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 three MAP compositions on the physical and microbiological properties of a low fat Greek cheese known as "Anthotyros"

Anthotyros is a type of low fat cheese produced from a mixture of sheep and goat milk. Anthotyros cheese in Crete is produced from the whey of hard cheese such as kefalotyri and graviera. Anthotyros is a cheese which comes from the myzithra cheese (whey) dehydration. The dehydrated anthotyros’ physicochemical properties are moisture content of 35%, fat content in dry matter of 55% and low concentration of salt. The purpose of this study was to identify which of the three gas compositions applied; MAP₁:40% CO₂, 55% N₂, 5% O₂, MAP₂: 60% CO₂, 40% N₂ and MAP₃: 50% CO₂, 50% N₂ can lead to greater shelf life prolongation of anthotyros. The control samples were packaged in air. All cheese samples were kept under refrigeration (4 ± 0.5 °C) for 55 days. The statistical analysis of organoleptic characteristics was carried out by using the Principal Component Analysis (PCA) by means of JMP5.0.1.     

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.     

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.     

Nitrogen fixation by Anabaena cylindrica

Summary The effects of oxygen, light and photosynthesis inhibitors on nitrogenase activities in Anabaena cylindrica batch cultures were followed as a function of time after inoculation. During the early rapid growth period the nitrogenase activities of cultures grown under air/CO₂ or N₂/CO₂ were relatively resistant to oxygen and DCMU inhibition. These cultures also exhibited oxygen-dependent nitrogenase activity in the dark of up to 50% of that measured in the light. After active growth ceased the cultures continued to slowly grow for a prolonged period of time. The nitrogenase activities of these old cultures were very sensitive to oxygen and DCMU inhibition. These cultures also had little or no dark nitrogenase activities. The photosynthesis inhibitor DBMIB was not a specific inhibitor of light-driven electron transport since it inhibited both light and dark nitrogenase activities. Nitrogenase activities induced under oxygen-free/CO₂ gas mixtures initially were significantly more sensitive to oxygen inhibition than those induced under air/CO₂. We discuss these results in relation to heterocyst function.     

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.     

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.     

Impact of modified atmospheres on respiration of last instar larvae of the rice moth,Corcyra cephalonica (Lepidoptera: Pyralidae)

Abstract

Effect of modified atmospheres (MAs) containing CO₂ at 20, 40, 60 and 80% or containing N₂ at 97 and 98% on the mortality of Corcyra cephalonica Stainton (Lepidoptera: Pyralidae) sixth instar larvae was studied to determine the LT values at 30?°C. The respiration rates of untreated and treated larvae with 60% CO₂ and/or 98% N₂ at LT₅₀ were measured using Q-Box RP1LP low range respirometry package. Total protein and triglycerides of treated and untreated larvae were assayed. Complete larval mortality was recorded after 72 and 144?h of treatment with 60% CO₂ and 98% N₂, respectively. Calculated LT₅₀ values were 39.3 at 60% CO₂ and 87.5?h at 98% N₂ MAs. Respiration quotient (RQ) in the light of consumed O₂ and produced CO₂ of untreated larvae was 1.0 while it was 0.85 at 60% CO₂ and 0.72 at 98% N₂. Duration time necessary for produced CO₂ curve to reach the maximum point (2000?ppm) was significantly shorter at untreated larvae (27.64?min) in comparison with that recorded at CO₂ (35.48?min) which also significantly less than that obtained at N₂ (98.54?min). At all treatments, total protein was decreased while triglycerides were increased in comparison with control.     

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.     

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.     

Computational screening of ZIFs for CO2 separations

Using molecular simulations, we studied a diverse collection of zeolite–imidazolate frameworks (ZIFs) to evaluate their performances in adsorption- and membrane-based gas separations. Molecular simulations were performed for both single-component gases (CH₄, CO₂, H₂ and N₂) and binary gas mixtures (CO₂/CH₄, CO₂/N₂, CO₂/H₂ and CH₄/H₂) to predict the intrinsic and mixture selectivities of ZIFs. These two selectivities were compared to discuss the importance of multi-component mixture effects on making predictions about the separation performance of a material. Gas separation performances of ZIFs were compared with other nanoporous materials and our results showed that several ZIFs can outperform well-known zeolites and metal–organic frameworks in CO₂ separations. Several other properties of ZIFs such as gas permeability, working capacity and sorbent selection parameter were computed to identify the most promising materials in adsorption- and membrane-based separation of CO₂/CH₄, CO₂/N₂, CO₂/H₂ and CH₄/H₂.     

