Conservation en congélation et réfrigération de la viande hachée de boeuf et de porc: évolution de la flore microbienne et des propriétés physico-chimiques en cours de stockageFrozen and chilled minced meat (beef and pork): microbiol and physico-chemical evolution during storage

The minced meat market in Belgium is growing steadily; its share of the market has increased from 10 to 30% in three years. However, the mincing of meat can produce intense microbiol proliferation and thus cause food putrification.

Any changes occurring in meat, especially minced meat, are essentially of microbial origin, hence refrigeration is particularly important. With chilling, minimum temperatures must be maintained (0±1°C), since only temperatures below +3°C avoid any health risk linked with the growth of pathogens and production of toxins. Under chilled conditions the storage use of minced meat is four to five days. With freezing, temperatures of about - 18°C are needed to avoid the growth of bacteria, yeasts and mould. At this temperature micro-organisms are progressively rendered inactive, but destruction is never total. The kinetics of reducing micro-organism populations depends on the nature of the micro-organisms, the storage temperature (reduction is more intense at − 12°C that at − 18°C or at − 30°C) and the freezing rate (micro-organisms are better able to resist rapid freezing than slow freezing). One years storage at − 18°C will destroy 90 to 99% of the micro-organisms which were initially present in the product. Nevertheless, the chilled storage (+4°C) of thawed minced meat must not exceed three days.

The physico-chemical evolution of cold stored minced meat is explained. In chilled storage, the onset of flavour defects can be related to the measurement of volatile nitrogen. In frozen storage, the crystallisation of the water causes cellular breakdown. The role of packaging is important in avoiding superficial freeze-drying which is accompanied by browning. In addition, fatty matter can deteriorate by oxidation even at freezing temperatures. The degree of alteration of fats can be appreciated by the acidity index and peroxide index (showing that it is undesirable to store minced pork at − 18°C for more than nine months).

Use of a partial vacuum or modified atmosphere in combination with impermeable packaging will prolong the storage life of minced meat provided that the initial contamination is as low as possible and the maintenance of the cold chain is strictly respected.

Résumé

Le marché de la viande hachée progresse en Europe, du fait de plusieurs facteurs socio-économiques. Le hachage diminue considérablement la durée de conservation de la viande; sa consommation peut être dangereuse.

L'article analyse les points suivants: emballage, réfrigération et congélation (notamment vitesse de congélation), température et durée de conservation, atmosphères modifiées et leur influence sur les propriétés physico-chimiques de la viande et sur le comportement microbien.     

Spectroscopy of Er and Er–Yb-doped phosphate glasses

Optical absorption and emission properties of Er and Er–Yb-doped phosphate glasses are investigated both at low and room temperature in the near infrared spectral region between 800 and 2000 nm, and the results are thoroughly discussed in connection with the expected transitions originating from the crystal-field split ⁴I_15/2 and ⁴I_13/2 levels of the Er³⁺ ion. Accurate measurements of the ⁴I_13/2 fluorescence lifetimes and the determination of the stimulated emission cross section for the Er transition at 1.5 μm are also reported. Excited state absorption (ESA) from the metastable ⁴I_13/2 level towards the higher energy levels is measured in the 450–1200 nm spectral region. The ESA absorption peaks are in good agreement with the positions of the higher states of the 4f¹¹ Er³⁺ manifold.     

Study of capillary tubes in a transcritical CO2 refrigeration system

Capillary tubes have been used in refrigeration systems for many years, but not with a transcritical CO₂ system. In this article, the effects of capillary tubes in a transcritical CO₂ refrigeration system have been investigated experimentally and theoretically. Different types of capillary tubes with different lengths (0.5–4 m) and diameters (1–2 mm) have been tested. The result of this work is a static model, which is used in the further work to make a simulation model (static) of a complete refrigeration system. The model is based on Friedel's and Colebrook's pressure drop correlations.

