High Pressure Destruction Research Articles

Frozen-Phase High-Pressure Destruction Kinetics of Escherichia coli as Influenced by Application Mode, Substrate, and Enrichment Medium.

The synergistic effect of frozen-phase high pressure (HP) on the inactivation of E. coli ATCC 25922 cultures in suspension medium, Chinese bayberry juice (pH 3.0), and carrot juice (pH 6.5) was evaluated. The survivor count of E. coli remained at 3.36 log CFU/mL on a nonselective brain heart infusion (BHIA) medium, while no survivor was detected on a selective violet red bile agar (VRBA) medium after a 5 min hold pressure at 250 MPa in a frozen culture suspension. BHIA was suitable for safe testing of the injured E coli cells after HP treatment in frozen state. Frozen Chinese bayberry juice showed higher sensitivity to HP treatment for its matrix property with high sterilizing efficiency at 170 MPa. Two pulses exhibited a significant inactivation effect in frozen samples compared with one pulse, especially for the Chinese bayberry juice with different pressure levels. The destruction kinetics of HP pulse mode followed the first-order rate kinetics with a Zp value of 267 MPa in frozen carrot juice. Our results evaluated the influenced factors of frozen HP destruction effects, including the medium, substrate, and application mode. The frozen HP destruction kinetics of pulses afford us better understanding of the technology application in the food industry.

High pressure destruction kinetics of Clostridium botulinum (Group I, strain PA9508B) spores in milk at elevated temperatures

Milk inoculated with Clostridium botulinum spores (PA9508B) (107 CFU/mL) was subjected to high-pressure high-temperature treatment (HPHT) (700–900 MPa; 90–110 °C for 0–24 min) using an insulated sample chamber, as well as in a water bath (90–100 °C) (conventional) and surviving spores were enumerated. Destruction kinetics were well described by a first order kinetic model. Conventional heating D values ranged from 156 to 12 min with a z value of 7.8 °C. During HPHT, higher pressures and temperatures resulted in accelerated spore destruction rates. At 900 MPa, the associated D values were 14.5, 1.8 and 0.35 min at 90, 100 and 110 °C, respectively, much lower than the conventional D values. The pressure dependent ZT values were 11.2, 12.3, 12.4 °C at 700, 800, 900 MPa respectively, increasing with pressure. The temperature dependent ZP values were 470, 630, and 800 MPa at 90, 100, and 110 °C, respectively. By comparing ZT with ZP values, it was clear the spores were relatively more sensitive at higher temperatures than at higher pressures in this temperature-pressure range. D value trends beyond 120 °C indicated thermal inactivation was the principal mode of spore destruction and high pressure can protect spores under these conditions.

ENSURING SAFETY AT PNEUMOTEST OF THE PIPELINE

The work considers the fundamentals of human life during pneumatic testing of pipeline. Invalid strength pipe and high pressure destruction occurs in the form of explosion of the object, accompanied by the appearance of a shock wave. The shock wave is a transient process is very quick conversion of substances with the release of large amounts of energy in a small volume and is one of the most dangerous effects on humans. The typical width of the shock wave in the air – 10-4 mm (several lengths of free path of molecules). Small thickness of such waves gives possibility in many problems to consider it as a discontinuity surface. But in some cases, it is the structure of the shock wave. This task is of theoretical interest. For weak shock waves, a good agreement of experiment and theory gives a model taking into account viscosity and conductivity of the environment. For shock waves of sufficiently high intensity structure should take into account (consistently) the stage of establishment of thermodynamic equilibrium, the translational, rotational, for molecular gases even and vibrational degrees of freedom, in certain conditions, the dissociation and recombination of molecules, chemical reactions, the processes involving electrons (ionization, electronic excitation). In this paper we have investigated the dependence of the conditional probability of defeat of a man from a change in the overpressure of the shock wave of the explosion. On the basis of the conducted researches the measures to prevent the occurrence of the shock wave pneumatic tests: strict adherence to safety standards and conditions for the maintenance of pressure in the pipeline, ensure an acceptable working range of conditions of the pneumatic tests, the availability of required serviceable equipment and fittings.

