Influence of Modified Atmosphere Storage on Aflatoxin Production in High Moisture Corn

Samples of freshly harvested corn and remoistened corn were inoculated with Aspergillus flavus and stored for 4 weeks at about 27 C in air and three modified atmospheres. Aflatoxins and fat acidity were determined weekly. Corn stored in the modified atmospheres did not accumulate over 15 μg of aflatoxin B₁ per kg and 20 μg of total aflatoxins per kg. Corn from the high CO₂ treatment (61.7% CO₂, 8.7% O₂, and 29.6% N₂) was visibly molded at 4 weeks and had a higher fat acidity than the other treatments. In the N₂ (99.7% N₂ and 0.3% O₂) and controlled atmosphere (13.5% CO₂, 0.5% O₂, 84.8% N₂) treatments, a fermentation-like odor was detected. When the corn was removed from the modified atmospheres it deteriorated rapidly and was soon contaminated with aflatoxins.     

Study of changes in physicochemical and microbiological characteristics of shrimps (Melicertus kerathurus) stored under modified atmosphere packaging

Fresh minimally processed shrimps were stored under modified atmosphere packaging (60% CO₂:40% N₂ for MAP A and 92.9% N₂:5.1% CO₂:2% O₂ for MAP B) for 5 days at 3 °C. Total mesophiles, H₂S forming bacteria, Pseudomonas spp., Brochothrix thermosphacta, firmness, color and sensory parameters were investigated throughout the whole time of the experiment. During storage period samples stored under MAP B managed to retain firmness values close to the initial values. All microbial populations growth was suppressed by the presence of MAP A. Samples stored under MAP B managed to maintain their firmness values close to the initial ones while MAP A samples were significantly less firm (p < 0.05).     

The effect of addition of olive oil and "Aceto balsamico di Modena" wine vinegar in conjunction with active atmosphere packaging on the microbial and sensory quality of "Lollo Verde" lettuce and rocket salad

Fresh rocket “Eruca Sativa” and lettuce “Lollo Verde” leaves were stored with the addition of olive oil and wine vinegar “Aceto balsamico di Modena” under modified atmosphere packaging (MAP) (5% O₂/10% CO₂/85% N₂ for MAP A and 2% O₂/5% CO₂/93% N₂ for MAP B). The microbial (mesophilic, psychrotrophic bacteria and Enterobacteriacae), physical (color and firmness) and sensory parameters of samples were studied in relation to storage time (up to 10 days at 5 ± 1 °C). The effect of wine vinegar and the application of both MAP treatments reduced the growth of all bacteria populations (p < 0.05). Samples with olive oil stored under MAP A gave the best score for overall impression (3 and 2.1 for MAP A and B respectively at the 9th day of storage) while the addition of vinegar limited sensory shelf-life to 3 days (p < 0.05). Firmness was negatively affected by wine vinegar while samples with olive oil stored under MAP A maintained firmness close to normal. Color attributes were maintained better under both MAP treatments (p < 0.05).     

Effect of oxygen on photosynthesis by spinach leaf protoplasts

The photosynthetic CO₂ fixation by spinach leaf (Spinacia oleracea L. var. Kyoho) protoplasts was inhibited by substituting an atmosphere of N₂ with one of either air (21% O₂) or 100% O₂. The inhibitory effect of 100% O₂ was greater than that of air. The mode of inhibition by 100% O₂ and air was competitive with respect to CO₂; Ki(O₂) value was 0.32 mM at pH 7 and 0.28 mM at pH 8.5 The labeling patterns of compounds in protoplasts exposed to ¹⁴CO₂ in light after transferring them from N₂ to O₂ atmospheres were examined. There was no detectable ¹⁴CO₂ incorporation into glycolate under anaerobic and O₂ atmospheres; a more marked labeling of glycine occurred under an oxidative environment compared to that under the anaerobic condition, presumably because of a rapid transformation of glycolate to glycine in the protoplasts.     

