Safety assessment of dairy microorganisms: the Enterococcus genus

Unlike most of lactic acid bacteria, the Enterococcus genus is not considered "generally recognized as safe" (GRAS). Safety assessment for enterococci remains controversial. While enterococci are considered "positive" or useful in cheese technology, isolates of this genus have emerged as opportunistic pathogens for humans. Thus these bacteria have the paradoxical position of being useful in dairy fermentations, but also potentially dangerous. The aim of this review is to summarize both the positive and negative traits of enterococci that illustrate the controversial nature of this bacterial genus. According to food safety assessment guidelines, we propose a case-by-case evaluation of each potential technological strain and suggest several lines of research before using enterococci in fermented food products.     

Electrochemical performance of La1.6Sr0.4NiO4-Ag composite cathodes for intermediate-temperature solid oxide fuel cells

La_1.6Sr_0.4NiO₄-Ag (LSN-Ag) composite cathodes are prepared and characterized by XRD and SEM, respectively. The electrochemical properties of the composite cathodes are investigated using AC impedance and DC polarization methods from 500 to 700 °C under different oxygen partial pressures. The polarization resistance (R_p) decreases with the increase of Ag content in the composite electrode. The addition of 5 vol.% Ag in LSN results in the lowest R_p of 0.21 Ω cm² at 700 °C in air. Oxygen partial pressure dependence study indicates that the charge transfer process is the reaction rate limiting step, while the diffusion process has no sensitive to the Ag loading. LSN-5Ag cathode exhibits the lowest overpotential of about 32 mV at a current density of 144 mA cm⁻² at 700 °C in air.     

Lanthanide NIR luminescence for telecommunications, bioanalyses and solar energy conversion

Present-day advanced technologies heavily rely on the exciting magnetic and spectroscopic properties of lanthanide ions. In particular, their ability to generate well-characterized and intense near-infrared (NIR) luminescence is exploited in any modern fiber-optic telecommunication network. In this feature article, we first summarize the whereabouts underlying the design of highly luminescent NIR molecular edifices and materials. We then focus on describing the main trends in three applications related to this spectral range: telecommunications, biosciences, and solar energy conversion. In telecommunications, efforts concentrate presently on getting easily processable polymer-based waveguide amplifiers. Upconversion nanophosphors emitting in the visible after NIR excitation are now ubiquitous in many bioanalyses while their application to bio-imaging is still in its early stages; however, highly sensitive NIR-NIR systems start to be at hand for both in vitro and in vivo imaging, as well as dual probes combining magnetic resonance and optical imaging. Finally, both silicon-based and dye-sensitized solar cells benefit from the downconversion and upconversion capabilities of lanthanide ions to harvest UV and NIR solar light and to boost the overall quantum efficiency of these next-generation devices.     

Co-doped Sr2FeNbO6 as cathode materials for intermediate-temperature solid oxide fuel cells

Sr₂Fe_1−xCo_xNbO₆ (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr₂Fe_1−xCo_xNbO₆ electrodes are chemically compatible with the Zr_0.85Y_0.15O_1.925 (YSZ) and Ce_1.9Gd_0.1O_1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm⁻¹ is found for Sr₂Fe_0.1Co_0.9NbO₆ at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr₂Fe_0.1Co_0.9NbO₆ electrode, depending on the temperature. The Sr₂Fe_0.1Co_0.9NbO₆ electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm² at 750 °C in air, which indicates that the Sr₂Fe_0.1Co_0.9NbO₆ electrode is a promising cathode material for IT-SOFCs.     

The fluorimetric FAST method, a simple tool for the optimization of microwave pasteurization of milk

The effect of microwave pasteurization of cow's milk on its nutritional quality was examined by the FAST method (Fluorescence of Advanced Maillard products and Soluble Tryptophan). Raw milk samples were submitted to different laboratory scale in batch microwave treatments using a central composite experimental design based on specific power and treatment time. The FAST index and bacterial count were monitored to assess protein denaturation, modification by the Maillard reaction and pasteurization efficiency, respectively. High discrimination between samples indicated that the FAST method is a potent tool for estimating the deterioration of the milk quality during experimental microwave treatment. Thus, the FAST index can be effectively used as the continuous response in experimental designs set up and to maximize information economically. In short, the FAST method allows us to retain the rapidity of experimental design while providing the advantages of convenience and low cost.     

Monitoring in real time with a microelectrode the release of reactive oxygen and nitrogen species by a single macrophage stimulated by its membrane mechanical depolarization

Macrophages are key cells of the immune system. During phagocytosis, the macrophage engulfs a foreign bacterium, virus, or particle into a vacuole, the phagosome, wherein oxidants are produced to neutralize and decompose the threatening element. These oxidants derive from in situ production of superoxide and nitric oxide by specific enzymes. However, the chemical nature and sequence of release of these compounds is far from being completely determined. The aim of the present work was to study the fundamental mechanism of oxidant release by macrophages at the level of a single cell, in real time and quantitatively. The tip of a microelectrode was positioned at a micrometric distance from a macrophage in a culture to measure oxidative-burst release by the cell when it was submitted to physical stimulation. The ensuing release of electroactive reactive oxygen and nitrogen species was detected by amperometry and the exact nature of the compounds was characterized through comparison with in vitro electrochemical oxidation of H2O2, ONOO-, NO*, and NO2(-) solutions. These results enabled the calculation of time variations of emission flux for each species and the reconstruction of the original flux of production of primary species, O2*- and NO*, by the macrophage.     

