The values of gel hardness and storage modulus G ＇ of compound gelatin-myofibrillar protein gels formed in the attendance of different reagents were measured in order to understand the forces involved in the gel formation. It was found that adding urea distinctly decreased gel hardness. This suggests that hydrogen bond is the most important force responsible for gel formation and maintenance at low temperatures. Gel hardness could be changed by adjusting pH or by separately adding DTT, potassium bromate or SDS, indicating all electrostatic force, disulfide bond and hydrophobic interaction make a contribution to gel formation and maintenance. Increasing pH during heating treatment resulted in a lower G＇ value. Additions of DTT, SDS and urea were all able to decrease G＇value, and the most obvious decrease was observed when SDS was added. Therefore, it can be concluded that hydrophobic interaction plays the most vital role in the heat-induced gel formation between gelatin and myofibrillar.
The extract extracted from grape residue left after making wine with 70% ethanol under the assistance of ultrasonic was tested for its total phenolic content and in vitro antioxidant and antimicrobial activities in the present study. Total phenolic quantification was performed using Folin-Ciocalteu reagent. FRAP assay was used for the assessment of total antioxidant capacity, and the abilities to scavenge DPPH, superoxide anion, hydroxyl and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS) radical free radicals and to inhibit β-carotene/linoleic acid system were also measured. The inhibitory effects against five tested strains including Gram positive and negative strains were evaluated. It was found that the extract contained 106.4 mg/g total phenolic content, and had a FRAP value of (3.215 ± 0.017) mmol/g and IC50 values of 20.5, 52.5, 566.4 mg/L and 16.8 mg/L for DPPH, superoxide anion, hydroxyl and ABTS free radicals, respectively. The IC50 value of the extract forβ-carotene/linoleic acid system was 28.2 mg/L. It presented the best inhibitory effect against Staphylococcus aureus, with a minimum inhibitory concentration (MIC) of 900 μg/L, followed by Bacillus subtilis, Bacillus cereus, Escherichia coli and Aspergillus flavus. To sum up, the extract has excellent antioxidant performance, and its inhibitory effect against Gram positive strains is higher than that against Gram negative strains, but its anti-fungus effect is relatively weaker.
The mercury exposure in milled rice has become a hotspot in risk assessment. Considering the positively skewed contamination data, an economic and effective assessment must be based on an appropriate sample size. With the benefit of computer simulation, this paper set out to study the relationship between sample size and percentile estimate with Weibull distribution, which was used to fit the mercury contamination data. The simulation results showed that accurately estimating a higher percentile of positively skewed distribution, specially the one on the right side of peak, would require a larger sample size. And a larger sample size always resulted in a more accurate and more stable estimated percentile. As sample size increased to exceed 400, 700 and 1500, estimates of P95, P97.5 and P99 could obtain guaranteed accuracy and precision respectively, while a sample size of 1500 could only satisfy the accuracy but not precision of P99.9 estimates. Furthermore, insufficient samples would always lead to an underestimate of high percentile, and then lead to an underestimate of risk. When it comes to risk assessment of mercury exposure in milled rice, the in-depth study of sample size promises not only a possibility of an accurate result, but also an economical resource allocation.
Objective: The inhibitory effects of twenty-three food preservatives on three typical spoilage bacteria were evaluated and compared. Methods: The minimal inhibitory concentrations (MIC) of different preservatives for Micrococcus luteus, Bacillus subtilis and E.coli were determined by micro-dilution assay. Results: Among the 23 tested food preservatives, Nisin and ε-poly-L-lysine had the best inhibitory effect on Micrococcus luteus (G+ cocci), and their MICs were both 12.5 μg/mL. For Bacillus subtilis (G+ bacillus), the best antimicrobials were calcium propionate, diacetyl, citric acid, citral and D-sodium isoascorbiate, presenting an identical MIC of 6.25μg/mL. As for E.coli (G－ bacillus), hydrogen peroxide and diacetyl were the best preservatives, with an identical MIC of 25μg/mL. Conclusion: The bacteriostasis of various tested preservatives for the three typical spoilage bacteria is irregular and their combined use seems to be an approach for more effective bacteriostasis.
