Wiring horseradish peroxidase on gold nanoparticles-based nanostructured polymeric network for the construction of mediatorless hydrogen peroxide biosensor

Gold electrodes were functionalized with an electropolymerized matrix of Au nanoparticles modified with 2-mercaptoethanesulfonic acid, 3-mercaptophenyl boronic acid and p-aminothiophenol. The resulting nanostructured electroconductive matrix was used as support for the oriented immobilization of horseradish peroxidase to construct a reagentless amperometric biosensor for H₂O₂. The electrode, poised at 0.0 mV, exhibited a rapid response within 8 s and a linear calibration range from 5 μM to 1.1 mM H₂O₂. The sensitivity of the biosensor was determined as 498 μA/M cm², and its detection limit was 1.5 μM H₂O₂ at a signal-to-noise ratio of 3. The electrode retained 95% and 72% of its initial activity after 21 and 40 days of storage at 4 °C.     

Effect of Enzyme Treatments and Drying Temperatures on Methylpyrazine Content in Cocoa (Theobroma Cacao L.) Powder Extract

ABSTRACT:  The effects of combining enzyme treatments and heating protocols on pyrazine formation in cocoa powder extracts have been studied. Five commercial enzyme preparations containing protease and carbohydrase activities were initially assessed for their ability to release amino acids and reducing sugars, both of which are substrates for Maillard reactions. The enzyme preparation Flavourzyme was subsequently selected for further study given its ability to liberate both types of substrate. Cocoa powder solutions were treated with 2 doses of Flavourzyme and processed at 2 drying temperatures. The combination of the higher dose of the enzyme (12% w/w enzyme/substrate) and the higher drying temperature (150 °C) resulted in a synergistic increase in the concentration of methyl- and dimethylpyrazines. A statistically significant increase in the concentration of tetramethylpyrazine occurred in samples treated at 150 °C that was independent of the enzyme dose assayed. No significant changes in trimethylpyrazine content were detected in treated compared to untreated samples.     

Designing electrochemical interfaces with functionalized magnetic nanoparticles and wrapped carbon nanotubes as platforms for the construction of high-performance bienzyme biosensors

The design of a novel biosensing electrode surface, combining the advantages of magnetic ferrite nanoparticles (MNPs) functionalized with glutaraldehyde (GA) and poly(diallyldimethylammonium chloride) (PDDA)-coated multiwalled carbon nanotubes (MWCNTs) as platforms for the construction of high-performance multienzyme biosensors, is reported in this work. Before the immobilization of enzymes, GA-MNP/PDDA/MWCNT composites were prepared by wrapping of carboxylated MWCNTs with positively charged PDDA and interaction with GA-functionalized MNPs. The nanoconjugates were characterized by scanning electron microscopy (SEM) and electrochemistry. The electrode platform was used to construct a bienzyme biosensor for the determination of cholesterol, which implied coimmobilization of cholesterol oxidase (ChOx) and peroxidase (HRP) and the use of hydroquinone as redox mediator. Optimization of all variables involved in the preparation and analytical performance of the bienzyme electrode was accomplished. At an applied potential of -0.05 V, a linear calibration graph for cholesterol was obtained in the 0.01-0.95 mM concentration range. The detection limit (0.85 μM), the apparent Michaelis-Menten constant (1.57 mM), the stability of the biosensor, and the calculated activation energy can be advantageously compared with the analytical characteristics of other CNT-based cholesterol biosensors reported in the literature. Analysis of human serum spiked with cholesterol at different concentration levels yielded recoveries between 100% and 103%     

Comparison of the saturated salt and dynamic vapor sorption methods in obtaining the sorption properties of <Emphasis Type="Italic">Pinus pinea</Emphasis> L.

Several methods are available for obtaining the sorption isotherms of wood. Among these, the saturated salt and dynamic vapor sorption methods are the most frequently used ones. For the first time, the hygroscopic response of wood obtained using these two methods is compared. This is done by determining the 35 and 50?°C adsorption isotherms of juvenile and mature wood of Pinus pinea L. The hygroscopic behavior of the two types of wood is different, as the mature wood has a higher moisture content than the juvenile wood in the isotherms studied. Comparison of the static saturated salt method and dynamic vapor sorption shows few significant differences between the equilibrium moisture content obtained by each method during the adsorption process, both in a point by point comparison and in the comparison of quadratic polynomial forms of the Guggenheim Anderson-de Boer model. Moreover, in both methods the point of relative humidity from which multilayer sorption predominates over monolayer sorption is similar.     

