Shujuan Chen

Production, purification and structural study of an exopolysaccharide from Lactobacillus plantarum BC-25.

The exopolysaccharides (EPS) produced by Se-enriched Lactobacillus plantarum BC-25 was purified to illustrate its structure and conformational characterization. The yield of EPS (324.80mg/l) was obtained with a sodium selenite concentration of 6μg/ml. The results indicated that the EPS was soluble in water, but insoluble in organic solvents. The molecular weight of this highly thermal stability EPS was 1.83×10(4)Da and 1.33×10(4)Da with or without Se enriched respectively. The EPS was composed of mannose, galactose and glucose in a molar ratio of 92.21:1.79:6.00 and 91.36:2.44:6.20 with or without Se. This compound had a backbone of (1→2)-linked Man, (1→2.6)-linked Glc, (2→6)-linked Man, and (2→6)-linkedGal confirmed by GC-MS. IR analysis suggested that the EPS belonged to heteropolysaccharide with a pyran group, with possible presence of SeO and CSeC residues that Se may substitutes CH3 in -OCH3 in the polysaccharide as confirmed by NMR spectroscopy.

The characterization, selenylation and antidiabetic activity of mycelial polysaccharides from Catathelasma ventricosum

The mycelial polysaccharide from Catathelasma ventricosum (mCVP-1S) was found to be a heteropolysaccharide with an average size of 230kDa composed mainly of β-glucopyranosyl residues. The selenylation of mCVP-1S, performed using an HNO3-Na2SeO3 method, produced a series of selenized mCVP-1Ss (SemCVP-1Ss). Varying the reaction time, temperature and Na2SeO3 dosage altered the yield and selenium content of the SemCVP-1Ss. NMR spectra showed substitution mostly at C-6, and Congo red tests indicated excessive selenylation might destroy the triple-helical structure of SemCVP-1Ss. The antidiabetic activities of SemCVP-1Ss with varying selenium contents (low, middle and high) were tested in streptozotocin-induced diabetic mice. In SemCVP-1Ss with triple-helical structure, increasing selenium content enhanced antidiabetic activity, but damage to the triple-helical structure weakened antidiabetic activity. The ability of SemCVP-1Ss to normalize key biochemical parameters in diabetic mice was greater than that of the polysaccharide from the fruiting body of C. ventricosum.

Structural characterization and antidiabetic activity of a glucopyranose-rich heteropolysaccharide from Catathelasma ventricosum.

Polysaccharides, which are the main bioactive constituents of edible mushrooms, have been shown to have a variety of useful biological activities. In this study, a polysaccharide fraction from the edible mushroom Catathelasma ventricosum was purified using anion exchange and size exclusion chromatographies. The structure of the resulting polysaccharide, named CVP-1S, was characterized on the basis of partial acid hydrolysis, periodic acid oxidation, methylation analysis, gas chromatography-mass spectrometry, Fourier-transform infrared spectroscopy, 1D/2D NMR spectroscopy, scanning electron microscopy, and atomic force spectroscopy. The results showed that CVP-1S is a heteropolysaccharide consisting of glucose (94.2%), galactose (3.51%) and fucose (1.3%) with a molecular weight of 1.5×10(4)Da. Its backbone is mainly linked by (1→6)-β-d-Glcp glycosidic bonds, and branches are attached to the backbone through 1,3-linked glycosidic bonds. CVP-1S was also found to have antioxidant, hypoglycemic, and hypolipidemic activities in the streptozoicin-induced diabetic mouse model. From these results, we conclude that CVP-1S should receive further attention as a potential agent for the treatment and prevention of diabetes.

Use of Psychrotolerant Lactic Acid Bacteria (Lactobacillus spp. and Leuconostoc spp.) Isolated from Chinese Traditional Paocai for the Quality Improvement of Paocai Products

To improve the quality of Chinese traditional Paocai, two psychrotolerant lactic acid bacteria (LAB) strains were isolated from Paocai, and the quality of Chinese Paocai product using these two strains as starter cultures was compared to a control sample fermented with aged brine at 10 °C. The results suggested that the physicochemical and sensory features of Paocai fermented with psychrotolerant LAB were more suitable for industrial applications. The nitrite content of Paocai fermented with psychrotolerant LAB was 1 mg/kg, which was significantly lower than that of the control Paocai (P < 0.05). Low-temperature fermentation with the starter cultures of psychrotolerant LAB could effectively prevent overacidity and over-ripening of the Paocai products. Additionally, Paocai fermented with psychrotolerant LAB harbored relatively simple microbial flora as revealed by polymerase chain reaction-denaturing gradient gel electrophoresis. This study provides a basis for improving the quality of Chinese traditional Paocai and the large-scale production of low-temperature Chinese traditional Paocai products.

