Use of a pinhole to develop an active packaging system for kimchi,a Korean fermented vegetable

A pinhole in a packaging system for kimchi, a Korean lactic acid fermented vegetable, was found to actively modify the headspace gas and improve the quality of the product. The effect of the presence of a pinhole on the headspace atmosphere and microbial flora was investigated in the packaging system and a prototype of this active packaging system was fabricated and tested for its effectiveness in improving quality. The incorporated pinhole eliminated pressure build-up in the package by allowing restricted flow of gas to the atmosphere. O₂ and N₂ gases in the headspace were flushed out by CO₂ gas produced continuously from lactic acid fermentation and this modified atmosphere enhanced the growth of lactic acid bacteria. In particular, the growth of Leuconostoc species, heterofermentative lactic acid bacteria, was promoted by the pinhole. The increased amount of heterofermentative lactic acid bacteria led to a higher accumulation of CO₂ in the package and this provided the kimchi with a stronger cool carbonic taste and a desirable flavour. An elaborate design of the pinhole incorporating microporous film and a gas adsorvent could be adopted to improve the kimchi packaging system by preventing leakage of fermentative aroma and possible contamination from outside atmosphere. © 1997 John Wiley & Sons, Ltd.     

Modified atmosphere packaging for green chili peppers

Modified atmosphere packages were designed and used for the packaging of green chili peppers. Respiration of green peppers at 10°C was characterized by the closed-system method as a function of O₂ and CO₂ concentrations, and was incorporated into mass balance equations of O₂ and CO₂ gases in order to predict the gas composition inside the package over time. From the prediction of atmospheres inside packages constructed of the available plastic films, three retail packages (110-g peppers) were designed and studied experimentally for their ability to modify the package atmosphere and to retain quality (moisture, ascorbic acid and chlorophyll). Pepper packages using 25 μm low-density polyethylene and 30 μm cast polypropylene could attain modified atmosphere close to the optimal gas concentrations (3% O₂ and 5% CO₂), and therefore provided better quality retention compared with unpackaged controls.     

Quality changes of treated fresh‐cut tropical fruits in rigid modified atmosphere packaging containers

There has been increasing demand for various fresh‐cut tropical fruits. However, their short shelf‐life has limited the market increase of this product. Quality changes (firmness, colour, total soluble solids (TSS), titratable acidity (TA), sensory quality and microbial safety) of fresh‐cut mangoes, pineapples, melons and mixes of these fruits were evaluated. Chemical treatments to reduce browning, firmness loss and decay of fresh‐cut tropical fruits were investigated. The most effective agents for fresh‐cut mangoes, pineapples and melons were 0.1m ascorbic acid, 0.2m ascorbic acid and 0.2m ascorbic acid + 0.2m calcium chloride, respectively. Fresh‐cut tropical fruits were packaged in various rigid containers (PET, OPS and OPLA). Gas composition in the package headspace and time to reach steady‐state condition varied among fresh‐cut packaging systems and affected their quality and shelf‐life. The effects of package permeability of O₂ and CO₂ on quality and shelf‐life of the fresh‐cut products are discussed. Extended shelf‐life was observed in fresh‐cut mangoes, pineapples and mixes packaged in PET due to reduced O₂ and elevated CO₂ atmosphere. A modified atmosphere of 6% O₂ and 14% CO₂ achieved in PET extended the shelf‐life of fresh‐cut pineapples from 6 to 13 days. Accumulation of CO₂ may impart an off‐odour of fresh‐cut fruits. The results suggested that the shelf‐life of fresh‐cut fruits could be extended by using proper rigid containers. Suitable mixes to create optimal equilibrium modified atmosphere had a potential to extend shelf‐life of short shelf‐life fresh‐cut tropical fruits. Copyright © 2006 John Wiley & Sons, Ltd.     

