Effect of carbon dioxide pressure on Listeria monocytogenes in physiological saline and foods

The effect of 15,30 and 60 atm CO₂pressure at 25,35 and 45°C on Listeria monocytogenes was studied. A biphasic curve was observed in the CO₂treatments. A primary curve was characterized with very little killing and a secondary curve was showed straight-line inactivation kinetics. An increase of pressure and/or temperature enhanced the antimicrobial effects of CO₂. Listeria monocytogenes suspended in physiological saline containing 1% brain–heart infusion broth was completely inactivated under 60 atm CO₂treatment in 115,75 and 60 min at 25,35 and 45°C, respectively. A minimum D -value was obtained under 60 atm CO₂pressure at 45°C. High pressure CO₂treatment technique can possibly be applied to reduce microbiol load in whole and skim milk; and carrot, orange, peach, and apple juices.     

Inactivation of Pectinesterase in Orange Juice by Supercritical Carbon Dioxide

Single strength orange juice was treated with supercritical carbon dioxide (CO₂) and the effect of process time, temperature and pressure on pectinesterase (PE) activity was determined. PE could be inactivated with supercritical CO₂ below temperatures necessary for thermal inactivation. Higher pressure, temperature and longer treatment time resulted in more inactivation. Inactivation kinetics showed activation energy was significantly reduced at SC C0₂ treatment at 31 MPa (97.4 KJ/mole), compared to identical treatments at atmospheric pressure (166.6 KJ/mole). D values ranged from 2673 min at atmospheric pressure and 40°C to 10 min at 31 MPa and 60°C. z value at atmospheric pressure was 8.8C°, and at 31 MPa 5.2C°.     

Antimicrobial Effect of Pressurized Carbon Dioxide on Listeria monocytogenes

Listeria monocytogenes was inactivated by carbon dioxide at 35 and 45°C under pressures of 70.3 and 210.9 μg/cm². Inactivation rates were sensitive to temperature and pressure. Other factors such as pH, moisture content, and environmental conditions of cell growth also influenced the effectiveness of CO₂ treatment. Bacteria were more difficult to inactivate when they were suspended in the medium with fat or oil, which may have protected the cells from penetration by CO₂. Fat in growth medium where Listeria monocytogenes cells were inoculated apparantly increased their resistance. Several methods may be useful for increasing inactivation rates.     

Effects of High Hydrostatic Pressure on Heat-Resistant and Heat-Sensitive Strains of Salmonella

Salmonella senftenberg 775W, a heat-resistant strain (D_57.5°C= 15.0 min) and Salmonella typhimurium ATCC 7136, a heat-sensitive strain (D_57.5°C=3.0 min), were subjected to hydrostatic pressures of 2,380 to 3,400 atmospheres (atm) at 23°C in phosphate buffer (63 mM, pH 7.0) and chicken medium (strained baby food). Survivor curves showed that cell death occurred in this pressure range and increased as pressure increased. Death was greater in buffer than in the chicken medium. S. senftenberg 775W was more sensitive to pressure than S. typhimurium 7136. Injury occurred over the range of pressures for both species. Recovery at 37°C was possible following pressurization for salmonellae in chicken but not in buffer.     

Antimicrobial effect of pressurised carbon dioxide on Enterococcus faecalis in physiological saline and foods

Inactivation of Enterococcus faecalis by high‐pressure CO₂ was investigated in a batch system. Two phases were observed in the survival curves. The earlier stage was characterised by a slow rate of decrease in the number of E faecalis. This rate increased sharply at the later stage. Enterococcus faecalis suspended in physiological saline was completely inactivated under 6.05 and 3.02 MPa CO₂ treatment in 18 and 80 min respectively at 35 ° C. The high pressure of CO₂ at 45 ° C was effective at sterilising orange, peach and carrot juices but ineffective for whole and skimmed milk. A minimum D‐value was obtained under 6.05 MPa CO₂ pressure at 45 ° C. Reduction rates of E faecalis were sensitive to pressure, temperature, exposure time, the initial number of cells and the suspending medium. © 2000 Society of Chemical Industry     

Antimicrobial effects of pressurised carbon dioxide on Brochothrix thermosphacta in broth and foods

Antimicrobial effects of high‐pressure CO₂ on Brochothrix thermosphacta were investigated in a batch system. Inactivation rates increased with increasing pressure, temperature and exposure time. B thermosphacta suspended in physiological saline was completely inactivated under 6.05, 3.02 and 1.51 MPaCO₂ treatment at 35 °C after 10, 25 and 50 min respectively. Two phases were observed in the survival curves. The earlier stage was characterised by a slow rate of decrease in the number of B thermosphacta, which increased sharply at the later stage. B thermosphacta suspended in brain heart infusion broth was completely inactivated under 6.05 MPaCO₂ treatment after 80, 50 and 30 min at 25, 35 and 45 °C respectively. About 6.90 and 5.93 log cycles of B thermosphacta were reduced under 6.05 MPaCO₂ pressure at 45 °C in whole and skimmed milk respectively. The sterilisation effects of 6.05 MPaCO₂ pressure at 45 °C on both B thermosphacta and aerobic plate count were observed after 150 and 120 min respectively in skinned meat. © 2000 Society of Chemical Industry     