The behaviour of an adiabatic capillary tube in a refrigeration cycle has been investigated theoretically. The conclusion is that the COP of a system with capillary tubes generally is better than when a fixed high pressure is used, but not as good as when variable optimal high pressure is used. Capillary tubes are especially interesting in applications where the evaporation pressure is constant and the temperature out of the gas cooler varies no more than ±10 K from the design condition. The reduction in COP is more significant at low temperatures out of the gas cooler.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Conservation en congélation et réfrigération de la viande hachée de boeuf et de porc: évolution de la flore microbienne et des propriétés physico-chimiques en cours de stockage

The minced meat market in Belgium is growing steadily; its share of the market has increased from 10 to 30% in three years. However, the mincing of meat can produce intense microbiol proliferation and thus cause food putrification.Any changes occurring in meat, especially minced meat, are essentially of microbial origin, hence refrigeration is particularly important. With chilling, minimum temperatures must be maintained (0±1°C), since only temperatures below +3°C avoid any health risk linked with the growth of pathogens and production of toxins. Under chilled conditions the storage use of minced meat is four to five days. With freezing, temperatures of about - 18°C are needed to avoid the growth of bacteria, yeasts and mould. At this temperature micro-organisms are progressively rendered inactive, but destruction is never total. The kinetics of reducing micro-organism populations depends on the nature of the micro-organisms, the storage temperature (reduction is more intense at − 12°C that at − 18°C or at − 30°C) and the freezing rate (micro-organisms are better able to resist rapid freezing than slow freezing). One years storage at − 18°C will destroy 90 to 99% of the micro-organisms which were initially present in the product. Nevertheless, the chilled storage (+4°C) of thawed minced meat must not exceed three days.The physico-chemical evolution of cold stored minced meat is explained. In chilled storage, the onset of flavour defects can be related to the measurement of volatile nitrogen. In frozen storage, the crystallisation of the water causes cellular breakdown. The role of packaging is important in avoiding superficial freeze-drying which is accompanied by browning. In addition, fatty matter can deteriorate by oxidation even at freezing temperatures. The degree of alteration of fats can be appreciated by the acidity index and peroxide index (showing that it is undesirable to store minced pork at − 18°C for more than nine months).Use of a partial vacuum or modified atmosphere in combination with impermeable packaging will prolong the storage life of minced meat provided that the initial contamination is as low as possible and the maintenance of the cold chain is strictly respected.

Résumé

Le marché de la viande hachée progresse en Europe, du fait de plusieurs facteurs socio-économiques. Le hachage diminue considérablement la durée de conservation de la viande; sa consommation peut être dangereuse.L'article analyse les points suivants: emballage, réfrigération et congélation (notamment vitesse de congélation), température et durée de conservation, atmosphères modifiées et leur influence sur les propriétés physico-chimiques de la viande et sur le comportement microbien.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.     

Dynamic nuclear polarization in crystals of Nd:LaAlO3, a polarized La target for a test of time-reversal invariance

Dynamic nuclear polarization (DNP) has been performed in a magnetic field of 2.35 T at a temperature below 0.3 K in crystals of Nd³⁺ :LaAlO₃. A Q-meter NMR-system was used to measure the polarization of the ²⁷Al and ¹³⁹La nuclei and allowed to characterize the quality of the crystals. The ¹³⁹La polarizations of +47.5% and −56.5% achieved represent an important step in the development of a polarized ¹³⁹La target for a test of time reversal invariance in low-energy neutron reactions.     

Étude électrique de couches minces de polymère obtenues dans une décharge luminescente II: Caractérisation électrique sous champ alternatif

The aim of this study was to investigate the electrical characteristics under alternating stress of a metal-polymer-metal structure, the dielectric of which was a thin layer created by a glow discharge in styrene.

The study, carried out in the 250 Hz–100 kHz range between −90° and 150°C, indicates two different domains for the variations of ε_r and ε_r'. Using bi-logarithmic coordinates the variation of the a.c. conductivity σ_ac(Ω) obeys the law σ_ac(Ω)∝Ω for temperatures lower than 50°C.

In order to explain this result, two hypotheses are proposed: that dipolar fluctuations occur and that a hopping process takes place.     