Preservation of cold‐stored guavas influenced by package materials

The objective of this study was to evaluate the influence of package materials on the preservation of cold‐stored ‘Kumagai’ guavas. The treatments were: PO2, co‐extruded polyolephinic film with gas injection (5% O₂/5% CO₂/N₂); PO3, co‐extruded polyolephinic film with gas injection (5% O₂/5% CO₂/N₂); LDPE, linear low density polyethylene film; LDPE‐gas, linear low density polyethylene film with gas injection (3% O₂/8% CO₂/N₂); PVC, polyvinylchloride stretch film; PO1, co‐extruded polyolephinic film and control: non‐packaged guavas. Guavas were stored at 10 ± 1°C/80–90% RH for 21 days, and then transferred to room temperature. Gas composition within the package headspace was analysed during storage and the physical and chemical characteristics of the guavas were evaluated daily during ripening. The modified atmosphere provided by PO1 film was insufficient to promote the benefit of senescence control. Although PVC provided an atmosphere close to that recommended, it did not preserve the colour and pulp firmness. PO2, PO3, LDPE and LDPE‐gas retarded the senescence process of the guavas during 21 days at 10°C plus 2 days at room temperature, but harmed the normal ripening of guavas in some aspects. This can be explained by reduced O₂ and elevated CO₂ levels within these four packages. None of the packages influenced the titratable acidity and the soluble solids, but they did harm ascorbic acid synthesis. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of oxygen concentration on the shelf‐life of fresh pork packed in a modified atmosphere

Freshly slaughtered meat was packed in modified atmosphere packs (MAP) containing 5%, 15%, 25%, 35%, 45% and 55% O₂ along with 20% CO₂ in each package and stored for 8 days at 4°C. The samples were evaluated on the 8th day in terms of TVBN total volatile base nitrogen (TVBN) value, thiobarbituric acid reactive substances (TBARs) value, colour acceptability score, overall acceptability score and total microbial count. The result indicated better effects for 45% and 55% O₂‐containing MAP; however, the TBARs value of 45% O₂ atmosphere was significantly lower, without having significant differences in other evaluation criteria, than in the 55% O₂ package; hence 45% O₂ and 20% CO₂ gas mixture were selected as the most appropriate gas composition for fresh pork packaging. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling a modified atmosphere packaging system for fresh scallops (Argopecten purpuratus)

Seafood is a highly perishable food, which has a relative short shelf‐life. Modified atmosphere packaging (MAP) is a system that offers a way of extending the shelf‐life of seafood products, maintaining quality and inhibiting bacterial growth. The objective of this research was to study and determine the optimal conditions for packaging scallops in a modified atmosphere system, which includes CO₂/O₂/N₂ mixture, headspace:food ratio and storage temperature, utilizing an integrated mathematical model for MAP systems with its respective experimental validation. For validation purposes, two experiments were conducted, using gas mixtures of: (a) 45% CO₂/10% O₂/45% N₂; and (b) 60% CO₂/10% O₂/30% N₂. In addition, two experiments, at 6°C and 20°C, were conducted to obtain the shelf‐life model, utilizing the following gas mixtures: 30% CO₂/10% O₂/60% N₂; 45% CO₂/10% O₂/45% N₂; 60% CO₂/10% O₂/30% N₂; and 75% CO₂/10% O₂/15% N₂. Gas mixtures with CO₂ concentrations between 30% and 70% and different headspace:food ratios were tested during simulations. The optimal conditions for scallop storage were a 60% CO₂/10% O₂/30% N₂ gas mixture and a headspace:food ratio of 2:1. With these conditions, a simulated shelf‐life of 21 days was obtained. Optimal conditions consider maximum shelf‐life, an adequate film collapse criterion, and time to reach the pseudo‐equilibrium condition. The predictive mathematical model, coupled with experimental studies for specific products, can be efficiently utilized to evaluate packaging alternatives (size, material and selected thickness) for different temperatures and initial gas concentration scenarios of MAP products. Copyright © 2006 John Wiley & Sons, Ltd.     

