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Conventional fossil fuel-based packaging materials often brings of food safety and serious environmental pollution. It is significant to develop an environmentally-friendly packaging material. In this work, a levan-chitosan (LE/CS) blend film was fabricated via the solution casting method. The films were evaluated by Fourier transform infrared spectroscopy and X-ray diffraction, indicating the formation of hydrogen bonds between chitosan and levan. The mechanical properties of LE/CS films demonstrated a mechanical strength higher than CS films, and the best tensile strength appeared at a ratio of LE/CS (1:1) up to 18.78 ± 0.73 MPa. The addition of levan caused a significant increase in absorption of UV light with a reduction in swelling water of the blend films from 29.13 ± 0.53 % of chitosan film to 2.07 ± 0.27 % of LE/CS (1:1) film. A higher contact angle and lower WVP were observed for LE/CS blend films. LE/CS blend films were then used as packaging material for fresh pork and were well maintained the qualities. The study suggested that the new blend film might have a good prospect as a food packaging material. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a Bacillus halotolerans (B. halotolerans) strain DT1 capable of producing exopolysaccharides (EPS) was isolated from dried cabbages of Tianjin, a local fermented vegetable product. Three distinct polysaccharide fractions were isolated from the fermentation broth of DT1, namely, DT1-0, DT1-2, and DT1-5. The structural composition and properties of these fractions were investigated. The predominant EPS, DT1-0, was identified as a novel heteropolysaccharide composed of fructose and glucose with branched structures. The repeating unit was determined to be [4)-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-β-D-Fruf-(2→6)-β-D-Fruf-(2→6-)-β-D-Fruf-(2→], with fructose and glucose connected by β-(2→1) and α-(1→4) glycosidic linkages between the third fructose and the first glucose, respectively. The molecular weight (Mw) was estimated to be 4.253 × 103 Da. DT1-0 presented a smooth and porous surface structure as observed through SEM and exhibited a water-holding capacity of 504 ± 5.3%, maximum thermal stability at 245 °C, and an oil-holding capacity of 387 ± 1.9% for coconut oil. DT1-2 was identified as a fructooligosaccharide. DT1-5 was characterized as a polysaccharide composed of glucose and fructose. In conclusion, these findings provide substantial support for the further application of B. subtilis strain DT1 and its EPS fractions, DT1-0, DT1-2, and DT1-5, as potential alternatives for functional food additives or ingredients. [ABSTRACT FROM AUTHOR]

Leuconostoc mesenteroides DRP105 isolated from Chinese sauerkraut juice is an intensive producer of dextran. We report the complete genome sequence of Leu. mesenteroides DRP105. This strain contains a dextransucrase gene (dsr) involved in the production of dextran, possibly composed of glucose monomers. To explore the dextran synthesis mechanism of Leu. mesenteroides DRP105, we constructed a dsr-deficient strain derived from Leu. mesenteroides DRP105 using the Cre-loxP recombination system. The secondary structure prediction results showed that Leu. mesenteroides DRP105 dextransucrase (Dsr) was coded by dsr and contained 17.07% α-helices, 29.55% β-sheets, 10.18% β-turns, and 43.20% random coils. We also analyzed the dextran yield, monosaccharide change, organic acid, and amino-acid content of Leu. mesenteroides DRP105 and Leu. mesenteroides DRP105−Δdsr. The result showed that the lack of dsr changed the Leu. mesenteroides DRP105 sugar metabolism pathway, which in turn affected the production of metabolites. [ABSTRACT FROM AUTHOR]

Oxidized dextrans (ODex) with different oxidation degrees were prepared by periodate oxidation. Chitosan (CS) and ε-polylysine (PL) were crosslinked with ODex and incorporated with protocatechuic acid (PA) to enhance the properties of the chitosan-based films. FT-IR, XPS and XRD analysis showed that the aldehyde groups of ODex were covalently crosslinked with amino groups of CS and PL through Schiff base reaction, and PA interacted with the film components through non-covalent bonds. The results of SEM and AFM indicated that the film structure became denser with the addition of ODex. Increasing crosslinking degree resulted in deepened color and improved the UV-blocking ability of the films, which was caused by the increase of C N groups. Covalent crosslinking significantly reduced the moisture content, swelling degree and water solubility. The film with 50% ODex had the highest mechanical strength (31.72 MPa) and modulus of elasticity (885.54 MPa). The results of water vapor permeability, thermal properties and PA release experiments also indicated the crosslinking of the films by ODex. The incorporation of PA significantly improved the antioxidant activity of the films, but to some extent, the antibacterial activity of the films decreased due to the consumption of amino groups by crosslinking. In addition, application experiments suggested that crosslinked films could maintain the quality and freshness of chilled meat for a longer period than that of PE plastic films. The study suggested that the new crosslinked films might have good prospects as food packaging materials. [Display omitted] • Dextrans were oxidized to form oxidized dextrans with different oxidation degrees. • Chitosan and ε-polylysine were crosslinked with oxidized dextran. • The water resistance of the crosslinked films was significantly improved. • Protocatechuic acid and crosslinking improved the properties of the films. • Crosslinked films retarded spoilage of chilled meat. [ABSTRACT FROM AUTHOR]

The control of Aspergillus niger (A. niger) is of great significance for the agricultural economy and food safety. In this study, the antifungal effect and mechanism of iturin A from Bacillus amyloliquefaciens (CGMCC No. 8473) against A. niger (ATCC 16404) were investigated using biochemical analyses and proteomics. Changes in a mycelium treated with iturin A were observed using scanning electron microscopy and transmission electron microscopy, including mycelial twisting and collapse, organelle disintegration, and intracellular vacuolization. The cytomembrane integrity of A. niger was affected by iturin A, as detected by propidium iodide staining. In addition, the generation of excess reactive oxygen species, the hyperpolarization of the mitochondrial membrane potential and malondialdehyde accumulation also indicated that iturin A induced apoptosis in A. niger through the oxidative stress pathway. Proteomics results showed that 310 proteins were differentially expressed in the A. niger mycelium exposed to iturin A, including 159 upregulated proteins and 151 downregulated proteins, which were mainly associated with energy metabolism of A. niger. We propose that iturin A might inhibit the growth of A. niger by disrupting cytomembrane integrity, via oxidative stress, and by interfering with glycolysis/gluconeogenesis and the tricarboxylic acid cycle. Overall, iturin A is a promising antifungal agent that provides a rationale for controlling A. niger contamination in food. [ABSTRACT FROM AUTHOR]

This study aimed to explore the protective effects of L-theanine supplementation on the diquat-challenged weaned piglets. A total of 160 weaned piglets were randomly divided into 4 groups using a 2 × 2 two-factor design, there were 4 replicates per group and 10 pigs per replicate. Piglets were fed diets (with 1000 mg/kg L-theanine addition or not), then challenged with diquat or saline on day 7. 21 days after challenge, two pigs from each replicate were selected for sample collection. Results showed that supplement with 1000 mg/kg L-theanine down-regulated the diarrhea rate, serum D-lactate level, tumor necrosis factor-α, and phosphorylation of extracellular regulated protein kinases (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK) signaling in pigs without diquat challenge (p < 0.05). While for diquat-challenged piglets, L-theanine addition increased average daily gain, jejunum villus height, and interferon-γ level (p < 0.05). Meanwhile, L-theanine addition decreased the diarrhea rates and mortality, serum D-lactate level, and phosphorylation of ERK and JNK in diquat-challenged pigs (p < 0.05). These results demonstrate that L-theanine pretreatment could alleviate diquat-induced oxidative stress and improve intestinal barrier function in diquat-challenged weaned piglets, which can be attributed to suppression of MAPK phosphorylation signaling pathways. [ABSTRACT FROM AUTHOR]

A total of fifty-six strains of lactic acid bacteria isolated from Chinese sauerkraut juice from Shenyang were screened for glucansucrase production. Among them, strain DRP105 was detected to produce highest yield of glucansucrase in MRS broth, which was identified to be Leuconostoc mesenteroides. Based on Plackett-Burman Experiment, sucrose, sodium acetate and initial pH were found to be the most significant factors for glucansucrase production of L. mesenteroides DRP105. Afterwards, effects of the three main factors on glucansucrase activity were further investigated by central composite design, and the optimum composition was sucrose 35.74 g L−1, sodium acetate 6.46 g L−1 and initial pH 5.90. Optimum results showed that glucansucrase activity was increased to 6.26 ± 0.09 U mL−1 in 24 h fermentation, 33.19% higher than before. Our study also suggested that Tween 80 and dextran have potential to improve glucansucrase stability at temperature (30 °C) higher than enzyme storage temperature in crude fermented broth. [ABSTRACT FROM AUTHOR]