Optical constants of polycrystalline CuGaTe2 films

Thin films of CuGaTe₂ with thicknesses in the range, 0.1–1.0 μm were deposited on Corning 7059 glass substrates by flash evaporation. The substrate temperatures, T_s, were maintained in the range 373–623 K. The transmittance of the films was recorded in the wavelength range 900–2500 nm. The dependence of the optical band gap, E_g, on substrate temperature showed that the value of E_g varied from 1.21 eV to 1.24 eV. The variation of refractive index and extinction coefficient with photon energy was studied from which the material properties such as the limiting value of dielectric constant, ε_∞, plasma frequency, ω_p, and hole effective mass, m_h^*, were evaluated as ε_∞ = 7.59, ω_p = 1.47 × 10¹⁴ and m_h^* = 1.25 m₀.     

Effect of radiation trapping on the emission properties of Er: I13/2 → I15/2 transition in oxide glasses

The effect of radiation trapping on the emission properties of Er³⁺-doped tellurite and phosphate glasses has been investigated as the function of sample thickness and doping concentration. It was found that radiation trapping exists generally in two glass matrices, even at low doping concentration (0.1 mol% Er₂O₃). The larger effect of radiation trapping in tellurite glasses compared with phosphate glasses is due to its larger emission cross-section at 1.5 μm band and the spectral overlap between the emission and absorption spectra of Er³⁺: ⁴I_13/2 ↔ ⁴I_15/2transition. Due to radiation trapping, the measured lifetime of the Er³⁺: ⁴I_13/2 level in tellurite glasses increases by about 11–37% with increasing the sample thickness at the different erbium doping concentration, while 6–17% for phosphate glasses. And the full-width at half maximum of fluorescence (FWHM) of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses increased by about 15–64% with increasing the sample thickness, while 11–55% for phosphate glasses. It caused a high overestimation on the figure of merits (FOM) for amplifier bandwidth (σ_e × FWHM).     

Molecular beam epitaxy of CdTe and CdxHg1−xTe on InSb

The crystalline quality of InSb substrates and their transparency in the 8–12 μm IR window compare favourably with those of CdTe. We report the first results obtained for Cd_xHg_1−xTe (CMT) layers grown using molecular beam epitaxy over a buffer layer of CdTe on InSb. The (100)-oriented InSb wafer is chemically cleaned prior to thermal treatment which may be accompanied by ion beam cleaning; this process leads to a (2x4) reconstructed surface. Characterization of the surface using Auger spectroscopy, UV photoemission spectroscopy and X-ray photoelectron spectroscopy shows that it is free from oxygen and carbon. CdTe is grown at a substrate temperature of 523 K using a single CdTe cell. When 0.5 μm of CdTe has grown, the substrate temperature is lowered and the CMT is deposited epitaxially using three different cells for cadmium, mercury and tellurium. The layers exhibit X-ray rocking curves 6' wide and n-type conductivity with n = 3× 10¹⁵ cm⁻³ and μ = 40 000 cm² V⁻¹ s⁻¹. Measurement of the strain in each layer shows that CMT is totally relaxed on the CdTe which in turn grows coherently on the InSb.     

Charging kinetics in virgin and 1 MeV-electron irradiated yttria-stabilized zirconia in the 300–1000 K range

A study performed with a dedicated scanning electron microscope (SEM) on the surface electrical properties of (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystals irradiated with 1 MeV electrons is presented. When compared with virgin YSZ, the 1 MeV-irradiated YSZ shows a decrease of the intrinsic total electron emission coefficient σ₀ and an increase of the time constant τ associated with the charging kinetics of the material at room temperature. These measurements performed with the SEM beam at 10 keV indicate that the defects induced by the 1 MeV-electron irradiation generate a positive electric field of the order of 0.5 × 10⁶ V/m at a depth of about 1 μm that prevents electrons to escape. When the SEM beam with a 1.1 keV energy is used, a smaller field (0.5 × 10³ V/m) is detected closer to the surface (20 nm). The fading of these fields during the thermal annealing in the 400–1000 K temperature range provides information on the nature of defects induced by the 1 MeV-electron irradiation.     

