The effect of water movement on the transport of dicyandiamide,ammonium and urea in unsaturated soils

A laboratory experiment was conducted to investigate the relative mobility of dicyandiamide (DCD) and jointly applied ammoniacal salts or urea in three different soils of lower Egypt, and to determine the extent to which DCD separates from N-fertilizer in unsaturated soil undergoing leaching. The experimental results suggest that, under conditions of water flow, DCD is readily separated from NH₄⁺ but parts from urea to a far lesser extent. The large difference in mobility between DCD and NH₄⁺ should severely limit the effectiveness of DCD as a nitrification inhibitor in the three soils considered when applied in conjunction with ammoniacal salts. In two out of three cases, the situation is similarly unfavorable in the case of joint DCD and urea application. However, the observation that DCD, in a low CEC sandy loam, moves within the soil solution at a slightly lower rate than urea suggests that joint application with urea would keep at least part of the DCD in contact with the NH₄⁺ ions and, therefore, would preserve some of the effectiveness of DCD under leaching conditions in this soil.     

Mass spectrometry based sensor strategies for the authentication of oysters according to geographical origin

This study was undertaken to investigate the relevance of using the pyrolysis-MS (Py-MS) technique to discriminate the production area of oysters harvested over two years and to assess from the data of the second year of harvest the potential of an alternative MS-based technique, the solid phase microextraction-MS (SPME-MS), to perform this discrimination. Oysters were harvested in various areas of France, and models of discrimination according to harvest season were built from Py-MS fingerprints and from virtual SPME-MS fingerprints obtained by summing the mass spectra generated by the SPME-GC-MS system. The treatment of the Py-MS data by a 21-12-3 artificial neural networks led to a correct classification of only 89.2% of the oyster samples according to shoreline. The misclassifications thus did not allow use of the Py-MS technique as a relevant tool for authentication of oyster origin. The assessment of the potential of the virtual SPME-MS fingerprints to discriminate the production area of oysters was undertaken on a part of the sample set. The virtual SPME-MS data were pretreated according to two methods, filtering of raw data (FRD) and comprehensive combinatory standard correction (CCSC), a recently developed chemometric method used for the correction of instrumental signal drifts in MS systems. The results obtained with the virtual SPME-MS fingerprints are promising because this technique, when the data were pretreated by the CCSC method, led to a successful discrimination of the oyster samples not only according to shoreline but also according to production region. This study confirms that an efficient correction method (CCSC) of instrumental drifts can considerably increase the discriminative information contained in the volatile fraction of food products.     

Kinetics of formation and functional properties of conjugates prepared by dry-state incubation of beta-lactoglobulin/acacia gum electrostatic complexes

The formation of conjugates between beta-lactoglobulin and acacia gum based on electrostatic complexes formed at pH 4.2 was investigated upon dry-state incubation for up to 14 days at 60 degrees C and 79% relative humidity (RH). By means of SEC-HPLC and RP-HPLC, it was shown that the beta-lactoglobulin incubated alone was able to form polymers with molecular masses higher than 200 kDa until 50% of the initial monomeric protein disappeared after 14 days. In the presence of acacia gum at initial protein to polysaccharide weight mixing ratios of 2:1 and 1:2, only 35% of the initial beta-lactoglobulin monomers disappeared after 14 days. Using RP-HPLC, an apparent reaction order of 2 was found for the disappearance of monomeric beta-lactoglobulin both in the presence or absence of acacia gum. However, the reaction rate was faster in the absence of acacia gum. SDS-PAGE electrophoresis with silver staining confirmed the formation of beta-lactoglobulin/acacia gum conjugates. The solubility curves of the incubated beta-lactoglobulin showed a minimum around pH 4-5. By contrast, the minimum of solubility of the beta-lactoglobulin/acacia gum incubated mixtures shifted to lower pH values compared to initial mixtures. The conjugates exhibited higher foam capacity than the incubated protein as well as lower equilibrium air/water surface tension. Conjugation at ratio 1:2 led to increased interfacial viscosity (300 mN s m(-1) at 0.01 Hz) compared to beta-lactoglobulin alone (100 mN s m(-1) at 0.01 Hz), but similar interfacial elasticity (30-40 mN m(-1)). The foam capacity of the conjugates was significantly higher than that of the incubated beta-lactoglobulin as well as foam expansion and drainage time, especially at pH 5.3, i.e., higher than the pH of formation of the conjugates.     

