Amino acid catabolism by Lactococcus lactis during milk fermentation

Two wild-type Lactococcus lactis strains isolated from naturally Tunisian fermented milk (Leben), and one laboratory strain, were used to investigate the ability of L. lactis to transform amino acids into aroma compounds during milk fermentation. The α-ketoacid acceptor used for leucine transamination, the first step of catabolism, was identified by gas chromatography/mass spectrometry analysis of the ¹⁵N-labelled amino acids that formed from ¹⁵N-labelled leucine in fermented milk. Furthermore, the amino acids produced or catabolized by the laboratory strain via transamination were identified by comparing the free amino acids in milk fermented with the wild-type strain and the double mutant for aromatic and branched-chain aminotransferases, which cannot transaminate amino acids. The three L. lactis strains strongly catabolized leucine and valine during milk fermentation. The principal amino acid formed via leucine and valine transamination was glutamate indicating that α-ketoglutarate was the principal α-ketoacid acceptor and was generated during milk fermentation.     

Monitoring of Martensitic Transformation in Austenitic Stainless Steel 304 L by Eddy Currents

A nondestructive eddy current technique has been applied to cyclic-strain induced martensitic transformation (MT) monitoring in austenitic stainless steel 304 L. During plastic deformation, the austenite transforms locally in martensite. Transformed martensite distribution depends on the geometry of the specimen under test (rectangular section in this work): transformation occurs first in the corners, later close to the flat free surfaces, and finally in the bulk. The obtained value is then representative of a small volume of the sample. Local measurements with an eddy current probe proved to be sensitive to this kind of transformation and even quantitatively after calibration. This article proposes a procedure to calibrate the eddy current response in order to determine the fraction of martensite formed under the probe without the need of X-ray measurements.     

Effects of impurities on the lattice dynamics of nanocrystalline silicon for thermoelectric application

Doped silicon nanoparticles were exposed to air and sintered to form nanocrystalline silicon. The composition, microstructure, and structural defects were investigated with TEM, XRD, and PDF and the lattice dynamics was evaluated with measurements of the heat capacity, of the elastic constants with resonant ultrasound spectroscopy and of the density of phonon states (DPS) with inelastic neutron scattering. The results were combined and reveal that the samples contain a large amount of silicon dioxide and exhibit properties that deviate from bulk silicon. Both in the reduced DPS and in the heat capacity a Boson peak at low energies, characteristic of amorphous SiO₂, is observed. The thermal conductivity is strongly reduced due to nanostructuration and the incorporation of impurities.     

Magnesiothermic Reduction Process Applied to the Powder Production of U(Mo) Fissile Particles

Uranium‐molybdenum alloy powders are obtained by a new synthetic route deriving from the Kroll process which avoids a “melting‐solidification” step. This alternative process consists in the reduction of uranium dioxide by magnesium in presence of Mo in a sealed Mo crucible heated at temperatures ranging from 750 to 1100 °C for dwell periods ranging from 12 to 48 h. An appropriate quenching allows the retention of the high temperature bcc‐form γ–U(Mo). The side products are easily removed by a soaking into a diluted hydrochloric acid solution under sonication. The agglomerates have a typical size in the range 10–200 µm, with an irregular shape. They display even at the periphery equiaxed grains with homogeneous distribution of Mo. Small closed porosity, which seems to be preferentially located at the grain boundaries corresponds to roughly 2% of the volume fraction.     

Outward electron transfer by Saccharomyces cerevisiae monitored with a bi‐cathodic microbial fuel cell‐type activity sensor

A Janus head‐like bi‐cathodic microbial fuel cell was constructed to monitor the electron transfer from Saccharomyces cerevisiae to a woven carbon anode. The experiments were conducted during an ethanol cultivation of 170 g/l glucose in the presence and absence of yeast‐peptone medium. First, using a basic fuel‐cell type activity sensor, it was shown that yeast‐peptone medium contains electroactive compounds. For this purpose, 1% solutions of soy peptone and yeast extract were subjected to oxidative conditions, using a microbial fuel cell set‐up corresponding to a typical galvanic cell, consisting of culture medium in the anodic half‐cell and 0.5 M K₃Fe(CN)₆ in the cathodic half‐cell. Second, using a bi‐cathodic microbial fuel cell, it was shown that electrons were transferred from yeast cells to the carbon anode. The participation of electroactive compounds in the electron transport was separated as background current. This result was verified by applying medium‐free conditions, where only glucose was fed, confirming that electrons are transferred from yeast cells to the woven carbon anode. Knowledge about the electron transfer through the cell membrane is of importance in amperometric online monitoring of yeast fermentations and for electricity production with microbial fuel cells. Copyright © 2009 John Wiley & Sons, Ltd.     

The application of Near-Infrared Reflectance Spectroscopy (NIRS) to detect melamine adulteration of soya bean meal

Soya bean products are used widely in the animal feed industry as a protein based feed ingredient and have been found to be adulterated with melamine. This was highlighted in the Chinese scandal of 2008. Dehulled soya (GM and non-GM), soya hulls and toasted soya were contaminated with melamine and spectra were generated using Near Infrared Reflectance Spectroscopy (NIRS). By applying chemometrics to the spectral data, excellent calibration models and prediction statistics were obtained. The coefficients of determination (R²) were found to be 0.89–0.99 depending on the mathematical algorithm used, the data pre-processing applied and the sample type used. The corresponding values for the root mean square error of calibration and prediction were found to be 0.081–0.276% and 0.134–0.368%, respectively, again depending on the chemometric treatment applied to the data and sample type. In addition, adopting a qualitative approach with the spectral data and applying PCA, it was possible to discriminate between the four samples types and also, by generation of Cooman’s plots, possible to distinguish between adulterated and non-adulterated samples.     

Typology of atoll rims in Tuamotu Archipelago (French Polynesia) at landscape scale using SPOT HRV images

The lagoon of an atoll is separated from the ocean by a rim. As the rim controls the flux of water between ocean and lagoon, its structure is one of the major forcing factors of the biological processes that depend on the renewal rate of lagoonal water. Characterizing rim structure and its degree of hydrodynamic aperture is mandatory for comparing the functioning of different atoll lagoons. This paper characterizes at landscape scale the different types of rims of the atolls of the Tuamotu Archipelago (French Polynesia) using SPOT HRV multi-spectral images. The classification of 117 segments of rims highlights nine different rims. They differ in the relative importance of vegetated, submerged, intertidal and emerged domains. These classes are recognized with accuracy greater than 85% using a simple statistical supervised algorithm. A gradient of hydrodynamic aperture is described, from 0.02% very closed rim exposed to the north, to 0.65% wide open rim exposed to dominant southern swell. We show that most of these nine rims have a preferential exposure. According to the direction of the dominant swell in the Tuamotu region, such exposure may explain the structure of the rims and their degree of hydrodynamic aperture. We discuss the implications of these results for research and management.