Showing papers in "High Pressure Research in 2000"

Effects of high pressure on colour and texture of fish

Abstract: The effect of high pressure on the colour of fish species was investigated to evaluate the range of high pressure treatments that did not influence the appearance of the fish. High pressure treatments during 5 minutes higher than 150-200MPa resulted in a cooked appearance of pollack (Pollachius virens), mackerel (Scomber scombrus), tuna (Thunnus thynnus), cod (Gadus morhua), salmon trout (Salmon trutta), carp (Cyprinus carpio), plaice (Pleuronectus platessa) and anglerfish (Lophius piscatorius). Only octopus (Octopus vulgaris) retained a raw appearance till 400-800MPa. The influence of high pressure on the texture of cod (Gadus morhua) was evaluated after frozen storage up to 6 months. The hardness increased as a result of high pressure processing at 200 and 400 MPa. During storage only minor changes of the hardness occurred. Even the non-pressurised sample showed only a small increase in the hardness during storage.

Thermoelastic behaviour of hexagonal graphite-like boron nitride

Abstract: A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P3 = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B0[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B1 = 10.5 + 0.0016(T [K] - 298). These values are for samples with P3 = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results.

Mechanisms of martensitic transformations in boron nitride and conditions of their development

Abstract: The dependence of the pressure threshold of martensitic transformations on the disordering degree of starting structures is considered for graphite-like BN into diamond-like BN modifications transitions. The effect of loading conditions on transformation mechanisms of rhombohedral BN into zinc blende or wurtzite modifications is analyzed also. Analytical relations obtained allow to explain the experimental data and to predict a behavior of various graphite-like structures under different p, T conditions.

Modeling pressure-ionization of hydrogen in the context of astrophysics

Abstract: The recent development of techniques for laser-driven shock compression of hydrogen has opened the door to the experimental determination of its behavior under conditions characteristic of stellar and planetary interiors. The new data probe the equation of state (EOS) of dense hydrogen in the complex regime of pressure ionization. The structure and evolution of dense astrophysical bodies depend on whether the pressure ionization of hydrogen occurs continuously or through a “plasma phase transition” (PPT) between a molecular state and a plasma state. For the first time, the new experiments constrain predictions for the PPT. We show here that the EOS model developed by Saumon and Chabrier can successfully account for the data, and we propose an experiment that should provide a definitive test of the predicted PPT of hydrogen. The usefulness of the chemical picture for computing astrophysical EOS and in modeling pressure ionization is discussed.

Textural changes in bovine meat treated with high pressure

Abstract: The effect of high pressure (HP) treatment on mechanical resistance of post-rigor bovine meat (muscles Biceps femoris and Longissimus dor si) pressurised at low temperature (10°C) was studied. Two levels of pressure were used, 130 and 520 MPa for 260 s. The results show that HP treatment affects significantly (p < 0.05) the mechanical resistance of both raw and cooked meat (1 h at 65°C). Mechanical resistance of pressurised samples was higher than that of untreated samples. Among treated samples, those samples pressurised at 520 MPa showed higher toughness than those pressurised at 130 MPa. Increase of mechanical resistance is due to changes that occurs on the myofibrillar fraction rather than on the connective component. Based on these results, these treatment conditions seem to be ineffective to improved beef tenderness.

Effects of pressure on protein structure

Abstract: The main targets for the pressure induced changes in proteins are those regions primarily stabilised by hydrophobic and electrostatic interactions, since hydrogen bonds are almost pressure insensitive. Thus pressure treated proteins may well have very different structures to their native or heat treated counterparts and as a consequence different functionalities. This concept is used to discuss how pressure can modify the foaming, emulsifying and gelling properties of some food proteins and can also be used to modify the activity of some enzymes of importance in dictating food quality.