The crude polysaccharide (MCP) extracted from the fruits of Momordica charantial was subjected to DEAE-cellulose column chromatographic separation and Sephadex G-100 column chromatographic fractionation and a polysaccharide fraction with a high ability to scavenge superoxide anion and hydroxyl free radicals, named MCP Ia, was obtained. According to UV spectroscopic analysis and cellulose acetate membrane electrophoresis, MCP Ia was a single composition. Its monosaccharide composition was determined by HPLC to consist of L-rhamnose, D-xylose, D-fructose and D-galactose, in a molar ratio of 4.4:2.3:1:5.7, with the possibility of containing glucose. The IR spectral analysis showed that there were intramolecular hydrogen bond and intermolecular hydrogen bond in MCP Ia. In addition, the existences of stretching vibration of the carbon-hydrogen and deformation vibration of hydroxyl group and characteristic absorption of ribofuranoside were also demonstrated. Therefore, MCP Ia is a typical polysaccharide.
Walnut protein was hydrolyzed with neutral protease to eight different degrees of hydrolysis (DHs), and the hydrolysates obtained were comparatively characterized for their solubility, emulsifying properties, foaming properties, surface hydrophobicity and nitrogen recovery. All eight walnut protein hydrolysates presented a much higher solubility than walnut protein, reaching higher than 85%. The hydrolysate with 9.29% DH had the strongest emulsifying capacity and foaming capacity. Increasing DH resulted in a lower surface hydrophobicity but a higher nitrogen recovery, reaching 88.42% at a DH of 11.76%.
The crude ethanol extract from the leaves of Eucommia ulmoides was applied to XDA-8 type macroporous resin, followed by gradient elution with different concentrations (20%, 40%, 60% and 80%) of ethanol, and four fractions were obtained. The abilities of the four fractions to scavenge hydroxyl, superoxide anion and DPPH free radicals were measured. Meanwhile, the contents of polyphenols and total flavonoids in them were determined. It was found that all the four fractions had excellent scavenging effect on hydroxyl, superoxide anion and DPPH free radicals in a dose-dependent way. This biological activity might be related to total flavonoids and polyphenols, and polyphenols play a leading role. After eluting XDA-8 type macroporous resin with different concentrations of ethanol, eluates were obtained as antioxidants with different chemical composition.
A crude globulin extract from naked oat seeds was prepared by Osborne method and purified by salting-out and Sephadex G-100 gel filtration chromatography, and the crude extract was separated into two fractions (I and II). The crude globulin extract, its salting-out purification product and fractions I and II were subjected to SDS-PAGE analysis and antioxidant activity evaluation. Oat seed globulins exhibited 60% degree of saturation with ammonium sulphate. The molecular weight distribution of fraction I consisted of 44, 34 － 29kD and25 kD, and that of fraction I was 25, 23, 19 kD. Among the four materials, fraction I had the strongest scavenging effect on hydroxyl, superoxide anion and DPPH free radicals, with IC50 values of 3.73, 0.016 mg/mL and 1.033 mg/mL, respectively, and its hydroxyl free radical scavenging effect was higher than that of VC. However, the free radical scavenging effect of fraction II was lower than those of all three other materials.
The static adsorption behavior of Zn2+ on β-cyclodextrin polymer (β-CDP) microspheres prepared by crosslinking of β-cyclodextrin with epichlorohydrin and subsequent reversed-phase emulsion polymerization was investigated, and the isothermal adsorption curves and the adsorption thermodynamics and kinetics characteristics were measured at different temperatures. Meanwhile, structural changes in β-CDP microspheres before and after Zn2+ adsorption were examined through FT-IR spectroscopic and X-ray diffraction (XRD) observations and thermogravimetric analysis (TGA), and the adsorption mechanism was also discussed. The results showed that the adsorption of Zn2+ on β-CDP microspheres complied with both Langmuir and Freundlich isotherm adsorption equations. The enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG) for Zn2+ adsorbed by β-CDP microspheres at different temperatures were all negative, meaning that the adsorption of Zn2+ on β-CDP microspheres is a spontaneous and exothermic process. β-CDP microspheres adsorbed Zn2+ mainly through physical adsorption, coordination adsorption, and so on, which could enhance the thermostability of crosslinked chains and damage the crystal structure of β-CDP microspheres.