The optical and electrical properties of copper indium di-selenide thin films

Thin films of copper indium di-selenide (CIS) with a wide range of compositions near stoichiometry have been formed on glass substrates in vacuum by the stacked elemental layer (SEL) deposition technique. The compositional and optical properties of the films have been measured by proton-induced X-ray emission (PIXE) and spectrophotometry (photon wavelength range of 300–2500 nm), respectively. Electrical conductivity (σ), charge-carrier concentration (n), and Hall mobility (μ_H) were measured at temperatures ranging from 143 to 400 K. It was found that more indium-rich films have higher energy gaps than less indium-rich ones while more Cu-rich films have lower energy gaps than less Cu-rich films. The sub-bandgap absorption of photons is minimum in the samples having Cu/In ≈ 1 and it again decreases, as Cu/In ratio becomes less than 0.60. Indium-rich films show n-type conductivities while near-stoichiometric and copper-rich films have p-type conductivities. At 300 K σ, n and μ_H of the films vary from 2.15 × 10⁻³ to 1.60 × 10⁻¹ (Ω cm)⁻¹, 2.28 × 10¹⁵ to 5.74 × 10¹⁷ cm⁻³ and 1.74 to 5.88 cm² (V s)⁻¹, respectively, and are dependent on the composition of the films. All the films were found to be non-degenerate. The ionization energies for acceptors and donors vary between 12 and 24, and 3 and 8 meV, respectively, and they are correlated well with the Cu/In ratios. The crystallites of the films were found to be partially depleted in charge carriers.     

Theoretical evaluation of trans-critical CO2 systems in supermarket refrigeration. Part II: System modifications and comparisons of different solutions

The performance of CO₂ refrigeration systems strongly depends on the operating conditions. The specific characteristics of low critical temperature and high operating pressure limit its applications and imply the implementation of different control strategies. This study compares the performance of different CO₂ system solutions for supermarket refrigeration with R404A system. Some possible modifications and improvements on the CO₂ system have been investigated. The COP of the investigated CO₂ system solution can be improved by about 3–7% along the ambient temperature range of 10–40 °C. The annual energy consumption calculations in three different climates; cold, moderate and hot, show that the centralized trans-critical CO₂ system is good solution for cold climates whereas the NH₃–CO₂ cascade system has the lowest energy consumption in hot climates. Both systems proved to be good alternatives to R404A DX system for supermarket refrigeration.     

一维β-SiAlON材料可控合成

以Si粉、Al粉和Al₂O₃粉为原料压制成条样, 在1650~1850 K氮气和埋Si₃N₄颗粒气氛下分别合成了β-SiAlON晶须、带状和柱状晶, 并系统研究了一维β-SiAlON材料可控合成条件, 进而结合热力学分析了一维β-SiAlON材料的生长机制。结果表明: 以Si粉、Al粉和Al₂O₃为原料, 在氮气(纯度99.9%)和埋Si₃N₄颗粒气氛下在1650~1850 K保温6 h, 可以合成不同形貌的一维β-SiAlON材料。生长温度是一维β-SiAlON材料形貌控制的关键因素。生长温度为1650 K时, 合成了β-SiAlON晶须, 晶须直径200~400 nm, 长径比100~1000; 生长温度在1700~1800 K时, 可以合成β-SiAlON带状晶体, 厚度为200 nm, 宽度为1~4 μm, 长宽比在10~20之间; 生长温度升高至1800 K时, 出现大量柱状晶体。结合晶须显微结构形貌和热力学分析, β-SiAlON晶须的生长机制为气-固(VS)生长机制。     

