Storage of poultry meat under modified atmospheres or vacuum packs: possible role of microbial metabolites as indicator of spoilage

The effect of carbon dioxide (100%), nitrogen (100%), carbon dioxide/oxygen (20% : 80%) or vacuum pack at 3 and 10°C was studied on the microbial flora, in skinless poultry breast fillets or thigh meat. Lactic acid bacteria and Brochothrix thermosphacta were the predominant organisms in samples stored in vacuum packs, carbon dioxide and nitrogen. Pseudomonads grew only in oxygen/carbon dioxide packaging systems. The concentration of lactate diminished in both thigh and breast meat during storage at 3 and 10°C. This decrease was more pronounced in thigh meat stored under 20% : 80% carbon dioxide/oxygen. Acetate increased to varying degrees in all samples regardless of the storage conditions.     

Is Helicobacter pylori a True Microaerophile?

BACKGROUND: There is no general consensus about the specific oxygen and carbon dioxide requirements of the human pathogen Helicobacter pylori. This bacterium is considered a microaerophile and consequently, it is grown under atmospheres at oxygen tensions 5-19% and carbon dioxide tensions 5-10%, both for clinical and basic and applied research purposes. The current study compared the growth of H. pylori in vitro, under various gas atmospheres, and determined some specific changes in the physiology of bacteria grown under different oxygen partial pressures. METHODS: Measurements of bacterial growth under various conditions were carried out employing classical solid and liquid culture techniques. Enzymatic activities were measured using spectrophotometric assays. RESULTS: H. pylori and all the other Helicobacter spp. tested had an absolute requirement for elevated carbon dioxide concentrations in the growth atmosphere. In contrast with other Helicobacter spp., H. pylori can tolerate elevated oxygen tensions when grown at high bacterial concentrations. Under 5% CO(2), the bacterium showed similar growth in liquid cultures under oxygen tensions from microaerobic (< 5%) to fully aerobic (21%) at cell densities higher than 5 x 10(5) cfu/ml for media supplemented with horse serum and 5 x 10(7) cfu/ml for media supplemented with beta-cyclodextrin. Evidence that changes occurred in the physiology of H. pylori was obtained by comparing the activities of ferredoxin:NADH (nicotinamide adenine dinucleotide) oxidoreductases of bacteria grown under microaerobic and aerobic atmospheres. CONCLUSIONS: H. pylori is a capnophile able to grow equally well in vitro under microaerobic or aerobic conditions at high bacterial concentrations, and behaved like oxygen-sensitive microaerophiles at low cell densities. Some characteristics of H. pylori cells grown in vitro under microaerobic conditions appeared to mimic better the physiology of organisms grown in their natural niche in the human stomach.     

Gametocytogenesis of Leucocytozoon caulleryi in In Vitro Culture: Effect of Human Red Blood Cells on the Development of Second-Generation Merozoites

For investigating development of second-generation merozoites of Leucocytozoon caulleryi into mature gametocytes, infected erythrocytes from chickens at 15 d after sporozoites inoculation were cultured in RPMI-1640 modified medium supplemented with 10% horse serum and 0.5 ml of human erythrocytes (type O). When culture was carried out at 37°C in a humidified atmosphere of 5% CO₂ for 7 d, the very small number of second-generation merozoites developed into morphologically mature gametocytes. However, in the high carbon dioxide and low oxygen condition, mature gametocytes weren't observed in cluture. The role of human erythrocytes added has not been clarified yet.     

Lactate dehydrogenase isoenzyme pattern and total LDH activity in the lung and liver of rats chronically exposed to low and high oxygen concentrations.

Young adult rats were continuously exposed for 44 and 84 days to environments containing 9–11%, 20%, and 80% oxygen. Low and high oxygen atmospheres were achieved by using boxes laminated with silicone rubber membranes which have a differing permeability for oxygen on one side and for carbon dioxide and nitrogen on the other. Animals exposed to both extreme concentrations significantly slowed body growth, and the weight of the lungs was proportionally less. The pattern of LDH isoenzymes in the lung showed the presence of all five characteristically changing isoenzymes in relation to oxygen concentration. A marked increase of M subunits in the LDH in lungs of rats exposed to low oxygen indicated a higher tissue concentration of lactate. Thus, the percentage of M subunits was significantly higher in low oxygen and significantly lower in lungs of rats exposed to high oxygen as compared to controls. Under the same experimental conditions there were no changes in the liver LDH isoenzyme pattern. Total LDH activity in the lungs of rats exposed to either extreme oxygen atmosphere was significantly elevated as compared to controls kept at an ambient atmosphere. It is concluded that chronic exposure of rats to low as well as to high oxygen was injurious to the lung tissue, as evidenced by total LDH activity. Thus, LDH isoenzyme pattern in the lung reflected the actual gas exposure (pO₂), rather than local tissue metabolism.     