Liquid chromatography-mass spectrometry and 15N metabolic labeling for quantitative metabolic profiling

Metabolomics, i.e., the global analysis of cellular metabolites, is becoming a powerful tool for gaining insights into biological functions in the postgenomic context. However, absolute quantitation of endogenous metabolites in biological media remains an issue, and available technologies for the analysis of metabolome still lack robustness and accuracy. We describe here a new method based on liquid chromatography-mass spectrometry and (15)N uniform metabolic labeling of Saccharomyces cerevisiae for accurate and absolute quantitation of nitrogen-containing cell metabolites in metabolic profiling experiments. As a proof of concept study, eight sulfur metabolites involved in the glutathione biosynthesis pathway (i.e., cysteine, homocysteine, methionine, gamma-glutamylcysteine, cystathionine, reduced and oxidized forms of glutathione, and S-adenosylhomocysteine) were simultaneously quantified. The analytical method has been validated by studies of stability, selectivity, precision, and linearity and by the determination of the limits of detection and quantification. It was then applied to the analysis of extracts from cadmium-treated yeasts. In these conditions, the intracellular concentrations of most of the metabolites involved in the glutathione biosynthesis pathway were increased when compared to control extracts. These data correlate with previous proteomic results and also underline the importance of glutathione in cadmium detoxication.     

Optical properties of randomly distributed soot: improved polarimetric and intensity scattering functions

Reference scattering curves for polarization and intensity produced by aggregates and agglomerates of ethylene and kerosene soot are obtained for scattering angles in the 10-170 degrees range. The polarization measurements were obtained with the Propriétés Optiques des Grains Astronomiques et Atmosphériques instrument for particles that levitate in microgravity during parabolic flights and on the ground by an air draught technique. The intensity measurements were obtained also on the ground with a Laboratoire de Metéorologie Physique nephelometer. The maximum polarization is of the order of 80% at a scattering angle of 80 degrees at lambda = 632.8 nm and approximately 75% at an angle of 90 degrees at lambda = 543.5 nm. The polarization increases by approximately 10% when the size of the agglomerate increases from 10 microm to a few hundred micrometers. The intensity curve exhibits a strong increase at small scattering angles. These reference curves will be used in the near future for the detection of stratospheric soot by remote-sensing measurement techniques.     

Immunoaffinity purification and characterization of 4-hydroxy-2-nonenal- and malondialdehyde-modified peptides by electrospray ionization tandem mass spectrometry

Two methods based on specific immunoaffinity enrichment followed by electrospray ionization (ESI) mass spectrometry (MS) have been developed for the specific analysis of 4-hydroxy-2-nonenal (HNE)- and malondialdehyde (MDA)-modified proteins (Michael and Schiff base adducts, respectively). Anti-HNE antibodies were immobilized on CNBr-activated sepharose, and the immunosorbent produced was used for the enrichment of HNE-adducted peptides originating from a model peptide modification and a tryptic digest of modified apomyoglobin. A further immunosorbent was produced by anti-dinitrophenyl immobilization and assayed for selective extraction of peptides modified with HNE and MDA that were initially converted to their respective hydrazones. Subsequent analysis and characterization of the different purified fractions by ESI-MS (MS/MS) revealed that the two immunosorbents enable efficient and specific enrichment of the carbonyl adducted proteins. This approach lowers substantially the detection limit of such modifications and, thus, enables better assessment and characterization of carbonyl modifications in biological and food systems.     

Sensitization to doxorubicin resistance in breast cancer cell lines by tamoxifen and megestrol acetate

Acquired drug resistance is a major factor in the failure of doxorubicin-based chemotherapy in breast cancer. We determined the ability of megestrol acetate and/or tamoxifen to reverse doxorubicin drug resistance in a doxorubicin-resistant breast cancer line (the human MCF-7/ADR). The cytotoxicity of doxorubicin, megestrol acetate, and/or tamoxifen was determined in the sensitive and resistant cell lines utilizing the sulphorhodamine B assay. Tamoxifen alone produced an IC50 (concentration resulting in 50% inhibition of control growth) of 10.6 microM, whereas megestrol acetate alone resulted in an IC50 of 48.7 microM in the MCF-7/ADR cell line. The IC50 of doxorubicin in MCF-7/ADR was 1.9 microM. Neither megestrol acetate alone nor tamoxifen alone at 1 or 5 microM altered the IC50 of doxorubicin. However, the combination of tamoxifen (1 or 5 microM) and megestrol acetate (1 or 5 microM) synergistically sensitized MCF-7/ADR cells. Additionally, megestrol acetate and tamoxifen inhibited iodoarylazidoprazosin binding to P-glycoprotein, and, in their presence, there was an increased doxorubicin accumulation in the MCF-7/ADR cells. Furthermore, the combination of tamoxifen and megestrol acetate had much less effect on the cytotoxicity of doxorubicin in MCF-7 wild-type cells. Clinically achievable concentrations of tamoxifen and megestrol acetate can largely sensitize MCF-7/ADR to doxorubicin. The combination of these three drugs in a clinical trial may be informative.