Inhibition of psychrotrophic bacteria in raw milk by immobilized lactic acid bacteria

Summary Cells ofLactococcus lactis orLactobacillus helveticus were immobilized in calcium-alginate beads, added to raw milk, and incubated 48 h at 7°C. The addition of 2.7×10⁷ immobilizedLc.lactis or 13×10⁷ immobilizedLb. helveticus cells per mL reduced the development of the psychrotrophic bacteria of raw milk by approximately 50%. The pH of the raw milk dropped 0.10 to 0.22 units under these conditions. Periodic agitation of the seeded raw milk increased the inhibitory activity of the immobilized lactic acid bacteria (LAB). Free LAB cells in the system were only of 0.5% of total LAB. The use of immobilized LAB to inhibit psychrotrophic bacteria might be extended to raw milks destined to the manufacture of non-fermented dairy products.     

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.     

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.     

A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres

The action of an electric discharge on reduced gas mixtures such as H₂O, CH₄ and NH₃ (or N₂) results in the production of several biologically important organic compounds including amino acids. However, it is now generally held that the early Earth’s atmosphere was likely not reducing, but was dominated by N₂ and CO₂. The synthesis of organic compounds by the action of electric discharges on neutral gas mixtures has been shown to be much less efficient. We show here that contrary to previous reports, significant amounts of amino acids are produced from neutral gas mixtures. The low yields previously reported appear to be the outcome of oxidation of the organic compounds during hydrolytic workup by nitrite and nitrate produced in the reactions. The yield of amino acids is greatly increased when oxidation inhibitors, such as ferrous iron, are added prior to hydrolysis. Organic synthesis from neutral atmospheres may have depended on the oceanic availability of oxidation inhibitors as well as on the nature of the primitive atmosphere itself. The results reported here suggest that endogenous synthesis from neutral atmospheres may be more important than previously thought. Stanley L. Miller died May 20, 2007.     

Study on the potential of cold-active lipases from psychrotrophic fungi for detergent formulation

Lipases from psychrotrophic fungal isolates BPF4 and BPF6 identified as Penicilium canesense and Pseudogymnoascus roseus respectively were characterized for their compatibility towards laundry detergent. BPF4 and BPF6 lipases showed maximum activity at pH 11 and 9 respectively and at 40?°C. The residual activities at 20?°C and 4?°C of BPF4 lipase were 35% and 20% and of BPF6 lipase were 70% and 20?°C respectively. Both the enzymes were stable at 4?°C, 20?°C and 40?°C for 2?h losing at the most 20% of activities. Both the enzymes were metalloenzymes with activity enhancement by nearly threefold by Ca²⁺. Contrary to BPF6 lipase, BPF4 enzyme was not stimulated by EDTA nor inhibited, rather stimulated by SDS and Triton X-100 by 125% and 330% respectively. Both the lipases showed minor to moderate inhibition by NaClO₃ and H₂O₂, and exhibited nearly 90% residual activity after 1?h of incubation in selected detergent brands thus indicating potential for their inclusion in detergent formulation thereby facilitating cold-washing as a step towards mitigation of climate change.     

Stunning pigs with nitrogen and carbon dioxide mixtures: effects on animal welfare and meat quality

