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Find video protocols related to scientific articles indexed in Pubmed.
Evaluation of the associations between vascular endothelial function and coronary artery stenosis in patients with elevated blood pressure during coronary angiography.
Heart Surg Forum
PUBLISHED: 07-09-2014
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The aim of the present study is to explore the correlation between vascular endothelial function and coronary artery stenosis in non-hypertensive patients with elevated blood pressure under stress.
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Innovative assistant extraction of flavonoids from pine (Larix olgensis Henry) needles by high-density steam flash-explosion.
J. Agric. Food Chem.
PUBLISHED: 04-21-2014
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High-density steam flash-explosion (HDSF) was first employed to extract flavonoids from pine needles. The HDSF treatment was performed at a steam pressure of 0.5-2.0 MPa for 20-120 s. Scanning electron microscopy and high-performance liquid chromatography combined with photodiode-array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS) were used to characterize the morphological changes and analyze flavonoids of pine needles before and after HDSF treatment. Our results indicated that, after steam explosion at 1.5 MPa for 60 s, the flavonoids extracted reached 50.8 rutin equivalents mg/g dry weight, which was 2.54-fold as that of the untreated sample. HDSF pretreatment caused the formation of large micropores on the pine needles and production of particles, as well as the removal of wax layers. Compared to microwave-assisted, ultrasound-assisted, and solvent extraction, HDSF pretreatment took only 30 min to reach a maximum yield of 47.0 rutin equivalents mg/g flavonoids extract after pine needles were treated at 1.5 MPa for 80 s. In addition, after HDSF treatment, the aglycones were 3.17 times higher than that of untreated pine needles, while glycosides were lower by 57% (in HPLC-DAD individuals' sum) due to hydrolysis of flavonoids glycosides. It can be concluded that HDSF is a practical pretreatment for extraction of flavonoids and conversion in the healthy food and pharmaceutical industries.
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Preparation of immobilized glucose oxidase and its application in improving breadmaking quality of commercial wheat flour.
Food Chem
PUBLISHED: 03-20-2014
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Preparation of immobilized glucose oxidase (GO) on chitosan (CS)-sodium tripolyphosphate (TPP) and its application in improving breadmaking quality of commercial wheat flour were investigated. The optimum conditions for GO immobilization were: viscosity of CS: 700cP, ratio of CS to TPP (w/w): 5 to 1, and GO concentration 100U/mL. The obtained CSTPP-GO was 5?m-diameter particle with a pseudo-spherical shape. By addition of CSTPP-GO (400U/kg flour) and fungal ?-amylase (62.5U/kg flour), bread springiness slightly increased from 0.923 to 0.940, specific volume of crumb increased by 13.48% and hardness decreased by 19.22%, compared to addition of KBrO3 (60mg/kg flour). It could be concluded that CSTPP-GO combined with fungal ?-amylase had potential application in improving breadmaking quality of commercial wheat flour.
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Improving digestibility of feather meal by steam flash explosion.
J. Agric. Food Chem.
PUBLISHED: 03-19-2014
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Poultry feathers are available in large quantities. However, natural feathers have poor digestibility and are often considered as solid wastes. To improve the digestibility of poultry feathers, steam flash explosion (SFE) was applied to duck feathers at different pressures ranging from 0.5 to 2.5 MPa for 1 min. The pepsin digestibility, disulfide bond content, and major secondary structure component (?-sheets) of duck feathers before and after the process were examined. The results showed that SFE could effectively increase pepsin digestibility of feather meal. Under the optimal conditions (1.8 MPa for 1 min), the pepsin digestibility of exploded feather meal achieved approximately 91%, which was about 9 times higher than that of the original feathers. The pepsin digestibility was highly correlated with the degree of reduction of disulfide bonds (R(2) = 0.98) and slightly negatively correlated with ?-sheet structure. SFE is an effective method to improve the bio-utilization of feather meal.
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Adsorption-based immobilization of Caldicellulosiruptor saccharolyticus cellobiose 2-epimerase on Bacillus subtilis spores.
Biotechnol. Appl. Biochem.
PUBLISHED: 03-06-2014
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Nonrecombinant spore was examined as a novel immobilization support to adsorb enzymes. Caldicellulosiruptor saccharolyticus cellobiose 2-epimerase (CsCE), efficiently producing lactulose using lactose as a single substrate, was immobilized on Bacillus subtilis spores via adsorption. The immobilization process was optimized, and the properties of immobilized CsCE and the interactions between the enzyme and spores were also investigated. Under the optimized conditions (pH 4.5, temperature 4 °C, reaction time 2 H, and initial enzyme concentration 2.4 mg/mL), the maximum adsorbed amount of CsCE was 1.47 mg/10(11) spores, and the enzyme activity recovery was 79.4%. The spore-immobilized CsCE presented a higher pH and thermal stability than a free enzyme. Total desorption of the immobilized enzyme was only achieved by treatment with 1.0 M NaCl at pH 1.0, indicating a strong adsorption between CsCE and B. subtilis spores. Efficient binding may require a potent combination of electrostatic and hydrophobic interactions between spores and an enzyme. The immobilized CsCE was applied to produce 395 g/L lactulose after 4 H. Moreover, the spores could be regenerated and the spore-immobilized enzyme showed good reusability as it retained approximately 70% of its initial activity after eight recycles.
