The response surface optimization of exopolysaccharide produced by Weissella confusa XG-3 and its rheological property

Structure and Properties of Exopolysaccharide Produced by Gluconobacter frateurii and Its Potential Applications

An exopolysaccharide (EPS)-producing bacterium was isolated from apricot fermentation broth and identified as Gluconobacter frateurii HDC-08 (accession number: OK036475.1). HDC-08 EPS is a linear homopolysaccharide mainly composed of glucose linked by α-(1,6) glucoside bonds. It contains C, H, N and S elements, with a molecular weight of 4.774 × 106 Da. Microscopically, it has a smooth, glossy and compact sheet structure. It is an amorphous noncrystalline substance with irregular coils. Moreover, the EPS showed surface hydrophobicity and high thermal stability with a degradation temperature of 250.76 °C. In addition, it had strong antioxidant properties against DPPH radicals, ABPS radicals, hydroxyl radicals and H2O2. The EPS exhibited high metal-chelating activity and strong emulsifying ability for soybean oil, petroleum ether and diesel oil. The milk solidification test indicated that the EPS had good potential in fermented dairy products. In general, all the results demonstrate that HDC-08 EPS has promise for commercial applications as a food additive and antioxidant.

Evaluation of antioxidation, regulation of glycolipid metabolism and potential as food additives of exopolysaccharide from Sporidiobolus pararoseus PFY-Z1

At present, there are relatively few studies on the production of exopolysaccharide (EPS) by yeasts. Therefore, exploring the properties of EPS produced by yeast can not only enrich the source of EPS, but also play an important role in its future application in the food field. The aim of this study was to explore the biological activities of EPS (named SPZ) from Sporidiobolus pararoseus PFY-Z1, as well as the dynamic changes in physical and chemical properties that occur during simulated gastrointestinal digestion, and the effects of SPZ on microbial metabolites during fecal fermentation in vitro. The results revealed that SPZ had good water solubility index, water-holding capacity, emulsifying ability, coagulated skim milk, antioxidant properties, hypoglycemic activities, and bile acid-binding abilities. Furthermore, the content of reducing sugars increased from 1.20 ± 0.03 to 3.34 ± 0.11 mg/mL after gastrointestinal digestion, and had little effect on antioxidant activities. Moreover, SPZ could promote the production of short-chain fatty acids during fermentation for 48 h, in particular, propionic acid and n-butyric acid increased to 1.89 ± 0.08 and 0.82 ± 0.04 mmol/L, respectively. Besides this, SPZ could inhibit LPS production. In general, this study can help us to better understand the potential bioactivities, and the changes in bio-activities of compounds after digestion of SPZ.

Optimization, Probiotic Characteristics, and Rheological Properties of Exopolysaccharides from Lactiplantibacillus plantarum MC5

This study optimized the exopolysaccharides (EPS) production for Lactiplantibacillus plantarum MC5 (Lp. plantarum MC5) and evaluated the resistance to human simulated digestive juices, antioxidant activity in vitro, and rheological properties of EPS-MC5. The results showed that maximum EPS production of 345.98 mg/L (about 1.5-old greater than the initial production) was obtained at optimal conditions of inoculum size (4.0%), incubation time (30 h), incubation temperature (34.0 °C), and initial pH value (6.40). Furthermore, the resisting-digestion capacity of EPS-MC5 after 180 min in α-amylase, simulated gastric juice (pH 2.0, 3.0, 4.0), and simulated intestinal juice (pH 6.8) was 98.59%, 98.62%, 98.78%, 98.86%, and 98.74%, respectively. In addition, the radical scavenging rates of DPPH•, ABTS•, •OH, and ferric-iron reducing power (OD700) of EPS-MC5 were 73.33%, 87.74%, 46.07%, and 1.20, respectively. Furthermore, rheological results showed that the EPS-MC5 had a higher apparent viscosity (3.01 Pa) and shear stress (41.78 Pa), and the viscoelastic modulus (84.02 and 161.02 Pa at the shear frequency of 100 Hz). These results provide a new insight into the application of EPS in human health and functional foods, which could also improve theoretical guidance for the industrial application of EPS.

Structural characterization and partial properties of dextran produced by Leuconostoc mesenteroides RSG7 from pepino

Exopolysaccharides (EPSs) produced by lactic acid bacteria possess various bioactivities and potential attractions for scientific exploration and commercial development. An EPS-producing bacterial strain, RSG7, was previously isolated from the pepino and identified as Leuconostoc mesenteroides. Based on the analyses of high-performance size exclusion chromatography, high-performance ion chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and methylation, the RSG7 EPS was identified as a dextran with a molecular weight of 5.47 × 10⁶ Da and consisted of α-(1→6) glycosidic linkages as backbone and α-(1→2), α-(1→3), α-(1→4), and α-(1→6) glycosidic linkages as side chains. Scanning electron microscopy observed a honeycomb-like porous structure of RSG7 dextran, and this dextran formed aggregations with irregular hill-shaped lumps according to atomic force microscopy analysis. Physical-chemical investigations suggested that RSG7 dextran possessed excellent viscosity at high concentration, low temperature, and high pH; showed a superior emulsifying capacity of tested vegetable oils than that of hydrocarbons; and owned the maximal flocculating activity (10.74 ± 0.23) and flocculating rate (93.46 ± 0.07%) in the suspended solid of activated carbon. In addition, the dextran could coagulate sucrose-supplemented milk and implied potential probiotics in vitro. Together, these results collectively describe a valuable dextran with unique characteristics for exploitation in food applications.