Objective: To provide a scientific basis for pear-jujube production with both high fruit yield and quality under watersaving irrigation. Method: The fruits of seven to eight year old dwarfing close planting pear-jujube trees receiving three drip irrigation regimes (assigned into the experimental groups), which were different in irrigation amount and frequency, or receiving no irrigation treatment (assigned into the control group) were measured for the content of total phenolics, total flavonoids and vitamin C, phenolic composition, and the antioxidant properties including the abilities to inhibit lipid peroxidation and scavenge DPPH and ABTS free radicals and reducing power. Results: Under the drip irrigation regimes designed in our study, irrigation amount and frequency had no significant effect on total phenolic content. But the contents of total flavonoids, vitamin C, and the three main compounds of flavonoids in pear-jujube fruits, catechin, epicatechin and rutin, were all significantly affected by different drip irrigation regimes. The four models of antioxidant capacity all showed significant discrepancies (P < 0.05) among different regimes, which were significantly correlated with total flavonoids content, but neither antioxidant capacity and total flavonoids content linearly increased with increasing irrigation amount and frequency. Conclusion: Irrigation with appropriate amount and frequency is an important guarantee for the high-fruit-yield and water-saving production of high-quality jujube.
Physico-chemical parameters, sensory evaluation, textural characteristics, microstructural characteristics and color of three kinds of commercial chicken ham sausages were studied in this study. The results showed that the three kinds of chicken sausages were significantly different in hardness, gumminess, chewiness, lightness and whiteness, while no significant difference observed in springiness and cohesiveness. For each of them, the values of harness, gumminess and chewiness were decreased sequentially. Chicken ham sausages A and B exhibited comparatively better physichemical parameters. Sausage A was the best in aroma; the sausage with the best mouthfeeling, microstructure and color was sausage B; and the tenderness of sausage C was the best. Considering collectively, sausage B has the best comprehensive quality.
The objective of this study was to evaluate the effect of sugar chain structure in baicalin on its antioxidant activity and further explore its structure-antioxidant activity relationship. Partial 6-carboxy groups on the sugar chains in baicalin were selectively esterified by chemical synthesis. Baicalin and its derivatives were structurally characterized by means of TLC and 13C NMR techniques, and their antioxidant activities were measured on a Photochem antioxidant analyzer. The derivatives synthesized through selective esterification were identified to be ethyl ester (2), n-butyl ester (3) and benzyl-ester (4). Baicalin had higher antioxidant activity than them, indicating that 6-carboxy group is essential for the antioxidant activity of baicalin.
Soy bean isolate (SPI) was subjected to irradiation treatment for physical modification in the present study. Changes in water and oil binding capacity and emulsifying properties were measured before and after irradiation treatment. Meanwhile, Statistical correlations between water and oil binding capacity and emulsifying properties were analyzed. No obvious change inwater binding capacity was observed after irradiation treatment. Irradiation treatment at a dose of 4 kGy resulted in the lowest oil binding capacity and the highest emulsifying capacity. Moreover, the emulsifying capacity and emulsion stability of SPI could be both increased by decreasing oil binding capacity and increasing irradiation dose.
In this study, the molecular weight distribution and monosaccharide composition of polysaccharides from the pileus, stipe and spore of Ganoderma atrum were analyzed by using high performance gel permeation chromatography (HPGPC) and gas chromatography (GC), respectively. Significant differences were found among the polysaccharides from the three different parts of Ganoderma atrum, which were also tested for their antioxidant activity. The polysaccharide from Ganoderma atrum pileus possessed the best hydroxyl free radical scavenging activity and reducing capacity (FRAP). The polysaccharide from the stipe of Ganoderma atrum showed the best abilities to scavenge DPPH and hydroxyl free radicals and to inhibit heat-induced oxidation in a β-carotene/linoleic acid model system. However, the polysaccharide from the spore of Ganoderma atrum had worse antioxidant effect in vitro but remarkably better metal ion chelating capacity in comparison with the ones from the pileus and stipe of Ganoderma atrum. This study will provide useful references for making full use of Ganoderma atrum resources.
