Pressurization Treatments Research Articles

Effect of Vacuum Impregnation and High Hydrostatic Pressure Treatments on Shelf Life, Physicochemical, and Sensory Properties of Seabream Fillets

Marination is commonly used to preserve fish, which, in combination with other non-thermal technologies, such as vacuum impregnation and high hydrostatic pressure, may help to preserve freshness and extend shelf life. In addition, marination may mask changes in physicochemical properties and the sensory attributes of fish resulting from intense pressurization treatments. In this study, we evaluated the effects of vacuum impregnation (50 mbar for 5 min) alone or in combination with a moderate pressurization treatment (250 MPa for 6 min) on the physicochemical properties, microbiological and oxidative stability, and sensory properties of refrigerated seabream fillets. Compared to conventional marination, vacuum impregnation alone had no effect on the aforementioned properties, except for a higher perception of lemon aroma (0.9 vs. 1.6). However, vacuum impregnation with pressurization reduced the total viable mesophilic aerobic bacteria to counts below 4 log colony forming units (CFU)/g after 16 days of storage at ≤ 2 °C, compared to 6 log CFU/g with conventional marination. Additionally, the color and texture were affected by the pressurization treatment. However, color was more susceptible, and at the beginning of storage, lightness was higher in the pressurized samples than in the control (52 vs. 78). Regardless, this whitening effect and other minor changes in texture and sensory properties compared to conventional marination with vacuum impregnation with pressurization can be considered of little relevance considering the increase in shelf life, the lack of lipid oxidation (maintained at low and similar levels as those of the non-pressurized samples), and the intrinsic whitening effects of certain marinades.

High-pressure structuring of milk protein concentrate: Effect of pH and calcium

In this study, we investigated the effect of pH and calcium on the structural properties of gels created by high-pressure processing (HPP, 600 MPa, 5°C, 3 min) of milk protein concentrate (MPC, 12.5% protein). The pH level of the MPC was varied between 6.6 and 5.1 by adding glucono-δ-lactone (GDL), and the calcium content was varied from 24 to 36 mg of Ca/g of protein by adding calcium chloride. The rheological properties and microstructure of the pressure-treated MPC were assessed. The pressurization treatments and analytical testing were conducted in triplicate. Data were analyzed statistically using one-way ANOVA with Tukey's honestly significant difference post hoc tests. A pressurization time of 3 min was sufficient to induce gel formation in MPC at pH 6.6, so it was used throughout the study. Adjusting either pH or calcium affected the structure of the HPP-created milk protein gels, likely by influencing electrostatic interactions and shifting the calcium-phosphate balance. Gels were formed after pressurization of MPC at pH above 5.3, and increasing the pH from 5.3 to 6.6 resulted in stronger gels with higher values of elastic moduli (G'). At neutral pH (6.6), adding calcium to MPC further increased G'. Scanning electron microscopy showed that reducing pH or adding calcium resulted in more porous, aggregated microstructures. These findings demonstrate the potential of HPP to create a variety of structures using MPC, facilitating a new pathway from dairy protein ingredients to novel, gel-based, high-protein foods, such as puddings or on-the-go protein bars.

Dynamic-Change Laws of the Porosity and Permeability of Low- to Medium-Rank Coals under Heating and Pressurization Treatments in the Eastern Junggar Basin, China

Deep coalbed methane exists in high-temperature and high-pressure reservoirs. To elucidate the dynamic-change laws of the deep coal reservoir porosity and permeability characteristics in the process of coalbed methane production, based on three pieces of low- to medium-rank coal samples in the eastern Junggar Basin, Xinjiang, we analyse their mercury-injection pore structures. We measured the porosity and permeability of the coal samples at various temperatures and confining pressures by high-temperature and confining pressure testing. The results show that the porosity of a coal sample decreases exponentially with increasing effective stress. With increasing temperature, the initial porosity increases for two pieces of relatively low-rank coal samples. The increased rate of porosity decreases with increasing confining pressure. With increasing temperature, the initial porosity of a relatively high-rank coal sample decreases, and the rate of change of the porosity become faster. An exponential relationship exists between the porosity and permeability. With increasing coal rank, the initial porosity and permeability decrease. The change rate of the permeability decreases with increasing porosity.

Pore structure of selected Chinese coals with heating and pressurization treatments

Pore structure of Chinese coals with heating and pressurization treatments was studied using small angle X-ray scattering (SAXS), N2 adsorption/desorption isotherms and scanning electron microscope (SEM). SAXS was performed for some samples after heat treatment at seven elevated temperatures from 25 to 250° at 0 MPa and for other samples with hydrostatic pressure treatment at 0, 5, 10, 15 and 20 MPa at the room temperature. The results show that N2 adsorption isotherm together with SAXS could be a comprehensive method to evaluate the pore shape and the pore size distribution: the pore shapes are generally spherical for low rank coal and they are mainly ellipsoidal for high rank coal. All these measurements were then interpreted using the fractal theory to reveal relationship between surface fractals and coal rank, and the evolution of surface fractals under heating and pressurization treatments. The results show that surface fractal dimension (D s) changes with different treating temperature and pressure and maximum vitrinite reflectance (R o,m). Especially in the bituminous stage, D s shows an increasing trend with R o,m under varied temperatures. Moreover, D s shows an increasing trend with increasing temperature before 200°, and a decreasing trend after 200°. Furthermore, the results show that D s has a more complex relationship with R o,m under varied treating temperature than that under varied treating pressure.