Metal–CO2 Batteries on the Road: CO2 from Contamination Gas to Energy Source

Rechargeable nonaqueous metal–air batteries attract much attention for their high theoretical energy density, especially in the last decade. However, most reported metal–air batteries are actually operated in a pure O₂ atmosphere, while CO₂ and moisture in ambient air can significantly impact the electrochemical performance of metal–O₂ batteries. In the study of CO₂ contamination on metal–O₂ batteries, it has been gradually found that CO₂ can be utilized as the reactant gas alone; namely, metal–CO₂ batteries can work. On the other hand, investigations on CO₂ fixation are in focus due to the potential threat of CO₂ on global climate change, especially for its steadily increasing concentration in the atmosphere. The exploitation of CO₂ in energy storage systems represents an alternative approach towards clean recycling and utilization of CO₂. Here, the aim is to provide a timely summary of recent achievements in metal–CO₂ batteries, and inspire new ideas for new energy storage systems. Moreover, critical issues associated with reaction mechanisms and potential directions for future studies are discussed.     

Prediction of plastic film thickness based on gas permeability and validation with ‘Kyoho’ table grapes for optimal modified atmosphere packaging

Modified atmosphere packaging (MAP) storage has become a useful technique for extending the shelf life of fruit and vegetables. However, the success of MAP depends on many factors, including types of fresh products, storage conditions, and the characteristics of the packaging films. To achieve the optimal gas composition in the package headspace and improve the postharvest quality of fresh produce, the packaging film with appropriate barrier properties needs to be selected. This study aimed to predict the film thickness by applying produce respiration rate and package film permeability data measured in given product weight and storage conditions. An available film (eg, 25‐μm‐thick low‐density polyethylene) was used to pack fresh produce, and the respiration rate of fresh produce and in‐package O₂ and CO₂ concentrations at steady state were measured. Permeability of the film was calculated based on mass balance, and the thickness of the film could be predicted if the recommended target O₂ and CO₂ concentration was obtained from the literature. To validate the predicted thickness value, an experiment was conducted by packaging fresh table grapes in bags of the predicted thickness. The effect of packaging with different film thicknesses on the quality of the fruit was determined. The results showed good agreement between the predicted and the experimental in‐bag O₂ and CO₂ concentrations, and the MAP with predicted thickness (90 μm) film was more effective in maintaining postharvest quality of grapes during low‐temperature storage than the thinner films (30 and 60 μm) and the control.     

Evaluation of plastic packages for guava refrigerated preservation

Guavas cv. ‘Kumagai’ were packed in several plastic materials and stored at 10°C and 85–90% relative humidity (RH) for 7, 14, 21 and 28 days (+3 days at 25°C). The plastic materials studied were: multilayer co‐extruded polyolephine film with selective permeability (PSP), low‐density polyethylene film (LDPE), LDPE film with mineral incorporation (LDPEm) and heat‐shrinkable polyolephine film (SHR). Guavas not packed were taken as control samples. The physicochemical characteristics of the fruits, O₂ and CO₂ transmission rates of the packaging materials and gas composition at the package headspace were evaluated. The LDPE film, 69 µm in thickness, with the lowest permeability to both O₂ and CO₂, led to anaerobiosis and high CO₂ concentration inside the packages and promoted physiological disturbances and changes in fruit flavour. The SHR film, 15 µm in thickness, was the most permeable to CO₂ and had quite high O₂ transmission, which modified the inner atmosphere of the packages slightly. The fruits packed in this film showed a poorer quality than the controls, possibly due to the heat produced during the shrinking of the film. The LDPEm film, 24 µm in thickness, was almost as permeable to CO₂ but had reduced O₂ transmission, promoting an atmosphere of equilibrium of 3% O₂ and 4.5% CO₂. Fruits packed in this film kept their skin colour and pulp firmness, suitable for consumption up to 14 days. The PSP film, 35 µm in thickness, had the greatest O₂ transmission but just over half of the CO₂ transmission of LDPEm, promoting an atmosphere of equilibrium of 0.5% O₂ and 4.5% CO₂ inside the packages. Fruits packed in such packages kept their physicochemical characteristics up to 21 days. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of modified atmosphere packaging conditions on quality preservation of powdered infant formula