Does the antioxidant potential of high pressure treated apple juice change during storage

Abstract: Benefits of application of high hydrostatic pressure for liquid foods processing are relevant as it preserves several food qualities. In this study, effects of high pressure treatment on the antioxidant capacity of apple juice and apple puree have been examined. For this purpose, two tests have been performed, with a linoleic acid emulsion and β-carotene as marker, and with 2,2'-azino-bis-(ethylbenzothiazoline-6-sulfonic acid) di-ammonium salt radicals. When freshly squeezed apple juice was tested, high pressure treatments were more deleterious than high temperatures, although more than 75% of the total capacity was preserved after extreme conditions (600 MPa, 60°C, 30 min). After 1 month storage at 4°C, antioxidant potential of apple juice remained comparable to the one of fresh apple juice stored for 1 month at 4°C. Anaerobic conditions reduced extremely initial losses in antioxidant capacity of apple puree. High pressure treatments were not able to completely stop complex enzymatic reactions i...

Behaviour of E. coli 0157:H7 strains in model system and in raw meat by hpp: Microbial and technological aspects

Abstract: Verotoxigenic Escherichia coli (VTEC) is an important pathogen which can cause serious illnesses in humans. It is of particular importance to the meat industry to be able to completely destroy E. coli. A technique used to destroy E. coli could be the high pressure process. For this reason a mixture of 8 strains of E. coli 0157:H7 was inoculated in raw minced meat and in broth. These samples were treated at pressures up to 700 MPa at WC, causing up to 5 decimal reductions. HP treatment is also effective in decreasing microbial contamination and increasing the shelf-life of raw minced meat under refrigerated conditions. The texture of raw minced meat improved with HP level, while the colour was less characteristic in HP-treated samples; a combined HP-treatment caused less colour change than an individual HP-treatment. No difference in colour of cooked minced meat was observed in untreated and HP-treated samples. The texture of cooked minced meat improved in HP-treated samples.

Equations of state of MgO at high pressure and temperature

Abstract: A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.

High pressure measurement of n-dodecane heat capacity up to 100 MPa. Calculation from equations of state

Abstract: Isobaric heat capacities of liquid n-dodecane were measured at temperatures from 313.15 to 373.15 K and at pressures up to 100 MPa using a calorimetric device based on a Calvet calorimeter (Setaram (280). These experimental data were used to perform a comparative study in order to choose, from among the great number of equations of state proposed in the literature, the most appropriate to calculate the isobaric heat capacity.

Phase diagram of aqueous solution at high pressure and low temperature

Abstract: This paper presents a constant mass high pressure isothermal calorimeter and describes the range of applications that this type of equipment can deal with. As an example, the thermophysical properties of an aqueous solution of MgSO4 at low temperature and at high pressure have been investigated. The main results showed that the phase change heat of the solution decreased with increasing pressure and the phase change temperature of the eutectic concentration was depressed under high pressure. Those changes could be related to the MgSO4 solubility and to water latent heat changes.

Effects of pressure on the two polymorphs of [Co(NH3)5NO2]I2: The anisotropy of lattice distortion and a phase transition

Abstract: The effect of pressure on the two polymorphs of [CO(NH3)5NO2]I2 (phase I-orthorhombic, S.G. Pnma; phase II-monoclinic, S.G. C2/m) was studied by X-ray powder diffraction in a diamond anvil cell (DAC). In the presence of the ethanol-methanol-water mixture used as a pressure-transmitting liquid polymorph I was shown to undergo a phase transition at pressures between 0.45 GPa and 0.65 GPa. The diffraction pattern of the high-pressure phase (phase III) could be indexed as tetragonal with lattice parameters similar to those, which were previously reported for polymorph II in a 'pseudotetragonal setting'. The lattice distortions of phases II and III were studied at pressures up to 3.2 GPa and 3.7 GPa, correspondingly, and were shown to be very similar. Phases II and III were supposed to be very closely related. If poly(chlortrifluorethylen)-oil was used as a pressure-transmitting medium, no phase transitions were observed in phase I of [CO(NH3)5NO2I2 at least up to 1.8 GPa (the point when poly(chlortri...

Pressure-assisted cold unfolding of proteins and its effects on the conformational stability compared to pressure and heat unfolding

Abstract: The pressure-assisted cold unfolding of metmyoglobin was investigated and the cold unfolded state was compared to the heat and pressure unfolded states. Conformationally and mechanistically the pressure and cold unfolding processes are found to be very alike, while the heat unfolding shows some pronounced differences. We also propose a hypothesis on protein aggregation.