Combined treatments of high-pressure with the lactoperoxidase system or lactoferrin on the inactivation of Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 in beef carpaccio

The effect of high hydrostatic pressure (HHP) treatments in combination with the lactoperoxidase system (LPOS) or activated lactoferrin (ALF) on Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Enteritidis and Escherichia coli O157:H7 was investigated in cured beef carpaccio stored at 8 °C or 22 °C during 7 d. HHP (450 MPa for 5 min) reduced pathogen levels by 1–3 log units and the antimicrobial effect remained during 7 d of storage under temperature abuse conditions at 8 °C and at 22 °C. The individual application of LPOS and ALF did not affect the survival of the three pathogens studied during storage. However, a synergistic bactericidal interaction between LPOS and HHP was observed against S. Enteritidis and E. coli O157:H7. Combined treatments of HHP with LPOS would be useful to reduce the intensity of pressurization treatments diminishing changes in the quality of meat products.

Functional analysis of embolism induced by air injection in Acer rubrum and Salix nigra.

The goal of this study was to assess the effect of induced embolism with air injection treatments on the function of xylem in Acer rubrum L. and Salix nigra Marsh. Measurements made on mature trees of A. rubrum showed that pneumatic pressurization treatments that created a pressure gradient of 5.5 MPa across pit membranes (ΔPpit) had no effect on stomatal conductance or on branch-level sap flow. The same air injection treatments made on 3-year-old potted A. rubrum plants also had no effect on whole plant transpiration. A separate study made on mature A. rubrum trees showed that 3.0 and 5.5 MPa of ΔPpit values resulted in an immediate 100% loss in hydraulic conductance (PLC) in petioles. However, the observed change in PLC was short lived, and significant hydraulic recovery occurred within 5–10 min post air-pressurization treatments. Similar experiments conducted on S. nigra plants exposed to ΔPpit of 3 MPa resulted in a rapid decline in whole plant transpiration followed by leaf wilting and eventual plant death, showing that this species lacks the ability to recover from induced embolism. A survey that measured the effect of air-pressurization treatments on seven other species showed that some species are very sensitive to induction of embolism resulting in leaf wilting and branch death while others show minimal to no effect despite that in each case, the applied ΔPpit of 5.5 MPa significantly exceeded any native stress that these plants would experience naturally.

초고압 열처리가 가열 돈육의 품질특성에 미치는 효과

This study evaluated the effects of thermal processing combined with high pressure on the properties of cooked pork. Pressurization followed by heating (PFH), heating followed by pressurization (HFP) and heating under pressurization (HUP) treatments were compared to a heated only control. Cooked meat without simultaneous pressurization showed little or no decrease in water binding properties relative to the control, regardless of the sequence of pressurization and heating. However, HUP treated pork had significantly higher water binding properties than the control (p<0.05). The pH values of all treatments were not significantly different with the exception of HUP at 300 MPa. The HUP treated pork showed the best tenderizing effects among all the treatments tested and the effect was more significant at increased pressure levels (p<0.05). In addition, increasing pressure levels significantly increased the L-values of pork (p<0.05). PFH and HFP treated pork had significantly lower a-values (p<0.05), while no significant differences were observed in HUP. HUP treated pork had the lowest b-values at 100 MPa. however, the differences were not significant at increasing pressure levels. These results indicate that heating under pressure is the best cooking condition for improving the quality characteristics of pork without adversely affecting its appearance.

Mechanism of the inactivation of bacterial spores by reciprocal pressurization treatment.

The mechanism of the inactivation of Bacillus subtilis spores by reciprocal pressurization (RP) was unclear. Therefore, the mechanism was investigated. To investigate the effects of RP and continuous pressurization (CP) treatments on the inactivation and injury of B. subtilis spores, spores were treated at 25, 35, 45 and 55 degrees C under 200, 300 and 400 MPa. RP treatment was effective in injuring and inactivating spores. Scanning electron microscopy and transmission electron microscopy observation showed that spores treated by RP treatment were more morphologically and structurally changed than the ones treated by CP treatment. There were significant differences between the release of dipicolinic acid (pyridine-2,6-dicarboxylic acid) by RP and CP treatments. From this result, it was concluded that the core fraction was released into the spore suspension. The mechanism of RP treatment is believed to work as follows: hydrostatic pressure treatment initiated germination of bacterial spores, and the repeated rapid decompression caused disruption, injury and inactivation of the germinated spores. This study indicated that the physical injury of bacterial spores was effective to inactivate the bacterial spores through the disruption of spores and leakage of their contents.