In this study, the rheological properties of the neutral exopolysaccharide (EPS) produced by Streptococcus thermophilus ST1 isolated from spontaneously fermented products were studied. The results showed that the aqueous EPS solution was a typical non-Newtonian pseudoplastic fluid, and its flow behavior was affected by concentration, temperature, shearing time and pH. The viscosity of EPS solutions increased when the concentration was increased. The higher the concentration was, the more serious the phenomenon of shear thinning was. The viscosity of EPS solutions had little change with good temperature resistance at 10 － 80 ℃. With increasing shearing time from 0 to 900 s, the solution viscosity always showed a downward trend. The viscosity of the EPS solution at pH 4 was relatively stable, while the viscosity at pH 7 and pH 10 greatly decreased with increasing shear rate. The viscosity of skim milk was significantly increased by adding 1 g/100 mL EPS. However, as the shear rate was increased, the viscosity-enhancing effect became smaller.
The molecule of dihydromyricetin (DMY) was chemically modified with lauroyl chloride, producing dihydromyricetin laurate (DMYL). The solubility and antioxidant properties of DMY andDMYL were explored. The results showed that the solubility of DMYL in oil phase increased 20 － 300 times when compared with DMY. The solubility of DMYL in oil phase increased with the increase of esterification degree. The scavenging effects of DMYL on DPPH free radicals and H2O2 in polar solvents were both weaker than those of DMY, decreasing with the increase of esterification degree. However, the inhibitory effect of DMYL on lecithin peroxidation induced by Fe2+/VC was markedly superior to that of DMY and not affected by the esterification degree. It is suggested that the antioxidant properties of DMY and DMYL are influenced by both solubility and the amount of hydroxyl groups.
In this experiment, we studied the changes in chemical composition and texture parameters of sufu (fermented tofu) during processing. The results showed that: 1) the contents of protein and fat progressively decreased, and pH initially increased, followed by a decrease, and the contents of free amino acids and free fatty acids gradually increased during the fermentation of sufu; 2) the chemical constituents in sufu with lower salt contents were all higher, of which the ripening period was shorter; 3) the hardness of sufu first increased and then decreased during its fermentation, and the adhesiveness displayed a gradual increase, while the springiness gradually decreased; 4) sufu showed little changes in both harness and springiness during the last 10 days of post-ripening; and 5) higher salt content in sufu resulted in higher hardness and springiness but lower adhesiveness.
The two functional components including methyl caffeate and ethyl caffeate in purple sweet potato were obtained sequentially by extraction with hot ethanol, reextraction with ethyl acetate and high-speed countercurrent chromatographic (HSCCC) separation. The two compounds were identified by 1H NMR, 13C NMR, ESI-MS and element analysis.
Pulsed electric field treatment was applied to enhance asparagine-fructose model Maillard reaction. The effect of pulsed treatment time on the pH, browning degree (A294 nm), acrylamide and 5-hydroxymethyl-2-furfural (HMF) contents determined by HPLC and DPPH radical scavenging capacity of Maillard reaction products (MRPs) between asparagines and fructose and fructose consumption were analyzed at the same field intensities (5, 10, 15 kV/cm and 20 kV/cm) using 60 ℃ water bath heating as the control. The Maillard reaction between asparagines and fructose was markedly promoted by pulsed electric field treatment. Browning degree and DPPH radical scavenging capacity after the reaction were both positively correlated with pulsed treatment time or field intensity. Besides, almost neither acrylamide nor 5-hydroxymethyl-2-furaldehyde was detected in MRPs derived from pulsed electric field treatment at different field intensities or from water bath heating.
After being subjected to wet heat treatment or treatment with different pH solutions, metal complexing agents or sulfhydryl agents, winged beans were defatted with petroleum ether, vacuum dried, powdered and soaked in 0.01 mL/L, pH 7.0 PBS solution with gentle stirring to extract lipoxygenase (Lox) into the supernatant. The enzyme solutions obtained were comparatively measured for their Lox enzyme activity to probe the effects of different treatments on the stability of Lox in winged beans. The Lox from winged beans treated with pH 8－9 solutions had the highest relative enzyme activity, suggesting that this enzyme is stable in this pH range, whereas pH values below 3 could dramatically inactivate it. Also, the enzyme was greatly inactivated by 90 ℃ heat treatment. Pairwise combined uses of sulfhydryl agents (L-cysteine and thioglycol) with metal complexing agents (citric acid, EDTA and tartaric acid) gave better inactivating effect on the enzyme as compared to their sole uses.
