Low O2 Atmosphere Research Articles

Low O2 and high CO2 atmospheres have no impact on efficacy of phytosanitary irradiation doses for Drosophila suzukii larvae

Use of irradiation as a phytosanitary treatment has been restricted in atmospheres with low O2 because extreme low O2 exposure can potentially induce radioprotective responses and enhance survival after irradiation. In addition to being low in O2, many controlled atmosphere treatments and modified atmosphere packaging materials maintain high CO2 levels along with low O2. Few studies have combinatorically tested the combined effects of high CO2 and low O2 on radiation sensitivity, and none have done so in a fully factorial design. Here we exposed larvae of the fly Drosophila suzukii to a range of concentrations of low O2 and high CO2 at a series of radiation doses up to 60 Gy. We found that low levels of O2 (≤ 5 kPa) induced a radioprotective response, with the radioprotective response greatest at the lowest O2 concentrations (2.5 & 0 kPa). Adding CO2 significantly decreased this protective response of low O2 on healthy adult emergence when O2 was 2.5 & 5 kPa, but this effect was only apparent at lower radiation doses, well below those used for phytosanitary treatments for this pest. Our study suggests that either controlled atmospheres or modified atmosphere packaging will not challenge the efficiency of phytosanitary irradiation for D. suzukii, and that high CO2 may act as an additional mitigation measure to disinfest insect pests from fresh commodities.

Controllable Poly(L-lactic acid) Soft Film with Respirability and Its Effect on Strawberry Preservation

Gas permeability of films is essentially important for fresh products packaging. The flexible poly(e-caprolactone) (PCL) was incorporated into the backbone of poly(L-lactic acid) (PLLA) to improve the flexibility and gas permeability of PLLA. The effects of different PCL middle blocks on the mechanical properties, oxygen (O2), carbon dioxide (CO2) and water vapor permeative properties of PLLA-PCL-PLLA triblock copolymers were evaluated, as well as its preservation effect on strawberry. The results showed that both the PCL and PLLA blocks kept amorphous state, and phase separation occurred in this immiscible system. The PCL play a role of gas passage, the CO2 permeability and CO2/O2 perm-selective ratio of neat PLLA film improved 2–3 times with the incorporation of higher molecular weight PCL. In addition, the PLLA-PCL-PLLA films presented a better toughness after large insertion of flexible PCL. Storing experiments showed that the low O2 and high CO2 atmosphere was established inside the package due to the good gas exchange performance of films. Moreover, strawberries still maintained the good sensory quality and Vitamin C contents on 24th day. Such biodegradable PLLA soft films are of great potential in fresh product packaging.

Self-catalytic-grown SnOx nanocones for light outcoupling enhancement in organic light-emitting diodes

Light extraction in organic light-emitting diodes (OLEDs) was improved by applying SnOx nanocones grown via thermal annealing in a low-O2 atmosphere. SnOx was easily fabricated through thermal processing after Sn deposition. The diameter of the SnOx nanocones was controlled by changing the deposition thickness of Sn. The SnOx nanocones induced strong Mie scattering, which reduced the total internal reflection in the glass substrate. Consequently, the OLED with SnOx nanocones exhibited a 23% increase in the external quantum efficiency compared with a reference device.

Respiratory and low-temperature sweetening responses of fresh-cut potato (Solanum tuberosum L.) tubers to low oxygen

