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The global carbon dioxide in the atmosphere is predicted to rise due to fossil fuel emissions during the next century. Carbon dioxide is soluble in water and partially dissociates into bicarbonate and carbonate, releasing protons that decrease the pH. This change in pH is expected to play a critical role in some earth systems, such as the hydrosphere, where ocean acidification affects the survival of marine organisms. This study used aqueous solutions consisting of water with sodium bicarbonate, Miller's lysogeny broth, Roswell Park Memorial Institute 1640 medium, and Dulbecco's Modified Eagle Medium to develop a colourimetric method for the quantification of dissolved carbon dioxide. Various environmental testing conditions were studied using a fluorescent microplate spectrophotometer. The temperature varied between 27 and 42 °C, and the carbon dioxide levels ranged from 0.20 to 10% v/v in the air. The data showed that the amount of dissolved carbon dioxide decreased by 50% in broth solutions, while the reduction in water samples was approximately 18% when the temperature rose from 27 to 42 °C. Furthermore, the composition of the solutions impacted the amount of gas dissolved. The highest amount of dissolved carbon dioxide was observed in the water sample with the lowest salinity, which reached 20,000 ppm CO2 at 27 °C. The lowest amount of dissolved carbon dioxide concentrations was obtained in Miller's lysogeny broth with the highest salinity level, which reached 1200 ppm under the same conditions. The results obtained can be considered a robust estimation method to calculate the amount of dissolved carbon dioxide under different conditions. [ABSTRACT FROM AUTHOR]

Studies were undertaken to investigate the effect of different modified atmospheric packaging (MAP) gaseous combinations on Campylobacter and the natural microflora on poultry fillets. Skinless chicken fillets were stored in gaseous mixtures of 10%, 30%, 50%, 70% and 90% CO2 balanced with N2, 80:20% O2:N2 and 40:30:30% CO2:O2:N2 and control conditions (air) at 2 °C. Samples were analysed periodically for (previously inoculated) Campylobacter, total viable counts (TVC) (mesophiles), TVC (psychrophiles), Enterobacteriaceae, Pseudomonas and lactic acid bacteria (LAB) over 17 days of storage. The carbon dioxide solubility was determined by monitoring the changes in the headspace volume over time using a buoyancy technique and performing calculations based on volumetric measurements and the Henry's constant. Henry's constant was also used to estimate the oxygen solubility in the chicken fillets. The presence of O2 in the MAP gaseous mixtures increased the rate of Campylobacter decline on poultry fillets but in general the counts obtained in aerobic versus anaerobic packs were not significantly (P > 0.05) different. CO2 inhibited the growth of TVC, TEC, LAB and Pseudomonas but only at MAP gaseous combinations containing 50-90% CO2 where concentrations of up to 2000 ppm CO2 were recorded in the fillets after 5 days. Under these conditions a shelf-life in excess of 17 days at 2 °C was obtained. Although, dissolved O2, at levels of 33 ppm in 80:20% O2:N2 packs after 3 days, reduced Campylobacter, it also favoured the growth of the other microbes on the chicken. The optimum gaseous mixture for achieving the combined objectives of reducing Campylobacter and extending shelf was therefore 40:30:30 CO2:O2:N2, which achieved a shelf-life in excess of 14 days. [ABSTRACT FROM AUTHOR]