DPPH radical scavenging properties of antioxidants are generally evaluated by determining absorbance (A517 nm) at 517 nm wavelength. Herein, the radical scavenging mechanisms of ascorbic acid on DPPH radicals were investigated by UV-Vis spectrometric, electrochemical and mass spectrometric determinations. It was found that DPPH existed in two different forms, radical form (DPPH·) and highly conjugated form (DPPH+), and ascorbic acid could scavenge both of them in the solution. Generally, the two forms of DPPH were at equilibrium in the solution. This makes it possible to indirectly evaluate DPPH radical scavenging properties of the same kinds of antioxidants based on A517 nm changes of DPPH+, but for different kinds of antioxidants, it is impossible to correctly evaluate radical scavenging properties because of their different relative scavenging effects on the two forms of DPPH.
Elastic modulus is the inherent basic characteristics of vermicelli. It is not only an important parameter indicating quality evaluation, but also one of the principal indexes deciding dry vermicelli texture. Three methods, three-point bending, compressive rod post-buckling and tensile method, were followed in the determination of dry vermicelli elastic modulus on TA-XT2i texture analyzer to establish the best methods for determining the elastic modulus of different shaped forms of dry vermicelli. Tensile method was found to be a method most suitable for the determination of various shaped forms of dry vermicelli among the three methods and give an elastic modulus of 1.419 × 109 N/m2 (9.57% moisture content). However, the best method for determining straight line-shaped vermicelli was compressive rod post-buckling, and its best test conditions were sample length of 100 mm and rotational angle of 20°. Moreover, a significantly linear negative correlation (R2 = 0.9510) between moisture content and elastic modulus was found in the present study, and the linear regression equation was as follows: E = (－ 0.1812ω + 3.237) × 109.
An improved fuzzy comprehensive evaluation method was developed and used to evaluate the sensory quality of three different brands of chopped hot pepper in this study. Meanwhile, the texture and color of these samples were determined using a texture analyzer and a colorimeter to further verify the accuracy of evaluation results. The results showed that the improved fuzzy evaluation method had high accuracy in dealing with high degree of fuzzy comprehensive sensory evaluation problems.
The fruit skins of different five cultivars of eggplants were extracted with hydrochloride acid-acidified ethanol (1:9, V/V) under the assistance of ultrasonic to comparatively determine anthocyanidin contents in them and evaluate the effects of natural light exposure ways, indoor natural light exposure in combination with heating at different temperatures for 1 h, pH, metal ions in solution, common food additives, oxidizers and reducers on the stability of the extracted anthocyanidins. The skin of Brown eggplant contained the largest amount of anthocyanidins among five cultivars. The content of anthocyanidins in purple eggplant skin was approximately 86.48%－82.74% higher than that in green eggplant skin. The anthocyanidins extracted from the fruit skins of five cultivars of eggplants were all kept stable under light avoiding, low-temperature, weakly acidic and weakly alkaline conditions. Mg2+ had color-enhancing effect on them, while the presence of Mn2+, Zn2+ or Cu2+ made the color lighter. VC also did so. All sucrose, citric acid and sodium benzoate could protect the color to some extent. However, no resistance to oxidizers or reducers was observed. These data suggest that anthocyanidins derived from eggplant skin have extensive application prospects.
Additions of three antioxidants, vitamins C and E and tea polyphenols together to the curing agent were used for the traditional processing of salted pork to investigate the effect of their amounts on N-nitrosodimethylamine (NDMA) residue in salted pork by single-factor experiments. NDMA residue was gradually decreased with increasing amounts of VC (VE and tea ployphenols both fixed at 300 mg/kg) and VE (VC and tea ployphenols fixed at 400 mg/kg and 300 mg/kg, respectively) additions up to 500 mg/kg and 400 mg/kg, respectively, and then tended to be stable at higher levels. As the amount of added tea ployphenols (VC and VE fixed at 400 mg/kg and 300 mg/kg, respectively) increased, NDMA residue displayed a tendency to first decrease, reaching its minimum at 300 mg/kg, and then increase.