Enzymatic browning (EB) has impeded the commercialization of fresh-cut (FC) potato. However, recently introduced Innate®-engineered cultivars with silenced polyphenol oxidase (PPO) have overcome this obstacle. As a supplement to refrigeration, low O2 atmosphere may extend the shelf-life of FC potato by reducing wound-induced respiration, associated dry matter loss, EB, and low-temperature sweetening (LTS). Determining the O2 concentration that minimizes these deteriorative physiological processes without invoking anaerobic metabolism is prerequisite to designing effective modified atmosphere packaging (MAP). Accordingly, FC tubers of cultivars Russet Burbank (RB), Ranger Russet (RR), and their Innate® counterparts, CultivATE®, GenerATE®, and GlaciATE®, were stored (4 °C) in ten O2 atmospheres ranging from 0 to 21 kPa to determine the lower oxygen limit (LOL) for aerobic respiration and effects on LTS and EB. FC tissue stored at 21 kPa O2 displayed a prominent cold-induced respiratory acclimation response (RAR), characterized by an initial decline in respiration rate followed by a steady increase through 48 h. The RAR decreased with O2 and was extinguished at ≤1.5 kPa. Lowering O2 from 21-7 kPa had little effect on tissue respiration; however, rates fell from 4.23 to 3.41 μg kg−1 s−1 as O2 decreased from 7 to 3.5 kPa, followed by a further 79% reduction to 0.70 μg kg−1 s−1 at 0 kPa O2. Tissue lactate profiles revealed the onset of anaerobic metabolism at ca 1.5 kPa O2 for all cultivars. Importantly, lactate and ethanol accumulation were negligible through 16 d at ≥2 kPa O2 (= LOL) but increased considerably at ≤1 kPa. Low O2 attenuated the cold-induced synthesis of sucrose and reducing sugars in FC tissue from RB, and sucrose from GlaciATE® tubers in which acid invertase is silenced. Enzymatic browning of FC RB and RR tubers was inhibited by anoxia, but extensive at ≥0.5 kPa O2. FC Innate® tubers exhibited only minor EB at all O2 concentrations. Collectively, these data inform the further development of MAP for FC potato.

Response of pomegranate arils (cv. Wonderful) to low oxygen stress under active modified atmosphere condition.

Successful characterization of the relationship between respiration rate (RR) and low oxygen (O2 ) limit is critical for optimizing the modified atmosphere condition. It is well documented that a low O2 atmosphere reduces the RR of fresh produce, but could also lead to abiotic stress due to the accumulation of glycolysis end products. Therefore, this study investigated the response of pomegranate arils exposed to low O2 atmosphere (composed of 2 kPa O2 , 18 kPa carbon dioxide, and 80 kPa nitrogen) and identified the low O2 limit at 5 °C and 10 °C. The study aim was achieved by using real-time RR and respiration quotient (RQ) data, microbial growth, identifying changes in the fermentative volatile organic compounds profile, and the consumption of respiratory metabolites (organic acids and individual sugars). The gas concentrations changed significantly respective to the storage temperature and resulted in a significant change in the parameters studied. The response of pomegranate arils to low O2 stress involves making alterations to the metabolic composition, especially those involved in anaerobiosis, such as the accumulation of ethanol, and an immediate increase on RQ. Pomegranate arils (cv. Wonderful) can tolerate down to 1.9 kPa O2 and 2.3 kPa O2 concentrations at 5 °C and 10 °C respectively. © 2018 Society of Chemical Industry.

Interaction of bimetallic PtCo layers with bare and graphene-covered ZnO(0001) supports

PtCo bimetallic overlayers supported on bare and graphene covered ZnO(0001) substrates have been successfully prepared and used to investigate the effect of graphene interlayer on the arrangement and the redox behaviour of PtCo. We found that Co is readily oxidized at the PtCo/ZnO interface during annealing in ultra-high vacuum (UHV) and low pressure O2 atmosphere, while after inserting a layer of graphene in-between, the oxidation of Co is restricted. In addition, the reduction of Co oxides by H2 is more pronounced when PtCo is supported on graphene covered ZnO. Apart from the cobalt oxidation state, graphene insertion at the interface also influences the PtCo arrangement by favouring their intermixing. Raman spectra show that low intensity defects are introduced into graphene layer after the deposition of PtCo and are enhanced by high temperature annealing. This study highlights the prospect of using graphene to tune the interaction between alloys and oxide supports which finds potential applications in catalysis.