High pressure destruction kinetics along with combined effect of potassium sorbate and high pressure against Listeria monocytogenes in Indian white prawn muscle

High hydrostatic pressure treatment not only inactivates the pathogenic and spoilage microorganisms present in the food but also preserves its sensory and organoleptic characters and nutrient value. In this study, the high-pressure destruction kinetics of an important food-borne pathogen Listeria monocytogenes ATCC 19115 was studied in Indian white prawn (Fenneropenaeus indicus) muscle. Headless muscle of prawn was artificially spiked with L. monocytogenes ATCC 19115 at the level of approximately 107 CFU/g. The spiked samples were vacuum-packed in an ethylene vinyl alcohol (EVOH) pouch and then subjected to high-pressure treatment at different pressure levels (250, 300, 350 and 400 MPa) for different durations of time. Pressure D values were estimated at different pressure levels. The pressure D values at 250, 300, 350 and 400 MPa were estimated as 34.521, 11.806, 5.92 and 5.099 min, respectively. It was observed that, even after 400 MPa pressure treatment for 12 min, the concentration of the L. monocytogenes population was found to be 3.387 Log10 CFU/g. The combination of high pressure and potassium sorbate dip treatment (in acidic pH) was found to be very useful in inactivating L. monocytogenes. Potassium sorbate (0.1 %) dip for 15 min coupled with 250 and 350 MPa pressure reduced the level of L. monocytogenes by 2.345 and 5.908 Log10 CFU/g, respectively. Thus, it can be concluded that pressure treatment alone is not sufficient enough to inactivate this pathogen in prawn muscle. The combination of potassium sorbate with high-pressure treatment is a promising approach to inactivate L. monocytogenes in Indian white prawn muscle.

Kinetics of Escherichia coli inactivation in frozen aqueous suspensions by high pressure and its application to frozen chicken meat

High pressure destruction kinetics of Escherichia coli (ATCC 25922) in frozen and unfrozen aqueous suspensions were evaluated. Test samples were subjected to high pressure (HP) treatment at 200 to 400MPa for 0 to 10min at room temperature (∼20°C). K-type thermocouples were used to monitor sample temperatures. Sample temperature profile analysis indicated that ice phase transitions from Ice I to Ice III were induced in the frozen samples when the applied pressure was above 330MPa. Microbial survival curves indicated the D-values of E. coli associated with frozen samples were lower than those in unfrozen samples. The associated zp values of E. coli in frozen state (zp=196MPa) was lower than in unfrozen state (zp=250MPa) indicating E. coli in the frozen sample to be more pressure sensitive. A six-log reduction in E. coli was achieved in frozen samples after pressure treatment at >350MPa (example: 350MPa, 3min or 400MPa, 1min).

High-pressure destruction kinetics of Clostridium sporogenes ATCC 11437 spores in milk at elevated quasi-isothermal conditions

The high-pressure sterilization establishment requires data on isobaric and isothermal destruction kinetics of baro-resistant pathogenic and spoilage bacterial spores. In this study, Clostridium sporogenes 11437 spores (10 7 CFU/ml) inoculated in milk were subjected to different pressure, temperature and time ( P, T, t) combination treatments (700–900 MPa; 80–100 °C; 0–32 min). An insulated chamber was used to enclose the test samples during the treatment for maintaining isobaric and quasi-isothermal processing conditions. Decimal reduction times ( D values) and pressure and temperature sensitivity parameters, Z T (pressure constant) and Z P (temperature constant) were evaluated using a 3 × 3 full factorial experimental design. HP treatments generally demonstrated a minor pressure pulse effect (PE) (no holding time) and the pressure hold time effect was well described by the first order model ( R 2 > 0.90). Higher pressures and higher temperatures resulted in a higher destruction rate and a higher microbial count reduction. At 900 MPa, the temperature corrected D values were 9.1, 3.8, 0.73 min at 80, 90, 100 °C, respectively. The thermal treatment at 0.1 MPa resulted in D values 833, 65.8, 26.3, 6.0 min at 80, 90, 95, 100 °C respectively. By comparison, HP processing resulted in a strong enhancement of spore destruction at all temperatures. Temperature corrected Z T values were 16.5, 16.9, 18.2 °C at 700, 800, 900 MPa, respectively, which were higher than the thermal z value 9.6 °C. Hence, the spores had lower temperature sensitivity at elevated pressures. Similarly, corrected Z P values were 714, 588, 1250 MPa at 80, 90, 100 °C, respectively, which illustrated lower pressure sensitivity at higher temperatures. By general comparison, it was concluded that within the range operating conditions employed, the spores were relatively more sensitive to temperature than to pressure.