Destruction of Salmonella enteritidis inoculated in liquid whole egg by high hydrostatic pressure: comparative study in selective and non-selective media

The destruction of Salmonella enteritidis inoculated in liquid whole egg at approximately 10⁷−10⁸cfu ml^−lwas studied under combinations of pressure (350 and 450 MPa), temperature (50, 20, 2 and −15°C) and time (5, 10, 15 min and cycles of 5+5 and 5+5+5 min). One non-selective medium (tryptone soy agar) and two selective media (brilliant green agar and salmonella-shigella) were used to evaluate viability of S. enteritidis after pressurization. The inactivation rate increased with pressure and exposure time, being minimal at 350 MPa and −15°C for 5 min (over 1 log₁₀of reduction) and reaching total inactivation (8 log₁₀of reduction) in several treatments at 50°C. Treatments in cycles showed greater effectiveness than continuous treatments of the same total time. The effect of pressure was enhanced by elevated temperatures. The higher counts were obtained in the non-selective medium, indicating the presence of injured cells after pressure treatment. D -values obtained for two temperatures (2 and 20°C) and different times (0–60 min) under controlled pressure (400 MPa) showed that microbial inactivation followed a first-order kinetics with a decimal reduction time evaluated in tryptone soy agar medium of 9·5 min at 2°C and 8·8 min at 20°C.     

Modeling the combined effect of high hydrostatic pressure and mild heat on the inactivation kinetics of Listeria monocytogenes Scott A in whole milk

The survival curves of Listeria monocytogenes Scott A inactivated by high hydrostatic pressure were obtained at four temperatures (22, 40, 45 and 50 °C) and two pressure levels (400 and 500 MPa) in UHT whole milk. Elevated temperatures substantially promoted the pressure inactivation of L. monocytogenes. A 5-min treatment of 500 MPa at 50 °C resulted in a more than 8-log₁₀ reduction of L. monocytogenes, while at 22 °C a 35-min treatment was needed to obtain the same level of inactivation. Tailing was observed in all survival curves, indicating that the linear model was not adequate for describing these curves. The log-logistic model consistently produced best fits to all survival curves and the modified Gompertz model the poorest. The Weibull model produced fits as good as the log-logistic model at the temperature range of 40–50 °C. The Weibull model provided reasonable predictions of inactivation of L. monocytogenes at temperature levels other than the experimental temperatures; however, the log-logistic model was found to be inferior at predicting inactivation.     

Inactivation of Lactobacillus fructivorans in physiological saline and unpasteurised sake using CO2 microbubbles at ambient temperature and low pressure

The ability of carbon dioxide microbubbles (MB‐CO₂) to inactivate Lactobacillus fructivorans suspended in physiological saline and unpasteurised sake at ambient temperature and a pressure lower than 2.0 MPa was investigated. The number of L. fructivorans cells in physiological saline solution containing 15% ethanol showed a 6‐log reduction following MB‐CO₂ treatment at 40 °C and 2.0 MPa for 50 min. The effectiveness of the treatment increased concomitantly with temperature, pressure and ethanol concentration of the sample solution but was unaffected by the glucose concentration in the sample solution. Furthermore, the number of L. fructivorans cells showed a 5‐log reduction in sake after MB‐CO₂ treatment at 40°C and 2.0 MPa for 60 min. Sensory evaluation revealed no significant difference between MB‐CO₂‐treated sake and unpasteurised sake. These results indicated that MB‐CO₂ treatment was highly effective for the inactivation of L. fructivorans and might become a practical method for pasteurising sake at ambient temperature.     

Inactivation of Escherichia coli by Carbon Dioxide under Pressure

Thermal inactivation of Escherichia coli was studied under CO₂ pressures of 1.2, 2.5, and 5 MPa at 25, 35, and 45°C. Two phases were observed in the destruction curves. The earlier stage was characterized by a slow rate of inactivation, which increased sharply at the later stage. An increase of pressure and/or temperature enhanced the antimicrobial effects of CO₂ under pressure. The effects on cell structure were studied by scanning electron microscopy and the specific mechanism of action appeared to be related to enzyme inactivation.     