The aim of this study was to assess the effect of exposure to the gas mixtures of 70% nitrogen (N₂) and 30% carbon dioxide (CO₂; 70N30C), 80% N₂ and 20% CO₂ (80N20C) and 85% N₂ and 15% CO₂ (85N15C) on aversion, stunning effectiveness and carcass, as well as meat quality in pigs, and to compare them with the commercial stunning of 90% CO₂ (90C). A total of 68 female pigs were divided into four groups and stunned with one of the gas mixtures. During the exposure to the gas, behavioural variables (retreat attempts, escape attempts, gasping, loss of balance, muscular excitation and vocalizations) were recorded, and at the end of the stunning, corneal reflex and rhythmic breathing were assessed. After slaughter, meat quality parameters such as pH at 45 min post mortem (pH45) and at 24 h post mortem (pHu), electrical conductivity, drip loss and colour, in the Longissimus thoracis (LT) and Semimembranosus (SM) muscles were measured, and the presence of ecchymosis on the hams was noted. The PROC MIXED and the PROC GENMOD of SAS® were used to analyse the parametric and binomial variables, respectively. The ‘gas mixture’ was always considered a fixed effect and the ‘live weight’ as a covariate. To assess the correlation between meat quality and behaviour measures, PROC CORR was used. Pigs exposed to 90C showed a higher percentage of escape attempts and gasping, a lower percentage of vocalization and shorter muscular excitation phase than pigs exposed to the other N₂ and CO₂ mixtures (P < 0.05). After stunning, no pig exposed to 90C showed corneal reflex or rhythmic breathing, whereas 85% and 92% of the animals exposed to N₂ and CO₂ mixtures showed corneal reflex and rhythmic breathing, respectively. Animals stunned with 80N20C and 85N15C had a lower pH45 (P < 0.01) than animals exposed to 90C. Electrical conductivity in the SM muscle was lower (P < 0.001) in 90C and 70N30C pigs than in 80N20C and 85N15C pigs, whereas in LT, it was lower (P < 0.05) in 90C pigs than in 85N15C. As the CO₂ concentration of the gas mixture was decreased, the prevalence of exudative pork increased. Twenty-five percent of animals exposed to N₂ and CO₂ mixtures (n = 68) had ecchymosis in their carcasses, whereas no animal stunned with 90C had ecchymosis. In conclusion, although N₂ and CO₂ stunning exhibit fewer signs of aversion than 90C, their induction time to unconsciousness is longer, and this may negatively affect meat and carcass quality.     

CO2- and Anaerobiosis-Induced Changes in Physiology and Gene Expression of Different Listeria monocytogenes Strains

Although carbon dioxide (CO₂) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO₂ concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N₂, and 100% CO₂. The CO₂-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO₂ as to other anaerobic, slightly acidic environments (100% N₂, pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO₂ and N₂ at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO₂-containing atmospheres. Together, our findings demonstrate that the CO₂-response is a partly strain-dependent complex mechanism. The possible links between the CO₂-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.     

Photorespiration-induced reduction of ribulose bisphosphate carboxylase activation level

Leaf photosynthesis and ribulose bisphosphate carboxylase activation level were inhibited in several mutants of the C₃ crucifer Arabidopsis thaliana which possess lesions in the photorespiratory pathway. This inhibition occurred when leaves were illuminated under a photorespiratory atmosphere (50% O₂, 350 microliters per liter CO₂, balance N₂), but not in nonphotorespiratory conditions (2% O₂, 350 microliters per liter CO₂, balance N₂). Inhibition of carboxylase activation level was observed in strains with deficient glycine decarboxylase, serine transhydroxymethylase, serine-glyoxylate aminotransferase, glutamate synthase, and chloroplast dicarboxylate transport activities, but inhibition did not occur in a glycolate-P phosphatase-deficient strain. Also, the photorespiration inhibitor aminoacetonitrile produced a decline in leaf and protoplast ribulose bisphosphate carboxylase activation level, but was without effect on intact chloroplasts. Fructose bisphosphatase, a light-activated enzyme which is strongly dependent on stromal pH and Mg²⁺ for regulation, was unaffected by conditions which caused inhibition of ribulose bisphosphate carboxylase. Thus, the mechanism of inhibition does not appear to involve changes in stromal Mg²⁺ and pH but rather is associated with metabolite flux through the photorespiratory pathway.     

Effect of inorganic carbon on photoautotrophic growth of microalga Chlorococcum littorale

The growth rate of a highly CO₂‐tolerant green alga, Chlorococcum littorale, was investigated in semi‐batch cultures at a temperature of 22°C, a light intensity of 170 μmol‐photon m^?2 s^?1 and CO₂ concentrations ranging from 1 to 50% (v/v) at atmospheric pressure. In the experiments, solutions were bubbled with CO₂ and N₂ gas mixtures to adjust CO₂ concentrations to minimize the influence of O₂. Growth rate, which was defined in terms of a specific growth rate μ, decreased with increasing CO₂ concentration at the conditions studied. The inhibition of growth by CO₂ gas could be attributed to the concentration of inorganic carbon in the culture medium. A growth model is proposed where key assumptions are the formation of bicarbonate ion HCO as substrate for algal growth and equilibrium between CO₂ inhibitor. The proposed growth model based on the Monod equation agreed with the experimental data to within 5% and provides better correlation than the conventional inhibition model, especially in the high CO₂ concentration region. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009