A chitosan/gelatin composite packaging film with antioxidant activity, bacteriostatic activity and pH responsiveness was prepared. Red cabbage pigment (RC) and enterocin CHQS were added as actives. In addition, different concentrations of citric acid (CA) were selected as crosslinking agents. Before that, in order to improve the yield of enterocin CHQS and simplify the purification process, we cloned and expressed CHQS in E. coli BL21 (DE3), resulting in an approximately 10-fold increase in yield. The appearances of the films were uniform and transparent with some UV-blocking ability. The results of antioxidant experiments of the films showed that the antioxidant capacity of the films was significantly increased by the addition of RC. Ammonia sensitivity experiments showed that the films could respond to volatile ammonia. Cross-linking improved the thermal stability, water sensitivity and photosensitivity of the films. FTIR and XPS revealed the mode of interaction between CHQS, CA, RC and the composite film structure. FTIR, XPS and XRD confirmed the cross-linking effect of CA. Atomic force microscopy showed that the addition of CA significantly increased the roughness of the film surface. The release experiments of RC showed that the cross-linking of CA promoted the release of active substances from the film and avoided the excessive release due to the dissolution breakage of the film. In addition, bacteria inhibition experiments showed that the addition of CA increased the antimicrobial properties of the films The experiments demonstrated that CHQS was effectively released and the bacteriocins in the films were stably preserved. [Display omitted] • Citric acid crosslinking improved smart packaging film properties. • Enterocin CHQS and red cabbage were added as active ingredients. • The water resistance of films containing citric acid improved significantly. • Enterocin CHQS might be kept stably in the films and released effectively. [ABSTRACT FROM AUTHOR]

Levan, a class of fructan with complex structure, has been found to have potential as a prebiotic. In this study, the polysaccharide was produced by in vitro catalysis (Cata-lev), structural analysis proved it was levan that possessed a branching degree of about 15% and molecular weight of 2.54 × 106 Da. Furthermore, SEM observation showed that Cata-lev was porous with loose flaky structure. Subsequently, the effects of five Cata-lev concentrations on the fermentation process, texture, nutraceutical, and sensory characteristics of set yogurts were investigated and compared to Fructooligosaccharides (FOS). The addition of Cata-lev could significantly (P < 0.05) increase the water holding capacity (WHC) of fermented yogurt (over 77%). The Cata-lev treatment groups exhibited superior system stability (Zeta and WHC) than FOS. Overall, this study expanded knowledge about levan structure and its potential utilization as a yogurt stabilizer. [Display omitted] • Structure analysis of levan synthesized in vitro , with about 15% branching degree. • The Cata-lev exhibited an excellent property of high-temperature resistance. • BM-2 Cata-lev presented the microstructure of loose, porous and multi-branched. • It indicated that supplement Cata-lev may improve texture and nutrition of yogurts. [ABSTRACT FROM AUTHOR]

Candida albicans is the most common fungal pathogen in hospital-acquired infections, which is extremely harmful to health. The increasing fungal infections is requiring the rapid development of novel antifungal agents. In this study, the antimicrobial activity of CHQS, an enterocin isolated from Enterococcus faecalis TG2 against C. albicans was confirmed by the minimum inhibitory concentration, minimum fungicidal concentration, and time–kill curve. Aniline blue and calcofluor white staining methods showed that CHQS remarkably affected β-1,3-glucan and chitin cell wall components and made cell wall more vulnerable. The C. albicans cell wall rupture and intracellular vacuolation were observed by TEM and SEM. Moreover, CHQS induced the accumulation of intracellular reactive oxygen species and decreased mitochondrial membrane potential. These results suggested that CHQS might have a complex multi-target antimicrobial mechanism against C. albicans. In addition, the use of CHQS combined with amphotericin B showed synergistic antimicrobial effects against C. albicans. In conclusion, enterocin CHQS, a natural product with antimicrobial effect, might has a bright future for the development of new antifungal drugs. [ABSTRACT FROM AUTHOR]

Listeria monocytogenes is a foodborne bacterial pathogen that seriously threatens dairy product safety and human health, hence effective and available antibacterial agents are urgently needed. This study aims to investigate the antibacterial mechanism of a recombinant enterocin CHQS against L. monocytogenes and its antibacterial effect on pasteurized milk. The minimum inhibitory concentration (MIC) of CHQS was 0.5 μg/mL in both TSB medium and tenfold diluted pasteurized milk. The anti- L. monocytogenes rate of 2 h reached 99.94% with the treatment of the 2 MIC of CHQS in the diluted pasteurized milk. CHQS led to the massive release of proteins and nucleic acids and the significant increase in propidium iodide (PI) uptake, indicating that integrity and permeability of the cell membrane were destroyed. The cell membrane and structure of L. monocytogenes were severely disrupted by observing with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intracellular reactive oxygen species (ROS) level was increased to 2.18-fold with the 2 MIC CHQS treatment. CHQS at sub-MICs inhibited the biofilm formation and motility of L. monocytogenes in a concentration-dependent manner. In MIC treatment group, the number of L. monocytogenes was 4.55 log 10 CFU/mL fewer than the control group and the bacterial abundance of L. monocytogenes remained a low level (0.22%) on the 12th day of storage at 4 °C in pasteurized milk. The study suggested the antibacterial mechanism of CHQS and its application potentiality in pasteurized milk. • The antibacterial mechanism of a recombinant enterocin CHQS against L. monocytogenes was investigated. • The antibacterial effect of CHQS on pasteurized milk was explored. • CHQS inhibited L. monocytogenes growth by disrupting the integrity and permeability of cell membranes. • CHQS can stimulate ROS generation and inhibit the motility and biofilm formation of L. monocytogenes. [ABSTRACT FROM AUTHOR]

Suancai, as a traditional fermented food in China with reputed health benefits, has piqued global attention for many years. In some circumstances, the microbial-driven fermentation may confer health (e.g., probiotics) or harm (e.g., antibiotic resistance genes) to the consumers. To better utilize beneficial traits, a deeper comprehension of the composition and functionality of the bacterial species harboring enzymes of catalytically active is required. On the other hand, ingestion of fermented food increases the likelihood of microbial antibiotic resistance genes (ARGs) spreading in the human gastrointestinal tract. Besides, the diversity and taxonomic origin of ARGs in suancai are little known. In our study, a metagenomic approach was employed to investigate distribution structures of CAZymes and ARGs in main bacterial species in suancai. Functional annotation using the CAZy database identified a total of 8796 CAZymes in metagenomic data. A total of 83 ARGs were detected against the CARD database. The most predominant ARG category is multidrug-resistant genes. The ARGs of antibiotic efflux mechanism are mostly in Proteobacteria. The resistance mechanism of ARGs in Firmicutes is primarily antibiotic inactivation, followed by antibiotic efflux. Due to the abundance of species with different ARGs, strict quality control including microbial species, particularly those with lots of ARGs, is vital for decreasing the risk of ARG absorption via consumption. Ultimately, we significantly widen the understanding of suancai microbiomes by using metagenomic sequencing to offer comprehensive information on the microbial functional potential (including CAZymes and ARGs content) of household suancai. [ABSTRACT FROM AUTHOR]