Antimicrobial resistance and resistance genes in Salmonella strains isolated from broiler chickens along the slaughtering process in China

A total of 189 Salmonella isolates were recovered from 627 samples which were collected from cecal contents of broilers, chicken carcasses, chicken meat after cutting step and frozen broiler chicken products along the slaughtering process at a slaughterhouse in Sichuan province of China. The Salmonella isolates were subjected to antimicrobial susceptibility testing to 10 categories of antimicrobial agents using the Kirby-Bauer disk diffusion method. Those antibiotics-resistant isolates were further investigated for the occurrence of resistance genes, the presence of class 1 integron as well as the associated gene cassettes, and the mutations within the gyrA and parC genes. Consequently, the prevalence of Salmonella was 30.14% (47.96% for cecal content, 18.78% for chicken carcasses, 31.33% for cutting meat and 14.00% for frozen meat, respectively). The predominant serotypes were S. Typhimurium (15.34%) and S. Enteritidis (69.84%). High resistance rates to the following drugs were observed: nalidixic acid (99.5%), ampicillin (87.8%), tetracycline (51.9%), ciprofloxacin (48.7%), trimethoprim/sulfamethoxazole (48.1%), and spectinomycin (34.4%). Antimicrobial resistance profiling showed that 60.8% of isolates were multidrug resistant (MDR), and MDR strains increased from 44.7% to 78.6% along the slaughtering line. 94.6% (n=157) of beta-lactam-resistant isolates harbored at least one resistance gene of blaTEM or blaCTX-M. The relatively low prevalence of aminoglycoside resistance genes (aac(3)-II, aac(3)-IV, and ant(2″)-I) was found in 49 (66.2%) of antibiotic-resistant isolates. The tetracycline resistance genes (tet(A), tet(B), tet(C), and tet(G) and sulfonamide resistance genes (sul1, sul2, and sul3) were identified in 84 (85.7%) and 89 (97.8%) antibiotic-resistant isolates respectively. floR was identified in 44 (97.8%) florfenicol-resistant isolates. Class 1 integron was detected in 37.4% (n=43) of the MDR isolates. Two different gene cassettes, blaOXA-30-aadA1 (19 isolates) and blaOXA-30-aadA1/drfA1-orfC (2 isolates), were identified in class 1 integron-positive isolates. 97.9% (184/188) of quinolone-resistant isolates had at least one mutation within gyrA or parC. Overall, antimicrobial resistance showed an increasing trend along the slaughtering process. The results showed that broiler chicken products in the slaughterhouse were contaminated with MDR Salmonella, which might originate from food producing animals to some extent, and cross-contamination during slaughter, and facilitate the dissemination of the resistance genes to consumers along the production chain, which suggests importance of controlling Salmonella during slaughter for public health, underlying strict hygiene method and HACCP management to reduce cross-contamination.

Effect of oxidized lipids stored under different temperatures on muscle protein oxidation in Sichuan-style sausages during ripening

This study was conceived to research muscle protein oxidation under the influence of four different degrees of oxidized lipids during the ripening of Sichuan-style sausages. Lipids were stored at different temperatures to obtain different oxidation degrees. To elucidate the relationship between lipid oxidation and protein oxidation, the indicators of lipid oxidation, protein oxidation and protein degradation were analysed. During ripening, the carbonyl, SH, SS and free amino acid contents changed significantly. The carbonyl and SS contents increased first in all samples, then decreased, whereas the SH content showed the opposite results. These results showed a positive correlation between protein oxidation and lipid oxidation. Lipids with a higher oxidation degree induced a stronger oxidation reaction to protein. Meanwhile, the results of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the influence of lipid oxidation on myofibrillar proteins was much more intense than on sarcoplasmic proteins.

Exopolysaccharides produced by yogurt-texture improving Lactobacillus plantarum RS20D and the immunoregulatory activity

The strain RS20D capable of significantly improving yogurt texture was isolated from traditional fermented vegetable products, and identified as Lactobacillus plantarum RS20D. The total exopolysaccharides (EPS) were prepared from reconstituted skim milk fermentation by RS20D, and purified through DEAE-Sepharose CL-6B and Sephadex G-100, and consequently the purified fraction designated as RS-r2 was obtained. The further work aimed to elucidate the structural features of RS-r2 via FT-IR spectrum, HPSEC and monosaccharide composition analysis was carried out. The results showed that RS-r2 was a novel acidic heteropolysaccharide mainly consisted of glucose, galactose and glucosamine in a molar ratio of 2.0:1.5:1. The molecular weight was estimated to be 1.69 × 106 Da. The EPS had a high degradation temperature (250 °C), suggesting its high thermal stability. SEM and AFM analysis of EPS further revealed chain microstructure anchored with many regular spherical shape in aqueous solution. In vitro test showed that total EPS secreted by RS20D could stimulate macrophage RAW264.7 to release NO significantly and up-regulated the gene expression of pro-inflammatory cytokines at the mRNA level. Current study suggested that RS20D could be a potential source of immunoregulatory polysaccharide and may be applied as a functional starter culture to improve yogurt texture in the dairy industry.