The effect of different modified atmospheres (100% N₂, 100% CO₂, 70% N₂/30% CO₂, 50% N₂/50% CO₂, and air) on the quality preservation of powdered infant formula was investigated by a storage test at 30°C. Metal can packages of 400 g per unit were stored for 493 days with periodic measurements of package gas composition and product quality attributes, which included peroxide value (POV), pH, titratable acidity, bifidobacteria count, hydroxymethylfurfural content, surface colour, and solubility. In the air package, POV as an oxidative quality index increased highly along with oxygen concentration decrease, reaching a maximum of 58.7 meq/kg lipid at 350 days. Compared with the air package, POV increase of the product was significantly lower, with all the O₂‐excluded modified atmosphere packages showing a maximum of 28.5 to 29.3 meq/kg at 350 days. Packages of high CO₂ concentration experienced a pH decrease and an acidity increase of the stored product caused by dissolution of CO₂. The count of bifidobacteria in the product was maintained higher after 119 days in the package of 100% CO₂ than in the other packages. Hydroxymethylfurfural content showed a slight increase after an initial period of slight decrease, with little difference among the package treatments. There were no significant changes in product solubility and surface colour during storage. Considering that the high CO₂ atmosphere helps the survival of bifidobacteria and protects the product from oxidation without negative effects on the other quality attributes, it is suggested for use in packaging of powdered infant formula.     

Porous Ultrahigh Gas‐Permeable Polypropylene Film and Application in Controlling In‐pack Atmosphere for Asparagus

Porous polypropylene (PP) films with greater gas permeability and lower permeability ratios (β) than existing commercial films were developed for fresh produce packaging. PP containing high content of beta‐form crystal was biaxially stretched under controlled conditions. Resulting porous films with uniquely high oxygen transmission rate (OTR) of 2 659 000 cm³?m^?2?d^?1, water vapor transmission rate of 67 g?m^?2?d^?1, and β value of 0.76 was used as a “breathable window” attached to the less permeable commercial BOPP (biaxially oriented PP) lidding film. Various sizes/areas of the breathable windows were designed and tested on packaging asparagus of 400 g, at 5°C. Results demonstrated that in‐pack O₂ and CO₂ concentrations could be practically controlled and modified by changing areas of the breathable windows. Altered porous high OTR area directly affected total gas permeation of the package. Optimum gas composition of Ο₂ and CΟ₂ within the recommended controlled atmosphere for asparagus, stored at 5°C, was effectively created and maintained in the package containing 25 cm² breathable window (15% of total film lid's area). The shelf life of asparagus under optimum modified atmosphere was extended to 29 days, as compared with <3 days in the normal, low OTR tray sealed with BOPP lidding film. Clearly, these developed porous ultrahigh permeable PP films can be useful materials in designing high OTR package with desirable in‐pack O₂ and CO₂ concentrations. Copyright © 2013 John Wiley & Sons, Ltd.     

Modified atmosphere packaging of fresh produce using microporous earthenware material

Microporous earthenware sheets of 5.5–5.6mm thickness were fabricated with or without a glazing treatment by passing through a sequential firing procedure in a furnace. Their microstructure and gas permeability against oxygen and carbon dioxide were measured and examined for their usability in modified atmosphere packaging of fresh produce. Compared with plastic packaging materials, earthenware sheets with a high proportion of micropores had very high gas permeability and gave CO₂:O₂ permeability ratios close to 1. Glazing treatment smoothed the surface by clogging the pores on the surface and significantly decreased gas permeability, without affecting the internal microstructure of the earthenware. When the earthenware sheet was combined with a plastic box and used in packaging for strawberries and enoki mushrooms at 5°C, its unique permeability properties developed a modified atmosphere that was beneficial for preserving the quality of the produce. Changes in the earthenware's permeability characteristics due to moisture adsorption and condensation need to be resolved so that the dynamic changes occurring in package atmosphere over time can be better understood. Copyright © 2006 John Wiley & Sons, Ltd.     

