Calcul d'energie de fautes d'empilement dans le dioxyde d'uranium

Energy computations of some (100), (110) and (111), planar defects were performed using an ionic bond model for stoichiometric uranium dioxyde. The repulsive contribution to the fault was estimated in two different ways, i.e. using the Born-Mayer classical treatment, or potentials derived from shell model calculations. The stability of the various defect configurations has been studied; on the basis of our numerical values, we may conclude that dislocation dissociation is unlikely in stoichiometric uranium dioxyde.     

Interaction of an odorant lactone with model phospholipid bilayers and its strong fluidizing action in yeast membrane

Some odorant lactones are naturally present in fruits or in fermented products; they can also be used as food additives and can be produced by microorganisms at the industrial scale by biotechnological processes. Gamma-decalactone was previously shown to have antimicrobial properties. We determined by infrared spectroscopy measurements that this compound rapidly diffused into model phospholipid bilayers (within 2 min), modifying the general physical state of a dimyristoyl-L-alpha-phosphatidylcholine (DMPC) film. In vivo, the lactone strongly increased membrane fluidity in the model yeast Yarrowia lipolytica, as evaluated by fluorescence anisotropy measurements. This effect was more important than that of benzyl alcohol, which is known as a fluidizing agent in living cells, and may explain the toxic action of gamma-decalactone in microorganisms.     

Study of ethanol-induced conformational changes of holo and apo alpha-lactalbumin by spectroscopy and limited proteolysis

This study was performed to contribute to the analysis of alpha-lactalbumin "molten globule" state by using spectral and proteolysis techniques. Samples of holo and apo alpha-lactalbumin in the presence of different concentrations of ethanol were analyzed. Results of fluorescence spectroscopy of both forms showed that as ethanol concentration increased, the tryptophanyl residues became more accessible to the solvent. Near circular dichroism spectra of holo alpha-lactalbumin indicated that its tertiary structure was maintained in 20% ethanol whereas it was altered in 30 and 40% ethanol. For apo alpha-lactalbumin, spectra were similar in all samples studied. Holo alpha-lactalbumin was resistant to trypsinolysis in 0% ethanol, whereas it was easily hydrolyzed in 20 and 30% ethanol. In the case of the apo form and in the absence of ethanol, 70% of the protein was degraded after 1 h. However, in the presence of 20 and 30% ethanol, the overall reaction rate was lowered. Peptides obtained after tryptic hydrolysis were identified by reversed-phase high-performance liquid chromatography coupled to mass spectrometry. Differences in population of produced peptides indicate the changes of folding intermediates present in the studied alpha-lactalbumin solutions. This study demonstrated that proteolytic enzymes are suitable tools to determine protein structure complementing physico-chemical studies.     

Histological and cell wall polysaccharide chemical variability among apricot varieties

The variability of histological and cell wall chemical characteristics of apricot were assessed in nine apricot varieties: Harogem, Goldrich, Hargrand, Iranien, Moniqui, Orangered^® Bhart, Stark Early Orange, Ravicille and Rouge du Roussillon. For chemical analyses, Iranien and Moniqui were harvested twice at two weeks interval and Goldrich parenchyma was subdivided into inner and outer tissue.     

Phytosanitary treatment of European pallets by microwave: developing a program to ensure compliance with ISPM 15 and monitoring its efficacy on the house longhorn beetle (Hylotrupes bajulus L.)

Microwave heating was recently approved by the FAO as a significantly effective phytosanitary treatment for wood packaging material. According to ISPM 15 (FAO 2009), the target organisms are eradicated if a temperature higher than 60 °C is maintained for 60 s across the entire profile of the board (i.e. 60 °C/60 s). A study using pallet boards was carried out in order to set up a treatment program that would meet ISPM 15 requirements in terms of wood temperature and insect mortality. A 4 m-long industrial tunnel oven (maximum power of 28.8 kW) was used to carry out the experiments. Temperature was measured by means of a VarioCAM^® infrared camera. The most relevant results found were: (i) achieving a mean temperature of 63.2 °C (Populus sp.) or 64.8 °C (Pinus sylvestris L.) on the upper surface of 22 mm-thick boards enabled compliance with FAO requirements (i.e. 60 °C/60 s), whatever the moisture content, basic density and initial temperature of the wood (provided the latter exceeded 0 °C); (ii) larvae >150 mg represented the most microwave-resistant life stage of Hylotrupes bajulus L.; (iii) the mortality rate of the larvae was influenced by the moisture content of the boards. Using the Gompertz model, the upper surface temperature was estimated that would be needed to achieve a 99.99683 % mortality rate (the Probit 9 mortality level of efficacy) for the most microwave-resistant life stage of H. bajulus. This temperature was estimated to be 46.8 and 57 °C for wood with >50 and <25 % moisture content, respectively.     

Rapid and non-destructive analysis of apricot fruit quality using FT-near-infrared spectroscopy

A non-destructive optical method based on near-infrared spectroscopy has been used for the evaluation of apricot fruit quality. Diffuse reflectance measurements (800–2500 nm), physical, physiological and biochemical measurements were performed individually on 877 apricot fruits from eight contrasted cultivars harvested at different ripening stages. Relationships between spectral wavelengths and quality attributes were evaluated by application of chemometric techniques based on partial least squares (PLS) on fruit set divided randomly into two groups: 598 fruits for calibration and 279 for validation. Good prediction performance was obtained for soluble solids and titratable acidity with correlation coefficients of 0.92 and 0.89 respectively and root mean square errors of prediction of 0.98% Brix and 3.62 meq 100 g⁻¹ FW respectively. For the other quality traits such as firmness, ethylene, individual sugars and organic acids, the prediction models were not satisfactorily accurate due to the high error of calibration and prediction.     

Effect of freezing treatments and yeast amount on sensory and physical properties of sweet bakery products

The frozen bakery market has grown significantly in developed countries over the past decade.     

Cell surface properties affect colonisation of raw milk by lactic acid bacteria at the microstructure level

Cell localisation in the matrix microstructure of fermented food is important for microbial activity and ripening. To evaluate the importance of physicochemical factors in these phenomena, the physicochemical behaviour of four strains of lactic acid bacteria were investigated after inoculation of raw milk or milk fractions. To discriminate between physicochemical and metabolic properties, media were (i) rapidly acidified to avoid cell division or (ii) bacteria were allowed to ferment milk. To evaluate the impact of milk components, cells were dispersed in protein or fatty globule fractions. From two Lactococcus lactis subsp. lactis biovar. diacetylactis strains selected from their different surface properties investigated in previous studies, after rapid acidification one was encountered in fatty globules and protein gels whereas the other was found in serum and on the surface of globules. After fermentation, the first one formed colonies in the lipid phase or next to it in the whey and the second formed colonies in the protein gel. Strains forming long chains (Lactobacillus bulgaricus and Streptococcus thermophilus) were always found in contact with fatty globules, where they developed. Our results suggest that localisation and subsequent spatial colonisation depend on the physicochemical properties of cell surfaces, on the structure in chains as well as on the metabolic ability to develop on proteins or lipids.