Effects of high hydrostatic pressure treatments on biogenic amine contents in goat cheeses during ripening.

The application of high-pressure treatment to accelerate cheese ripening may influence the occurrence and profile of biogenic amines. In some cases, high-pressure treatment could yield high amine content, whereas in others the amine concentrations were comparable with those in nontreated ones. Tyramine was the most affected amine. However, the influence of high pressure depended on the treatment applied. The highest amine concentrations were observed when 50 MPa for 72 h was applied, and in which, the content of tyramine was almost three times higher than in the untreated samples. On the contrary, when 400 MPa for 5 min or 400 MPa for 5 min plus 50 MPa for 72 h were applied contents of this amine were similar or lower than those found in control cheeses showing similar degrees of proteolysis. The higher proteolysis, induced by the pressurization treatments, was not correlated with the higher amine production.

Response to high-pressure, low-temperature treatment in vegetables: determination of survival rates of microbial populations using flow cytometry and detection of peroxidase activity using confocal microscopy.

Application of high hydrostatic pressure (200, 300, 350 and 400 MPa) at 5 degrees C for 30 min to different micro-organisms, including Gram-positive and Gram-negative bacteria, moulds and yeasts, proved to be more effective in inactivating these organisms than treatments at 20 degrees C for 10 min and at 10 degrees C for 20 min. Moulds, yeasts, Gram-negative bacteria and Listeria monocytogenes were most sensitive, and their populations were completely inactivated at pressures between 300 and 350 MPa. The same conditions of pressure, temperature, and time were applied to different vegetables (lettuce, tomato, asparagus, spinach, cauliflower and onion), achieving reductions of from 2-4 log units in both viable mesophiles and moulds and yeasts at pressures of between 300 and 400 MPa. Sensory characteristics were unaltered, especially in asparagus, onion, tomato and cauliflower, though slight browning was observed in cauliflower at 350 MPa. Flow cytometry was applied to certain of the microbial populations used in the above experiment before and after the pressurization treatment. The results were indicative of differing percentage survival rates depending on micro-organism type, with higher survival rates for Gram-positive bacteria, except L. monocytogenes, than in the other test micro-organisms. Growth of survivors was undetectable using the plate count method, suggesting that micro-organisms suffering from pressure stress were metabolically inactive though alive. The pressurization treatments did not inactivate the peroxidase responsible for browning in vegetables. Confocal microscopic examination of epidermal tissue from onion showed that the enzyme had been displaced to the cell interior. Use of low temperatures and moderately long pressurization times yielded improved inactivation of micro-organisms and better sensorial characteristics of the vegetables, and should lower industrial costs.

The effects of pressurization on the microstructure and mechanical properties of magnesium oxide

Changes in microstructure in single crystals of MgO, containing elastic discontinuities, which result from pressurization treatments in the range 0.2 to 2 GN m−2 have been studied using an etch-pitting technique. Complex dislocation arrays have been observed around cubical and spherical cavities and precipitates. The observations are discussed in terms of stress and strain criteria. Production of {100} and {110} cracks at high pressure is also described. Following a 1 GN m−2 pressurization the flow stress was observed to decrease by < 10% and this has been related to the induced dislocation density. In polycrystalline MgO the fracture strength was unaltered by pressurization but the critical temperature difference of thermal shock,ΔTC, was increased by 55K. This has similarly been attributed to the movement of pressurization-induced dislocations.

Hydrostatic pressure and the mechanical properties of NaCl polycrystals

Abstract The influence of hydrostatic pressure on the mechanical properties of extrusion-recrystallized NaCl polycrystals is examined. Interrupted compression tests show no effect of pressurization alone on the flow stress of these polycrystals. Small decreases in the flow stress occur upon reloading the specimen, regardless of the pressurization treatments, and are attributed to recovery between tests. These results, which are in contrast with reported tests on melt-grown polycrystals, show that the decrease in strength observed for polycrystals deformed in situ at 10 kbar, relative to those deformed at 1 atm, is not due to an increased density of mobile dislocations caused by pressurization alone.

Pressurization effects in chromium

Abstract Microstructural changes resulting from pressurization treatments have been studisd using transmission electron microscopy and an etch-pit technique; details of the etch-pit technique are given in an Appendix. ‘Free’ dislocations are produced at Cr2O3 particles in the chromium matrix due to the difference in compressibilities. Diffraction contrast analysis shows that the dislocation loops are prismatic and of vacancy type; their number is in reasonable agreement with strain calculations using compressibility data. The effect of pressurization on the tensile load/elongation curves for single crystals has been determined. The magnitude of the yield drop is decreased and the hardening rate for ‘single-slip’ orientations is increased, showing that the numerous pressure-induced dislocation sources lead to multiple slip from the onset of plastic flow. Etch-pit studies of the effects of various repeated pressurization and pressurization-ageing cycles correlate with changes in tensile characteristics.