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Adsorption characteristics of rebaudioside A and stevioside on cross-linked poly(styrene-co-divinylbenzene) macroporous resins functionalized with chloromethyl, amino and phenylboronic acid groups.
Food Chem
PUBLISHED: 02-20-2014
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The adsorptive separation of each steviol glycoside from aqueous solutions by polymeric adsorbents has attracted a lot of interest in recent years. The adsorption properties of chloromethylated cross-linked poly(styrene-co-divinylbenzene) macroporous resins, functionalised with chloromethyl, amino and phenylboronic acid groups, towards rebaudioside A and stevioside were studied. The results revealed that the resins with amino and phenylboronic acid groups preferred to adsorb stevioside rather than rebaudioside A, and their adsorption kinetics fitted a pseudo-second-order model. Isothermal equilibrium curves of rebaudioside A and stevioside showed a good fitness with the Langmuir and Freundlich models. The adsorption of rebaudioside A and stevioside onto resins was a spontaneous and exothermic process as indicated by the negative values in free energy and enthalpy. Results from the resin-packed column demonstrated that an effluent rich in rebaudioside A (purity 98%) was obtained prior to the breakthrough point of stevioside.
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Enzymatic production of lactulose and 1-lactulose: current state and perspectives.
Appl. Microbiol. Biotechnol.
PUBLISHED: 03-23-2013
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Lactulose, a synthetic ketose disaccharide, has been widely used in food and pharmaceutical industries as prebiotic food additives and drugs against constipation and hepatic encephalopathy. Lactulose has, so far, been produced chemically using lactose on a commercial scale. The key problems associated with such chemical process are the cost of removal of the catalyst and colored by-products and the product safety. Enzymatic production of lactulose is safe, environment-friendly, and simpler in comparison to the chemical method. As a promising alternative to the chemical method, enzymatic conversion of lactose into lactulose by ?-galactosidase or cellobiose 2-epimerase has recently gained a great deal of attention. This could be considered as a possible route for whey surplus because lactose is the major component of cheese whey. Herein, we summarize recent advances on the enzymatic synthesis of lactulose with emphasis on the selectivity of biocatalysts and their catalytic efficiency in free and immobilized forms. The production of 1-lactulose by enzymatic bioconversion of lactose has also been discussed. Furthermore, future research needs of ?-galactosidase and cellobiose 2-epimerase for the enzymatic synthesis of lactulose and 1-lactulose are reviewed.
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Expression, enzymatic characterization, and high-level production of glucose isomerase from Actinoplanes missouriensis CICIM B0118(A) in Escherichia coli.
Z. Naturforsch., C, J. Biosci.
PUBLISHED: 12-23-2011
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High-level production of recombinant glucose isomerase (rGI) is desirable for lactulose synthesis. In this study, the xylA gene encoding glucose isomerase from Actinoplanes missouriensis CICIM B0118(A) was cloned and expressed in E. coli BL21(DE3), and high-level production was performed by optimization of the medium composition. rGI was purified from a recombinant E. coli BL21(DE3) and characterized. The optimum pH value of the purified enzyme was 8.0 and it was relatively stable within the pH range of 7.0-9.0. Its optimum temperature was around 85 degrees C, and it exhibited good thermostability when the temperature was lower than 90 degrees C. The maximum enzyme activity required the presence of both Co2+ and Mg2+, at the concentrations of 200 microM and 8 mM, respectively. With high-level expression and the simple one-step chromatographic purification of the His-tagged recombinant enzyme, this GI could be used in industrial production of lactulose as a potential economic tool.
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Influence of pulsed electric field treatments on the volatile compounds of milk in comparison with pasteurized processing.