In order to avoid food poisoning for eating nitrite by mistake, Monascus pigment staining was used to provide a warning method for nitrite in food. Monascus pigments and sodium nitrite were homogeneously blended in three different ratios (1:10000, 5:10000 and 10:10000, m/m), and the effects of direct sunlight, illumination light (in a place free from direct sunlight), darkness, temperature, pH and sodium chloride on the stability of the resulting staining products. The staining product with 1:10000 Monascus pigments/sodium nitrite ratio presented the best stability in the dark, and the storage condition for stabilizing the staining product with 5:10000 Monascus pigments/sodium nitrite ratio (m/m) best was free from direct sunlight.
The microbial diversity of Tianyuan Jiangyuan soybean paste was analyzed by PCR-DGGE (polymerase chain reaction- denaturing gradient gel electrophoresis) technique. The results showed that Bacillus licheniformis (98%) and the closely related species of uncultured Leuconostoc sp. clone (100%) were the dominant bacteria during soybean paste fermentation. Bacillus assisted with fungi in decomposing proteins and starches in the raw materials. Leuconostoc sp. contributed to the formation of flavor compounds in soybean paste. The closely related species of Aspergillus oryzae (99%) were the dominant fungi during soybean paste fermentation. It mostly decomposed proteins and starches in the raw materials.
Thermophilic sporotrichum was cultured in a liquid medium with shaking for polygalacturonase production in this study. To improve polygalacturonase production, the culture medium composition and four fermentation conditions were optimized. The optimal culture medium composition found was composed of wheat bran 1.5%, (NH4)2SO4 0.5%, apple peel powder 3%, KH2PO4 0.1% and MgSO4·7H2O 0.025%, pH 6.0. The optimal values of the volume of the medium in a 250 mL conical flask, fermentation temperature and duration and shaking speed were determined to be 45 mL, 50 ℃, 96 h and 170 r/min, respectively. The fermentation broth obtained under the optimized conditions presented a polygalacturonase activity of 2768.97 U/mL.
Lithium chloride was used to induce the mutation of Ganoderma lucidum protoplasts in order to obtain high-yield triterpenes-producing mutants. The results showed that the optimal mutation condition was treatment with 0.3% lithium chloride, resulting in 72.8% fatality rate. The first generation of the mutant obtained exhibited intra- and extracellular triterpenes yields of 55.33 mg/g and 14.88×10-2 mg/mL, higher than those of the original strain by 461.72% and 136.57%, respectively. In comparison with the original strain, the second and third generations exhibited increases by 483.05% and 496.04% in intracellular triterpenes yield and by 158.66% and 171.38% in extracellular triterpenes yield. Therefore, it can be concluded that the mutant induced by 0.3% lithium chloride is genetically stable.
This study was aimed to develop suitable complete antigens based on either sunset yellow or tartrazine, two pigment compounds. Based on the chemical structural characteristics of the target molecules, we used various activation methods including succinic anhydride and mixed anhydride to acquire complete antigens. Bovine serum albumin (BSA) was served as the carrier protein to couple with the haptens. The results from ultra-violet spectral and high perform liquid chromatography-mass spectrometry analyses showed that the immunogen based on tartrazine was synthesized successfully. The coupling ratio of tartrazine to the carrier protein was 12, while that was only 6 for sunset yellow-BSA conjugate. The tartrazine-BSA conjugate prepared in this study can be used to induce the generation of the specific antibodies against tartrazine in animals.
Corn steep liquor was utilized by Streptococcus thermophilus as the main nitrogen source to produce L-lactic acid in the present study. To improve L-lactic acid production, the culture medium composition was optimized by response surface methodology. The optimal culture medium composition was determined to be composed of glucose 84 g/L, corn steep liquor 41 g/L, ammonium sulfate 1.3 g/L, and pH 6.5. An L-lactic acid yield of 11 g/L was obtained using the optimized medium, approximating to that (9.02 g/L) obtained using beef extract to substitute ammonium sulfate without any changes of three other factors, which resulted in a large reduction of production cost but effectively elevate productivity.