A plasma source, sustained by the application of a floating high voltage (±15 kV) to parallel-plate electrodes at 50 Hz, has been achieved in a helium/air mixture at atmospheric pressure (P = 105 Pa) contained in a zip-locked plastic package placed in the electrode gap. Some of the physical and antimicrobial properties of this apparatus were established with a view to ascertain its performance as a prototype for the disinfection of fresh produce. The current-voltage (I-V) and charge-voltage (Q-V) characteristics of the system were measured as a function of gap distance d, in the range (3 × 10³ = Pd = 1.0 × 104 Pa m). The electrical measurements showed this plasma source to exhibit the characteristic behaviour of a dielectric barrier discharge in the filamentary mode and its properties could be accurately interpreted by the two-capacitance in series model. The power consumed by the discharge and the reduced field strength were found to decrease quadratically from 12.0 W to 4.5 W and linearly from 140 Td to 50 Td, respectively, in the range studied. Emission spectra of the discharge were recorded on a relative intensity scale and the dominant spectral features could be assigned to strong vibrational bands in the 2+ and 1- systems of N2 and N2+, respectively, with other weak signatures from the NO and OH radicals and the N+, He and O atomic species. Absolute spectral intensities were also recorded and interpreted by comparison with the non-equilibrium synthetic spectra generated by the computer code SPECAIR. At an inter-electrode gap of 0.04 m, this comparison yielded typical values for the electron, vibrational and translational (gas) temperatures of (4980 ± 100) K, (2700 ± 200) K and (300 ± 100) K, respectively and an electron density of 1.0 × 1017 m-3. A Boltzmann plot also provided a value of (3200 ± 200 K) for the vibrational temperature. The antimicrobial efficacy was assessed by studying the resistance of both Escherichia coli K12 its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK selected to identify possible cellular responses and targets related with 5 min exposure to the active gas in proximity of, but not directly in, the path of the discharge filaments. Both the parent strain and mutants populations were significantly reduced by more than 1.5 log cycles in these conditions, showing the potential of the system. Post-treatment storage studies showed that some transcription regulators and specific genes related to oxidative stress play an important role in the E. coli repair mechanism and that plasma exposure affects specific cell regulator systems. [ABSTRACT FROM AUTHOR]

To investigate the effect of the oxidative stress of ozone on the microbial inactivation, cell membrane integrity and permeability and morphology changes of Escherichia coli. Escherichia coli BW 25113 and its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK genes were treated with ozone at a concentration of 6 μg ml for a period up to 240 s. A significant effect of ozone exposure on microbial inactivation was observed. After ozonation, minor effects on the cell membrane integrity and permeability were observed, while scanning electron microscopy analysis showed slightly altered cell surface structure. The results of this study suggest that cell lysis was not the major mechanism of microbial inactivation. The deletion of oxidative stress-related genes resulted in increased susceptibility of E. coli cells to ozone treatment, implying that they play an important role for protection against the radicals produced by ozone. However, DnaK that has previously been shown to protect against oxidative stress did not protect against ozone treatment in this study. Furthermore, RpoS was important for the survival against ozone. This study provides important information about the role of oxidative stress in the responses of E. coli during ozonation. [ABSTRACT FROM AUTHOR]

Traditionally, ozone processing within the food industry has focused on solid foods by either gaseous treatment or washing with ozonized water. However, with the FDA's approval of ozone as a direct additive to food, the potential for liquid applications has emerged. This study investigates the effect of ozone processing on microbial inactivation ( E. coli ATCC 25922 and NCTC 12900) and quality parameters (color, phenolic content) of cloudy apple juice. Apple juice samples were ozonated at room temperature (20 ± 1.5 °C) with a generated ozone concentration of 0.048 mg O at a constant flow rate of 0.12 L/min and treatment time of 0 to 10 min. E. coli inactivation kinetics in apple juice were described quantitatively by using the Shoulder log-linear and the Weibull model. Ozone treatment of E. coli in apple juice demonstrate that a desired 5 log reduction can be achieved within 5 min. Apple juice color ( L*, a*, and b*) and total phenols were significantly affected by ozone concentration and treatment time. [ABSTRACT FROM AUTHOR]