J. Food Sci.
PUBLISHED: 11-29-2010
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Effects of pulsed electric field (PEF) treatments on the volatile profiles of milk were studied and compared with pasteurized treatment of high temperature short time (HTST) (75 °C, 15 s). Volatile compounds were extracted by solid-phase micro-extraction (SPME) and identified by gas chromatography/mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O). A total of 37 volatile compounds were determined by GC-MS, and 19 volatile compounds were considered to be major contributors to the characteristic flavor of milk samples. PEF treatment resulted in an increase in aldehydes. Milk treated with PEF at 30 kV/cm showed the highest content of pentanal, hexanal, and nonanal, while heptanal and decanal contents were lower than in pasteurized milk, but higher than in raw milk. All the methyl ketones detected in PEF milk were lower than in pasteurized milk. No significant differences in acids (acetic acid, butanoic acid, hexanoic acid, octanoic acid, and decanoic acid), lactones, and alcohols were observed between pasteurized and PEF-treated samples; however, 2(5H)-furanone was only detected in PEF-treated milk. Although GC-MS results showed that there were some volatile differences between pasteurized and PEF-treated milk, GC-O data showed no significant difference between the 2 samples.
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Purification and characterization of inulin fructotransferase (DFA III-forming) from Arthrobacter aurescens SK 8.001.
Bioresour. Technol.
PUBLISHED: 04-06-2010
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The soil bacterium Arthrobacter aurescens SK 8.001 produces inulin fructotransferase (IFTase), and liquid chromatography-mass spectrometry (LC-MS) and carbon-13 nuclear magnetic resonance (13C NMR) analysis demonstrated that the main product of the enzyme was difructose anhydride III (DFA III). The IFTase was purified by ethanol precipitation, DEAE Sepharose Fast Flow, and Superdex 200 10/300 GL gel chromatography. Its molecular mass was estimated to be 40 kDa by SDS-PAGE and 35 kDa by gel filtration. The enzyme showed maximum activity at pH 5.5 and 60-70 °C, and retained 86.5% of its initial activity after incubation at 60 °C for 4 h. Chemical modification results suggested that a tryptophan residue is essential to enzyme activity. The N-terminal amino acid sequence was determined as AEGAKASPLNSPNVYDVT. The kinetic values, Km and Vmax, were estimated to be 0.52 mM and 0.3 ?mol/ml min. Nystose was observed to be the smallest substrate for the produced IFTase. This IFTase provides a promising way to utilize inulin for the production of DFA III.
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Investigation of the protein-protein aggregation of egg white proteins under pulsed electric fields.
J. Agric. Food Chem.
PUBLISHED: 03-25-2009
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Egg whites were exposed to pulsed electric fields (PEFs) to investigate the protein-protein aggregation. No insoluble protein aggregate was found when egg whites were exposed to PEFs at 25, 30, and 35 kV/cm for 400 micros. However, atomic force microscopy showed that the sizes of the protein particles increased. Native polyacrylamide gel electrophoresis (PAGE) demonstrated the existence of aggregates under PEFs at 35 kV/cm for 400 micros. Sodium dodecyl sulfate (SDS)-PAGE in the presence and absence of 2-mercaptoethanol further indicated that sulfhydryl-disulfide interchange reactions occurred under PEFs. Differential scanning calorimetry scans showed 400 micros of PEF treatment at 35 kV/cm denatured 16.5% proteins. Insoluble egg white protein aggregates were induced by PEF (35 kV/cm, 800 micros) and heat (60 degrees C, 3.5 min) treatments. Disulfide bonds were the dominant binding forces in the formation of protein aggregates. However, the weakly noncovalent bonds play a much more important role in the protein aggregation forming in heat treatment (60 degrees C, 3.5 min) than that in PEF treatment (35 kV/cm, 800 micros).
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Cold storage temperature following pulsed electric fields treatment to inactivate sublethally injured microorganisms and extend the shelf life of green tea infusions.
Int. J. Food Microbiol.
PUBLISHED: 01-14-2009
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In this work microbiological shelf life of green tea infusions processed by pulsed electric fields (PEF) treatment (38.4 kV/cm for 200 micros) were assessed at the three storage temperatures of 4, 25 and 37 degrees C, respectively. Immediately after PEF treatment, no viable bacterial cells were detected. However, significant recovery was observed during storage at 25 and 37 degrees C. The total aerobic microbial population increased rapidly in PEF-treated green tea infusions when stored at 25 and 37 degrees C for 14 and 7 days respectively. However, the microbial population remained under 1 log(10) CFU/ml when stored at 4 degrees C up to 180 days. These results demonstrated that a certain proportion of microbial cells in green tea infusions were sublethally injured by PEF treatment, and the recovery of apparently dead or intermediately damaged cells could increase the detected number of surviving microorganisms. In the present study PEF-treated green tea infusions were placed at 4 degrees C for various time, and then stored at 37 degrees C. Cold storage (4 degrees C for 7 days) following PEF treatment was found to be effective to delay or inhibit the repair process of sublethally injured cells and extend the microbiological shelf life of PEF-treated green tea infusions to more than 90 days at 37 degrees C.
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Production of 1-lactulose and lactulose using commercial ?-galactosidase from Kluyveromyces lactis in the presence of fructose.