The high-yield ε-poly-L-lysine-producing Streptomyces violaceusniger strain isolated and preserved in our laboratory was cultured to produceε-poly-L-lysine in this study. The mycelia-free supernatant obtained after the centrifugal separation of the fermentation broth was ultrafiltrated through 5 kD (larger than the molecular weight of ε-poly-L-lysine) polysulfone membrane and the filtrate was collected. The static adsorption and desorption characteristics of the filtrate on three different types of ion exchange resins were compared, and the dynamic adsorption and desorption of the filtrate on the selected resin were studied with respect to the effect of operation conditions on adsorption quantity and recovery. Based on the results from static adsorption and desorption, weakly acidic cation exchange resin HD-2 had excellent separation performance onε-poly-L-lysine. The best purification process forε-poly-L-lysine was that the sample to be separated was applied to a 22 mm×300 mm HD-2 column with a flow rate of 3 mL/min, followed by 0.1 mol/L NaCl elution with the same flow rate. Aε-poly-L-lysine recovery of 92.0% was achieved using the optimized purification process.
Three different strains (numbered as 001#, 010# and 012#) of antagonistic yeast Crytococcus laurentii were investigated to understand their phylogenetic relationships and metabolic fingerprints in Biolog microbial identification system and biodefense efficacies against the main pathogens of fruits and vegetables. The results indicated that strains 001# and 010# had a close phylogenetic relationship and there were 43 optimal and 13 utilizable carbon sources in both of their carbon source metabolic fingerprints. However, strain 012# was quite different from strains 001# and 010# in carbon source utilization. The biodefense efficacies of these three strains against the mains pathogens in pear, nectarine and asparagus exhibited a quiet difference, which might be related to the utilization of different types of carbon source in different antagonistic strains and the type and amount of special carbon sources in fruits and vegetables. Meanwhile, the difference in biodefense efficacy could be induced by different types and amounts of carbon sources in fruits and vegetables, which reveals the relationship between metabolic characteristics and evolutionary distance of strains. These investigations provide a theoretical fundamental for studying biodenfense mechanisms of antagonistic strains.
In this study, the preparation, fusion and regeneration of protoplasts from Agrocybe aegerita and Copyinds comatus were explored. Protoplasts were prepared from the four-day-old mycelia through hydrolysis for 4 h with a mixture of 1% pectase and 1% snailase both in 0.6 mol/L mannitol stabilizing the osmotic pressure (1:1, V/V) at 30 ℃. The optimal protoplast infusion conditions were determined to be: fusion at 30 ℃ for 30 min in the presence of 35% PEG (PEG4000) and 0.2 mol/L CaCl2 (pH 10) as the fusogenic agents. Inactivated protoplasts were used as the marks to pick fusants out, which were then regenerated on PDA plate medium. After the regeneration of fusants, a comparison of colonial phynotype and antagonistic experiments were made to validate them.
A high-yield astaxanthin-producing bacterial strain, named CTD004, was isolated from the soil in our university in this study, which exhibited an astaxanthin yield of 28.8 mg/L according to the UV-vis spectrophotometric measurement. The strain was preliminary identified to belong to the genus of Pseudomonas and be closely related to the strain GQ120653.1 based on colonial morphology and Gram staining observations, physiological and biochemical tests and 16S rDNA sequence phylogenetic analysis. The genetic mutagenesis of the strain was induced by UV light radiation to obtain a new strain with higher ability to produce astaxanthin. The optimal dilution multiple of suspended cells was 10-6, and the optimal induction time was 15 s. The astaxanthin yield of the mutant strain obtained was 64.6 mg/L, 35.8 mg/L higher than that of the starting strain. After 5-generation passage, the mutant strain still had excellent genetic stability.
Glucose oxidase (GOD) has gained considerable commercial importance due to its multitude of applications in the food, pharmaceutical, biotechnology and other industries. In the present investigation, a high GOC-producing strain was isolated from the soil of Wenwu Xuefeng farm in Fuzhou, and the fermentation medium was optimized by response surface methodology for higher GOD production by the isolated strain. The optimal medium composition determined consisted of glucose 109.41 g/L, complex nitrogen source (proteose peptone + (NH4)2SO4, 3:1, m/m) 37.36 g/L, Tween-80 37.15 g/L, MgSO4·7H2O 0.7 g/L, KH2PO4 2 g/L and KCl 0.5 g/L. A maximum GOD enzyme activity of 1.54 U/mL was obtained using the optimized fermentation medium, 31.6% higher than before optimization.