The effect of doubled CO2 on water use by alfalfa and orchard grass: simulating evapotranspiration using canopy conductance measurements

Alfalfa and orchard grass crops were grown at ambient and twice ambient carbon dioxide concentrations in field plots for several years in Beltsville, MD, using semi-open chambers. Canopy conductances throughout many days were determined from water vapour exchange measurements, and indicated significant reductions in canopy conductance to water vapour at elevated carbon dioxide in both species. However, recognizing that the artificial ventilation in the chambers made direct comparisons of evapotranspiration rates questionable, we used a soil–vegetation–atmosphere model to determine what field-scale evapotranspiration rates would have been with natural ventilation. Unlike the 'omega' approach, the model used allowed feedbacks between the canopy and the atmosphere, such that, for example, canopy conductance responses affected profiles of temperature and water vapour. Simulations indicated that although canopy conductances were lower at elevated carbon dioxide by as much as 20% in alfalfa and 60% in orchard grass, evapotranspiration rates never differed by more than 3% in alfalfa or 8% in orchard grass. Daily totals of evapotranspiration were only 1–2% lower at elevated carbon dioxide in alfalfa, and 2–5% lower in orchard grass. The results are partly explained by the fact that aerodynamic conductances to water vapour were generally smaller than the stomatal conductance, and also by canopy–atmosphere feedback processes which largely compensated for the lower conductance at elevated carbon dioxide by increasing the gradient for evaporation.     

A comparison of carbon dioxide production and oxygen uptake in sediment cores from four south Swedish lakes

Carbon dioxide production and oxygen uptake were measured in undisturbed sediment cores taken during winter from four lakes of different trophic state. Respiration was measured at 5, 10, 15 and 20°C at high oxygen saturation (75–100%). The respiratory quotient, calculated from the mean values of carbon dioxide production and oxygen uptake at each temperature for each lake, was 0.83–0.96 with a mean value for the four lakes of 0.90. At very low oxygen saturations (<10%) carbon dioxide production was 21–42% of the production at 20°C and high oxygen saturations. The results indicate that under aerobic conditions, oxygen uptake and carbon dioxide production are closely-coupled processes in these lake sediments.     

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C₃ species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C₃ species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 °C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 – 25 °C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 °C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Germination of Avena fatua under Different Gaseous Environments

The atmosphere in which seeds germinate can profoundly affect the level of germination and dormancy. Seeds were germinated in atmospheres containing various concentrations of carbon dioxide and oxygen. At the same time the effect of light on these systems was examined. The germination of partially dormant populations of wild oat seed is inhibited by white light. This response to light is most apparent when the curyopsis is enclosed in the pales. Investigations into the effect of the ambient atmosphere on germination have indicated that, while oxygen is a necessary factor in the germination of tliis species, carbon dioxide also has an effect. A lack of carbon dioxide increases the degree of light inhibition of germination; 3 per cent carbon dioxide (by volume) allows germination in light; 20 per cent carbon dioxide inhibits germination in light and darkness at all tested oxygen concentrations.     

Post-harvest biological control by Pantoea agglomerans (CPA-2) on Golden Delicious apples

AIMS: To investigate the potential of Pantoea agglomerans to control the major post-harvest diseases on Golden Delicious apples. METHODS AND RESULTS: In laboratory trials, a high level of control of Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer was obtained with P. agglomerans. In semi-commercial trials at 1degrees C in air and a low oxygen atmosphere, the reduction of blue mould was 81% and 100%, respectively, and control of grey mould was achieved equally with P. agglomerans and imazalil. In trials at 1degrees C and seven atmosphere conditions, maximum reduction in decay was 80% obtained at 3% O2-6% CO2. The population of P. agglomerans on apples followed the same pattern under all three atmosphere conditions studied. CONCLUSIONS: Pantoea agglomerans could be used effectively on apples under a wide range of temperature and atmosphere conditions. SIGNIFICANCE AND IMAPCT OF THE STUDY Pantoea agglomerans can be used as a biocontrol agent on apples at 8 x 10(7) cfu ml-1, the same concentration as in pears. This will facilitate the application of this biological control agent by the growers in packing houses.     