Hydrogen-treated hierarchical titanium oxide nanostructures for photoelectrochemical water splitting

Hierarchical titanium oxide nanostructures were synthesized by Pulsed Laser Deposition (PLD) and investigated as photoanodes for photoelectrochemical water splitting. An explorative combined approach to enhance TiO2 performance was based, on the one hand, on the employment of hydrogenation treatments with the aim of improving quantum efficiency and extending light absorption to the visible range; on the other hand, on the optimization of morphology and structure, to increase light harvesting and charge separation/transport. This approach was pursued by depositing at a fixed background pressure with variable oxygen content (to control the growth morphology and structure) and by annealing in a Ar/H2 mixture (in substitution of or in combination with air annealing), in order to induce crystallization to the anatase structure and reduction/hydrogenation of the material. Morphology, structure and optical properties were investigated by SEM, Raman spectroscopy, X-ray diffraction and UV–visible-IR spectroscopy. An optical absorption tail towards the visible range appeared after Ar/H2 annealing, without any significant modification of the nanoscale structure after the different thermal treatments. Photocurrent measurements under solar simulator illumination showed a noteworthy increase of photoresponse for Ar/O2-deposited samples with air annealing followed by Ar/H2 annealing. These findings can be ascribed to the combination between an improved charge transport of TiO2 deposited in low-O2 atmosphere and a hydrogenation effect on the nanostructures surface layers, leading to improved quantum efficiency.

Iron-dependent nitrogen cycling in a ferruginous lake and the nutrient status of Proterozoic oceans

Nitrogen limitation during the Proterozoic has been inferred from the great expanse of ocean anoxia under low-O2 atmospheres, which could have promoted NO3− reduction to N2 and fixed N loss from the ocean. The deep oceans were Fe rich (ferruginous) during much of this time, yet the dynamics of N cycling under such conditions remain entirely conceptual, as analogue environments are rare today. Here we use incubation experiments to show that a modern ferruginous basin, Kabuno Bay in East Africa, supports high rates of NO3− reduction. Although 60% of this NO3− is reduced to N2 through canonical denitrification, a large fraction (40%) is reduced to NH4+, leading to N retention rather than loss. We also find that NO3− reduction is Fe dependent, demonstrating that such reactions occur in natural ferruginous water columns. Numerical modelling of ferruginous upwelling systems, informed by our results from Kabuno Bay, demonstrates that NO3− reduction to NH4+ could have enhanced biological production, fuelling sulfate reduction and the development of mid-water euxinia overlying ferruginous deep oceans. This NO3− reduction to NH4+ could also have partly offset a negative feedback on biological production that accompanies oxygenation of the surface ocean. Our results indicate that N loss in ferruginous upwelling systems may not have kept pace with global N fixation at marine phosphorous concentrations (0.04–0.13 μM) indicated by the rock record. We therefore suggest that global marine biological production under ferruginous ocean conditions in the Proterozoic eon may thus have been P not N limited. Fixed nitrogen is lost from oxygen minimum zones. Experimental data from an anoxic lake show that the presence of Fe(II) limits this loss, suggesting that ancient anoxic and iron-rich oceans may not have been nitrogen limited.

Impacts of low and super-atmospheric oxygen concentrations on quality attributes, phytonutrient content and volatile compounds of minimally processed pomegranate arils (cv. Wonderful)

This study investigated the impact of modified atmosphere (MA) storage: at low oxygen (O2) (MA-1; 5kPa O2+10kPa CO2+85kPaN2), (MA-2; 10kPa O2+5kPa CO2+85kPaN2); super-atmospheric O2 (MA-3; 70kPa O2+10kPa CO2+85kPaN2); and air (MA-4; 21kPa O2+0.03kPa CO2+78kPaN2) on the physicochemical, phytonutrient, volatile organic compounds (VOCs) and microbiological quality of minimally processed ‘Wonderful’ pomegranate arils stored at 5°C for 12 d. In addition, the effect of temperature fluctuation on the physical and microbiology quality of arils was evaluated. Samples were removed from cold storage on each sampling day, and kept for 2 d at ambient (20°C) condition. Low O2 atmosphere (MA-1) best maintained phytonutrient content of arils at 5°C. Aerobic mesophilic bacteria, yeast and mould counts were found to be significantly lower under super-atmospheric O2 (MA-3) storage in comparison to other treatments at 5°C and ambient. A total of 25 volatile organic compounds (VOCs) were detected and identified for pomegranate ‘wonderful’ across the different MA conditions. Highest relative composition of VOCs was found in samples stored under MA-3. Temperature fluctuation had a significant impact on the physical and microbiology quality of pomegranate arils.