Effect of carbon dioxide on the inactivation of florida spiny lobster polyphenol oxidase

Florida spiny lobster (Panulirus argus) polyphenol oxidase (PPO) exposed to CO₂ (1 atm) at 33, 38, and 43°C showed a decrease in enzyme activity with increased heating time. Enzyme inactivation by CO₂ was faster for PPO heated at 43 than at 33 or 38°C. Inactivation kinetics revealed PPO was more labile to CO₂ and heat in the range 33–43°C than to heat alone. Kinetic data also revealed that CO₂, in addition to pH changes, was involved in the loss of PPO activity. Studies using get electrophoresis showed no differences in protein patterns and isoelectric point between CO₂-treated and non-treated control. The pH of CO₂-treated PPO stock solution was brought back from 5.4 to 8.0 after 6 weeks of frozen-storage and no enzyme reactivation was observed.     

The effect of oregano essential oil on survival/death of Salmonella typhimurium in meat stored at 5°C under aerobic,VP/MAP conditions

The effect of oregano essential oil and film permeability on the behaviour of Salmonella typhimurium in sterile and naturally contaminated beef fillets stored under aerobic, modified atmosphere consisting of 40% CO₂ /30% O₂ /30% N₂ (MAP) and a vacuum packaged (VP) environment was studied during storage at 5°C. In samples without oregano essential oil, the pathogen survived under all storage conditions. Addition of oregano essential oil at a concentration of 0·8% v/w resulted in an initial reduction of 1–2 log₁₀ cfu g⁻¹ of the majority of the microbial population of meat with lactic acid bacteria and S. typhimurium showing the greatest reductions in all gaseous environments regardless of film permeability. The use of VP/MAP at chill temperatures in conjunction with oregano essential oil as a means of controlling spoilage and safety of meat is discussed.     

Microbial and Sensory Effects of Combined High Hydrostatic Pressure and Dense Phase Carbon Dioxide Process on Feijoa Puree

High hydrostatic pressure (HHP) is used for microbial inactivation in foods. Addition of carbon dioxide (CO₂) to HHP can improve microbial and enzyme inactivation. This study investigated microbial effects of combined HHP and CO₂ on Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae, and evaluated sensory attributes of treated feijoa fruit puree (pH 3.2). Microorganisms in their growth media and feijoa puree were treated with HHP alone (HHP), or saturated with CO₂ at 1 atm (HHPcarb), or 0.4%w/w of CO₂ was injected into the package (HHPcarb+CO₂). Microbial samples were processed at 200 to 400 MPa, 25 °C, 2 to 6 min. Feijoa samples were processed at 600 MPa, 20 °C, 5 min, then served with and without added sucrose (10%w/w). Treated samples were analyzed for microbial viability and sensory evaluation. Addition of CO₂ enhanced microbial inactivation of HHP from 1.7‐log to 4.3‐log reduction in E. coli at 400 MPa, 4 min, and reduction of >6.5 logs in B. subtilis (vegetative cells) starting at 200 MPa, 2 min. For yeast, HHPcarb+CO₂ increased the inactivation of HHP from 4.7‐log to 6.2‐log reduction at 250 MPa, 4 min. The synergistic effect of CO₂ with HHP increased with increasing time and pressure. HHPcarb+CO₂ treatment did not alter the appearance and color, while affecting the texture and flavor of unsweetened feijoa samples. There were no differences in sensory attributes and preferences between HHPcarb+CO₂ and fresh sweetened products. Addition of CO₂ in HHP treatment can reduce process pressure and time, and better preserve product quality.     

Supercritical CO2 and N2O pasteurisation of peach and kiwi juice

The microbial inactivation and qualitative parameters (pH, sugar content, titratable acidity, absorbance at 420 nm and turbidity) of peach and kiwi juices treated at 35 °C with supercritical carbon dioxide (SC‐CO₂) and nitrous oxide (SC‐N₂O) were determined as a function of pressure and treatment time. Total inactivation of both naturally occurring microorganisms and Saccharomyces cerevisiae strain (10⁵ cfu mL^?1) was obtained after 15 min of SC‐CO₂/N₂O treatment, 10 MPa and 35 °C, for both juices. No significant changes in chemical‐physical or in sensorial characteristics between untreated and treated juice were detected. The results obtained demonstrate the feasibility and the potential of SC‐CO₂/N₂O treatment as an alternative low temperature pasteurisation process for peach and kiwi juices.     

Antimicrobial Effects of Pressured Carbon Dioxide in a Continuous Flow System

The application of microbubbles of pressured CO₂ greatly increased CO₂ concentration in the solution treated. By treatment at 6 MPa, 35°C and average residence time 15 min, L. brevis was completely inactivated at the level of dissolved CO₂,γ≧ 11 (γ, Kuenen's gas absorption coefficient). E. coli and S. cerevisiae required γ≧ 17, and T. versatilis required γ≧ 21 for complete inactivation. Z. rouxii could be sterilized at 20 MPa and 26. A comparison of the continuous and batch method showed that L. brevis was inactivated completely under pressured CO₂ > 0.16 g/cm³ with the continuous method and >0.9 g/cm³ with the batch method.     