Growth of Pseudomonas fluorescens in modified atmosphere packaged tofu

Aims: The objective was to study the growth of Pseudomonas in a food product (tofu) where it typically occurs as a spoilage organism, and when this product is stored under modified atmosphere. Methods and Results: A Pseudomonas strain was isolated from the endogenous microflora of tofu. Tofu was inoculated with the strain, packaged in different gas conditions (air, 100% N₂, 30% CO₂/70% N₂ or 100% CO₂) and stored under refrigerated conditions. Microbial loads and the headspace gas composition were monitored during storage. Conclusions: The strain was capable of growing in atmospheres containing no or limited amounts of oxygen and increased amounts of carbon dioxide. Even when 100% CO₂ was used, growth could not be inhibited completely. Significance and Impact of Study: In contrast to the general characteristics of the genus Pseudomonas (strictly aerobic, highly sensitive to CO₂), it should not be expected in the food industry that removing oxygen from the food package and increasing the carbon dioxide content, combined with cold storage, will easily avoid spoilage by Pseudomonas species. Guarantee of hygienic standards and combination of strategies with other microbial growth inhibiting measures should be implemented.     

Effect of oxygen and carbon dioxide on germination and growth ofRhizopus oligosporus on model media and soya beans

 The microcolony technique enables the effects of several atmospheric conditions on fungal growth to be studied by measuring the radius of the colony, while excluding effects of those conditions on germination of the sporangiospores. Various concentrations of oxygen and carbon dioxide in the gas environment were found to influence growth of Rhizopus oligosporus on malt extract/soya peptone/agar. The maximum radial growth rate was 1.48 mm/h and the maximum specific growth rate was 0.109 h^-1 at 30 °C. Oxygen became limiting below 1% (v/v), but growth remained possible at levels of 0.001% oxygen. Carbon dioxide stimulated growth at limiting oxygen levels. The specific growth rate increased from 0.043 h^-1 at 0.5% (v/v) oxygen and 0% (v/v) carbon dioxide to 0.096 h^-1 at 0.5% (v/v) oxygen and 5% (v/v) carbon dioxide. A mixture of 0.5% (v/v) oxygen and 35% (v/v) carbon dioxide inhibited growth. Delay of sporangiospore germination due to low (less than 0.001%) amounts of oxygen was not observed with the techniques used. Fungal activity in a rotating drum fermentor was more strongly affected by low levels of oxygen than was biomass formation on model media. High concentrations of carbon dioxide inhibited growth in the rotating drum fermentor at non-limiting levels of oxygen. It is concluded that aeration and heat removal are both essential aspects of optimization of large-scale solid-substrate bioreactors with Rh. oligosporus. Received: 5 August 1994/Received revision: 14 November 1994/Accepted: 5 December 1994     

Metabolic changes during phosphate deprivation in Englena in air and in oxygen

1. Euglena cells were grown in culture media containing either 20mm-phosphate or 20mum-phosphate, with ethanol or glucose as the sole source of carbon, and gassed with either air+carbon dioxide (95:5) or oxygen+carbon dioxide (95:5) at atmospheric pressure. 2. After growth in low-phosphate medium with ethanol as substrate, the cells developed signs of oxygen toxicity, as indicated by a decreased rate of respiration, a decreased net synthesis of paramylum and a failure to resume growth on replenishment of phosphate. 3. After growth in low-phosphate medium with glucose as substrate, the signs of oxygen toxicity were less apparent. 4. During phosphate deprivation the carotenoid content of Euglena increased more than threefold. This increase was largely prevented by exposure of the cells to oxygen+carbon dioxide (95:5) during growth. Oxygenation appears to interfere with ring closure of the common carotenoid precursor. 5. Mitochondria obtained from Euglena exposed to oxygen during phosphate deprivation, i.e. when signs of oxygen toxicity were evident, had greatly decreased activities of succinate dehydrogenase, succinate-cytochrome c oxidoreductase and NADH-cytochrome c oxidoreductase, compared with mitochondria obtained from Euglena exposed to oxygen in medium containing 20mm-phosphate.     