BACKGROUND Type 1 diabetes is an autoimmune disease that results in the specific destruction of insulin‐producing beta cells in the pancreas. The aim of this study was to investigate the mechanism of exopolysaccharide from Leuconostoc pseudomesenteroides XG5 (XG5 EPS) against type 1 diabetes. RESULTS: Long‐term drench of XG5 EPS delayed the onset of autoimmune diabetes and had fewer islets with high‐grade infiltration (an insulitis score of 3 or 4) than untreated NOD mice. Oral administration of 50 mg kg−1 d−1 XG5 EPS increased the insulin and glucagon‐like peptide‐1 (GLP‐1) levels of serum, stimulated GLP‐1 secretion and upregulated gcg mRNA expression of colon in NOD mice. Moreover, oral administration of 50 mg kg−1 d−1 XG5 EPS significantly increased total short‐chain fatty acids levels in the colon contents, especially those of acetic acid and butyric acid. In NCI‐H716 cells, 500 and 1000 μmol L−1 sodium butyrate promoted the secretion of GLP‐1 and upregulated the mRNA expression of gcg and PC3, while XG5 EPS and sodium acetate did not stimulate the GLP‐1 secretion. Therefore, long‐term drench of XG5 EPS delayed the onset of autoimmune diabetes, which may be directly correlated with the increase of butyrate in the colon of NOD mice. CONCLUSION: Long‐term drench of 50 mg kg−1 d−1 XG5 EPS promoted the expression and secretion of GLP‐1 by increasing the production of butyric acid, thereby delaying T1D onset in NOD mice. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Exopolysaccharide from Leuconostoc pseudomesenteroides XG5 (XG5 EPS) is a linear dextran that is built by glucose units via α-1,6 glycosidic bond. The primary objective of this study was to investigate the yield of XG5 EPS and its application in set yogurt. In laboratory scale, the culture conditions of XG5 EPS production were optimized using the L9 (33) orthogonal test. Here, the optimized yield of XG5 EPS was 26.02 g/L under the conditions of 100 g/L sucrose, initial pH 7.0, 25°C incubation, and 100 rpm for 36 h in a shaking flask. Based on the optimized parameters of laboratory scale, a pilot fed-batch fermentation was performed in a 50-L bioreactor with an adjusted agitation speed of 20 rpm. The XG5 EPS yield reached 40.07 g/L in fed-batch fermentation, which was 54% higher than that achieved in laboratory scale. In addition, XG5 EPS was added into set yogurt to investigate its effect on the stability of set yogurt. Our data demonstrated that the XG5 EPS improved the water-holding capacity, texture profile, and viscosity of set yogurt during cold storage compared with the controls. In particular, addition of 0.5% XG5 EPS increased the structure of 3-dimensional network of set yogurt, which eventually improved the physical stability of the set yogurt. Overall, this study provided new insights for exploring the pilot scale production and application of dextran. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a composite film was prepared with bacterial cellulose (BC) of Gluconacetobacter xylinus and cell-free supernatant (CFS) of Enterococcus faecium TJUQ1, which was named BC-E. The optimum conditions for the preparation of the composite film with a minimal antibacterial activity were the soak of BC in 80 AU/mL CFS for 6 h. By scanning electron microscope observation, the surface network structure of BC-E was denser than that of BC. The tensile strength of BC and BC-E was 4.65 ± 0.88 MPa and 16.30 ± 0.92 MPa, the elongation at break of BC and BC-E was 3.33 ± 0.89% and 31.60 ± 1.15%, respectively, indicating the mechanical properties of BC-E were significantly higher than that of BC (P < 0.05). The swelling ratio of BC-E (456.67 ± 7.20%) was lower than that of BC (1377.78 ± 9.07%), demonstrating BC-E films presented better water resistance. BC-E films were soaked with 320 AU/mL CFS, and then used to pack the ground meat with 6.55 log 10 CFU/g of Listeria monocytogenes. After 8 days of storage, the number of bacteria decreased by 3.16 log 10 CFU/g. Similarly, total mesophilic bacterial levels in the ground meat decreased by 2.41 log 10 CFU/g compared to control groups. • Antimicrobial materials with bacterial cellulose were prepared. • Enterococcus faecium TJUQ1 cell-free supernatant was successfully incorporated in bacterial cellulose. • Composites performed excellent physical and antibacterial properties. • Composites have potential applicability as antimicrobial packaging for food. [ABSTRACT FROM AUTHOR]

This study synthesized an antimicrobial peptide based on the bovine cathelicidin BMAP 27 sequence. It was found to have a broad spectrum of antibacterial activity, with exceptionally high activity against Salmonella. However, the antibacterial mechanism of BMAP 27 against Salmonella remains unclear. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of BMAP 27 against Salmonella enterica serovar Typhimurium were determined to be 2 μM and 4 μM, respectively. After treatment with 2 MIC of BMAP 27, the absorbance of DNA in centrifugal supernatant increased from 0.244 to 1.464, and that of protein rose from 0.174 to 0.774, respectively. BMAP 27 has compromised the cell membrane as observed through field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM), and confirmed by the propidium iodide (PI) test. The alkaline phosphatase (AKP) enzyme activity in the supernatant of the 2 MIC treatment group was 2.15 times higher than the control group, indicating extracellular membrane damage. BMAP 27 treatment increased intracellular ROS levels as tested by dichlorofluorescein diacetate (DCFH) staining. DNA interaction analysis revealed that BMAP 27 has a binding affinity towards DNA, causing its characteristic bands to disappear and peak intensity at 260 nm to reduce. Molecular docking identified its potential binding mode with DNA. The crystal violet biofilm staining results demonstrated that BMAP 27 inhibited S. Typhimurium biofilm formation by 43.1 % and cleared mature biofilms by 53.62 %. Confocal Laser scanning electron microscopy (CLSM) observed that BMAP 27 could kill bacteria within the biofilm and dislodge bacteria from the surface of glasses. Swimming tests identified that the motor capacity of S. Typhimurium was diminished by BMAP 27. By counting the total bacteria, BMAP 27 was revealed to exert bacteriostatic effects in chilled pork and orange juice, which might provide a basis for its application in the inhibition of Salmonella. [Display omitted] • BMAP 27 exhibited a broad bacteriostatic spectrum and strong bacteriostatic action against S. Typhimurium. • BMAP 27 disrupted both integrity and permeability of cell membrane and cell wall of S. Typhimurium. • BMAP 27 induced intracellular ROS generation and accumulation. • BMAP 27 impaired the swimming capacity of S. Typhimurium, inhibited biofilm formation and removed mature biofilms. • BMAP 27 exhibited a non-covalent binding affinity towards S. Typhimurium genomic DNA. [ABSTRACT FROM AUTHOR]

Heavy metal pollution seriously threatens human health and ecological environment. Due to high efficiency and excellent development prospect, adsorption technology has attracted worldwide attention. It is significant to develop renewable adsorbents with excellent adsorption performance. In this study, the Pb2+ and Zn2+ adsorption capacity of Ca-alginate immobilized and free (without immobilization) Leu. citreum B-2 extracellular polysaccharides (EPS) was investigated. Isotherm and kinetic models were used to evaluate the adsorption performance. The adsorbents were characterized by SEM, FT-IR and XPS spectroscopy. The maximum biosorption of Pb2+ 269.54 and Zn2+ 49.88 mg/g was achieved with immobilized EPS. Thermodynamic studies showed that the adsorption of Pb2+ and Zn2+ on EPS was a spontaneous and feasible process, and the adsorption properties of EPS were exothermic for lead and endothermic for zinc. All the adsorption processes conformed to the pseudo-second-order model and Langmuir adsorption isotherm model, indicating that the adsorption was mainly chemisorption taken placed on single adsorption surface. SEM results showed that the surface of EPS become denser after adsorption. FTIR and XPS analysis indicated that the adsorption mechanism mainly involved the complexation reaction and ion exchange of functional groups such as C O, O-C-O, -COOH and C-OH. [Display omitted] • Ca-alginate immobilized and free Leu. citreum B-2 EPS was used to remove Pb2+ and Zn2+. • Immobilized EPS has higher capacity of Pb2+ and Zn2+ biosorption than that of free EPS. • EPS binding to Pb2+ and Zn2+ was studied by SEM, FTIR and XPS methods. • C O, O-C-O, -COOH and C-OH in EPS all participated in the biosorption of Pb2+ and Zn2+. [ABSTRACT FROM AUTHOR]

• The recombination lipase was expressed in E. coli fused AcmA as purification and immobilization tag. • The recombination lipase was purified and immobilized by GEM particles in one step. • The inclusion body of the lipase could regain the activity by the purification of the GEM particles. • The lipase immobilized could be recycled. Lipases are important enzyme for industries. In this work, the recombinant lipase with an AcmA tag working as purification and immobilization tag was expressed in Escherichia coli. Gram-positive enhancer matrix (GEM) particles work to purify and immobilize the recombinant lipase. GEM particles are produced by boiling the cells of Lactococcus lactis NZ9000 to remove the DNA and most proteins. GEM particles specifically bind protein with the AcmA tag in the C-terminal. The recombinant lipase was in two forms, the soluble part and the inclusion body. GEM particles could purify and immobilize the lipase from the soluble part in one step. After the inclusion body being dissolved by 8 M urea, the enzyme activity was recycled by the GEM particles. The GEM particles could immobilize over 75% of the enzyme activity. The lipase immobilized was a basophilla enzyme with the optimal temperature was 30 °C. The activity of the lipase immobilized was 47.1U/ OD 600 GEM particles at optimal conditions. The enzyme catalysis did not need the ions added to improve the activity. The GEM particles had excellent enzyme activity reusability. [ABSTRACT FROM AUTHOR]

