified by morphological and 16S sequence analysis. The amount of EPS obtained was measured spectrophotometrically using glucose as standard with phenol sulfuric acid method. All three isolates produced higher amounts of EPS on M17 medium than Nutrient medium. When the fruit pulp was added to the medium, EPS production increased in all three isolates. When different nitrogen sources were added together with fruit pulp juice, EPS production increased. The highest amount of EPS produced by ATCC 19258 strain (21.570 mg/L) and S3 isolate (29.131 mg/L) is the medium where mixed fruit pulp juice and nitrogen source is tryptophan. It has been shown that EPS production is increased by adding fruit pulps to the prepared media. It is thought that apricot pulp can be a good alternative in EPS production especially in the evaluation of wastes. Also, antiquorum sensing activity of the highest amount EPS was determined by using Chromobacterium violaceum CV026 strain and found effective on violacein pigment inhibition and C6-AHL production of biosensor strain.

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.

Structural characterisation of EPS of Streptococcus thermophilus S-3 and its application in milk fermentation

The application of Streptococcus thermophilus S-3 into yogurt production was studied and the structural properties of the generated exopolysaccharides (EPS-S3) were characterized. The proposed structure of EPS-S3 was obtained. EPS-S3 contained a high ratio of N-Acetyl-galactosamine with the Mw of 574 kDa, which was higher than that of AR333 (314 kD) leading to higher apparent viscosity. Streptococcus thermophilus strain S-3 was co-cultured with Lactobacillus delbrueckii for yogut production which highly increased the acidifying rate and post-acidification rate. The quality of the co-cultured yogurts in terms of apparent viscosity, syneresis capacity, water holding capacity and rheological properties were much better than that by using Lactobacillus bulgaricus only. The production mechanism of EPS-S3 from gene regulated level was also discussed which is helpful to facilitate the application of Streptococcus thermophilus strain into milk production.

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 characterization and antioxidant potential of a novel exopolysaccharide produced by Bacillus velezensis SN-1 from spontaneously fermented Da-Jiang

The aim of this study was to characterize the exopolysaccharide (EPS) produced by Bacillus velezensis SN-1 (B. velezensis SN-1) (EPS-SN-1), which was isolated from the fermented Da jiang. The microbe made crude exopolysaccharides EPS-SN-1 was produced throughout the bacterial growth period, and the highest yield (2.7 g/L) was obtained with sucrose as the carbon source. As per high performance liquid chromatography (HPLC), EPS-SN-1 is a heteropolysaccharide consisting of glucose, mannose and fructose, with a high molecular weight of 2.21 × 10⁵ Da. FTIR spectra further indicated the presence of hydroxyl and carbonyl groups, and NMR analysis confirmed both α- and β-glycosidic bonds. Furthermore, differential scanning calorimetry (DSC) showed that EPS-SN-1 has high thermal stability with fusion point of 270.7 °C. Finally, EPS-SN-1 demonstrated strong antioxidant capacity via its ability to scavenge hydroxyl radical (^•OH), 1,1-diphenyl-2-picrylhydrazyl (DPPH^•) radical, ABTS radical (ABTS^•+) and oxygen radical (O₂^-•). Taken together, EPS-SN-1 is a promising natural antioxidant and probiotic with potential applications in the food industry.

Production and molecular structure of heteropolysaccharides from two lactic acid bacteria

In the dairy industry, exopolysaccharides (EPS) produced in situ from lactic acid bacteria are of great interest because of their contribution to product texture. Some EPS cause ropiness which might be linked to specific physical and chemical EPS properties. EPS show a broad variety of chemical structures and, because analysis is rather complex, it is still a major challenge to establish structure-function relationships. The aim of this study was to produce EPS with different degree of ropiness, perform in-depth structural elucidations and relate this information to their behaviour in aqueous solutions. After cultivation of Streptococcus thermophilus DGCC7919 and Lactococcus lactis LL-2A and subsequent EPS isolation, both EPS showed similar macromolecular properties, but pronounced differences in monosaccharide composition and glycosidic linkages. Our data suggests that mainly the side chains in the EPS from LL-2A might be responsible for a higher ropiness than that observed for EPS from DGCC7919.

Structural characterization and anticomplement activities of three acidic homogeneous polysaccharides from Artemisia annua

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia annua L. is a heat-clearing Chinese medicine and well-known for its antimalarial constituent, artemisinin. It has gained increasing attention for its anti-inflammatory and immunoregulatory activities. Interestingly, the crude polysaccahrides of A. annua exhibited potent anticomplement activity. This study was to isolate and characterize its anticomplement homogeneous polysaccharides from A. annua, and reveal the relationship between structures and anticomplement activities of the isolated polysaccharides.

MATERIALS AND METHODS

Water-soluble crude polysaccharides from the aerial parts of A. annua were extracted and fractionated by DEAE-cellulose and Sephacryl S-300 gel permeation chromatography. Homogeneity, molecular weight, monosaccharide composition, methylation and NMR analysis were performed to characterize the structures of homogeneous polysaccharides. Their anticomplement activities and targeting components in the complement activation cascade were evaluated by hemolytic assays.