Combined effects of pressure and temperature on enzyme stability

Abstract: The effect of high temperature and high hydrostatic pressure on the residual hydrolytic activity of a commercial Rhizomucor miehei lipase has been studied. Inactivation at high temperature and/or high pressure was carried out. Under non-denaturing pressure conditions, results showed that pressurisation protects enzymes against thermal deactivation. This is in accordance with previous results obtained with enzymes from mesophilic sources, such as invertase and galactosidases.

Recent studies on pressure-induced chemical changes in food constituents

Abstract: The application of high hydrostatic pressure is one of the most promising novel minimal processing methods for food preservation. Under optimal process conditions the natural fresh properties of foods are retained. Pressure is an important thermodynamic factor as is temperature. Both pressure and temperature may influence the position of a chemical reaction equilibrium and the reaction rate. Examples of pressure effects on food quality related reactions are presented The effect of pressure on reactions resulting in flavour or colour defects or the formation of undesirable substances and the effect of pressure on the stability of valuable constituents like vitamin A or sulforaphane.

Pressure-induced phase transitions in gypsum

Abstract: We report high-pressure Raman scattering spectroscopy and energy dispersive X-ray diffraction investigations on gypsum, CaSO4 · 2H2O, at room temperature in a diamond cell. With increasing pressure, measurements indicate that CaSO4 · 2H2O undergoes two stages of crystalline-state phase transitions at 5 and 9 GPa, and then converts to a disordered phase above 11 GPa. The structures of the three high-pressure phases of gypsum have not been determined yet. These phases are tentatively named as “post-gypsum-I” (PG-I), “post-gypsum-II” (PG-II) and “disordered” according to the sequence of their appearance with pressure. Gypsum shows anisotropic compressibility along three crystallographic axes with b > c > a below 5 GPa. The difference in the behavior of the two OH stretching modes in gypsum is attributed to the different reduction rate in the hydrogen bonding distances by the anisotropic axial compressibility.

Pressure and photo-induced phase transitions in sulphur investigated by Raman spectroscopy

Abstract: The phase transition of orthorhombic sulphur α-S8 to a high pressure amorphous sulphur allotrope (a-S) has been investigated by Raman spectroscopy. The conversion is found to be induced by the absorption of laser light and can be discussed in terms of ring opening followed by cis-trans conversion of the dihedral angle of S8 molecules. Laser energy and transition pressure are correlated due to the pressure tuned red shift of the absorption edge of α-S8. The amorphous (a-S) phase is observed up to 15 GPa at laser intensities below 30μW/μm2 at 514.5 and 488.0 nm. Above this threshold power a-S transforms into a second photo-induced phase (p-S), whose discrete Raman spectrum implies an ordered molecular and crystalline structure. By further increasing pressure crystalline S6 can be created which is found to be the dominant molecular species at pressures above 10 GPa and low temperatures. A phase diagram in the range T < 300 K and p < 15 GPa is also presented.

Estimating intensity errors of powder diffraction data from area detectors

Abstract: It is shown how error estimates for intensities derived from area detector data in powder diffraction experiments should be calculated. It is demonstrated that the uncritical application of standard weighting schemes to the derived one dimensional data in subsequent least-squares refinements results in meaningless goodness of fit values less than unity that prohibit the evaluation of the quality of the fit. Moreover, it is shown that the calculated estimated standard deviations of the fitted parameters can only be calculated correctly when the true uncertainties of the measured intensities are known.

Cooling by adiabatic (DE)pressurization - the barocaloric effect

Abstract: The barocaloric effect reflects a new cooling principle at low temperatures without the need of liquefied gases nor magnetic fields as used in other cooling techniques. A pressure induced structural and/or magnetic phase transition is used to obtain a significant change in the system's entropy which leads to its cooling if done adiabatically. The effect is illustrated for the two rare earth compounds Pr1 − xLaxNio3 and Cex(La,Y)1 − xSb using a structural and a magnetic phase transition, respectively. In situ experiments on Cex(La,Y)1−xSb are presented and reveal a cooling rate of up to 2 K per 0·5 GPa pressure change at working temperatures below 20 K for x=1 and up to 0·42 K per 0·24 GPa for x=0·85 at around 10K.