Package Headspace Composition Changes of Chill‐Stored Perishable Foods in Relation to Microbial Spoilage

In order to find a convenient way to monitor and control the microbial quality and shelf life of chill‐stored perishable foods, microbial growth and package headspace gas concentration changes were measured during storage of three foods (seasoned pork meat, Manila clam and seasoned spinach) at 10°C, and their interrelationship was investigated. Aerobic bacterial count was the highest among the measured counts of microbial groups including specific spoilage organisms and thus may be potentially used as an index of microbial spoilage of the foods. Spoilage bacterial growth on the foods accompanied O₂ depletion and CO₂ build‐up in package headspace with some delay. There was a wide variation among the foods in the headspace package atmospheric change resulting from or related to microbial spoilage. Except for CO₂ production of Manila clam, lag times of the O₂ and CO₂ changes, determined by applying logistic function, amounted to 10^5.1–10^7.3 CFU/g, which is in the range of the microbial quality limit commonly used for shelf life determination. Overall, lag times of gas concentration changes may be used as an indicator of shelf life periods of perishable foods to a limited extent. Copyright © 2011 John Wiley & Sons, Ltd.     

Methodology for determining the appropriate selectivity of mass transfer devices for modified atmosphere packaging of fresh produce

Perforations or polymeric membranes are not capable of simultaneously providing optimum O₂ and CO₂ levels for many fruits and vegetables contained in modified atmosphere packaging. However, combining these two gas transfer devices, either in series or in parallel, can provide the required gas selectivities to create optimal modified atmosphere conditions. A methodology for determining the perforation and membrane surface areas for individual and combined systems is described. Gradient diagrams are used to calculate the optimum system selectivity, ΔpO₂ and ΔpCO₂. These values can be used to select the appropriate gas exchange devices and to determine the appropriate perforation and membrane surface area.     

The unstructured two-dimensional grid-based computation of selective thermal radiation in CO<Subscript>2</Subscript>-N<Subscript>2</Subscript> mixture flows

The possibility of applying the P ₁ approximation of the spherical harmonics method to the computation of the radiant heat transfer in heterogeneous volumes of complicated geometry is investigated. This approximation is used to evaluate the radiant heating of the surface of a spacecraft descending in the Martian atmosphere. The chemical composition of the gas heated behind the shock wave is calculated by using a kinetic model including 79 chemical reactions and ten components, such as CO₂, CO, C, O, O₂, C₂, N, N₂, CN, and NO. The optical properties are set by a spectral multigroup model computed with the help of the ASTEROID computer code with averaging over the rotational molecular spectrum structure in each group. The mechanisms of the radiant heating of the surface of descent space vehicles in the Martian atmosphere are studied.     

Compensation of Pinhole Defects in Food Packages by Application of Iron‐based Oxygen Scavenging Multilayer Films

To protect sensitive food products from oxidative deterioration, multilayer barrier film systems and also modified atmosphere packaging are widely applied. However, the preservation of food quality in such packaging systems may be compromised by the presence of defects in the sealing layer of the films, especially when these are below a critical size, typically the detection limit of standard leak testers of 10 µm. The addition of an oxygen scavenger (OS) layer in barrier film structures could therefore provide extended protection against O₂ penetration through such defects. In this study, O₂ absorption of different multilayer film structures including an iron‐based OS were investigated under defined gas atmospheres. Measurement cells were thereby covered with plastic films of defined O₂ permeability to simulate conditions in a food package during storage with pinhole defect sizes of 10 and 17 µm. The results indicated that the OS film structures applied could only compensate for a defect size of 10 µm in the sealing layer. Analysis of the O₂ absorption of different multilayer film structures at 85% and 100% relative humidity showed that higher humidity accelerates the activation of the scavenger. After full activation, the scavenger kinetics are the same for 85% and 100% relative humidity. Long‐term storage experiments using the most effective film structure from the preliminary experiments were carried out to compare O₂ absorption of a snack food product in packages with and without an OS. The analyzed linear gradient of the reaction of the OS film and food product, respectively, indicated first‐order reaction kinetics with corresponding reaction constants calculated to be K (food product) 0.021 mg (O₂) mbar (O₂)^?1 day^?1 and K (OS film) 0.066 mg (O₂) mbar (O₂)^?1 day^?1. The reaction velocity of the OS was thus three times faster than that of the food. The applicability of OS multilayer film systems to compensate a critical pinhole defect size of 10 µm for sensitive food products could therefore be confirmed. The measurement of quality parameters for the status of lipid oxidation processes would help to verify this result. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of Si,Mn, and water vapour on the microstructure of protective scales grown on Fe–20Cr in CO2 gas