RESULTS

Three homogeneous polysaccharides (AAP01-1, AAP01-2 and AAP01-3) were obtained from A. annua. AAP01-1 was composed of seven monosaccharides, including mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose and arabinose. AAP01-2 and AAP01-3 had similar monosaccharides with AAP01-1, except the absence of glucuronic acid. They were all branched acidic heteropolysaccharides with different contents of galacturonic acid (8%, 28% and 15% for AAP01-1, AAP01-2 and AAP01-3, respectively). AAP01-2 showed potent anticomplement activity with CH₅₀ value of 0.360 ± 0.020 mg/mL through the classical pathway and AP₅₀ value of 0.547 ± 0.033 mg/mL through the alternative pathway. AAP01-3 exhibited slightly weaker activity (CH₅₀: 1.120 ± 0.052 mg/mL, AP₅₀: 1.283 ± 0.061 mg/mL), while AAP01-1 was inactive. Moreover, AAP01-2 acted on C1q, C3, C4, C5 and C9 components and AAP01-3 interacted with C3, C4 and C5 components in the activation cascade of complement system.

CONCLUSION

These results indicated that the relatively high contents of galacturonic acid were important for anticomplement activities of the polysaccharides from A. annua. The anticomplement polysaccharides are another kind of bioactive constituents conferring heat-clearing effects of A. annua.

Exopolysaccharide from Streptococcus thermophilus as stabilizer in fermented dairy: Binding kinetics and interactions with casein of milk

Exopolysaccharides (EPSs) from lactic acid bacteria have great effect on the quality of fermented milk products. However, the mechanism for the quality improvement has not been well described. This study aimed to investigate the molecular binding kinetics and interactions between EPS obtained from Streptococcus thermophilus AR333 (EPS333) and casein of milk (CM) in a simulated acidifying process. The results indicated that EPS333 had a significant effect on the stability of casein micelles at acidic pH (6.0-4.5) according to the turbidity, ζ-potential, particle size and distribution analysis. The adsorption-desorption study by bio-layer interferometry identified the direct affinity binding between EPS333 and CM, the interactive moiety of casein was α-casein, rather than β- or κ-casein. Fluorescence quenching analysis revealed that the force types of interaction between EPS333 and CM were dynamically changeable during the acidifying process, mainly from electrostatic interaction at pH 7.0-6.5, to hydrophobic or hydrogen bonding at pH 6.5-5.5, and then transferred to electrostatic interaction again at pH 5.5-5.0. Conclusively, EPS333 could bind with CM directly via different binding forces during acidifying process to stabilize the properties of casein micelles.

Genomic and phenotypic analyses of exopolysaccharide biosynthesis in Streptococcus thermophilus S-3

Streptococcus thermophilus, one of the most important industrial lactic acid bacteria, is widely used as a starter culture in the dairy industry. Streptococcus thermophilus S-3 isolated from Chinese traditional dairy products has shown great potential for the production of larger amounts of exopolysaccharides (EPS), which significantly affect the organoleptic properties of fermented milk products. To understand the relationship between the genotype and phenotype of S. thermophilus S-3 in terms of EPS biosynthesis, its genome of strain S-3 was sequenced and the genes related to carbohydrate utilization, nucleotide sugars synthesis, and EPS biosynthesis were investigated. The genomic analysis revealed that S. thermophilus S-3 can use sucrose, mannose, glucose, galactose, and lactose. Phenotypic analysis showed that S-3 prefers fermenting lactose to fermenting glucose or galactose. The genetic analysis of nucleotide sugars and EPS biosynthesis revealed that S-3 can synthesize uridine diphosphate (UDP)-glucose, deoxythymidine diphosphate-glucose, deoxythymidine diphosphate-rhamnose, UDP-galactose, UDP-N-acetylgalactosamine, and UDP-N-acetylglucosamine. A high yield of EPS from S-3 cultivated with lactose rather than glucose as the carbon source was correlated with high transcriptional levels of the genes associated with metabolism of these nucleotide sugars and EPS biosynthesis. Our results provide a better understanding of EPS biosynthesis in S. thermophilus and can facilitate enhanced EPS production by lactic acid bacteria fermentation via genetic and metabolic engineering approaches.

Characterization and immunomodulatory activity of an exopolysaccharide produced by Lactobacillus plantarum JLK0142 isolated from fermented dairy tofu

A purified neutral exopolysaccharide (EPS) designated as EPS0142 was obtained from Lactobacillus plantarum JLK0142. EPS0142 consisted of glucose and galactose in an approximate molar ratio of 2.13:1.06 and had a molecular weight of 1.34 × 10⁵ Da. The FT-IR spectrum showed that EPS0142 had a typical polysaccharide absorption pattern. ¹H NMR and ¹³C NMR spectra analysis showed the presence of N-acetylated sugar residues. EPS0142 had no toxic effects on RAW 264.7 cells and significantly improved their phagocytic activity and NO secretion in vitro. Further in vivo studies revealed that the spleen index and splenic lymphocyte proliferation activities of the cyclophosphamide-induced immunosuppression mice treated with a middle-dose (50 mg/kg body weight) or a high-dose (100 mg/kg body weight) of EPS0142 were significantly increased (P < 0.01). In addition, the intestinal immunoglobulin A (sIgA) content and the serum levels of the cytokines, IL-2 and TNF-α, were also significantly (P < 0.05) improved in the high-dose EPS0142 group compared to that in the model control group. These data indicate that the EPS isolated from L. plantarum JLK0142 can effectively improve the immunomodulatory activity of RAW 264.7 cells and stimulate the immune system in cyclophosphamide-induced immunosuppressed mice.