A new source of bacterial myrosinase isolated from endophytic Bacillus sp. NGB-B10, and its relevance in biological control activity

Plant metabolism interacts strongly with the plant microbiome. Glucosinolates, secondary metabolites synthesized by Brassica plants, are hydrolyzed by myrosinase into bioactive compounds of great importance in human health and plant protection. Compared with myrosinase from plant sources, myrosinase enzymes of microbial origin have not been extensively investigated. Therefore, seven endophytic strains corresponding to Bacillus sp. were isolated from Eruca vesicaria ssp. sativa plants that could hydrolyse glucosinolates (sinigrin) in the culture medium and showed myrosinase activity (0.08–19.92 U mL⁻¹). The bglA myrosinase-related gene encoding the 6-phospho-β-glucosidase (GH 1) from Bacillus sp. NGB-B10, the most active myrosinase-producing bacterium, was successfully identified. Response surface methodology (RSM) was applied to statistically optimize culture conditions for myrosinase production from Bacillus sp. strain NGB-B10. The Plackett–Burman design indicated that nitrogen concentration, incubation period, and agitation speed were the significant parameters in myrosinase production. The application of the Box–Behnken design of RSM resulted in a 10.03-fold increase in enzyme activity as compared to the non-optimized culture conditions. The myrosinase was partially purified by 40% fractionation followed by SDS-PAGE analysis which yielded two subunits that had a molecular weight of 38.6 and 35.0 KDa. The purified enzyme was stable under a broad range of pH (5.5–10) and temperatures (10–65 °C). The hydrolysis products released by bacterial myrosinase from some glucosinolate extracts had higher and/or equivalent in vitro antagonistic activity against several phytopathogenic fungi compared to the nystatin (a broad-spectrum antifungal agent). This study provides original information about a new source of bacterial myrosinase and affords an optimized method to enhance myrosinase production.

Artificial neural network modeling and statistical optimization of medium components to enhance production of exopolysaccharide by Bacillus sp. EPS003

Microbial Exopolysaccharides (EPS) have a wide range of applications in food, cosmetics, agriculture, pharmaceutical industries, and environmental bioremediation. The present study aims at enhancing the production of EPS from a soil-isolate Bacillus sp. EPS003. Effects of carbon and nitrogen sources and process conditions were evaluated one factor at a time. Box-Behnken design has been used and a 2.5-fold increase in yield is reported after optimizing the most influential parameters sucrose, yeast extract, and peptone as identified by the Plackett-Burman method. An artificial neural network (ANN) with two different topologies (EPS-NN1 and EPS-NN2) was developed. On comparing prediction accuracy, EPS-NN2 formulated as one input layer with four input variables (sucrose, yeast extract, peptone, biomass), a single hidden layer with seven neurons and EPS yield in the output layer showed a high coefficient of determination (R²-0.98) and low error (NRMSE-0.024). This study concludes that the consideration of biomass value has increased the prediction accuracy of the model.

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.

Complete Genome Sequence of Weissella confusa LM1 and Comparative Genomic Analysis

The genus Weissella is attracting an increasing amount of attention because of its multiple functions and probiotic potential. In particular, the species Weissella confusa is known to have great potential in industrial applications and exhibits numerous biological functions. However, the knowledge on this bacterium in insects is not investigated. Here, we isolated and identified W. confusa as the dominant lactic acid bacteria in the gut of the migratory locust. We named this strain W. confusa LM1, which is the first genome of an insect-derived W. confusa strain with one complete chromosome and one complete plasmid. Among all W. confusa strains, W. confusa LM1 had the largest genome. Its genome was the closest to that of W. confusa 1001271B_151109_G12, a strain from human feces. Our results provided accurate evolutionary relationships of known Weissella species and W. confusa strains. Based on genomic analysis, the pan-genome of W. confusa is in an open state. Most strains of W. confusa had the unique genes, indicating that these strains can adapt to different ecological niches and organisms. However, the variation of strain-specific genes did represent significant correlations with their hosts and ecological niches. These strains were predicted to have low potential to produce secondary metabolites. Furthermore, no antibiotic resistance genes were identified. At the same time, virulence factors associated with toxin production and secretion system were not found, indicating that W. confusa strains were not sufficient to perform virulence. Our study facilitated the discovery of the functions of W. confusa LM1 in locust biology and their potential application to locust management.

The response surface optimization of exopolysaccharide produced by Saccharomyces cerevisiae Y3 and its partial characterization

Response surface methodology (RSM) was used to optimize the conditions of exopolysaccharides (EPSs) by Saccharomyces cerevisiae Y3. The results indicated that the yield of EPS reached 4.52 ± 0.14 g/L with 10.30% (w/v) sucrose, 0.64% (w/v) yeast extract, liquid volume 141.5 mL, which was 2.40 times the original EPS yield. Y3 EPS contained 83.65 ± 0.16% of total sugars, 15.27 ± 0.26% of uronic acid, 0.78 ± 0.02% of protein and 0.30 ± 0.12% of sulfuric acid groups. Y3 EPS maintained a relatively low viscosity, with intrinsic viscosities of 306.58 mL/g (25 °C) and 200.91 mL/g (35 °C), respectively. The EPS had high water solubility index (WSI), high water holding capacity (WHC) and good emulsifying ability (EA). Meanwhile, the EPS could absorb metal ions such as Cu²⁺, Fe²⁺ and Zn²⁺. In addition, Y3 EPS exhibited good antioxidant properties and coagulated skim milk with a concentration-dependent manner. These results indicated that S. cerevisiae Y3 EPS had applicable prospects in medicine, food, especially the dairy industry.

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.