High-pressure destruction kinetics of Clostridium sporogenes spores in ground beef at elevated temperatures

High pressure (HP) is an alternative technique for thermal sterilization of foods with minimum quality loss. HP destruction kinetics of bacterial spores is essential to establishing sterilization process, but knowledge in this field is still very limited. In this study, destruction kinetics was investigated using Clostridium sporogenes PA 3679 (ATCC7955) spores in extra-lean ground beef (5 g each sealed in a sterile plastic bag). Duplicated samples were subjected to HP treatments at 700, 800 and 900 MPa in a HP system equipped with a Polyoxymethylene insulator to maintain constant temperatures at 80, 90 and 100 °C during pressure-holding time. The kinetic parameters of the spores ( D- and Z-values) were evaluated at these pressures and temperatures. For the pressure from 700 to 900 MPa, D-values ranged from 15.8 to 7.0 and 1.5 to 0.63 min at 80 and 100 °C, respectively. The pressure resistance of Z T( P) value was 520–563 MPa at 80–100 °C. The temperature resistance of Z P( T) value was 19.1–19.7 °C at 700–900 MPa, much higher than that at atmospheric condition (12.4 °C). A regression model was generated which can be used to predict D-value or the death time of a minimum process under given pressure and temperature conditions. HP treatment with elevated temperatures can destroy bacterial spores with a shorter time or lower temperature than conventional thermal processing. This study provides useful information for the achievement of a safe HP sterilization process.

Effects of fat, casein and lactose on high-pressure destruction of Escherichia coli K12 (ATCC-29055) in milk

High-pressure (HP) destruction of Escherichia coli K12 suspended in commercial pasteurized milk (0, 3.25 and 5% fat), peptone water (0.1%), and phosphate buffer (0.2 mol/l Na 2HPO 4 and 0.2 mol/l NaH 2PO 4) supplemented with different amounts of casein or lactose (1–4%) was investigated. HP treatment resulted in the highest level of E. coli destruction in the buffer (possibly because it contained no nutrients), followed by those in peptone water and least in milk. Therefore, milk and peptone provided some baro-protection to the destruction of E. coli during the HP treatment. Fat content in milk between 0, 3.25 and 5% had no significant ( P > 0.05) influence on the HP destruction of E. coli. The supplement of either casein or lactose to milk did not influence the level of HP destruction of E. coli. However, the baro-protection became significant during HP treatment when casein or lactose was added the buffer. The buffer solution supplemented with 1–4% casein showed a baro-protective effect equivalent to that in milk. Lactose supplement to buffer also caused baro-protection, though the effect was relatively less pronounced. However, no significant difference in the baro-protection effect was observed among the buffer samples supplemented with different levels (1, 2 and 4%) of lactose or casein. Therefore the major contributors for baro-protection of E. coli in milk during HP treatment appear to be casein and lactose, rather than the fat content.

Compression Heating and Temperature Control for High-Pressure Destruction of Bacterial Spores: An Experimental Method for Kinetics Evaluation

High-pressure (HP) processing is considered as an alternative technique for thermal sterilization of high quality foods. Adiabatic compression during pressurization allows for quick increase in temperature of food products, which is reversed when the pressure is released, thereby providing rapid heating and cooling conditions and hence short process times. However, during the pressure holding time, the product experiences a temperature drop as a result of heat loss to the vessel. The temperature variation during the process and the synergistic effect of temperature and pressure make it difficult to get the required accurate data on microbial spore destruction kinetics. In this study, a polyoxymethylene (POM)-insulated chamber was evaluated for temperature control in the test sample during pressure treatment. Temperature variations in the HP system were measured in milk test samples inside the POM insulator and pressure medium in the HP vessel under various conditions of pressures (500–900 MPa) and initial temperatures (20–80 °C). Results demonstrated that the POM chamber had good thermal-insulation characteristics under pressure and was able to maintain stable operating conditions for microbial spore destruction kinetics. Based on the measured adiabatic temperature change, the required initial temperatures for the test sample and pressure medium were generated as a quadratic function of pressure and temperature. The setup was then verified for pressure inactivation of Clostridium sporogenes (PA 3679) spores in ultra-heat-treated milk. The better temperature stability of test samples during treatment provided a means to gather accurate data on HP destruction kinetics of the microbial spores.