Microbial and sensory quality of "Lollo verde" lettuce and rocket salad stored under active atmosphere packaging

Samples of fresh rocket “Eruca Sativa” were stored either alone or with the addition of lettuce “Lollo verde” leaves under two different atmosphere modifications (5% O₂ and 10% CO₂ for MAP A and 2% O₂ and 5% CO₂ for MAP B). Throughout the storage period of 10 days the microbial (mesophilic, psychrotrophic bacteria and Enterobacteriacae) populations, firmness, color and organoleptic parameters were monitored. Elevated CO₂ levels created by both atmosphere modifications inhibited mesophile and psychrophile growth (p < 0.05). Color was better maintained in MAP samples. Shelf life of rocket leaves was extended by 4 days under MAP A while mixed salads shelf life was limited to 9 days.     

Survival of Aspergillus flavus and Fusarium moniliforme in High-Moisture Corn Stored Under Modified Atmospheres

Freshly harvested high-moisture corn with 29.4% moisture and corn remoistened to 19.6% moisture were inoculated with Aspergillus flavus Link ex Fr. and stored for 4 weeks at about 27 C in air (0.03% CO₂, 21% O₂, and 78% N₂) and three modified atmospheres: (i) 99.7% N₂ and 0.3% O₂; (ii) 61.7% CO₂, 8.7% O₂, and 29.6% N₂; and (iii) 13.5% CO₂, 0.5% O₂, and 84.8% N₂. Kernel infections by A. flavus, Fusarium moniliforme (Sheld.) Snyd. et Hans., and other fungi were monitored weekly. The modified-atmosphere treatments delayed deterioration by A. flavus and F. moniliforme, but their growth was not completely stopped. A. flavus survived better in the remoistened than in the freshly harvested corn. F. moniliforme survived in both. A. flavus and F. moniliforme were the dominant fungi in corn removed from the modified atmospheres and exposed to normal air for 1 week.     

Effect of several MAP compositions on the microbiological and sensory properties of Graviera cheese

The shelf life of Graviera cheese, a full fat cheese produced in Heraklion (Crete Greece), was investigated. Graviera cheese was stored at 4 °C for up to 90 days in polyamide packages under three different modified atmosphere compositions. Control cheeses were packaged in air whereas MAP mixtures were MAP₁: 40% CO₂/55% N₂/5% O₂, MAP₂: 60% CO₂/40% N₂ and MAP₃: 50% CO₂/50% N₂. Sampling of product was carried out every 10 days to investigate its sensory quality and microbiological characteristics. Ten trained panelists participated in the sensory panel to evaluate the cheeses for external appearance (color, texture), taste, and flavor in a scale from 1 to 10 (1 very poor, 10 very good). The microbiological analysis revealed that there were no colonies of Staphylococcus aureus and Listeria monocytogenes whereas both Escherichia coli and Total Viable Counts (TVC) increased strongly in control samples but were inhibited under all MAP compositions.     

Carbon dioxide effects on ethanol production, pyruvate decarboxylase, and alcohol dehydrogenase activities in anaerobic sweet potato roots

The effect of varied anaerobic atmospheres on the metabolism of sweet potato (Ipomoea batatas [L.] Lam.) roots was studied. The internal gas atmospheres of storage roots changed rapidly when the roots were submerged under water. O₂ and N₂ gases disappeared quickly and were replaced by CO₂. There were no appreciable differences in gas composition among the four cultivars that were studied. Under different anaerobic conditions, ethanol concentration in the roots was highest in a CO₂ environment, followed by submergence and a N₂ environment in all the cultivars except one. A positive relationship was found between ethanol production and pyruvate decarboxylase activity from both 100% CO₂-treated and 100% N₂-treated roots. CO₂ atmospheres also resulted in higher pyruvate decarboxylase activity than did N₂ atmospheres. Concentrations of CO₂ were higher within anaerobic roots than those in the ambient anaerobic atmosphere. The level of pyruvate decarboxylase and ethanol in anaerobic roots was proportional to the ambient CO₂ concentration. The measurable activity of pyruvate decarboxylase that was present in the roots was about 100 times less than that of alcohol dehydrogenase. Considering these observations, it is suggested that the rate-limiting enzyme for ethanol biosynthesis in sweet potato storage roots under anoxia is likely to be pyruvate decarboxylase rather than alcohol dehydrogenase.     