Hepatic Uptake and Tissue Distribution of Liposomes: Influence of Vesicle Size

The size-dependent disposition of liposomes in rats was studied. Liposomes consisting of phosphatidylcholine, cholesterol, dicetylphospate and alphatocopherol in a molar ratio of 4:4:1:1, containing a trace of [¹⁴C]-labeled cholesterol as a marker of the lipid phase, were prepared and sized by extruding through polycarbonate membrane. [³H]-inulin was used as a marker of the aqueous phase. In situ liver perfusion in rats showed that hepatic extraction of liposomes was significant for multilamellar vesicles (MLVs) larger than 0.4 μm (0.40, 0.82 and 1.31 μm) and small unilamellar vesicles (SUV), but negligible for 0.25 μm MLV. Pharmacokinetic analysis after intravenous (i.v.) injection showed that the area under the plasma elimination curve (AUC) was significantly higher, but the volume of distribution (Vd) and the elimination rate constant (ke) were significantly lower for the 0.25 μm than for the 1.31 μm liposomes. Comparing the distribution of 1.36 and 0.25 μm MLVs after i.v. injection, the 1.31 μm MLV showed a significantly higher concentration in liver and spleen, but lower concentration in plasma and kidney, than the 0.26 μm in terms of dose percent. These results suggest that size is one of the important factors affecting the fate of liposmes in vivo. There must be a minimun size for effective uptake of liposomes by the reticuloendothelial system. If below the minimum effective uptake size, the MLV should remain in higher concentration in circulation.     

Incorporating Runs Rules into Hotelling's χ2 Control Charts

This paper illustrates a simple and effective method of incorporating runs rules into Hotelling χ² control charts. A Markov chain will be used to obtain a desired in-control average run length (ARL). Comparisons between the basic multivariate χ² control chart and the multivariate χ² control chart, which incorporates the various runs rules, are based on their respective ARL performances. All multivariate χ² control charts that incorporate the various runs rules have shown better ARL performance compared to the basic multivariate χ² control chart for small shifts in distance λ from the in-control mean vector μ₀ to the out-of-control mean vector μ_s. An example of the application, based on the proposed method, is also given.     

Optically active Er–Yb codoped Y2O3 films produced by pulsed laser deposition

Optically active Er³⁺:Yb³⁺ codoped Y₂O₃ films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y₂O₃ targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 10²¹ at cm^− 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb³⁺ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 10²⁰ at cm^− 3 and total rare-earth concentration ≈ 1.8 × 10²¹ at cm^− 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion.     

Mechanical spectroscopy of polymer-magnetite composites

Mechanical properties of magnetite (Fe₃O₄) filled polypropylene (PP) prepared in an extrusion and injection molding process were investigated. Various grades of magnetite were used. Mechanical spectroscopy was performed in a temperature range from 173 to 428 K with frequencies from 10⁻¹ to 10² Hz, and the crystallinity of test samples was estimated. Damping spectra show an peak of the principal relaxation (285 K) at the glass transition temperature, a relaxation β-peak (220 K) attributed to local motions in the amorphous phase and an ′-peak (365 K) attributed to the relaxation in crystalline parts of the polymer. These peaks correspond to drops of the storage modulus.

The -peak is decreased by the extrusion process while the ′-peak is increased compared to not extruded PP. At high temperatures a drastic increase of the loss factor superposes the ′-peak for higher filler loadings. The crystallinity of the polymer matrices varies between 25 and 37%. At low temperatures the storage modulus increases with an increase in the magnetite fraction. The used particle size distributions show no significant influences on the storage moduli for temperatures from 173 to 285 K, whereas for temperatures above 285 K smaller mean particle sizes lead to higher storage moduli and lower loss factors.     

Ultra intense glass laser system and laser–plasma interactions

The 30 TW GEKKO MII short pulse laser (25 J in 0.71 ps at 1 μm) is completed and is used for fast ignitor and particle accelerator research. The photon pressure of the laser at 10¹⁷-10¹⁸ W/cm² pushed the critical and quarter critical density plasmas forward, resulting in the strong red shifts of the second (2ω₀) and three-halves (3ω₀/2) harmonic emissions backscattered from CH or CD planes. A few hundred keV proton and deuteron emissions are also observed from CD planes.