High pressure destruction kinetics of Escherichia coli (O157:H7) and Listeria monocytogenes (Scott A) in a fish slurry

High pressure (HP) destruction kinetics of Escherichia coli (O157:H7) and Listeria monocytogenes (Scott A) in mackerel ( Scomber scombrus) were evaluated. Filleted fish were made into a slurry with peptone water and inoculated with the respective microbial strain to prepare a stock culture containing 10 6–10 7 CFU/ml. Samples were prepared for pressure treatment by heat-sealing 10 ml portions of stock culture in sterile plastic bags. Pressure treatments (250 and 400 MPa for 0–60 min) were given at room temperature (20–25 °C) in an isostatic press. Survival curves were established based on residual counts following treatment. Destruction kinetics were described as a dual effect, an initial destruction resulting from a pressure pulse (pulse effect) followed by a first order rate of destruction during the pressure holding time. E. coli was found to be more sensitive to pulse pressure than L. monocytogenes. Significant differences ( p < 0.05) in high pressure resistance ( D-value) were found between the two microorganisms. D-values of E. coli were higher than for L. monocytogenes at pressure levels ⩾350 MPa, while a reverse trend was observed at lower pressures. The associated z p values indicated that the destruction rate of L. monocytogenes ( z p = 103 MPa) was more sensitive to changes in pressure than E. coli ( z p = 185 MPa). Challenge studies with the more resistant pathogen, E. coli (10 7/ml), showed that a 10 D treatment followed by refrigerated storage (4–12 °C) prevented its recovery/growth.

High‐Pressure Destruction Kinetics of E. coli(29055) in Apple Juice

ABSTRACTHigh‐pressure (HP) destruction of Escherichia coli (29055) in apple juice was evaluated (150 to 400 MPa; 0 to 80 min at 25 °C) based on a dual destruction behavior consisting of pressure pulse and pressure hold (first order rate) effects. Enumeration was carried out in brain‐heart infusion agar (BHIA) and violet‐red bile agar (VRBA) to differentiate between surviving cells with and without injury. A pressure pulse at 400 MPa destroyed the entire population (108 CFU/mL) of E. coli. During pressure‐hold, D values (decimal reduction time) of E. coli decreased with an increase in pressure, and D values from BHIA (survivors including injured cells) were higher than from VRBA (survivors excluding injured cells). Thus, an increasing number of cells were initially injured than killed with HP treatment until finally killed. Pressure dependency of D was described by z‐value model with associated zp values (pressure range to result in a decimal change in D values) of 126 and 140 MPa on BHIA and VRBA.

High pressure destruction kinetics of Leuconostoc mesenteroides and Saccharomyces cerevisiae in single strength and concentrated orange juice

High pressure (HP) destruction of Leucoonostoc mesenteroides and Saccharomyces cerevisiae in single strength and concentrated orange juice by high hydrostatic pressure treatment was evaluated at selected pressures (100–400 MPa) and holding times (0–120 min) at 20 °C. Kinetic analysis of the microbial survivor data was evaluated based on the biphasic destruction behavior consisting of: (i) an instantaneous pressure kill (IPK) effect due to pressurization–depressurization with no hold-time (pressure-pulse); and (ii) a subsequent semi-logarithmic (first order) destruction during the pressure hold-time. IPK values were enhanced at higher pressure levels and were more pronounced for S. cerevisiae than for L. mesenteroides. During the pressure-hold, as expected, the associated D values (decimal reduction time) decreased with an increase in pressure. However, S. cerevisiae had higher D values, especially in concentrated orange juice, suggesting a higher pressure resistance than L. mesenteroides. The pressure dependency of kinetic parameters was well described by the conventional death time model with associated z p values (pressure range to result in a decimal change in D values) of 137 and 135 MPa in the single strength orange juice and 251 and 287 MPa in the concentrate, respectively, for L. mesenteroides and S. cerevisiae.

High pressure (HP) destruction kinetics of Listeria monocytogenes Scott A in raw milk

Raw milk containing the natural microflora (NM) and an inoculated 24 h culture of Listeria monocytogenes Scott A (10 6 cfuml −1 each) were heat sealed in dual peel sterilization pouches and subjected to high pressure (HP) treatment at 150 to 400 MPa for selected holding times of up to 120 min. HP destruction of NM and L. monocytogenes were evaluated based on first order kinetics, pressure destruction time (PDT) and Arrhenius type models. Results showed a dual effect pressure destruction of microorganisms consisting of (i) an instantaneous pressure kill effect (IPK) with the application of a pressure pulse (no holding time) and (ii) a subsequent first order rate of destruction during the pressure holding time. In general, both IPK and rate constants (k-values) increased with an increase in pressure while the corresponding decimal reduction times (D-values) decreased. The IPK was more pronounced with L. monocytogenes than NM. However, the kinetic parameters indicated a larger pressure resistance for L. monocytogenes. Pressure dependency of kinetic parameters was well described by both pressure destruction time (PDT) and Arrhenius models ( R 2>0.95). The z p values (PDT) were 266 and 244 MPa and ΔV ≠ (Arrhenius) values were −2.11 and −2.30 × 10 −5 m 3mol −1 for L. monocytogenes Scott A and NM, respectively.