MODELING FREQUENCY DISTRIBUTION of STEADY-STATE O2 PARTIAL PRESSURES IN MODIFIED-ATMOSPHERE PACKAGES

A mathematical model was developed to predict the frequency distribution of steady-state O₂ partial pressures in modified-atmosphere packages of fresh and minimally processed fruits and vegetables. Variation in O₂ uptake was predicted to have relatively larger influence on the package O₂ distribution than variation in film permeability to O₂. the model also predicted that the range of O₂ partial pressures in the packages would be larger for the products with lower K_1/2 (a constant in product O₂ uptake equation) values. the percent deviation of package O₂ partial pressures from [O₂]_med increased with [O₂]_med up to about 3 kPa and gradually decreased thereafter. Package O₂ distribution was symmetrical at higher [O₂]_med but became gradually asymmetrical with decreasing [O₂]_med from 6 kPa. the model was used to predict target [O₂]_med for the design of modified-atmosphere packages for different probability levels of having package O₂ being equal to or less than a minimum tolerable level of the product.     

Effects of gas atmosphere and temperature on the respiration rates of whole and sliced mushrooms (Agaricus bisporus)--implications for film permeability in modified atmosphere packages

ABSTRACT:  An open flowthrough respirometer was used to determine the respiration rates of whole and sliced mushrooms as a function of O₂, CO₂, and storage temperature. Respiration rates were measured under the following O₂ concentrations: 20, 15, 10, 5, and 2% at 5 temperatures (4, 8, 10, 13, and 16 °C). The effects of 5 CO₂ concentrations (0, 2, 5, 10, 15%) at two O₂ levels (2 and 20%) were also examined at these temperatures. Mushroom respiration increased with temperature following an Arrhenius-type relationship; activation energies and corresponding Q₁₀ values were calculated. Lowering the oxygen concentration significantly decreased the respiration rate. The effects of reducing O₂ levels were greater at higher storage temperatures. Both activation energies and Q₁₀ values were lower under reduced O₂ atmospheres compared with those in air. A Michaelis–Menten enzyme kinetics model was evaluated for describing the influence of gas concentrations on respiration rate. The effects of O₂ fitted the O₂ enzyme kinetics model well. CO₂ exhibited small inhibitory effects on respiration of whole and sliced mushrooms, especially at low O₂ concentrations and low temperatures. The enzyme model was used to predict respiration under an optimal modified atmosphere for mushrooms, and the required film O₂ and CO₂ permeabilities were defined for key pack design parameters.     

Color Development of Squid Skin as Affected by Oxygen Concentrations

ABSTRACT:  Color development of squid skin was controlled by O₂ concentration for storage. When stored above 10% O_2, the color index (CI) as an index of color development of skin increased in 24 h, and decreased gradually with further storage. The CI profile at 10% O₂ was practically identical to that in air. When stored at 0.1% O₂, in the presence of N₂, the CI increased partly in 6 h and decreased. Morphological observation of chromatophore distinguished the CI increase at 0.1% and 10% O₂ by their shape and size distribution. However, the storage of squid at O₂ concentration between 2.5% and 7% practically did not change the CI for at least 48 h. ATP content of skin was kept unchanged when the storage atmosphere contained O₂ concentration at 2.5% up to 48 h, while the content decreased rapidly with a half decrease in 6 h when stored at 0.1% O₂. It was demonstrated clearly that ATP is regenerated in the presence of O₂, but the ATP concentration did not determine the CI change during the storage. Exposure to high concentration of O₂ might induce a full color development of squid skin.     

Improved use of oxygen scavengers to stabilize the colour of retail-ready meat cuts stored in modified atmospheres

A series of three experiments were conducted to develop a retail packaging system suitable for use in centralized meat processing and packaging operations using modified atmosphere master packaging (MAP) of display-ready beef and pork cuts. It was shown that oxygen (O₂) scavengers were needed inside retail trays, lidded or over-wrapped trays could be used with equal success but inclusion of a grid inside the retail tray was not required. It was established that a minimum of eight O₂ scavengers with an O₂ absorption rate high enough to achieve an O₂ half-life of 0.6–0.7 h in the pack atmosphere were needed where the O₂ concentration could otherwise remain ≤500 ppm at any time during storage. Composite results from these experiments clearly showed that the best performance resulted from use of hard plastic retail trays containing eight O₂ scavengers, with high O₂ absorption rate, when placed underneath an absorbent pad and over-wrapped with an O₂ permeable film. Small holes in two corners of the O₂ permeable film to permit free exchange of atmospheres within the retail packages facilitated O₂ reduction during MAP storage.     