Effect of Environmental Factors in Aerobiosis and Anaerobiosis on the Growth and Activity of Propionic Acid Bacteria Evaluated by Pressure Measurement

The effects of air, N₂ and CO₂ atmospheres on the growth and metabolism of P. shermanii CIP 10 30 27 under “optimum conditions” (pH 6.5, NaCl 0 %, temperature 30 °C) and “stressful conditions” (pH 5.3, NaCl 2.1 %, temperature 20 °C) simulating cheese ripening conditions were investigated using a pressure measurement technique. Under both conditions, the inhibition of growth was at its maximum when a CO₂ atmosphere with an increase in the lag phase (L_P) from 3 to 80 h and a reduction in the maximum rate of pressure variation (V_max,P) from 2.5 to 0.4 kPa/h was used. The production of metabolites was not affected under “optimum conditions”, but under “stressful conditions”, propionate production increased and higher ratios of propionate to acetate of up to 2.45 were observed. The effects of air and N₂ atmospheres on both growth and metabolite production were also examined.     

Biomass fast pyrolysis in a fluidized bed reactor under N2, CO2, CO, CH4 and H2 atmospheres

Biomass fast pyrolysis is one of the most promising technologies for biomass utilization. In order to increase its economic potential, pyrolysis gas is usually recycled to serve as carrier gas. In this study, biomass fast pyrolysis was carried out in a fluidized bed reactor using various main pyrolysis gas components, namely N₂, CO₂, CO, CH₄ and H₂, as carrier gases. The atmosphere effects on product yields and oil fraction compositions were investigated. Results show that CO atmosphere gave the lowest liquid yield (49.6%) compared to highest 58.7% obtained with CH₄. CO and H₂ atmospheres converted more oxygen into CO₂ and H₂O, respectively. GC/MS analysis of the liquid products shows that CO and CO₂ atmospheres produced less methoxy-containing compounds and more monofunctional phenols. The higher heating value of the obtained bio-oil under N₂ atmosphere is only 17.8 MJ/kg, while that under CO and H₂ atmospheres increased to 23.7 and 24.4 MJ/kg, respectively.     

Effect of Modified Atmospheres on the Growth and Extracellular Enzyme Activities of Psychrotrophs in Raw Milk

The conservation of food products within a controlled atmosphere is efficient in packaging. To extend the cold storage of raw milk, the effects of five gas atmospheres enriched with carbon dioxide and nitrogen were investigated. Treated and control milk were stored at 7 °C for 10 days and analyzed for microbial counts, pH, proteolysis and lipolysis. The addition of CO₂, N₂, or their mixture had a significant inhibitory effect on psychrotrophic growth. The generation times of these microorganisms were significantly longer in treated milk, particularly for yeasts where they amounted to 16.63 h. The maximum inhibition was observed when a gas mixture of 50 % CO₂ and 50 % N₂ was used. As a result, psychrotrophic growth was affected to 98 % whereas this inhibition did not exceed 78 % when CO₂ and 41 % N₂ were applied. Milk treatment under the conditions of 50 % CO₂ and 50 % N₂ gave significantly lower counts for all groups of psychrotrophs being more efficient against Enterobacteriaceae with 99.5 % of inhibition. Storage of raw milk under the tested atmospheres had a different effect on extracellular enzyme productions. Significant decreases in protease and lipase activities were observed during the storage at 7 °C. These enzyme activities were not detectable with pure CO₂ and a 50 % CO₂ and 50 % N₂ mixture. N₂ has shown to be the less efficient treatment against lipases (65 %) and proteases (95 %). With regard to growth, the course of the pH and the protease and lipase activities, the tested gas mixture of 50 % CO₂ and 50 % N₂ was more suitable for extending the shelf life of raw milk.     