Food Chem
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Production of 1-lactulose and lactulose using commercial ?-galactosidase DSM Maxilact® 5000 in the presence of fructose was investigated. Experiments were performed at 40 °C and pH 7.5. Lactose starting concentration was constantly 250 g/l. A novel transgalactosylation product 1-lactulose was detected besides lactulose. Effects of fructose concentration, reaction time and enzyme concentration on transgalactosylation reactions were discussed. In all reactions, the yield ratio 1-lactulose:lactulose was close to 3:1 due to the regioselectivity of ?-galactosidase. The maximum production of 1-lactulose and lactulose was approximately 22 and 8 g/l, respectively, when fructose concentration was increased to 100 g/l. Lactose hydrolysis was significantly retarded since fructose strongly attracted water molecules. Higher enzyme concentration can accelerate transgalactosylation reactions without affecting the maximum production of transgalactosylation products. Fructose was a more preferred galactosyl acceptor than lactose, since the synthesis of galactooligosacchairdes was found to be absolutely inhibited in the presence of fructose.
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Electrochemical reaction and oxidation of lecithin under pulsed electric fields (PEF) processing.
J. Agric. Food Chem.
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Pulsed electric fields (PEF) processing is a promising nonthermal food preservation technology, which is ongoing from laboratory and pilot plant scale levels to the industrial level. Currently, greater attention has been paid to side effects occurring during PEF treatment and the influences on food qualities and food components. The present study investigated the electrochemical reaction and oxidation of lecithin under PEF processing. Results showed that electrochemical reaction of NaCl solutions at different pH values occurred during PEF processing. Active chlorine, reactive oxygen, and free radicals were detected, which were related to the PEF parameters and pH values of the solution. Lecithin extracted from yolk was further selected to investigate the oxidation of food lipids under PEF processing, confirming the occurrence of oxidation of lecithin under PEF treatment. The oxidative agents induced by PEF might be responsible for the oxidation of extracted yolk lecithin. Moreover, this study found that vitamin C as a natural antioxidant could effectively quench free radicals and inhibit the oxidation of lipid in NaCl and lecithin solutions as model systems under PEF processing, representing a way to minimize the impact of PEF treatment on food qualities.
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Enzymatic synthesis and identification of oligosaccharides obtained by transgalactosylation of lactose in the presence of fructose using ?-galactosidase from Kluyveromyces lactis.
Food Chem
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The enzymatic transgalactosylation of lactose in the presence of fructose using ?-galactosidase from Kluyveromyces lactis (Kl?Gal) leading to the formation of oligosaccharides was investigated in detail. The reaction mixture was analyzed by high performance liquid chromatography with differential refraction detector (HPLC-RI) and two main transgalactosylation products were discovered. To elucidate their overall structures, the products were isolated and purified using preparative liquid chromatography and analyzed by LC/MS, one-dimensional (1D) and two-dimensional (2D) NMR studies. Allo-lactulose(?-d-galactopyranosyl-(1?1)-d-fructose) with two main isomers in D(2)O was identified to be the major transgalactosylation product while lactulose(?-d-galactopyranosyl-(1?4)-d-fructose) turned out to be the minor one, indicating that Kl?Gal was regioselective with respect to the primary C-1 hydroxyl group of fructose. The maximum yields of allo-lactulose and lactulose were 47.5 and 15.4g/l, respectively, at 66.5% lactose conversion (200g/l initial lactose concentration).
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Covalent immobilization of Kluyveromyces fragilis ?-galactosidase on magnetic nanosized epoxy support for synthesis of galacto-oligosaccharide.
Bioprocess Biosyst Eng
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The novel magnetic nanobeads with epoxy groups on the surface were prepared from glycidyl methacrylate (GMA), ethylene glycol dimethacrylate (EGDMA) and hydroxyethyl methacrylate (HEMA) via emulsifier-free emulsion polymerisation, and they were characterized by scanning electron microscopy and vibrating sample magnetometer. The magnetic poly(GMA-EDGMA-HEMA) nanobeads were used as support for covalent immobilization of Kluyveromyces fragilis ?-galactosidase, the maximum amount enzyme attached onto the support was 145.6 mg/g with activity recovery of 72.6%. The loading capacity of this novel support for K. fragilis ?-galactosidase was improved 2.6-folds compared with Eupergit® C (commercial epoxy support). The immobilized K. fragilis ?-galactosidase exhibited high catalytic activity for the reaction of galacto-oligosaccharide (GOS) synthesis, and a total of 2,240 g GOS were produced per gram of immobilized enzyme during consecutive batch reaction of 10 times. The immobilized biocatalyst retained 81.5% of its original activity after 10 reaction cycles.
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