Proteome analysis of the sarcoplasmic fraction of pig semimembranosus muscle: implications on meat color development

Two-dimensional electrophoresis was used to investigate sarcoplasmic protein expression in pig Semimembranosus muscles sampled 20 min after slaughter. Two groups (light and dark) of 12 animals were selected from 1000 pigs, based on meat L values measured 36 h postmortem. Twenty-two proteins or fragments (p < 0.05) were differentially expressed. Muscles leading to darker meat had a more oxidative metabolism, indicated by more abundant mitochondrial enzymes of the respiratory chain, hemoglobin, and chaperone or regulator proteins (HSP27, alphaB-crystallin, and glucose-regulated protein 58 kDa). Conversely, enzymes of glycolysis were overexpressed in the lighter group. Such samples were also characterized by higher levels of glutathione S-transferase omega, which can activate the RyR calcium channels, and higher levels of cyclophilin D. This protein pattern is likely to have severe implications on postmortem metabolism, namely, acceleration of ATP depletion and pH fall and subsequent enhanced protein denaturation, well-known to induce discoloration.     

The generation of aerosols by binary homogeneous nucleation

The rates of nucleation of liquid aerosols from the gaseous mixtures H₂SO₄ + H₂O and HNO₃ + H₂O at 25°C for various relative humidities (10 to 100%) and various activities of acid vapor are calculated using the Flood-Neumann-Döring-Reiss-Doyle theory of binary homogeneous nucleation. The activities of acid vapor needed for nucleation are 25 to 300 times smaller for H₂SO₄ + H₂O than for HNO₃ + H₂O. This is due to the much larger free energy of mixing in the liquid phase for H₂SO₄ + H₂O. Conversion from activities to actual pressures leads to concentrations of HNO₃ which are much too high to be found under normal atmospheric conditions. On the other hand, the concentrations of H₂SO₄ vapor needed to nucleate droplets in the H₂SO₄ + H₂O system are in the range 4(10^?5) to 1.3 (10^?2) ppm, a concentration which can result from photo-oxidation of SO₂ in the atmosphere. Calculations are made of the growth curves for H₂SO₄ + H₂O droplets (radius vs composition) at various relative humidities from the critical size radius up to a 1000 Å radius, corresponding to nuclei large enough to serve as condensation centers for heterogeneous nucleation. The limitations of binary homogeneous nucleation theory at extremely low concentrations of one of the components are discussed and it is shown that this theory becomes inapplicable if the actual vapor pressure of one component is below 10^?6 torr.     

Ascorbic acid oxidation in sucrose aqueous model systems at subzero temperatures

The reduction of Tempol by ascorbic acid in concentrated sucrose solutions was measured by electron paramagnetic resonance (EPR) at temperatures ranging from 16 to -16 degrees C. This method allowed the determination of the rate constants (k) of this fast reaction, by recording the Tempol reduction as a function of time. The two reactants were initially separated and had to migrate for the reaction to occur. The experimental findings were compared with predicted values according to the equation for diffusion-controlled reaction proposed by Atkins. The experimental reaction rate constants were observed to be lower than the calculated ones. However, the experimental values were found to be controlled by the temperature and viscosity changes of the reaction media, as expected for a diffusion-controlled reaction.     

Pesticide residues in heterogeneous plant populations, a model-based approach applied to nematicides in banana (Musa spp.)

Nematicides are widely used to control plant-parasitic nematodes in intensive export banana (Musa spp.) cropping systems. Data show that the concentration of fosthiazate in banana fruits varies from zero to 0.035 g kg-1, under the maximal residue limit (MRL=0.05 mg kg-1). The fosthiazate concentration in fruit is described by a Gaussian envelope curve function of the interval between pesticide application and fruit harvest (preharvest interval). The heterogeneity of phenological stages in a banana population increases over time, and thus the preharvest interval of fruits harvested after a pesticide application varies over time. A phenological model was used to simulate the long-term harvest dynamics of banana at field scale. Simulations show that the mean fosthiazate concentration in fruits varies according to nematicide application program, climate (temperature), and planting date of the banana field. This method is used to assess the percentage of harvested bunches that exceed a residue threshold and to help farmers minimize fosthiazate residues in bananas.     

A retrospective study of 30 cases of frozen lamellar corneal graft in dogs and cats

Frozen lamellar corneal grafts and nictitating membrane flaps were used in 18 dogs and 12 cats to repair deep corneal defects. In all dogs either melting corneal ulcers or descemetoceles were present. In the 12 cats, nine had either a melting corneal ulcer or descemetocele, two animals had acute bullous keratopathy, and one cat had corneal sequestrum. Initial vascularization with gradual clearing of the graft occurred during the first 45 days postoperatively. At 60 days postoperatively, all eyes were visual. Frequent postoperative complications included: focal dehiscence of the wound ( n  = 9); melting of part of the graft ( n  = 7); and pigmentation of the graft ( n  = 4). The frozen lamellar corneal graft was a very safe technique, and restored the tectonic and the optical function of the cornea. It provided the best results in corneas with nonperforating corneal defects. This technique provides poorer results when the cornea was perforated prior to surgery or during the surgical procedure.