Fuel pre-granulation for reducing NOx emissions from the iron ore sintering process

This study considered the effects of a granular fuel distribution state on the NOx emissions during the sintering process. The results show that fuel pre-granulation technology can be applied to wrapping fuel inside granules to form a double-layered granular structure. Because the in-diffusion of O2 is restricted in granules, the fuel inside the granules is burnt in a relatively low O2 atmosphere, which is conducive to inhibiting the conversion of fuel-N to NOx. Meanwhile, part of the generated NOx is reduced to N2 by CO during the out-diffusion process. Consequently, using fuel pre-granulation minimises the concentration of NOx emissions and fuel-N conversion rate. Sintering experiments confirmed that using pre-granulation reduced the concentration of NOx from 425ppm to 319ppm and the fuel-N conversion rate from 59.7% to 49.4% compared with conventional granulation. Therefore, controlling the fuel combustion behaviour by regulating its distribution in granules is an effective measure to reduce NOx emissions.

Effects of pure oxygen and reduced oxygen modified atmosphere packaging on the quality and microbial characteristics of fresh-cut pineapple

Introduction. Modified atmosphere packaging (MAP) is a preservation technique currently used by the fresh-cut fruit industry. Fruit quality may vary according to the concentration of oxygen (O2 ) in the packaging. However, there is no published research on the effects of a pure O2 modified atmosphere in the packaging of fresh-cut pineapple. There are also no comparative studies of the differences between pure O2 and conventional low O2 MAP on the quality of fresh-cut pineapple. Materials and methods. Pineapple slices were sealed with a tray sealer using a polyethylene (PE) / polypropylene (PP) composite film and one of the following atmosphere treatments: (4% O2 + 5% CO2 ), (100% O2 ), and ambient air (control). We evaluated the effects on quality and microbial spoilage of fresh-cut pineapple. Results and discussion. Both modified atmosphere treatments delayed decreases in firmness, soluble solid contents (SSC), reducing sugar, and ascorbic acid. Pineapple slices packaged in pure O2 contained lower amounts of sugar and ascorbic acid and displayed more browning than the slices in the low O2 concentration. Additionally, both modified atmosphere treatments strongly delayed the growth of microorganisms. Aerobic bacteria, yeast and mold levels in pineapple slices packaged in pure O2 were higher than those packaged with the low O2 atmosphere during long-term storage. Conclusion. Modified atmosphere packaging using low O2 concentration (4% O2 + 5% CO2 ) was better able to maintain the quality of fresh-cut pineapple than packaging with pure O2 atmosphere.

Stratigraphic expression of Earth's deepest 13C excursion in the Wonoka Formation of South Australia