Enterococcus faecium TJUQ1 with high bacteriocin-producing ability was isolated from pickled Chinese celery. In this study, enterocin TJUQ1 was purified by ammonium sulfate precipitation, reversed-phase chromatography (Sep-Pak C 8) and cation-exchange chromatography. The activity of the purified bacteriocin was 44,566.41 ± 874.69 AU/mg, which corresponds to a purification fold of 35.89 ± 2.34. The molecular mass was 5520 Da by MALDI-TOF MS and Tris-Tricine SDS-PAGE. The result of LC-MS/MS showed that the bacteriocin shared 59.15% identity with enterocin produced by E. faecium GN (accession no. O34071). PCR amplification revealed that E. faecium TJUQ1 possesses a gene encoding enterocin B with 60% identity to enterocin B. Circular dichroism (CD) spectroscopy showed that the molecular conformation was 32.6% helix, 19.5% beta, 12.9% turn and 35.0% random. The stability of enterocin TJUQ1 was measured. After exposure at 121 °C for 15 min, the residual antimicrobial activity of enterocin TJUQ1 was 85.95 ± 1.32%. The antimicrobial activity of enterocin TJUQ1 was still active over a pH range of 3–11. Enterocin TJUQ1 was inactivated after exposure to proteolytic enzymes but was not inactivated by lipase or amylase. These results showed that enterocin TJUQ1 was a novel class II bacteriocin. Enterocin TJUQ1 showed wide antibacterial activity against food-borne gram-negative and gram-positive pathogens, such as Staphylococcus aureus , Listeria monocytogenes , Escherichia coli and Salmonella enterica. The MIC was 5.26 ± 0.24 μg/mL against L. monocytogenes CMCC 1595. SEM and TEM were used to observe the changes in the morphological and intracellular organization of L. monocytogenes CMCC 1595 cells treated with enterocin TJUQ1. The results demonstrated that enterocin TJUQ1 increased extracellular electrical conductivity, facilitated pore formation, triggered the release of UV-absorbing materials, ATP and LDH, and even caused cell lysis in L. monocytogenes CMCC 1595 cells. Based on the characterization, the wide inhibitory spectrum and mode of action determined so far, enterocin TJUQ1 is a potential preservative for the food industry. The present study described the purification, characterization and mode of action of enterocin TJUQ1, which is generated by Enterococcus faecium TJUQ1. The activity of the purified bacteriocin was 44,566.41 ± 874.69 AU/mg, which corresponds to a purification fold of 35.89 ± 2.34. The molecular mass was 5520 Da by MALDI-TOF MS and Tris-Tricine SDS-PAGE. LC-MS/MS and PCR amplification indicated that enterocin TJUQ1 is a novel bacteriocin. The residual antimicrobial activity of enterocin TJUQ1 was 85.95 ± 1.32% after exposure at 121 °C for 15 min. The antimicrobial activity of enterocin TJUQ1 was still active over a pH range of 3–11. These results showed that enterocin TJUQ1 was a novel class II bacteriocin. Enterocin TJUQ1 showed wide antibacterial activity against food-borne gram-negative and gram-positive pathogens. The mode of action of enterocin TJUQ1 against L. monocytogenes CMCC 1595 showed that enterocin TJUQ1 increased membrane permeability, destroyed membrane integrity, and eventually led to cell death. Unlabelled Image • An enterocin TJUQ1 was purified from Enterococcus faecium TJUQ1 through three steps. • Tris-Tricine SDS-PAGE, MALDI-TOF MS and LC-MS/MS indicated that the enterocin was a novel enterocin. • Enterocin TJUQ1 showed a broad-spectrum antibacterial activity against both Gram-positive and Gram-negative food-borne pathogens. • The mode of action of enterocin TJUQ1 against L. monocytogenes CMCC 1595 was studied. [ABSTRACT FROM AUTHOR]

Immobilization of the enzyme benefits the catalytic industry a lot. The gram-positive enhancer matrix (GEM) particles could purify and immobilize the recombinant α-amylase in one step without changing the enzymatic character. The enzyme immobilized by GEM particles exhibited good reusability and storage stability. The denaturants dissolved some of the GEM particles and a part of the GEM particles could bear the denaturants. The GEM particles had strong binding ability to the recombination protein with the AcmA tag even when the denaturants existed. The inclusion body was dissolved by urea and then bound by the GEM particles. The GEM particles binding the recombination protein were separated by centrifugation and resuspended in the renaturation solution. GEM particles were recycled by repeating the boiling procedure used in preparing them. The recombination α-amylase without any tag was obtained by digestion and separated via centrifugation. Altogether, our findings suggest that GEM particles have the potential to function as both immobilization and purification materials to bind the soluble recombinant protein with the AcmA tag and the inclusion body dissolved in the denaturants. [ABSTRACT FROM AUTHOR]

In this study, we described the optimization of fermentation conditions and biochemical properties of exopolysaccharide (EPS) produced by Leuconostoc citreum B-2. The results of response surface methodology showed that the yield of B-2 EPS was 59.33 ± 1.34 g/L, which was 5.93 times before. The degradation temperature of the B-2 EPS was 313 °C, indicating that it had high thermal stability. B-2 EPS had certain antioxidant activity, especially it had strong scavenging ability to H 2 O 2. Higher concentrations of B-2 EPS had better emulsifying property on vegetable oils than hydrocarbons. Furthermore, our results also showed that B-2 EPS had the ability to coagulate milk and promote the growth of probiotic bacteria. • The yield of EPS from Leuconostoc citreum B-2 was increased 4.93-fold by RSM. • The degradation temperature of B-2 EPS was 313 °C, showing good thermal stability. • B-2 EPS had certain antioxidant activity, especially for H 2 O 2. • The emulsifying activity of B-2 EPS on vegetable oils was higher than hydrocarbons. • B-2 EPS could make skim milk coagulate and had a certain probiotic function. The fermentation conditions for exopolysaccharides (EPS) with a highly branched structure extracted from Leuconostoc citreum B-2 were optimized by response surface methodology (RSM). The results showed that under the optimal fermentation conditions of sucrose, yeast extract and pH of 99.80 g/L, 5.94 g/L and 6.12, respectively, the B-2 EPS yield was 59.33 ± 1.34 g/L, which was 5.93 times greater than that from the initial nonoptimized conditions. Chemical composition analysis showed that the carbon, hydrogen, nitrogen and sulfur contents of the B-2 pure EPS (P-EPS) were 39.05 ± 0.25%, 7.19 ± 0.08%, 0.72 ± 0.03% and 0%, respectively. The content of uronic acid was high, reaching 20.94 ± 6.30%. B-2 EPS had certain 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl (·OH), superoxide anion (O2−), hydrogen peroxide (H 2 O 2), nitroso radical (NO2−) scavenging abilities and reducing power. The degradation temperature of the B-2 EPS was 313 °C, indicating that B-2 EPS have high thermal stability. The emulsification effect on vegetable oils was better than that of hydrocarbons. The EPS produced by Leu. citreum B-2 was activated in different concentrations of sucrose-supplemented skimmed milk, which caused the skimmed milk to have different degrees of solidification. Moreover, B-2 EPS promoted the growth of probiotic bacteria, especially Lactobacillus delbrueckii. [ABSTRACT FROM AUTHOR]

• PC EPS is a dextran consisting of consecutive α-(1→6)-linked D-glucopyranose units. • The dextran polymer showed an irregular sheet structure and porous surface. • The dextran displayed heat tolerance and high viscosity at low pH properties. • The dextran could coagulate sucrose-supplemented milk. • The dextran has potential applications in food and dairy processing. An exopolysaccharide (EPS)-producing bacterial strain, PC, was isolated from pickled Chinese cabbage and identified as Leuconostoc pseudomesenteroides. EPS yield was up to 30.5 g/L when bacteria were cultivated in Man-Rogosa-Sharpe (MRS) medium containing 5% sucrose at 30°C for 48 h. Further analysis by gas chromatography, high performance size exclusion chromatography, and nuclear magnetic resonance revealed that the EPS consisted of glucose with α-(1→6) linkages and had a molecular weight of 3.13 × 106 Da. Scanning-electron microscopy demonstrated an irregular sheet structure and porous surface, and lumps with an average height of 77.803 nm were observed by atomic force microscopy. Physical-chemical analysis showed that the EPS exhibited excellent thermal stability and possessed high viscosity at high concentration, low temperature and acidic pH, making it promising to be used in thermal processed foods and fermentation of acidic food products. Milk solidification test also suggested the promising potential for application as a dairy and food additive since the EPS could activate the solidification of sucrose-supplemented milk. Taken together, this study provides a commercial guidance for the practical application of PC EPS in food industry and other areas. [ABSTRACT FROM AUTHOR]