Efficacy of Beauveria bassiana for control of Tribolium castaneum with reduced oxygen and increased carbon dioxide

This study investigated the effect of atmosphere modification, a widely adopted means of insect control in stored products, on the efficacy of Beauveria bassiana for one of the most difficult to control pests, Tribolium castaneum. Oxygen reduction to 5% (±1%) as opposed to CO₂ elevation to 40% (±2%) for the first 72 h of fungus exposure resulted in significantly greater larval mortality than fungus exposure under ambient atmospheres. Both treatments reduced pupation of older larvae suggesting that slowed development may be a beneficial factor for fungal efficacy. CO₂ elevation but not O₂ reduction significantly affected the mortality of adult beetles that were exposed to the fungus. Carbon dioxide elevation significantly reduced B. bassiana’s germination and growth rates, but oxygen reduction did not.     

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.     

Some biophysical principles underlying the controlled atmosphere storage of plant material

Controlled atmosphere (CA) storage is of use for commodities which potentially can undergo rapid and unacceptable biochemical change. In air, the oxygen status of most plant material, including fleshy storage organs and fruits, suffices, even in the centre, for cytochrome oxidase to be fully saturated. Conflict of evidence exists as to possible O₂ and CO₂ gradients in fruit which, though physiologically unimportant in air, could be important under CA conditions. CA storage gives possible control of internal O₂ from o to about 80–95%; internal CO₂ from about 3–4 to 100%; and both simultaneously to intermediate values. Calculated molarities of dissolved O₂, CO₂ and ethylene are given for various atmospheres. The differences in the O₂ concentrations recommended for different varieties of apple are not readily explicable. Varietal differences in susceptibility to CO₂ injury could possibly result from anatomical, rather than biochemical, differences. This could be determined partly by resolving the conflict of evidence mentioned above. Variability of plant material prevents precise control of intercellular atmosphere; recommended atmospheres can be designed only to avoid completely anaerobic conditions and a harmful level of CO₂ in the centre of the least permeable individual fruit or vegetable. Effects of low O₂ and high CO₂ are briefly described.     

Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus-indica

Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol⁻¹ CO₂ at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m⁻² d⁻¹). Elevated CO₂ and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO₂ enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO₂ enrichment enhanced daily net CO₂ uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol⁻¹ CO₂. Cladode chlorophyll content was lower in elevated CO₂ and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO₂ and at higher PPFD. The total plant nitrogen content was lower in elevated CO₂. The effect of elevated CO₂ on net CO₂ uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO₂ uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol⁻¹ CO₂. Averaged for the two CO₂ treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.     

Growth and tissue senescence inPrunus avium shoots grownin vitro at different CO3/O2 ratios

Summary The rate of metabolism and biosynthetic processes makein vitro cultures very sensitive to environmental changes, and therefore subject to physiological and morphological alterations leading to senescence in the short term. The effect of three different calibrated atmospheric compositions were studied duringin vitro culture ofPrunus avium shoots. At 0.034% CO₂-21% O₂ (vol/vol), which stimulate the natural atmosphere, the highest growth rate and chlorophyll content were recorded. When grown at 0.09% CO₂-8% O₂ (vol/vol), a favorable condition for photosynthesis and growth, cultures showed a higher percentage of dry matter and elevated ethylene production, but total chlorophyll was lower. These shoots were also highly lignified and fibrous with red pigmentation along the leaves and stems. At 0% CO₂-21% O₂ (vol/vol), in contrast, growth and ethylene formation were inhibited; chlorophyll content was lowest in comparison with the other two environmental conditions, but regreening of tissues was observed after the first half of the culture period. Senescence symptoms, as indicated by decreased chlorophyll, appeared after about 18 d of culture for tissues grown in CO₂-containing atmospheres. These experiments provided evidence that in CO₂-enriched cultures biomass production steadily increased even when chlorophyll decreased. A possible role of CO₂ in promoting tissue-senescence through activation of photooxidative events and ethylene synthesis is discussed.     