The most negative carbon isotope excursion in Earth history is found in carbonate rocks of the Ediacaran Period (635-541 Ma). Known colloquially as the “Shuram” excursion, workers have long noted its broad concordance with the rise of abundant macro-scale fossils in the rock record, collectively known as the “Ediacaran Biota.” Thus, the Shuram excursion has been interpreted by many in the context of a dramatically changing redox state of the Ediacaran oceans—for example, a result of methane cycling in a low O2 atmosphere, the final destruction of a large pool of recalcitrant dissolved organic carbon (DOC), and the step-wise oxidation of the Ediacaran oceans. More recently, diagenetic interpretations of the Shuram excursion have challenged the various redox models, with the very negative δ13C values of Ediacaran carbonates explained via sedimentary in-growth of very δ13C depleted authigenic carbonates, meteoric alteration or late-stage burial diagenesis. A stratigraphic and sedimentological context is required to discriminate between these explanatory models, and to determine whether the Shuram excursion can be used to evaluate oxygenation in terminal Neoproterozoic oceans. Here we present chemo-stratigraphic data (δ13C, δ18O, and trace element abundances) from 15 measured sections of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia. In some locations, the Wonoka Fm. is ∼700 meters (m) of mixed shelf limestones and siliciclastics that record a 17 permil δ13C excursion (−12 to +5‰). Further north in the basin, the Wonoka Fm. is host to deep (∼1 km) paleocanyons, which are partly filled by tabular-clast carbonate breccias. Canyon-filling ceased during ongoing sedimentation on the shelf interior (the “canyon-shoulder”), as evidenced by upper canyon-shoulder units that overlie and cap certain canyon-fill sequences. The unprecedented size of the chemostratigraphic dataset presented here (2671 δ13C-δ18O measurements from the canyon-shoulder, 1393 δ13C-δ18O measurements from canyon clasts, and 11 different trace elements measured on 247 Wonoka Fm. carbonate samples), when coupled with the unique canyon-shoulder to canyon-fill depositional system of the Wonoka Fm., allows for new insights into Ediacaran carbon isotope systematics. The excursion is preserved in a remarkably consistent fashion across 12,000 km2 of basin area; fabric-altering diagenesis, where present, occurs at the sub-meter vertical scale, results in

A substoichiometric tungsten oxide catalyst provides a sustainable and efficient counter electrode for dye-sensitized solar cells

Development of Pt-free catalyst materials for the counter electrode (CE) in dye-sensitized solar cells (DSSCs) has been regarded as one of the crucial steps to improving energy conversion efficiency and cost effectiveness of DSSCs. In this work, low cost tungsten oxide (WO3-x) counter electrodes, prepared by annealing tungsten metal sheets under an Ar and low O2 atmosphere, exhibited high catalytic activity and energy conversion efficiency. The highest efficiency achieved here for DSSCs with WO3-x counter electrodes, was 5.25%, obtained from a 500°C annealed tungsten sheet. TEM and XPS analysis suggested the formation of sub-stoichiometric tungsten oxide layer (∼WO2.6) with the presence of W6+, W5+ and W4+ oxidation states at the tungsten metal surface after the 500°C annealing. Only W6+ and W5+ oxidation states were detected after a 600°C annealing indicating the formation of a more stoichiometric tungsten oxide layer (∼WO2.8) and resulting in a drop in efficiency of the DSSC. We suggest that mixed valence tungsten states account for the excellent catalytic activity and good electrical conductivity as evidenced by the highest cyclic voltammetry response of 0.76mA/cm2 and the lowest impedance value of 44.33Ω, respectively.

Oxidative stability of n-3-enriched chicken patties under different package-atmosphere conditions

The oxidation processes were studied in chicken patties, enriched with n-3 fatty acids, after 8days of storage at 4°C, under different aerobic conditions, and following heat treatment. Significant effects were seen on lipid and cholesterol oxidation and the sensory qualities for whole flaxseed addition in the chicken feed (i.e., n-3 fatty acid enrichment), and for the different package-atmosphere conditions. For the raw chicken patties, n-3 enrichment increased the colour L∗ values while, after the heat treatment, there were higher thiobarbituric acid-reactive substances (TBARs) and cholesterol oxidation products (COPs), and the rancidity was more pronounced. In comparison with the low O2 (<0.5%) package-atmosphere condition, O2 enrichment (80%) increased the instrumentally measured colour values, TBARs, total and individual COPs, and the rancidity became pronounced. The most suitable package-atmosphere condition of these raw n-3-enriched chicken patties is a very low O2 atmosphere, with or without an O2 scavenger.