Dynamics of hydrogen-bonded water networks under high pressure: Neutron scattering and computer simulation

Abstract: Molecular dynamics simulation of proton-ordered high pressure ice modifications II and IX was performed. Dynamics of both isotope varieties, H2O and D2O, was simulated. Rectangular simulation box of ice II contained 576 and that of ice IX 768 molecules. The average kinetic energy corresponded to 82 and 201 K for ice II and to 87 and 203 K for ice IX. One-phonon densities of states were calculated via Fourier transformation of velocity autocorrelation functions and compared with those found experimentally from inelastic incoherent neutron scattering. This characteristic was calculated for all the molecules, as well as for the molecules of a particular crystallographic type. Both simulated ice modifications contain molecules of two different structural types. Dynamic characteristics of molecules of different types are slightly different. Splitting of the librational peak at about 60–70meV observed in the ice II experimental spectrum is mainly due to such difference. In the case of ice II simulated ...

New packaging solutions for high pressure treatments of food

Abstract: High pressure is a promising technology for developing new processes in food treatment. In most cases, pre-packaged foods are used in high pressure treatments (HP). Consequently, the behavior of the package under treatment conditions is an important factor. The following work was devoted to the evaluation of different packages under high pressure conditions in the presence of different substances used as simulants. Three main characterizations were carried out after HP treatment: mechanical resistance, barrier properties and integrity. The experimental results using multilayer plastic films (PA/PE) have led to the selection of several solutions which may be used as packages for high pressure treatments.

Pressure and temperature-dependent raman study of ZnWO4

Abstract: The Raman spectra of monoclinic ZnWO4 (c4 2h-space group) are reported over wide ranges of pressure (0-24GPa) and temperature (13-970 K). All 18 Raman active pho-nons are observed throughout these ranges. Combining the pressure and temperature Raman data, an identification scheme is suggested which makes possible to distinguish the internal modes (vibrations in the octahedral WO6 units) from the external ones (pure lattice modes). All phonons harden with pressure, thus showing normal positive dω/dP slopes, and soften with temperature in the region 250 - 970 K (normal negative dω/dT slopes). However, two phonons show a change of slope sign below 300 K, resulting in small positive slopes at low temperatures. Since the pressure dependence of these two phonons is normal and linear, it is concluded that their anomalous, non-linear dependence with temperature is due to anharmonic (temperature induced) phonon interactions rather that volume expansion. It is found that ZnWO4 remains stable throughout the...

Potential applications of high pressures in pharmaceutical science and medicine

Abstract: High pressure (HP) technology appears to be of paramount interest for valuable applications in pharmacy and medicine, owing to academic studies and industrial developments of this technology for food processing. The main potential application of HP between 100 MPa and 1200 MPa (1 kbar to 12kbar) is the inactivation of biological agents (bacteria, moulds, yeasts, virus and even prions) which allows the sterilization (i.e, “pascalization”) of thermo-, chemo-, or radio-sensitive materials and chemicals. The immunogenicity of some pressure-killed bacteria or virus suggests also the potentiality of making new vaccines. Another interest of the HP technology is the possibility of storage at subzero temperatures without freezing of cells and animal tissues to be used for cells and organs for transplant. HP engineering may be used for enzyme-catalyzed synthesis of fine chemicals, production of modified proteins of medical or pharmaceutical interest, and organic synthesis of pharmaceuticals.