Inactivation of yeasts in grape juice using a continuous dense phase carbon dioxide processing system

The effects of dense phase CO₂ processing parameters, including temperature (25 and 35 °C), CO₂ concentration (0, 85 and 170 g kg⁻¹) and pressure (6.9, 27.6 and 48.3 MPa), on yeast survival and sensory properties of grape juice were investigated. The dense phase CO₂ process resulted in more than a 6 log reduction in yeast population. As the CO₂ to juice concentration, temperature and pressure increased, the inactivation rate increased. CO₂ in the supercritical state was more effective in inactivating yeast than in the subcritical state. The process did not cause detectable flavor degradation. Dense phase CO₂ processing can be an effective non‐thermal alternative process for pasteurization of grape juice. Copyright © 2005 Society of Chemical Industry     

EFFECT OF SUPERCRITICAL CARBON DIOXIDE ON MICROBIAL POPULATIONS IN SINGLE STRENGTH ORANGE JUICE1

The effect of supercritical carbon dioxide on aerobic total plate count (TPC) of fresh-squeezed and quick-frozen single strength orange juice from Valencia oranges was studied. Orange juice was treated with SC CO₂ at different temperatures (35° to 60°C) and pressures (8.3 to 33.1 MPa). SC CO₂ treatment at 35°C reduced the TPC by 2 log cycles after 1 h treatment at 33 MPa. At 45°C and 33 MPa 2 log cycles reduction required 45 mins, and 15 mins treatment was sufficient at 60°C. D values of temperature control samples decreased as temperature increased, while that of supercritically treated juice decreased as pressure increased. D values at 35, 45 and 60°C of the supercritically treated juice at 33.1 MPa were calculated as 28, 22.6 and 12.7 min, respectively. The calculated values of z were 180°C, 167°C and 72°C at 8.3 MPa, 20.7 MPa and 33.1 MPa, respectively.     

Inactivation Kinetics of Lactobacillus plantarum by High Pressure Carbon Dioxide

Inactivation kinetics of Lactobacillus plantarum by high pressure CO₂ was investigated to understand the mechanism of microbial inactivation. The inactivation rates increased with pressure, temperature and exposure time, and with decreasing pH of media. Microbial inactivation was governed essentially by penetration of CO₂ into cells and its effectiveness could be improved by the enhanced transfer rate. Microbial reduction of 8 log cycles was observed within 120 min under CO₂ pressure of 70 kg/cm² at 30°C. We hypothesized that the cell death resulted from the lowered intracellular pH and damage to the cell membrane due to penetration of CO₂. Pressurized CO₂ treatment is a potential nonthermal technology for food preservation.     

Salmonella Inactivation in Liquid Whole Egg by Thermoradiation

Salmonella enteritidis in liquid whole egg (LWE) was inactivated using heat, radiation and thermoradiation (combined heat and radiation). Rates of Salmonella inactivation were determined as a function of radiation dose, temperature, initial cell number and pH. Thermoradiation caused a greater reduction in viable cell number than either heat or radiation alone. This effect was more pronounced at pH 6.5 than at pH 7.0, and more so at 60°C than at 50°C. The lower the initial cell number, the faster the rate of Salmonella inactivation. Physical denaturation of LWE was not apparent after thermoradiation below 60°C, and endogenous egg white lysozyme was not affected by thermoradiation (19.5 krad, 60°C) treatment.     

EFFECTS OF HYDROSTATIC PRESSURE ON ALPHA-MACROGLOBULIN AND SELECTED PROTEASES

The enzymes, chymotrypsin, trypsin, collagenase and cathepsin C, as well as the protease inhibitor, α₂-macroglobulin, have been shown to be susceptible to hydrostatic pressure inactivation. a₂-Macroglobulin lost about 15% activity at a pressure of 2,000 atm and as much as 80% at 3,000 atm pressure applied for 1 h in both cases. Thermal stability studies also indicated the protein to be completely denatured at about 75C. The enzymes were also inactivated to various extents depending on the amount of pressure and the duration of application, The degree of susceptibility to pressures ranging between 2,000–4,000 atm applied for time periods ranging from 5–60 min was found to be as follows: chymotrypsin < cathepsin < trypsin < collagenase. The hydrostatic pressure effects were irreversible when pressure-treated enzymes were stored at room temperature (20–25C), but showed various levels of reactivation when stored at refrigerated temperatures (4–7C).