The Effect of an Oxygen-free Atmosphere on Net Photosynthesis and Transpiration of Barley (Hordeum vulgare L.) and Wheat (Triticum aestivum L.) Leaves

Stomata of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) leaves failed to open in the light and close in the dark or respond to changes in the CO₂ concentration of the atmosphere in either light or dark when the leaves were in an O₂-free atmosphere. In contrast, the expected responses to environmental changes were found in atmospheres containing 1.5% O₂. It appears that O₂ is necessary for both opening and closing of wheat and barley stomata.     

Atmospheric conditions required for the growth ofGaleola septentrionalis seedlings

The seedling of an achlorophyllous orchid,Galeola septentrionalis, requires for its early growth anomalous atmospheric conditions appropriate to each process of development. The most favorable atmosphere for the enlargement of protocorm consists of 10% O₂, 6% CO₂ and 84% N₂ at a pressure of 1.4 kg/cm². Tolerable ranges of atmospheric pressure, concentrations of O₂ and CO₂ were 1.1–2.0 kg/cm², 5–12% and 2–10%, respectively. Such a range for culture temperatures was 20–26 C. Subsequent development of the seedlings was little influenced by atmospheric pressure (1.0–1.8 kg/cm²) and concentration of CO₂ (0–8%), but influenced by O₂ concentration. Optimum and tolerable concentrations of O₂ were 10–15% and 5–19.7%, respectively. These atmospheres are discussed hypothetically as the conditions required to pass an inevitable process specific to the epigenetic ontogeny of scobiform (sawdusty) seeds.     

Anaerobic stimulation of root exudates and disease of peas

Summary The relationships between root exudation, root disease and anaerobic root stresses were investigated. Sand culture and mist chamber studies demonstrated that low O₂ and high CO₂ reduced plant growth and increased the exudation of ethanol, amino acids, and sugars by pea roots. The relative loss of ethanol by roots was much greater in treatments with atmospheres of N₂ containing 30% CO₂ than in treatments of air containing 30% CO₂ or N₂. Ethanol was not detected in the nutrient solution of aerated plant roots. Atmospheres of N₂ plus 30% CO₂ caused 500% greater mycelial growth ofFusarium solani f. sp.pisi and 400% more disease of inoculated pea roots. Relative losses of four amino acids and four sugars were much greater in atmospheres of N₂ plus 30% CO₂ than in N₂ or air.     

CO2 enhances effects of hypoxia on mortality,development, and gene expression in cowpea bruchid, Callosobruchus maculatus

Modified atmosphere based on lack of O₂ offers a safe, residue-free alternative to chemical fumigants for pest control in stored grains. In this study, we intended to determine whether elevated CO₂ (at a biologically achievable level) has an enhanced suppressive effect over low O₂ atmosphere alone on the cowpea bruchid (Callosobruchus maculatus), a storage pest of cowpea and other legumes. Experiments were performed under two modified atmospheric conditions, (1) 2% O₂ + 18% CO₂ + 80% N₂ and (2) 2% O₂ + 98% N₂. Both hypoxic environments significantly affected the development and survival of all insect developmental stages. Eggs were most vulnerable to hypoxia, particularly at the early stage (4–6 h old), surviving only up to a maximum of 2 days in both treatments. These were followed by adults, pupae and larvae, in order of decreasing susceptibility. The 3rd and 4th instar larvae were most resilient to hypoxia and could survive up to 20 days of low O₂. The presence of 18% CO₂ significantly increased the mortality of adults, the later stage of eggs, as well as 1st and 4th instar larvae caused by hypoxia. However, the surviving insects exhibited faster development, evidenced by their earlier emergence from cowpea seeds compared to those without CO₂. One interesting observation was the frequent, premature opening of the emergence windows in the 4th instar larvae when CO₂ was involved. This phenomenon was not observed at all in insects stressed by low O₂ alone. Differential expression profiling of metabolic genes and proteolytic activity of midgut digestive enzymes suggested that the rate of metabolic activity could contribute in part to the difference in insect development and survival under hypoxia in the presence and absence of CO₂.