Preparation of magnetic molecularly imprinted polymers with double functional monomers for the extraction and detection of chloramphenicol in food

In this study, an efficient, selective, and simple analytical method for the extraction of chloramphenicol (CAP) from food using magnetic molecularly imprinted polymers (MMIPs) as the solid-phase extraction (SPE) sorbent was successfully developed. MMIPs with varying ratios of methacrylic acid to acrylamide were prepared by suspension polymerization on the surface of double-bond-modified Fe3O4 magnetic nanoparticles. Further, these MMIPs were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, as well as using a vibrating sample magnetometer. Furthermore, the adsorption capacities of MMIPs and MNIPs were investigated by binding experiments. Methodology evaluation for the detection of CAP from food was carried out using MMIPs as the SPE sorbent. By using an external magnetic field, MMIPs were separated by a simple and rapid method. The diameter of the so-obtained MMIPs, exhibiting good monodispersity, was 400-700 nm. The MMIPs exhibited the maximum apparent adsorption capacity of up to 42.60 mg g-1 with good selectivity. For the detection of food samples, the linear response range was 0.02-10.00 mg L-1, with a detection limit of 10 μg L-1, and intra- and inter-day stabilities ranged from 1.34% to 1.89% and from 1.76% to 2.77%, respectively, with good recoveries (95.31%-106.89%) and satisfactory relative standard deviations (1.21%-2.60%).

Purification, characterization and antioxidant activity of the exopolysaccharide from Weissella cibaria SJ14 isolated from Sichuan paocai

In the present study, an exopolysaccharide (EPS)-producing strain SJ14 isolated from Sichuan paocai was identified as Weissella cibaria, with a typical ropy phenotype. W. cibaria SJ14 possessed good capabilities of acid production, salt tolerance, and nitrite depletion. The crude polysaccharides were obtained from the culture supernatant of strain SJ14 and further fractionated by DEAE-Sepharose Fast Flow ion-exchange and Sephadex G-100 size-exclusion chromatography. Consequently, two acidic EPS fractions (EPS-1 and EPS-3) were obtained with the average molecular weights of 7.12 × 104 and 3.01 × 104 Da, respectively. They were heteropolysaccharides, among which EPS-1 were rich in mannose, and composed of mannose, glucose, galactose, arabinose, xylose, and rhamnose in a molar ratio of 23.79: 4.80: 1.66: 1.00: 0.21: 0.09, whereas EPS-3 consisted of galactose, mannose, glucose, and arabinose in a molar ratio of 7.47: 3.69: 1.00: 0.85 were rich in galactose. Two EPS fractions also exhibited potential antioxidant properties in vitro, showing strong scavenging activities on three kinds of free radicals and reducing power, and the antioxidant activities of EPS-1 were significantly stronger than that of EPS-3.

Label-free and enzyme-free sensitive fluorescent method for detection of viable Escherichia coli O157:H7

We have developed a label-free, enzyme-free, modification-free and DNA extraction-free fluorescent aptasensing (LEFA) method for detection of E. coli O157:H7 based on G-quadruplex formation using two ingeniously designed hairpin probes (GHP1 and GHP2). In the presence of E. coli O157:H7, it released the single stranded initiation sequence (IS) resulting in the toehold strand displacement between GHP1 and GHP2, which in turn led to the cyclic reuse of the production of DNA assemblies with numerous G-quadruplex structures and initiation sequences. Then these G-quadruplex structures can be recognized quickly by N-methyl mesoporphyrin IX (NMM) resulting in significantly enhanced fluorescence. The LEFA method was successfully implemented for detecting E. coli O157:H7 with a detection limit of 66 CFU/mL in pure culture, 10 CFU/mL and 1 CFU/mL after pre-incubation of the milk and tap water for 4 and 8 h, respectively. Moreover, the strategy could distinguish viable E. coli O157:H7 from dead E. coli O157:H7 and other species of pathogen cells. Furthermore, the whole process of the strategy is accomplished within 100 min. The results indicated that the approach may be used to effectively control potential microbial hazards in human health, food safety, and animal husbandry.