In this study, artificial antigens for organophosphate insecticide triazophos including one immunogen and two coating antigens were prepared. The hapten (TZPM-Hap) of organophosphate insecticide triazophos was coupled to bovine serum albumin (BSA) by the active ester method to prepare the artificial immunogen TZPM-A-BSA. Coupling of TZPM-Hap to ovalbumin (OVA) by the active ester method or the mixed anhydride method produced the two coating antigens TZPM-A-OVA and TZPM-M-OVA, respectively. Balb/c mice were immunized with the immunogen, and the splenocytes of the immunized mice were fused with Sp2/0 cells to generate monoclonal antibody (McAbs). A hybridoma cell line (FC3) secreting antitriazophos McAbs was obtained, whose subtype was IgM. Compared with TZPM-M-OVA, better sensitivity in the icELISA format using TZPM-A-OVA was found, which demonstrated 9.7μg/L of IC50, 1.0μg/L of LOD, and 2.5－100.0μg/L of work range (IC20－IC80). The McAbs showed no obvious cross-reactivity with other structural-related organophosphate pesticides. The result indicated that one hybridoma cell line with high specificity and sensitivity was obtained, which will be of importance to develop an ELISA kit for triazophos in the future.
A kinetic model of glutathione production by batch fermentation with Saccharomyces cerevisiae Y518 was studied by using malt sprout extract as the carbon source in a 7.5 L fermenter. The kinetic models for cell growth, glutathione production and substrate consumption were developed respectively by Logistic equation, Luedeking-Piret equation and materials balance equation through optimal parameter estimation and nonlinear fitting. The optimal set of parameters was estimated by fitting the model to experimental data. The results predicted by the model were in good agreement with the experimental observations and showed that the models could provide a reasonable description for the batch fermentation of glutathione.
Theγ-aminobutyric acid (GABA) synthesis was conducted through biotransformation of Streptococcus salivarius subsp. thermophilus Y-2 cells to explore the effects of pH, reaction temperature, salts, surfactant, substrate concentration, strain concentration and addition of pyridoxal phosphate (PLP) on the production of GABA. Results indicated that the optimal reaction system included 25 g/L wet cells, 40 mmol/L BaCl2, 0.02% Triton X-100, 47.5 g/L L-monosodium glutanate, and 90.0 g/L L-glutamic acid. The optimal reaction conditions of this reaction system were reaction temperature of 40 ℃, reaction pH of 4.5, stirring speed of 100 r/min and reaction time of 72 h. Under these optimal conditions, the yield of GABA was up to (87.16 ± 4.33) g/L and biotransformation rate of GABA in moles was (97.60 ± 4.71)%. The total productivity of the cells was (48.42 ± 2.41) mg/(h·g).
The co-cultured cells of Lactobacillus bμlgaricus1.1480 and Streptococcus thermophilus6038 were labeled with different concentrations of 5-(and) 6-carboxyfluorescein diacetate (5(6)-cFDA) in different solvents in order to explore the affecting factors of 5(6)-cFDA labeling. The initial percentages of lactic acid bacterial cells labeled with 5(6)-cFDA in double distilled water, PBS or dimethyl sulfoxide (DMSO) were 94.8%, 95.2% and 99.77%, respectively, which were decreased to 51.53%, 55.6% and 96.7% after 30 days. The cell suspension at a cell density of 1.0 × 106 cells/mL was added with different volumes of 5 mg/mL 5(6)-cFDA to desired final concentrations (1.09 × 10-7, 2.17 × 10-7, 4.35 × 10-7, 6.25 × 10-7, 8.7 × 10-7 and 10.87 × 10-7 mol/L). The diluted cell suspension containing 6.52×10-7 mol/L 5(6)-cFDA showed the best labeling efficiency and there was a linear relationship between cell labeling efficiency and the final concentration of 5(6)-cFDA ranging between 1.09 × 10-7 and 6.25 × 10-7 mol/L. It was also demonstrated that a cell density between 1×106 and 1×107 cells/mL was suitable for flow cytometric (FCM) determination of living cells, with a high labeling efficiency. The buffer at pH 7 had the smallest effect on cell viability and fluorescence intensity and the resulting labeling efficiency reached 98.3%.