The production optimization, partial characterization and properties of an exopolysaccharide (EPS) from Lactobacillus sakei L3 were performed. Sucrose concentration, initial pH and inoculation volume were the most significant variables that improved the L3 EPS production in a three-level Plackett-Burman design. The maximum EPS yield of 69.65 g/L (2.16-fold greater than the original yield) was obtained under optimal conditions of 127.80 g/L sucrose, initial pH 6.87 and 3.15% inoculation volume. Chemical analyses revealed that the observed EPS bioactivity was mainly due to the sugar moieties. The chain conformation was characterized by the Congo red test, a β -elimination reaction and circular dichroism, which indicated that the L3 EPS exhibited a random coil structure and O-linkages in aqueous solution, and the EPS concentration did not alter the EPS chain conformation but did modify the hydrogen-bond interactions and chirality of the polysaccharide. The purified L3 EPS exhibited high water solubility, probiotic effects and emulsification activity. The L3 EPS at 2.0 mg/mL formed a highly active and stable emulsion with sunflower oil, with EA, ES 24 , ES 48 and ES 72 indices of 62.30 ± 0.06%, 57.95 ± 0.18%, 42.73 ± 0.26% and 43.05 ± 0.08%, respectively. These results collectively describe a high-yield EPS with unique characteristics for exploitation in large-scale industrial food applications. Unlabelled Image • The production of L3 EPS was optimized using Plackett-Burman design and RSM. • The observed EPS bioactivity was mainly due to the sugar moieties. • EPS with O-glycosylation exhibited random coil structure in aqueous solution. • EPS displayed hydrophilicity, probiotic and emulsification properties in vitro. • EPS has potential applications in food processing. [ABSTRACT FROM AUTHOR]

A glucansucrase encoding gene was cloned into pET-28a(+) vector and expression in Escherichia coli BL21(DE3). An about 160 kDa recombinant glucansucrase was purified with a yield of 50.73% and a 4.02-fold increase in activity. The 1464 amino acid residue enzyme belongs to the GH70 subfamily and shares 90% similarity with Leuconostoc sp. glucansucrase. The optimal temperature and pH were 30 °C and pH 5.5, and 80% of activity was retained after incubation at 10–30 °C and pH 5–7. Enzyme activity was strongly activated by Ca2+ and Mn2+ and inhibited by various metal ions and chemical agents, and a high affinity for sucrose (K m = 11.6 mM, V max = 8.1 mmol/(mL·min)). Circular dichroism (CD) and Raman spectra collectively indicated a high proportion of random coil structure. The presented study described the gene cloning, expression, purification, and characterization of glucansucrase from Leuconostoc mesenteroides TDS2-19. Sequence analysis indicated that it attaches to glucansucrase family: GH 70 family. The recombinant enzyme was purified to 4.02 fold with a specific activity of 35.85 U/mg and the molecular weight was about 160 kDa. The enzyme demonstrated its optimum activity at pH 5.5 and 30 °C. Enzyme activity was strongly activated by Ca2+ and Mn2+ and inhibited by various metal ions and chemical agents. Circular dichroism (CD) and Raman spectra collectively indicated a high proportion of random coil structure. Unlabelled Image • Gene encoding dextransucrase from Leuconostoc mesenteroides was cloned. • A 160 kDa recombinant dextransucrase was purified with a 4.02-fold increase in activity. • This optimal temperature and pH of recombinant dextransucrase were 30 °C and pH 5.5. • The dextransucrase was a random coil protein. [ABSTRACT FROM AUTHOR]

Polymicrobial biofilms often form on the surfaces of food-processing machinery, causing equipment damage and posing a contamination risk for the foods processed by the system. The composition of the microbial communities that make up these biofilms is largely unknown, especially in the dairy industry. To address this deficit, we investigated the bacterial composition of biofilms that form on the surfaces of equipment during dairy processing using Illumina MiSeq sequencing and culture-dependent methods. Illumina sequencing identified eight phyla, comprising six classes, ten orders, fifteen families, eighteen genera, and eighteen species. In contrast, only eight species were isolated from the same samples using the culture-based method. To determine the ability of the identified bacteria to form biofilms, biofilm formation analysis via crystal violet staining was performed. Five of the eight culturable species, Acinetobacter baumannii, Acinetobacter junii, Enterococcus faecalis, Corynebacterium callunae, and Stenotrophomonas maltophilia, were able to form biofilms. Since most of the identified bacteria are potential food-borne or opportunistic pathogens, this study provides guidance for quality control of products produced in dairy processing facilities. [ABSTRACT FROM AUTHOR]

Abstract α-Amylases are important enzymes in industry. A recombinant α-amylase with a secretion signal peptide and an AcmA tag was expressed in Escherichia coli to improve the yield. The induction concentrations were optimized, and the temperature had a significant influence on soluble expression and secretion. A visible band could be obtained when the induction was conducted at 16 °C. The gram-positive enhancer matrix (GEM) particles could separate and purify the recombinant α-amylase with the AcmA tag, and no visible band could be seen in the culture even after the culture was concentrated ten times. The solution and concentration of the recombinant α-amylase could be adjusted by GEM particles. The recombinant untagged α-amylase was obtained after digestion. The α-amylase was characterized. The recombinant α-amylase was a thermophilic enzyme with a broad pH tolerance. In addition, the enzyme activity of the recombinant α-amylase was independent of Ca2+. The recombinant α-amylase contained the OmpA signal peptide and the AcmA tag and was expressed and purified quickly and easily. Graphical abstract In this study, the recombination α-amylase with a secretion signal peptide and a AcmA tag was expressed in Escherichia coli. The induction concentrations were optimized and the temperature had significant influence on the soluble expression and secretion. The gram-positive enhancer matrix (GEM) particles could separate and purify the recombination α-amylase with the AcmA tag. After being digested, the recombination α-amylase without tag was obtained. The recombination α-amylase was a thermophilic enzyme with broad tolerance of the pH. The enzyme activity of the recombination α-amylase was independent of the Ca2+. Unlabelled Image Highlights • The recombination α-amylase was expressed and secreted by the signal peptide OmpA. • The recombination α-amylase was purified by the GEM particles. • The α-amylase without any tag was obtained after being digested. • The recombination α-amylase was a thermophilic enzyme with broad tolerance of the pH. • The enzyme activity of the recombination α-amylase was independent of the Ca2+. [ABSTRACT FROM AUTHOR]

Abstract This study aims to examine the inhibitory effects of the bacteriocin CHQS, produced by Enterococcus faecalis TG2, and its mode of action against Listeria ivanovii DSMZ 20750T, which is one of the pathogens sensitive to CHQS. The minimum inhibitory concentration, minimum bactericide concentration and time-inhibition curves were measured to confirm the strong effects of CHQS on L. ivanovii DSMZ 20750T, and its antibacterial mode of action was studied by observing the changes in cell membrane permeability, integrity, and proton motive force. The minimum inhibitory concentration and minimum bactericide concentration of CHQS were 26.74 ng/mL and 107.30 ng/mL, respectively, demonstrating that CHQS exhibited significantly strong and rapid antibacterial efficacy towards L. ivanovii DSMZ 20750T. The results showed that CHQS led to the leakage of K+ and electrolytes, the massive release of ATP and UV-absorbing materials, and the collapse of the proton motive force. The micrographs of scanning electron and transmission electron microscopy demonstrate the severe cellular destruction and release of intracellular substances induced by bacteriocin CHQS. Collectively, this study reveals the antibacterial activity and mode of action of CHQS against L. ivanovii DSMZ 20750T and demonstrates the mode of action of the inhibition by bacteriocins. Highlights • This is the first report on the antibacterial action mode of bacteriocin CHQS. • Bacteriocin CHQS exhibited a strong antibacterial efficacy on Listeria ivanovii. • Bacteriocin CHQS induced cell membrane permeable, causing the efflux of K+, ATP. • Morphological changes on Listeria ivanovii were visualized by SEM and TEM analyses. [ABSTRACT FROM AUTHOR]