The Effect of Storage in Various Gaseous Atmospheres on the Microflora of Lamb Chops Held at—1°C

The effect of different gaseous atmospheres on the development of the bacterial flora on lamb chops stored at –1°C was examined. The atmospheres were air, nitrogen, hydrogen, and mixtures of air + carbon dioxide, oxygen + nitrogen, oxygen + carbon dioxide, nitrogen + carbon dioxide and hydrogen + carbon dioxide (gas ratio = 80:20, v/v). Storage life of chops ranged from two weeks in air to eight weeks in oxygen-free atmospheres. At the end of storage life Microbacterium thermosphactum was present as a major constituent of the bacterial flora in all atmospheres. In oxygen + carbon dioxide it was the predominant organism. In all other oxygen containing atmospheres, Pseudomonas spp. made up a large proportion of the flora. Strains of Enterobacteriaceae occurred in low-oxygen and oxygen-free atmospheres, and Lactobacillus spp. occurred in oxygen-free atmospheres.     

Carbon dioxide inhibition of yeast growth in biomass production

Saccharomyces cerevisiae was grown under aerobic and substrate-limiting conditions for efficient biomass production. Under these conditions, where the sugar substrate was fed incrementally, the growth pattern of the yeast cells was found to be uniform, as indicated by a constant respiratory quotient during the entire growing period. The effect of carbon dioxide was investigated by replacing portions of the nitrogen in the air stream with carbon dioxide, while maintaining the oxygen content at the normal 20% level, so that identical oxygen transfer rate and atmospheric pressure were maintained for all experiments with different partial pressures of carbon dioxide. Inhibition of yeast growth was negligible below 20% CO₂ in the aeration mixture. Slight inhibition was noted at the 40% CO₂ level and significant inhibition was noted above the 50% CO₂, level, corresponding to 1.6 × 10^?2M of dissolved CO₂ in the fermentor broth. High carbon dioxide content in the gas phase also inhibited the fermentation activity of baker's yeast.     

Oxygen tolerance of strictly aerobic hydrogen-oxidizing bacteria

Growth of various bacteria, especially aerobic hydrogen-oxidizing bacteria, in the presence of 2 to 100% (v/v) oxygen in the gas atmosphere was evaluated. The bacterial strains included Alcaligenes eutrophus, A. paradoxus, Aquaspirillum autotrophicum, Arthrobacter spec. strain 11X, Escherichia coli, Arthrobacter globiformis, Nocardia opaca, N. autotrophica, Paracoccus denitrificans, Pseudomonas facilis, P. putida, and Xanthobacter autotrophicus. Under heterotrophic conditions with fructose or gluconate as substrates neither colony formation on solid medium nor the growth rates in liquid media were drastically impaired by up to 100% oxygen. In contrast, autotrophic growth — with hydrogen, carbon dioxide and up to 80% oxygen in the gas atmosphere — was strongly depressed by high oxygen concentrations. However, only the growth rate, not the viability of the cells, was decreased. Growth retardation was accompanied by a decrease of hydrogenase activity.The work was supported by the Deutsche Forschungsgemeinschaft.     

Responses of trees to elevated carbon dioxide and climate change

The enhancement in photosynthesis at elevated concentration of carbon dioxide level than the ambient level existing in the atmosphere is widely known. However, many of the earlier studies were based on instantaneous responses of plants grown in pots. The availability of field chambers for growing trees, and long-term exposure studies of tree species to elevated carbon dioxide, has changed much of our views on carbon dioxide acting as a fertiliser. Several tree species showed acclimation or even down-regulation of photosynthetic responses while a few of them showed higher photosynthesis and better growth responses. Whether elevated levels of carbon dioxide can serve as a fertilizer in a changed climate scenario still remains an unresolved question. Forest-Air-Carbon dioxide-Enrichment (FACE) sites monitored at several locations have shown lately, that the acclimation or down regulation as reported in chamber studies is not as wide-spread as originally thought. FACE studies predict that there could be an increase of 23–28% productivity of trees at least till 2050. However, the increase in global temperature could also lead to increased respiration, and limitation of minerals in the soil could lead to reduced responses in growth. Elevated carbon dioxide induces partial closure of leaf stomata, which could lead to reduced transpiration and more economical use of water by the trees. Even if the carbon dioxide acts as a fertilizer, the responses are more pronounced only in young trees. And if there are variations in species responses to growth due to elevated carbon dioxide, only some species are going to dominate the natural vegetation. This will have serious implications on the biodiversity and the structure of the ecosystems. This paper reviews the research done on trees using elevated CO₂ and tries to draw conclusions based on different methods used for the study. It also discusses the possible functional variations in some tree species due to climate change.     

