Renpeng Du

Optimization, purification and structural characterization of a dextran produced by L. mesenteroides isolated from Chinese sauerkraut

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 117.48g/L, sodium acetate 4.10g/L, and initial pH 6.88. Optimum results showed that EPS yield was increased to 71.23±2.25g/L in 48h fermentation, 31.24% higher than before. The molecular weight (Mw) of ESP was 8.79×107Da, 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.

Characterization of a dextran produced by Leuconostoc pseudomesenteroides XG5 from homemade wine

A water-souble exopolysaccharide (EPS) produced by Leuconostoc pseudomesenteroides XG5 from homemade wine was investigated. The EPS yield of 35.5g/L was achieved at 30°C for 48h in De Man-Rogosa-Sharpe (MRS) medium containing 12.5% sucrose. The EPS was a dextran composed exclusively of glucose and the molecular weight was 2.6×106Da. Fourier transform infrared spectra and nuclear magnetic resonance spectra revealed that the EPS was a dextran containing D-glucose residues in a linear chain with consecutive α-(1→6) linkages. Scanning electron microscopy of the EPS appeared a highly branched and porous structure. Rheological studies showed that the EPS had higher viscosity in 0.1M KCl solution, at lower temperature, or at acidic pH. Thermal gravimetric analysis and differential scanning calorimetric indicated that the EPS had excellent thermal stability with a degradation temperature of 313.80°C and melting point at 274.14°C. Water solubility index and water holding capacity of XG5 dextran were 90.2% and 412% respectively. The results suggest that L. pseudomesenteroides XG5 might be widely used in the production of linear dextran which has potential to serve as natural agent applied in food and other fields.

Production and characterization of bacterial cellulose produced by Gluconacetobacter xylinus isolated from Chinese persimmon vinegar

This study aimed to characterize the structural and physico-mechanical properties of bacterial cellulose (BC) produced by Gluconoacetobacter xylinus TJU-S8 which was isolated from Chinese persimmon vinegar. Thermogravimetric analysis (TGA) showed that BC exhibited a good thermal stability. Solid-state nuclear magnetic resonance (NMR), fourier transform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) analysis revealed that BC had a typical crystalline form of the cellulose I. The BC membrane had typical characteristics such as nanodimensional network and microfibrils obtained by scanning electron microscopy (SEM). Moreover, the bacterial cellulose chitosan (BC-C) membrane and bacterial cellulose carboxymethyl chitosan (BC-CC) membrane were synthesized which showed significant inhibition against the growth of both Escherichia coli and Staphylococcus aureus. These results indicated superior properties of BC that advocated its effectiveness for various applications.

Optimization, chain conformation and characterization of exopolysaccharide isolated from Leuconostoc mesenteroides DRP105

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 86.83g/L, tryptone 15.47g/L, initial pH7.18 and maximum yield was 53.79±0.78g/L in 36h 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.

Isolation, purification and characterization of exopolysaccharide produced by Leuconostoc pseudomesenteroides YF32 from soybean paste

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 48h, the EPS was purified, and a yield of 12.5g/L was achieved. The weight-average molecular weight (Mw) was 5.54×106Da 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), 1H, 13C 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.

Characterization of highly branched dextran produced by Leuconostoc citreum B-2 from pineapple fermented product

A strain Leuconostoc citreum B-2 was isolated from homemade fermentation product of pineapple and its polysaccharide yield was 28.3g/L after cultivating the strain in Man-Rogosa-Sharpe (MRS) medium with 75g/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 3.77×106Da. 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.

Optimization and purification of glucansucrase produced by Leuconostoc mesenteroides DRP2-19 isolated from Chinese Sauerkraut

Abstract 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.

Optimization and partial characterization of ca-independent α-amylase from Bacillus amyloliquefaciens BH1

Abstract 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.

Purification and characterization of novel thermostable and Ca-independent α -amylase produced by Bacillus amyloliquefaciens BH072

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 Km and Vmax 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 Ca2+ 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.