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 (4–6h 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 20days 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.

Preharvest and postharvest factors related to off-odours of fresh-cut iceberg lettuce

The influence of different preharvest and postharvest factors affecting off-odour development of fresh-cut iceberg lettuce in low-O2 modified atmospheres (MA) was investigated. Fresh-cut iceberg lettuce developed undesirable off-odours under low O2 and elevated CO2 atmospheres. A strong relationship between CO2 concentration and off-odour development was observed. Significant differences in off-odour development existed among different cultivars in two harvests in consecutive years. The influence of maturity stage was evaluated, comparing fresh-cut product from immature and over-mature heads with commercial ones. Higher CO2 concentrations and higher accumulation of ethanol and acetaldehyde were detected in the headspace of MA-packed lettuce from immature heads. Differences in respiration rate of the fresh-cut product from heads cultivated during the winter–spring seasons were around 30%. Respiration rate of fresh-cut iceberg lettuce increased when medium temperature during cultivation increased. Changes in the product weight generated different CO2 levels which correlated with the production of ethanol and acetaldehyde and other off-odour metabolites related with the lipoxygenase (LOX) pathway such as hexanal, 1-hexanol, and cis-3-hexen-1-ol. Volatile compounds such as cis-3-hexen-1-ol, β-elemene, ethyl acetate and dimethyl sulphide increased their content more than 10 times compared with other volatiles. Moreover, differences in the initial flushed gas-mixture with or without CO2 showed higher CO2 concentrations and the development of stronger off-odours when samples were flushed with an enriched CO2 gas-mixture. In summary, visual quality of fresh-cut iceberg lettuce is important but so are odour and flavour. MAP currently used for fresh-cut lettuce may need some modification to inhibit off-odours and achieve better aroma and flavour qualities for preserving “freshness” of the cut product. Screening for cultivars with low browning potential and fermentation, harvested at optimum maturity stage and with an adequate package design are recommended.

Residual effects of low oxygen storage of mature green fruit on ripening processes and ester biosynthesis during ripening in bananas

Mature green banana (Musa sapientum L. cv. Cavendish) fruit were stored in 0.5%, 2%, or 21% O2 for 7 days at 20°C before ripening was initiated by ethylene. Residual effects of low O2 storage in mature green fruit on ripening and ester biosynthesis in fruit were investigated during ripening for up to 6 d at 20°C. Concentrations of ethanol in mature green fruit did not change during storage in both 21% and 2% O2 atmospheres, but increased in fruit stored in 0.5% O2. The activities of alcohol dehydrogenase (ADH) in 2% and 21% O2 atmospheres remained very low throughout the storage period, but significantly increased with 0.5% O2. After transferring fruit to regular air and trigging ripening with ethylene, yellowing of peel, fruit softening and hydrolysis of starch in fruit stored in low O2 atmospheres were slower than in the control. Fruit stored in low O2 also showed a delayed onset of the climacteric peak. The activities of ADH were lower in the low O2 stored fruit than in the control fruit. Productions of ethyl acetate, isoamyl acetate, and isobutyl acetate were remarkably suppressed by low O2 storage. Alcohol acetyltransferase activity increased gradually with storage time in all treatments, being significantly lower in fruit with low O2 pretreatments. The results indicate that low O2 plus room temperature storage can extend storage life of bananas with the sacrifice of a low production of ester volatiles.