Use of wild Lactobacillus strains in an adjunct culture for a Roncal-type cheese

The effect of an added adjunct culture consisting of facultatively heterofermentative lactobacilli (FHL) on the volatile compounds and sensory characteristics of a Spanish ewes'-milk cheese was examined. Three cheese batches were prepared using a commercial starter, one from raw milk, another from pasteurized milk, and a third from pasteurized milk with an added culture of wild Lactobacillus. paracasei+Lb. plantarum. Analysis of the volatile compounds was carried out by the purge and trap method and gas chromatography with a mass spectrometer and disclosed a total of 86 compounds belonging to the chemical families hydrocarbons, fatty acids, esters, ketones, aldehydes, and alcohols. After ageing for 120 and 240 days, the cheese samples underwent sensory analysis by a panel of expert assessors. The attributes evaluated were characteristic odour and odour intensity and characteristic aroma and aroma intensity. Pasteurization of the milk had an effect on the formation of certain volatile compounds, adversely affecting the characteristic flavour of the cheese. Use of the adjunct culture in addition to the commercial starter improved the flavour of the cheese made from the pasteurized milk, which earned sensory scores similar to those awarded to the cheese made from the raw milk. Use of adjunct cultures consisting of indigenous FHL strains could help to conserve the traditional characteristics of Roncal cheese made from pasteurized milk, although some technical adjustments to the Regulations would be needed.     

Thermal properties of doughs formulated with enzymes and starters

 Thermal properties (gelatinization, amylose-lipid complex dissociation and amylopectin retrogradation) of bread samples formulated with two different quality wheat flours, two enzymes (α-amylase/pentosanase, lipase and their mixture), and three microbial sourdough starters were studied with a differential scanning calorimeter. The carbohydrases modified gelatinization temperature and enthalpy, whilst the lipase modified the amylose-lipid complex dissociation. The enthalpy of amylopectin retrogradation was significantly influenced only by the storage of breads. Second-order interactive effects of enzymes with flour or starter were found for gelatinization and/or amylose-lipid complex dissociation parameters. Some interesting relationships were observed between thermal and textural properties of fresh and stored breads. Received: 22 September 1998 / Revised version: 28 October 1998     

Development of a kinetic model for the oxidation of methane over Pd/Al2O3 at dry and wet conditions

The kinetics of the oxidation of methane over a commercial 0.5% Pd on γ-Al₂O₃ catalyst has been studied in a lab-scale fixed-bed reactor, the effect of temperature, and methane, oxygen and water partial pressures being investigated, in a range of interest for environmental applications. Different Eley–Rideal, Langmuir–Hinshelwood and Mars–van Krevelen models were fitted to the experimental results, the best fitting being obtained for a Mars–van Krevelen model that considers slow desorption of the reaction products. The model parameters obtained both from differential and integral treatment of the experimental data are in good agreement with each other. A modification of the proposed model, taking into account that water is adsorbed over oxidised sites, is also able to model the inhibition produced by steam.     

Control of the Mechanical Asymmetry in an Extruded MN11 Alloy by Static Annealing

An extruded Mg-1 wt pct Mn-1 wt pct Nd (MN11) alloy with a recrystallized microstructure and a weak texture was subjected to different thermal treatments at temperatures ranging from 548 K to 673 K (275 °C to 400 °C) for time intervals between 1 and 45 hours. Room-temperature mechanical tests were carried out in tension and compression at 10^?3 s^?1 in order to investigate the effect of annealing on the mechanical behavior. Microstructural examinations revealed that both the annealing temperature and time have little effect on the grain size and on the texture, which are mainly controlled by the presence of thermally stable Mn-containing particles and by the segregation of Nd to the grain boundaries. However, the composition and distribution of the Nd-containing particles vary significantly for the different annealing conditions. The annealed bars exhibit a subtle change in the tensile and compressive yield stress relative to the as-extruded bar and a somewhat larger mechanical asymmetry. The present results suggest that the Nd-containing phases, as well as Nd solute atoms, play a significant role in the mechanical behavior of the MN11 alloy by changing the relative critical resolved shear stress of the different deformation modes.     

Concentration of trichloroethylene in breast milk and household water from nogales, Arizona

The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid-liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL. TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (ρ = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index <14 (RR = 5.2, p = 0.02). Based on average breast milk consumption, TCE intake for 5% of the infants may exceed the proposed U.S. EPA Reference Dose. Results of this exploratory study warrant more in depth studies to understand risk of TCE exposures from breast milk intake.