Towards an easy carbon dioxide reduction in aqueous solution

Abstract: The homogeneous hydrogenation of carbon dioxide into formate anion has been investigated in aqueous solution, using water soluble ruthenium(II)-phosphine (meta-monosulphonated triphenylphosphine, TPPMS; and 1,3,5-triaza-7-phosphaadamantane, PTA) complexes as catalysts. These reactions take place in amine free medium under mild conditions, bicarbonate anion is more active than carbon dioxide in the reduction. The initial turnover frequency of the reduction increases with increasing H-2 pressure, as it was observed in situ by C-13 and H-1 NMR spectroscopy. High pressure FT-IR were used to find evidence for the formation of the catalytically active ruthenium hydride species.

Neutron diffraction studies of hydrogen-bonded ices at high pressure

Abstract: Abstract The development of the Paris-Edinburgh cell has extended the pressure range for neutron diffraction by a full order of magnitude to 30 GPa. This advance has provided a wealth of new information on the high-pressure behaviour of ices such as water-ice, ammonia, methane and hydrogen sulphide. We have now put in place technique developments to permit loading of water-gas mixtures into the Paris-Edinburgh cell.

Fruit preservation under high hydrostatic pressure

Abstract: This study was designed to present a fruit-dessert preserved with high hydrostatic pressure. Enzymatic browning reactions in some fruits and vegetables appear to be activated by pressurization. High hydrostatic pressure extents the shelf-life of fruits decreasing microbial population. Colour in fruits is one of the attributes that produces a deleterious effect after HP treatment. Melon is a good product to be preserved with HP without any pre-treatment. Ascorbic acid concentrations between 10-20mM prevent the browning. The final product was acceptable to consumers and the shelf life of the fruit-dessert was several weeks longer whereas the control sample fermented.

Raman studies of the high pressure effects in high Tc superconductors

Abstract: The effect of a hydrostatic pressure (up to 6GPa) on the Raman spectra of YBa2Cu3Ox(x = 6.5 and overdoped) single crystals is investigated in the temperature range 77-300 K in connection with all available data in the literature for the other oxygen concentrations. All five strong modes (4Ag+1B1g) are examined for both oxygen doping and compared with previously published results. From the systematic investigation of the phonon spectral characteristics with the application of pressure, the formation or disappearance of the phases is examined. The results provide a spectroscopic support for the changes induced by the hydrostatic pressure on the chain ordering and the corresponding phases.

Effects of high pressure treatment on fermentation processes during ripening of Gouda cheese

Abstract: High pressures ranging 50 to 400 MPa were applied to Gouda cheese cylinders and evolution of the volatile fraction was followed during three weeks. No new volatiles were recovered after simultaneous distillation-extraction, but some effects of high pressure on the fermentation processes were observed. Thus butyric acid and acetoin were found in lower concentrations after ripening of pressurized samples. Nevertheless differences in the volatile profile were not large enough to suggest an effect of high pressure on the acceleration of Gouda cheese ripening.

Influence of high pressure treatment on rheological and other properties of egg white

Abstract: The paper deals with the influence of high pressure treatment of fresh egg white on its properties and protein composition (individual amino-acids predicted as a function of pressure and time levels). The rheological properties are changed by high pressure from Newtonian to non-Newtonian behaviour, with increasing apparent viscosity as the pressure and time increased. The pH, whipping ability, foam stability, gel strength of heat induced gels after treatment and the whole protein content, were also predicted. The results showed that the foam stability is increased with increasing pressure and time of processing. The foam volume is also increased with pressure. The pH did not change with pressure or time of processing. Composition of proteins as indicated by individual amino-acids did not exhibit statistically important changes. Gel strength of heat induced gels prepared from previously pressured liquid whites showed no important change of values with pressure or time of treatment. The modulus of ...

Pressure inactivation of fungal spores in aqueous model solutions and in real food systems

Abstract: Conidiospores from Penicillium expansum and ascospores from Eurotium repens were exposed to high hydrostatic pressure in isotonic salt solution, apple and broccoli juice. Kinetic measurements were done at 4,25 and 40 or 45°C. The shape of the inactivation curves was strongly dependent on the temperature. Asco- and conidiospores were found to behave in a contrary way. The fastest reduction for conidiospores was found at 4°C, for ascospores best inactivation was achieved at 45°C. High pressure inactivation of spores in apple or broccoli juice was nearly the same as in isotonic salt solution.