Controlled and modified atmospheres influence chilling injury, fruit quality and antioxidative system of Japanese plums (Prunus salicina Lindell)

SummaryOur objective was to compare the effects of controlled atmosphere (CA) and modified atmosphere packaging (MAP) on fruit quality, chilling injury (CI) and pro‐ and antioxidative systems in ‘Blackamber’ Japanese plums. Matured fruit were stored for 5 and 8 weeks at 0–1 °C in normal air, CA‐1 (1% O2 + 3% CO2), CA‐2 (2.5% O2 + 3% CO2) and MAP (~10% O2 and 3.8% CO2). CA was more effective than MAP in retention of flesh firmness and titratable acidity during cold storage. Fruit stored in CA‐1 showed reduced CI and membrane lipid peroxidation after 5 and 8 weeks of cold storage. Low O2 atmospheres appeared to limit the generation of reactive oxygen species (ROS) and their efficient scavenging through the concerted action of superoxide dismutase and peroxidase. The role of ascorbate–glutathione (AsA–GSH) cycle in the regulation of oxidative stress was also studied during and after storage in different atmospheres. In conclusion, optimum CA conditions delayed fruit ripening and CI through augmentation of antioxidative metabolism and suppression of oxidative processes.

Postharvest oxidative behaviour of 1-methylcyclopropene treated Japanese plums (Prunus salicina Lindell) during storage under controlled and modified atmospheres

Storage atmosphere composition is an important factor affecting potential storage life, susceptibility to physiological disorders and overall quality of fruit. We investigated the effects of controlled/modified atmospheres (CA/MA) on fruit quality, lipid peroxidation, and enzymatic and non-enzymatic antioxidative system in 1-MCP treated Japanese plums cv. ‘Blackamber’ during cold storage. Commercially mature fruit pretreated with 1-MCP (0.6μLL−1 for 12h) were stored for 5 and 8weeks at 0–1°C in different storage atmospheres, viz. normal air, 1% O2 and 3% CO2 (CA-1), 2.5% O2 and 3% CO2 (CA-2) and modified atmospheres (∼10% O2 and 3.8% CO2) generated through packaging in low density polyethylene bags. The results showed that storage under CA-1 and CA-2 was beneficial in delaying fruit ripening, retarding lipid peroxidation and reducing incidence and severity of chilling injury (CI) during 5 and 8 weeks of storage compared to normal air and MAP. The activities of enzymes involved in ascorbate–glutathione (AA–GSH) cycle were determined to explain the redox status of ascorbate and glutathione as influenced by storage atmospheres. CA conditions were favourable for the glutathione pool and the enzymes related to restoration of glutathione in the AA–GSH cycle, but the effects of CA on the ascorbate pool were not favourable. The data suggested that the enzymatic and non-enzymatic antioxidative systems were efficiently operating under low O2 atmospheres to scavenge reactive oxygen species produced in response to long-term chilling and gas stresses. CA conditions appeared to be limiting oxidative processes to some extent resulting in reduced oxidative damage. In conclusion, the development of CI, which is a manifestation of oxidative damage to the fruit tissue, can be significantly reduced through synergistic beneficial effects of CA and pretreatment with 1-MCP in Japanese plums.

Oxygen interacts with priming, moisture content and temperature to affect the longevity of lettuce and onion seeds

AbstractLettuce (Lactuca sativaL.) and onion (Allium cepaL.) seeds have relatively short longevity during storage and their germination is sensitive to environmental stress. Seed priming (controlled hydration followed by drying) can improve seed germination under stressful conditions, inducing faster and more uniform germination over broader temperature ranges, but it can also reduce seed longevity in storage. Controlled deterioration (CD) tests are often employed to study longevity by ageing seeds rapidly at elevated temperature and moisture content, and primed seeds are particularly sensitive to CD conditions. As reactive oxygen (O2) species are thought to be involved in seed deterioration, we tested whether storage under reduced O2atmospheres (0 and 2% O2) would extend the longevity of primed and non-primed seeds under low relative humidity (RH) (33% RH+37°C) and CD (75% RH+50°C) storage conditions. The longevity of both non-primed and primed lettuce seeds in low RH storage was extended by anaerobic environments, but the effect of O2was much less under CD conditions. In onion, only primed seeds exhibited a beneficial effect of low O2atmospheres under both types of ageing conditions. In both species, storage under anaerobic conditions was beneficial for extending the longevity of primed seeds, but was not able to ameliorate fully the negative effect of priming on storage life.