An exopolysaccharide (EPS) was produced by Leuconostoc pseudomesenteroides DRP-5 isolated from homemade wine. The EPS was obtained with ethanol extraction, which was further purified by chromatography of Sephadex G-100 to get a purified fraction. The monosaccharide composition of the EPS was glucose, and its molecular weight (Mw) was 6.23 × 10 6 Da, as determined by gas chromatography (GC) and high-performance size-exclusion chromatography (HPSEC). Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance spectra (NMR) showed that the EPS was a linear glucan with α-(1→6)-linked glucosidic bonds. The water holding capacity (WHC), water solubility index (WSI) and emulsifying activity (EA) of DRP-5 EPS were 296.76 ± 18.93%, 98.62 ± 3.57% and 87.22 ± 2.18%, respectively. DRP-5 EPS have a higher degradation temperature of 278.36 °C, suggesting high thermal stability of the EPS. Also, DRP-5 EPS was found to have moderate 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, hydroxyl radical, superoxide anion radical, 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical, Fe 2+ scavenging activities and reducing power. All these characteristics suggest that DRP-5 EPS might have potential applications in the pharmaceutical, cosmetic and food industries. [ABSTRACT FROM AUTHOR]

Strain Bacillus amyloliquefaciens BH1 was evaluated for the generation of α-amylase. Culture conditions and medium components were optimized by a statistical approach for the optimal generation of α-amylase with response surface methodology (RSM) method. The Plackett-Burman (PB) design was executed to select the fermentation variables and Central composite design (CCD) for optimizing significant factors influencing production. The optimum levels for highest generation of α-amylase activity (198.26 ± 3.54 U/mL) were measured. A 1.69-fold improve generation was acquired in comparison with the non-optimized. Partial characterization of the α-amylase indicated optimal pH and temperature at 7.0 and 40 °C, respectively. Crude α-amylase maintained a constant pH range 5.0-8.0 and 30-70 °C. The α-amylase was independent of Ca2+, and the activity was inhibited by Fe3+, Co2+, Cu2+, and Hg2+. The thermo and pH stability of the α-amylase indicate its extensive application in the food and pharmaceutical industries. [ABSTRACT FROM AUTHOR]

In the present study, a novel α -amylase produced by Bacillus amyloliquefaciens BH072 was purified and characterized. The molecular weight of purified α -amylase was approximately 68 kDa, determined by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) and ten amino acid of N-terminal was NSGLNGYLTH. The kinetic parameters K m and V max were 4.27 ± 0.21 mg/mL and 987.34 ± 23.34 U/mg, respectively. Purified α -amylase showed maximal activity at pH 7 and 60 °C. Enzyme remained stable in pH range 6.0–7.0 and 50–80 °C. The activity of the α -amylase was Ca 2+ independent and stability in the presence of surfactant, oxidizing and bleaching agents. The β -mercaptoethanol and EDTA greatly enhanced and reduced α -amylase activity, respectively. This enzyme has high hydrolysis rate toward corn, wheat and potato starch and hydrolyzes soluble starch to glucose, maltose, maltotriose and maltotetraose, indicating that the α -amylase represents a promising candidate for applications in the food industry. [ABSTRACT FROM AUTHOR]

A water-soluble exopolysaccharide (EPS)-producing strain YF32 was isolated from soybean paste, which was then identified as Leuconostoc pseudomesenteroides . After culturing the strain in Man-Rogosa-Sharpe (MRS) medium containing 5% sucrose at 30 °C for 48 h, the EPS was purified, and a yield of 12.5 g/L was achieved. The weight-average molecular weight (Mw) was 5.54 × 10 6 Da by high-performance size-exclusion chromatography (HPSEC). The structural characterization of the purified EPS was determined by gas chromatography (GC), Fourier transform infrared (FT-IR), 1 H, 13 C nuclear magnetic resonance (NMR) spectroscopy. The results demonstrated that the exopolysaccharide was glucan with a peak, a linear backbone composed of consecutive α-(1 → 6)-linked d -glucopyranose units. No branching was observed in the dextran structure. The degradation temperature (Td) of EPS was 307.62 °C, which suggested that dextran exhibited high thermal stability. YF32 dextran also showed high water solubility and emulsibility. All results suggested that dextran has the potential to be applied in food fields as a food additive. [ABSTRACT FROM AUTHOR]

A strain Leuconostoc citreum B-2 was isolated from homemade fermentation product of pineapple and its polysaccharide yield was 28.3 g/L after cultivating the strain in Man-Rogosa-Sharpe (MRS) medium with 75 g/L sucrose. The exopolysaccharide (EPS) was characterized by gas chromatography (GC), Fourier-transform infrared (FT-IR) spectra, high-performance size-exclusion chromatography (HPSEC), nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscope (SEM) analysis in present study. The monosaccharide composition of EPS was glucose and molecular weight was 3.77 × 10 6 Da. FT-IR and NMR spectra revealed that the B-2 EPS was composed of 75% α-(1 → 6) linked d -glucopyranose units existing in the main chain with 19% α-(1 → 3) branching and only a few α-(1 → 2) branching. The SEM of the dried EPS appeared irregular sheets with glittering surface and compact structure. Water solubility index and water holding capacity of B-2 EPS were 80% and 450%, respectively. All the mentioned characteristics suggested that the EPS has a potential application in the food, cosmetic and pharmaceuticals industry. [ABSTRACT FROM AUTHOR]

Strain DRP2-19 was detected to produce high yield of glucansucrase in MRS broth, which was identified to be Leuconostoc mesenteroides. In order for industrial glucansucrase production of L. mesenteroides DRP2-19, a one-factor test was conducted, then response surface method was applied to optimize its yield and discover the best production condition. Based on Plackett-Burman (PB) experiment, sucrose, Ca2+, and initial pH were found to be the most significant factors for glucansucrase production. Afterwards, effects of the three main factors on glucansucrase activity were further investigated by central composite design and the optimum composition was sucrose 35.87 g/L, Ca2+ 0.21 mmol/L, and initial pH 5.56. Optimum results showed that glucansucrase activity was increased to 3.94 ± 0.43 U/mL in 24 hr fermentation, 2.66-fold higher than before. In addition, the crude enzyme was purified using ammonium sulfate precipitation, ion-exchange chromatography, and gel filtration. The molecular weight of glucansucrase was determined as approximately 170 kDa by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme was purified 15.77-fold and showed a final specific activity of 338.56 U/mg protein. [ABSTRACT FROM AUTHOR]

Response surface methodology (RSM) was used to optimize the fermentation condition of exopolysaccharide (EPS) producing strain Leuconostoc mesenteroides DRP105. Result showed that the optimum condition was sucrose 86.83 g/L, tryptone 15.47 g/L, initial pH 7.18 and maximum yield was 53.79 ± 0.78 g/L in 36 h fermentation. Chain conformation was characterized by Congo red test, β -elimination and circular dichroism (CD), which indicated that the EPS was O-linkage and exhibited random coil structure in aqueous solution. CD results concluded hydrogen-bond interaction and chirality might be connected with concentration. Purified EPS has a higher degradation temperature of 279.42 °C, suggesting high thermal stability of the EPS. The absolute value of zeta potential and particle size were enhanced with increasing concentration. Crude EPS and its purified fraction were found to have moderate DPPH, hydroxyl, superoxide anion radicals scavenging activities and reducing power. This study provided a high yield EPS with unique characteristics for industrial applications. [ABSTRACT FROM AUTHOR]

A novel evaluation assay for molecular beacon (MB)-binding system was developed by microscale thermophoresis (MST) and thymine–mercuric–thymine coordination chemistry which was applied for the detection of mercury (II) ion (Hg 2+ ) upon opening the hairpin and facilitating fluorescence recovery through binding with suitable mismatched target. The affinities between the loop of MBs and the complementary ssDNAs in the binding system were varied, determined and optimized by MST in the presence or absence of Hg 2+ . It suggested that the relative low background could be obtained when the number of mismatches of ssDNA was four and in the present of Hg 2+ displayed strong recovery of fluorescence. The lowest detection limit of Hg 2+ was 3 nM which was below the maximum contaminant level defined by U.S. Environmental Protection Agency (10 nM). The working range was 5–320 nM with negligible possible interference from the different background composition of water samples by optimization of the binding conditions. Through evaluating by MST, the molecular interaction mechanism was elaborated and the rapid, sensitive and selective detection of Hg 2+ was achieved by the designed MB-binding system. It herein has great potential for appraising and analyzing molecular interaction among the interactants. [ABSTRACT FROM AUTHOR]