Effect of modified Fenton's reaction on microbial activity and removal of PAHs in creosote oil contaminated soil

This study describes the removal of polycyclic aromatic hydrocarbons (PAHs) from creosote oil contaminated soil by modified Fenton's reaction in laboratory-scale column experiments and subsequent aerobic biodegradation of PAHs by indigenous bacteria during incubation of the soil. The effect of hydrogen peroxide addition for 4 and 10 days and saturation of soil with H(2)O(2) on was studied. In both experiments the H(2)O(2) dosage was 0.4 g H(2)O(2)/g soil. In completely H(2)O(2)-saturated soil the removal of PAHs (44% within 4 days) by modified Fenton reaction was uniform over the entire soil column. In non-uniformly saturated soil, PAH removal was higher in completely saturated soil (52% in 10 days) compared to partially saturated soil, with only 25% in 10 days. The effect of the modified Fenton's reaction on the microbial activity in the soil was assessed based on toxicity tests towards Vibrio fischeri, enumeration of viable and dead cells, microbial extracellular enzyme activity, and oxygen consumption and carbon dioxide production during soil incubation. During the laboratory-scale column experiments, the toxicity of column leachate towards Vibrio fischeri increased as a result of the modified Fenton's reaction. The activities of the microbial extracellular enzymes acetate- and acidic phosphomono-esterase were lower in the incubated modified Fenton's treated soil compared to extracellular enzyme activities in untreated soil. Abundance of viable cells was lower in incubated modified Fenton treated soil than in untreated soil. Incubation of soil in serum bottles at 20 degrees C resulted in consumption of oxygen and formation of carbon dioxide, indicating aerobic biodegradation of organic compounds. In untreated soil 20-30% of the PAHs were biodegraded during 2 months of incubation. Incubation of chemically treated soil slightly increased PAH-removal compared to PAH-removal in untreated soil.     

Physiological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strain

Abstract. The metabolic rates, as expressed by oxygen (O₂) consumption, carbon dioxide (CO₂) production, and losses in wet and dry weights, were examined for adults of three strains of the red flour beetle Tribolium castaneum (Herbst), during exposure to two modified atmospheres (MAs). Exposure of a strain selected for resistance over twenty-one generations to an atmosphere of 65% CO₂, 20% O₂ and the balance nitrogen (N₂), termed a high carbon dioxide concentration atmosphere (HCC) and exposure of an unselected strain to HCC, showed considerable levels of aerobic metabolism during exposure. For the unselected strain water loss and mobilization of energy reserves were rapid and mortality was followed by rapid desiccation. For the HCC-resistant strain water balance was maintained and energy reserves were utilized more slowly over a prolonged period. Exposure of a strain selected for resistance over twenty-one generations to a low oxygen concentration atmosphere (LOC) of 0.5% O₂ in N₂, and an unselected strain to LOC, revealed that even at 0.5% O₂, metabolism was largely aerobic in both strains. Maintenance of water balance was not a major factor causing mortality of either strain during exposure to LOC. In air, metabolic rates of both the resistant strains were lower than that of the unselected strain.     

Oxygen enriched air supply in Escherichia coli processes: production of biomass and recombinant human growth hormone

In order to investigate the impact of high oxygen and carbon dioxide concentrations, Escherichia coli was grown in batch cultivations where the air supply was enriched with either oxygen or carbon dioxide. The effect of elevated concentrations of oxygen and carbon dioxide on stochiometric and kinetic constants was studied this way. The maximum growth rate was significantly reduced, the production of acetic acid and the biomass yield coefficient on glucose increased in cultures with carbon dioxide enriched air, compared to reference cultivations and cultivations with oxygen enriched air. The application of oxygen enriched air was studied in high cell density cultivations of Escherichia coli. Two production processes were chosen to investigate the impact of oxygen enrichment. Biomass concentration, specific growth rate, yield coefficient, respiration, mixed acid fermentation products and the product yield and quality for the recombinant product were investigated. First, a process for the production of biomass was investigated. Exponential growth could proceed for a longer time and higher growth rates could be maintained with oxygen enriched air supply. However, a higher specific oxygen consumption rate per glucose was measured after the start of the oxygen enrichment, indicating higher maintenance and consequently the growth rate and yield coefficient decreased drastically in the end of the process. Second, a process for the production of recombinant human growth hormone (rhGH) was investigated. Although the glucose feed rate and all medium components were doubled, the amount of produced biomass could only be increased by 77% when oxygen enriched air (40% oxygen) supply was applied. This was due to a decreased yield coefficient of biomass per glucose. The total amount of produced product was decreased by almost 50% compared to the control, although less proteolytically degraded variants were produced.