Abstract

Model alloys Fe–20Cr–0.5Si and Fe–20Cr–2Mn (wt-%) were exposed to Ar–20CO₂ and Ar–20CO₂–20H₂O at either 818 or 650°C. In dry gas, protective scales on Fe–20Cr–0.5Si consisted of an outer Cr₂O₃ layer and an inner SiO₂ layer. In wet gas, additional chromia whiskers were formed on top of the duplex scale. Chromia grains formed in wet gas were much smaller than those in dry gas. A TEM analysis revealed that phase constitutions of the protective scale on Fe–20Cr–2Mn were not uniform: Mn₃O₄ and MnCr₂O₄ above alloy grain boundaries and Mn₃O₄, Cr₂O₃ and MnCr₂O₄ on alloy grains. Formation of different oxides and morphologies are discussed in terms of changes in diffusion paths and thermodynamics caused by the presence of carbon and hydrogen.     

Scale formation mechanisms of martensitic steels in high CO2/H2O-containing gases simulating oxyfuel environments

Abstract

In oxyfuel power plants, metallic components will be exposed to service environments containing high amounts of CO₂ and water vapour. Therefore, the oxidation behaviour of a number of martensitic 9–12%Cr steels in a model gas mixture containing 70% CO₂–30% H₂O was studied in the temperature range 550–700°C. The results were compared with the behaviour in air, Ar–CO₂ and Ar–H₂O. It was found that in the CO₂- and/or H₂O-rich gases, the mentioned steels tended to form iron-rich oxide scales with significantly higher growth rates than the Cr-rich surface scales formed during air exposure. The iron-rich scales were formed as a result of a decreased flux of chromium in the bulk alloy toward the surface because of enhanced internal oxidation of chromium in the H₂O-containing gases and carbide formation in the CO₂-rich gases. Additionally, the presence of water vapour in the exposure atmosphere led to buckling of the outer haematite layer, apparently as a result of compressive oxide growth stresses. The Fe-base oxide scales formed in CO₂(–H₂O)-rich gases appeared to be permeable to CO₂ molecules resulting in substantial carburization of the steel.     

Effect of Initial Gas Flushing or Vacuum Packaging on the Ripening Dynamics and Preference for Kimchi,a Korean Fermented Vegetable

The effects of vacuum or modified atmosphere packaging conditions on the ripening dynamics of kimchi and sensory preference were investigated to determine the potential of initial atmospheric flushing as a method for improving quality at consumption. In all the packaging treatments (control of air, vacuumizing, CO₂ flushing and N₂ flushing), the partial pressures of O₂ and N₂ remained at nearly constant initial levels; therefore, the increases of package pressures were dominantly caused by the increases in the CO₂ partial pressures as a result of kimchi fermentation. The CO₂ production from kimchi was greater in the vacuumed and CO₂‐flushed packages. The initial vacuumed treatment helped to maintain relatively lower pressure during extended storage, and the pressure of the CO₂‐flushed package could have been reduced as a result of the high solubility of CO₂ in the aqueous product. Initial CO₂ flushing also provided the packaged product with a pleasant cool flavour at the properly ripened state.     

Sintering chemical reactions to increase thermal conductivity of aluminium nitride

Chemical reactions to increase thermal conductivity by decreasing oxygen contents during AlN sintering with an Y₂O₃ additive in a reducing nitrogen atmosphere with carbon were investigated. They were: Al₂O₃ + N₂ + 3CO ⇋ 2AlN + 3CO₂, Al₂Y₄O₉ + N₂ + 3CO ⇋ 2AlN + 2Y₂O₃ + 3CO₂ and Y₂O₃ + N₂ + 3CO ⇋ 2YN + 3CO₂. Some of the CO₂ gas reduced to CO gas in the presence of carbon by a chemical reaction: CO₂ + C ⇋ 2CO. These reactions were confirmed by examining oxygen contents, the grain boundary phases of the sintered AlN, and the trapped CO and CO₂ gases in the sintered bodies. These reducing reactions proceed with increasing sintering temperature and periods, and hence the thermal conductivity is increased.