A higher yield of dextran strain Leuconstoc mesenteroides TDS2-19 was isolated from Chinese sauerkraut juice. Effects of the three main factors on exopolysaccharide (EPS) yield were investigated by central composite design (CCD) and the optimum composition was sucrose 117.48 g/L, sodium acetate 4.10 g/L, and initial pH 6.88. Optimum results showed that EPS yield was increased to 71.23 ± 2.25 g/L in 48 h fermentation, 31.24% higher than before. The molecular weight (Mw) of ESP was 8.79 × 10 7 Da, as determined by high-performance size-exclusion chromatography (HPSEC). Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance spectra (NMR) showed that the polysaccharide synthesized by L. mesenteroides TDS2-19 in the MRS medium was dextran with a peak, a linear backbone composed of consecutive α-(1 → 6)-linked d -glucopyranose units. No branching was observed in the dextran structure. The present study suggested that L. mesenteroides TDS2-19 might be used for the industrial-scale production of linear dextran. [ABSTRACT FROM AUTHOR]

A water-soluble exopolysaccharide (EPS) was produced by Leuconostoc ctireum NM105 from homemade manchurian sauerkraut. After culturing the strain in Man–Rogosa–Sharpe medium containing 5% sucrose at 25 °C for 48 h, the EPS was purified and a yield of 23.5 g/L was achieved. The EPS consisted exclusively of glucose and the weight-average molecular weight was 1.01 × 10 8 Da. The structural characterization of the purified EPS determined by FT-IR, 1 H, 13 C and two-dimensional NMR spectroscopy demonstrated that the glucan contained α-(1 → 6)-linked d -glucopyranose units, 2,6-linked d -glucopyranose units and terminal α- d -glucopyranose units at a ratio of 1:1:1. The microstructure of the dried dextran appeared a sheet-like smooth glittering and highly branched surface. The NM105 dextran showed high water solubility and excellent water retention. All the results suggested that the highly α-(1 → 2) branched dextran might have the potential to serve as valuable polymers applied in foods, cosmetics and other fields. [ABSTRACT FROM AUTHOR]

A novel aptamer-based suspension array detection platform was designed for the sensitive, specific and rapid detection of human α-thrombin as a model. Thrombin was first recognized by a 29-mer biotinylated thrombin-binding aptamer (TBA) in solution. Then 15-mer TBA modified magnetic beads (MBs) captured the former TBA–thrombin to form an aptamer–thrombin–aptamer sandwich complex. The median fluorescence intensity obtained via suspension array technology was positively correlated with the thrombin concentration. The interactions between TBAs and thrombin were analyzed using microscale thermophoresis (MST). The dissociation constants could be respectively achieved to be 44.2 ± 1.36 nM (TBA1–thrombin) and 15.5 ± 0.637 nM (TBA2–thrombin), which demonstrated the high affinities of TBA–thrombin and greatly coincided with previous reports. Interaction conditions such as temperature, reaction time, and coupling protocol were optimized. The dynamic quantitative working range of the aptamer-based suspension array was 18.37–554.31 nM, and the coefficients of determination R2 were greater than 0.9975. The lowest detection limit of thrombin was 5.4 nM. This method was highly specific for thrombin without being affected by other analogs and interfering proteins. The recoveries of thrombin spiked in diluted human serum were in the range 82.6–114.2%. This innovative aptamer-based suspension array detection platform not only exhibits good sensitivity based on MBs facilitating highly efficient separation and amplification, but also suggests high specificity by the selective aptamer binding, thereby suggesting the expansive application prospects in research and clinical fields. [ABSTRACT FROM AUTHOR]

Adhesion is one of the significant virulence factors in enterohemorrhagic Escherichia coli (EHEC) O157:H7 pathogenesis. It is regulated by specific loci in the genome sequence. This study mainly focused on investigating the influence of ycbR gene and its encoded YCBR protein on the adhesion of EHEC O157:H7 to HEp-2 cells. In the first part, mutants of EHEC O157:H7 were constructed through Tn phoA mutagenesis and assayed for adherent ability. Six mutant strains with lost adherence to HEp-2 cells were isolated and then sequenced using a primer that hybridized to phoA sequence downstream of the fusion joint. The sequencing results indicated that the gene of eae and ycbR , between the initiation codon and the −10 sequence of Z4182, yciI , ARAC-type regulator protein, and high-affinity gluconate transporter of EHEC were all possibly related to adhesion. Of the six genes, the ycbR gene was cloned to the pET28a vector to analyze its function further. Recombinant YCBR protein fused to a His tag (YCBR-His) was expressed under IPTG induction and purified by Ni-NTA column. The purified protein was subcutaneously injected to rabbits to prepare antisera. The results of an adherence assay in the presence of anti-YCBR-His antibodies indicated that antibodies blocked the adherence of EHEC O157:H7 to HEp-2 cells. These observations suggested that ycbR encoded a novel adherence-associated determinant of EHEC O157:H7, which could contribute to the adhesive capacity of the bacteria. [ABSTRACT FROM AUTHOR]

This work describes an effective combined ultrafiltration (UF)-nanofiltration (NF) membrane process for the separation and concentration of pediocin PA-1 from fermentation broth. Three polysulfone (PS) membranes with MWCOs of 5, 10, and 30 kDa were tested for ultrafiltration effectiveness. The 10 kDa membrane was selected because it displayed high permeability, good pediocin PA-1 recovery and reduced fouling. When the volume concentration factor (VCF) of UF reached 2.5, continuous diafiltration (DF) was carried out. The optimal diafiltration factor (DFF) was 1. The permeate obtained from UF was then concentrated by NF. When the VCF of NF reached 4.5, pediocin PA-1 recovery loss was only 10.5%. This two-stage membrane process improved the loading solutions by 4.5-fold, allowing up to 71.6% recovery of pediocin PA-1. After the membrane process, the NF retentate could be concentrated and subjected to preparative chromatography to obtain purified pediocin PA-1, or it could be dried to obtain a rich pediocin PA-1 preservative. [ABSTRACT FROM AUTHOR]

Based on a combination of the molecular imprinting technique and polymerized crystalline colloidal array, we have developed an imprinted crystalline colloidal array (ICCA) chemical-sensing material for the real-time and label-free detection of diethylstilbestrol (DES) in aqueous solution. This novel sensing material was prepared by a noncovalent and self-assembly approach using liquid monodispersed DES-imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous nanocavities were derived from DES imprinting. Thus, the inherent high affinity of the nanocavities allowed ICCA to recognize DES with high specificity, and changes of the ordered periodic structure enabled ICCA to transfer the recognition events into readable optical signals (label-free). Owing to the special opal structure and without interference from the bulk hydrogel film, the ICCA enabled the rapid and sensitive detection of the target analyte. The understanding of the recognizing response has also been advanced by using molecular modeling software to compute rational interaction between the template molecules and the function monomers. After careful optimization of the assay conditions, the ICCA could decrease its diffraction intensity within just 7 min according to the DES concentration from 2 ng mL−1 to 8.192 μg mL−1, whereas there were no obvious diffraction intensity changes for the DES analogues. The adsorption results showed that the homogenous structure and large surface area of ICCA could improve its adsorption capacity. Therefore, such a sensing material with high selectivity, high sensitivity, high stability, and easy operation might offer an attractive alternative for establishing optical sensors for the rapid real-time monitoring of different residues in food and the environment. [ABSTRACT FROM AUTHOR]

A new erythritol-producing yeast (strain BH010) was isolated in this study. Analysis of the D1/D2 domain of the 26S rDNA sequence, the ITS/5.8S rDNA sequence, and the 18S rDNA sequence allowed the taxonomic position of strain BH010 to be discussed and it was identified and named Moniliella sp. BH010. Physiological characteristics were described. Scanning electron micrography clearly indicated that the cells were cylindrical to elliptical with an average size of 5 × 10 μm when growing in liquid medium, and that pseudohyphae and blastoconidia were observed when cultivated in agar plates. The erythritol reductase genes were cloned, sequenced, and analyzed. BLAST analysis and multiple sequence alignment demonstrated that erythritol reductase genes of Moniliella sp. BH010 shared very high homology with that of Trichosporonoides megachiliensis SNG-42 except for the presence of introns. The deduced amino acid sequences showed high homology to the aldo-keto reductase superfamily. [ABSTRACT FROM AUTHOR]