Abstract: Organic acids (e.g., lactic acid, acetic acid and citric acid) are popular preservatives. In this study, the Listeria innocua inactivation is investigated under dynamic conditions of pH and undissociated lactic acid ([LaH]). A combined primary (Weibull-type) and secondary model developed for the L. innocua inactivation under static conditions [Janssen, M., Geeraerd, A.H., Cappuyns, A., Garcia-Gonzalez, L., Schockaert, G., Van Houteghem, N., Vereecken, K.M., Debevere, J., Devlieghere, F., Van Impe, J.F., 2007. Individual and combined effects of pH and lactic acid concentration on L. innocua inactivation: development of a predictive model and assessment of experimental variability. Applied and Environmental Microbiology 73(5), 1601–1611] was applied to predict the microbial inactivation under dynamic conditions. Because of its non-autonomous character, two approaches were proposed for the application of the Weibull-type model to dynamic conditions. The results quantitatively indicated that the L. innocua cell population was able to develop an induced acid stress resistance under dynamic conditions of pH and [LaH]. From a modeling point of view, it needs to be stressed that (i) inactivation model equations and associated parameter values, derived under static conditions, may not be suitable for use as such under dynamic conditions, and (ii) non-autonomous dynamic models reveal additional technical intricacies in comparison with autonomous models. [Copyright &y& Elsevier]

The large potential of cold atmospheric plasma (CAP) for food decontamination has recently been recognized. Room-temperature gas plasmas can decontaminate foods without causing undesired changes. This innovative technology is a promising alternative for treating fresh produce. However, more fundamental studies are needed before its application in the food industry. The impact of the food structure on CAP decontamination efficacy of Salmonella Typhimurium and Listeria monocytogenes was studied. Cells were grown planktonically or as surface colonies in/onmodel systems. Both microorganismswere grown in lab culturemedia in petri dishes at 20 ?C until cells reached the stationary phase. Before CAP treatment, cellswere deposited in a liquid carrier, on a solid(like) surface or on a filter. A dielectric barrier discharge reactor generated helium-oxygen plasma, which was used to treat samples up to 10 min. Although L. monocytogenes is more resistant to CAP treatment, similar trends in inactivation behavior as for S. Typhimurium are observed, with log reductions in the range [1.0-2.9] for S. Typhimurium and [0.2-2.2] for L. monocytogenes. For both microorganisms, cells grown planktonically are easily inactivated, as compared to surface colonies. More stressing growth conditions, due to cell immobilization, result in more resistant cells during CAP treatment. The main difference between the inactivation support systems is the absence or presence of a shoulder phase. For experiments in the liquid carrier, which exhibit a long shoulder, the plasma components need to diffuse and penetrate through the medium. This explains the higher efficacies of CAP treatment on cells deposited on a solid(like) surface or on a filter. This research demonstrates that the food structure influences the cell inactivation behavior and efficacy of CAP, and indicates that food intrinsic factors need to be accounted when designing plasma treatment. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma (CAP) is a non-thermal decontamination technology capable of generating groups of antimicrobial agents including; photons, electrons, positively and negatively charged ions, atoms, free radicals and excited or non-excited molecules. CAP treatments (70 kV, 50 Hz) at different times (i.e. 15, 30, 60, 90 s) were applied to a broth system inoculated either with Escherichia coli NCTC 12900, E. coli ME 9062 or E. coli knockout mutants of soxS, rpoS and dnaK genes. Optical emission spectra were performed and the main antimicrobial reactive substances generated by CAP treatments were found to be N2, N2+, NO, Hα and He. After treatments, reduction levels of the studied bacteria were up to 0.5 log CFU/mL, no showing statistical differences. Moreover, the kinetic growth parameters were calculated by applying the 2-fold dilution method. μmax decreased in all bacteria when the time of CAP treatment increased. E. coli dnaK was the most sensitive mutant to plasma, showing no recovery after CAP of 60 and 90 s. In addition, CAP challenge test treatments were applied on butter head lettuce inoculated with E. coli NCTC 12900 with CAP treatments of 60 and 90 s reducing bacteria levels by more than 1.5 log CFU/cm2. [ABSTRACT FROM AUTHOR]