Abstract: A novel enzyme liked immunosorbent assay (ELISA) was developed for the detection of chloramphenicol (CAP). In this assay, the small molecular hapten (Hap) was directly coated on the surface of microtiter plates and biotin–streptavidin system (BSAS) was employed to improve the sensitivity of immunoassay (BSAS-direct Hap coated ELISA). The surface of microtiter plates was treated with glutaraldehyde (GA) polymer network to introduce aldehyde group, which was used to cross-link with amino group of CAP. Compared with conventional ELISA (the plates were coated with Hap–carrier protein conjugates), the modified plates presented significantly high antibody and antigen (Ab–Ag) affinity and showed excellent stability. And then the biotinylated monoclonal antibody (mAb) and HRP-labeled streptavidin were employed in this assay for amplification of signals. The sensitivity of BSAS-direct Hap coated ELISA was increased by approximately 20-folds and the stability was also improved greatly compared to conventional ELISA. Its 50% inhibition concentration (IC50) for CAP was 10.5ngmL−1 and the limit of detection (LOD) was 0.2ngmL−1 after optimization of reaction conditions. To our knowledge, this was one of the most sensitive immunoassay for CAP yet reported. In sample analysis, the results of CAP detected by this assay were in accordance with which obtained by conventional ELISA and high performance liquid chromatography (HPLC). Therefore, it is an attractive alternative compared to conventional immunoassays in routine supervision for residue detection in food and environment. [ABSTRACT FROM AUTHOR]

• The potential nitrogen metabolic pathways in the suancai fermentation were inferred. • Nitrite removal involved reduction of nitrite to ammonia and denitrification. • This study offers new insights for characterization and safety assessment of suancai. Chinese northeast suancai represents a typical and valuable food product that has been handed down by traditional household procedures over centuries. Nitrite is formed and accumulated during the suancai fermentation process and commonly causes food safety problems. The biogeochemical cycle of nitrite may provide a reference and guidance for the enzymatic degradation of nitrite in fermented food. The potential nitrogen metabolic pathways in the microbially driven suancai fermentation were reasonably inferred through monitoring nitrogen conversions and detecting the genes of different functional enzymes. Complex microbial metabolism is responsible for the unique nitrogen conversions during suancai fermentation. The metagenomic results showed that Pseudomonas with nitrate reductase genes (narG , narH , narI) and nitrite reductase genes (nirB , nirD) contributed the most to both nitrite reduction and nitrate reduction. The majority of the sequences of nitrate reductase and nitrite reductase were derived from the families of Pseudomonadaceae , Erwiniaceae and Yersiniaceae. According to the physicochemical analysis, the nitrite concentration of the fermentation broth reached the peak value (0.48 mM) and gradually decreased to the minimum (0.02 mM). The downward trend of the pH and nitrite concentration were closely associated with the nitrite enzymatic degradation period before the acid degradation period. Our results indicated that nitrite removal in suancai fermentation involved the reduction of nitrite to ammonia and denitrification, which were mainly contributed by the reduction of nitrite to ammonia mediated by the nirB/nirD enzyme (Indentified ECs: 1.7.1.15). This research offers new insights into the metagenome-based bioinformatic roles of the previously unstudied microorganisms in spontaneous suancai fermentation for the enzymatic degradation of nitrite. It provides helpful basis for the detection and even elimination of nitrite in suancai and for improving the safety level of suancai. [ABSTRACT FROM AUTHOR]

• Heterologous expression of two nitrite reductase subunits from Acidovorax wautersii. • Enzymatic activity range of temperature (20−60 °C) and pH (5.0–9.0). • Molecular dynamics simulations indicate specific amino residues of subunits. • Nitrite ion interacts with active site of enzyme by forming ligand hydrogen bonds. Large accumulation of nitrate in soil has resulted in soil salinization. Nitrate and nitrite reduction are of great importance for nitrogen assimilation, and understanding the specific roles of each participating reductase is necessary to describe the biochemical balance that dictates the bacteria responses to their environments. The genes encoding assimilatory nitrite reductase from Acidovorax wautersii QZ-4 were cloned and over-expressed in Escherichia coli. The molecular mass of over-expressed nitrite reductase was 91.75 kDa and 12.40 kDa for large subunit NirB and small subunit NirD, respectively. The purified recombinant enzyme showed broad activity range of temperature (20−60 °C) and pH (5.0–9.0). The optimum electron donor was MV + Na 2 S 2 O 4 , and NADH can be used as physiological electron donor. It was found that two important amino residues in NirD, Arg 90 and Arg 24 are critical for interaction with NirB, meanwhile, two amino residues of NirB such as Arg 257 and Asp 333 are found to be critical to interact with NirD. The nitrite ion was responsible for the unique interaction with the active site of NirB with the ligand quintuple hydrogen bonds with Arg 44 and Arg 128. These findings constitute a solid basis for valuable application of nitrite reduction in polluted environment, and give a reasonable explanation for the modes of action between enzyme from A. wautersii QZ-4 and nitrite ion. [ABSTRACT FROM AUTHOR]

• Heterologous biosynthesis of Oleanolic acid in Y. lipolytia was achieved. • The limitation of incomplete transformation of β-amyrin was solved by using omics tools. • Production titer was increased by P450 fusion and MVA pathway gene overexpression. Oleanolic acid (OA) is a pentacyclic triterpenoid known for its biological properties such as antioxidation activity. Herein, we developed an efficient biosynthetic pathway for OA production in Yarrowia lipolytica. The engineered strain, YL-OA0, produced 16.3 mg/L of OA, and the production efficiency was further increased by 5.65-fold to 92.1 mg/L following overexpression of the key genes involved in the mevalonate (MVA) pathway. Transcriptomic and metabolomic analyses demonstrated the increase in the percentage of unsaturated fatty acids. The electron transfer of the strain YL-OA7 was restricted. Therefore, we fused the gene encoding cytochrome P450 (CYP716A12) to that encoding NADPH-P450 reductase; this resulted in an increase in the OA yield to 129.9 mg/L in the strain YL-fuOA1. The strain YL-fuOA1 could produce 540.7 mg/L OA in fed-batch fermentation in a 5 L fermenter. This study shows the feasibility of the production of high value triterpenoid compounds using Y. lipolytica as a platform. [ABSTRACT FROM AUTHOR]

• Bacterial cellulose-chitooligosaccharide composites were prepared by immersion. • SEM, FT-IR and TGA demonstrated the incorporation of chitooligosaccharide. • Bacterial cellulose-chitooligosaccharide performed good antibacterial properties. • Composites modified with chitosan and chitooligosaccharide were compared. To synthesize biomaterials for antibacterial applications, chitosan (CS) and chitooligosaccharide (COS) were successfully incorporated into bacterial cellulose (BC) matrix respectively. The representative Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) were selected to evaluate the antibacterial effects of the composite membranes. The results manifested BC-CS and BC-COS membranes exhibited remarkable antibacterial properties against both bacteria with the inhibition ratio of 99.99 ± 0.01% (S. aureus) and 99.99 ± 0.01% (E. coli) for BC-CS, 99.64 ± 0.18% (S. aureus) and 90.56 ± 0.06% (E. coli) for BC-COS. The morphology obtained by scanning electron microscopy (SEM) showed BC-CS and BC-COS composite membranes possessed lower porosity and denser structure in comparison to pure BC. Moreover, in contrast with BC-CS, BC-COS performed better mechanical properties and also displayed stronger ABTS radical scavenging capacity of 92.62 ± 2.85%. These results suggested that the development of BC-COS composite membrane would open up the possibility for the antibacterial applications in food and medical fields. [ABSTRACT FROM AUTHOR]

• The EPS produced by Lac. sakei L3 was a consecutive α-(1→6)-linked dextran. • The dextran showed a branched and porous morphology. • The dextran possessed high viscosity under specific conditions and heat tolerance. • The dextran could coagulate sucrose-supplemented milk. • The dextran has potential applications in food processing. An exopolysaccharide (EPS)-producing bacterial strain L3 was isolated from Hubei sausage and identified as Lactobacillus sakei via morphological, physiological, biochemical and 16S rDNA analysis. FT-IR spectroscopy and NMR revealed that L3 EPS was a dextran containing d -glucose residues with α-1,6 glycosidic linkage. Rheological studies showed that it had high viscosity at high concentration, low temperature, and acidic pH (pH 3.0). Scanning electron microscopy of the L3 dextran demonstrated a porous and branched morphology, and atomic force microscopy showed lumps of varying height on the rough surface of the L3 EPS polymer. The EPS was thermally stable up to 272°C and could coagulate sucrose-supplemented milk. Together, these results suggested that L3 EPS might have potential applications in food processing and other areas. [ABSTRACT FROM AUTHOR]