Influence of oxygen concentration and temperature on respiratory characteristics of fresh-cut green onion

The characteristics of the respiration rates in precut green onion, as influenced by oxygen levels and temperature, were examined to provide design factors for modified atmosphere packaging (MAP). Fresh-cut green onions ( Allium fistulosum L.) were prepared and sealed, with and without a CO₂ absorbent, in gas-tight glass containers that had initially been purged with air or a gas mixture (O₂ 9%/N₂ balance). The containers were stored at different temperatures (0, 10, 20 °C). At 10 °C, the maximum O₂ uptake rate (V_m) and the O₂ concentration at half-maximum (K_m) uptake rate were 30.95 mL kg⁻¹ h⁻¹ and 1.63%, respectively. Regardless of temperature, the lower O₂ limit was estimated to be about 1.0% O₂ on the basis of respiratory quotient (RQ) increase. Respiration of cut green onion was dependent on O₂ concentration as well as temperature, as shown by applying the Michaelis–Menten type model and the Arrhenius equation. However, the presence of CO₂ had little effect on O₂ uptake of cut green onion at relatively high O₂ concentrations (≤20%).     

Respiration Rate of Sweet Cherries: 'Burlat', 'Sunburst' and 'Sweetheart' Cultivars

ABSTRACT: Oxygen depletion and CO₂ formation were measured using a closed system method at various temperatures. No CO₂ inhibition effect was observed. Respiration rates were related to O₂ concentration by a simple Michaelis-Menten equation. Lineweaver-Burk plots of respiratory rate versus O₂ concentration were nonlinear over the whole O₂ concentration range explored. However, this type of analysis allowed us to differentiate two O₂ concentration intervals (above and below 10%) in which the double reciprocal plots are linear. Respiration rates decreased with decreasing temperature following the Arrhenius law. The Michaelis-Menten equation constants V_m and K_m for the 3 cultivars at 2, 5, and 20°C are tabulated.     

Inhibition of Fungal Growth on Wheat and Rye Bread by Modified Atmosphere Packaging and Active Packaging Using Volatile Mustard Essential Oil

ABSTRACT: Wheat and rye bread artificially inoculated with molds were packed in modified atmospheres of 0%, 50%, 75%, or 100% CO₂ balanced with N₂, and 3 levels of residual O₂, 1%, 0.03%, or <0.01%/O₂-absorber, and stored for 30 to 35 d. Modified atmosphere packaging (MAP) was quantitatively more effective for rye bread because fewer mold species grew at elevated CO₂. However, the major rye bread contaminant, Penicillium roqueforti , was the overall most CO₂-resistant mold and only the use of O₂-absorber could prevent growth of this species. On wheat bread, the most CO₂-tolerant mold was Penicillium commune , growing in 99% CO₂ (with high residual O₂), and Aspergillus flavus was the mold species that grew at lowest O₂ in 75% CO₂ treatment. The spoilage yeast/"chalk mold" Endomyces fibuliger was less affected by the different O₂ levels than the true filamentous molds, and none of the tested MAP treatments could prevent growth, but lag-phase was increased with O₂-absorber on wheat bread and decreased with 1% residual O₂ on rye bread. Experiments with volatile mustard oil showed that A. flavus and Eurotium repens were the most mustard oil-resistant species on wheat and rye bread, respectively. A combination strategy with MAP and mustard oil proved most optimal, and total inhibition was achieved with 2 μL mustard oil/rye bread slice and between 2 and 3 μL/wheat bread. Results indicated that the nature and surface area of the product influences effectiveness of active packaging with mustard oil.     

EFFECT OF OXYGEN-ENRICHED ATMOSPHERES ON STORAGE QUALITY OF PACKAGED FRESH MEAT

SUMMARY —The extension of fresh meat shelf-life is important from both practical and theoretical points of view. Color is usually used as a measure of fresh meat quality during storage. Beef top-round slices were prepared using sanitary precautions. Meat slices were enclosed in a thermally sealed semi-rigid polyvinyl chloride tray system of special design. Face-to-face meat samples were used to compare the effects of high oxygen with normal air atmospheres. One package from each pair was evacuated and the atmosphere readjusted to approximately 90% oxygen through a septum. Packages were kept at 4 ± 0.5°C and gas chromatographic readings for CO₂, O₂ and N₂ were conducted daily. Spectrophotometric and bacteriological evaluations were made on selected pack ages during storage to determine pigment oxidation and microbial growth. Three experiments each containing six to eight pairs of samples were conducted. The generation of CO₂ was observed in two periods–the first immediately after packaging and lasting for 1–2 days, after which the CO₂ level remained approximately stable up to 8—9 days, when it again started to increase in correspondence with increased bacterial growth. There was more CO₂ produced than O₂ utilized in the stored samples. In the first stage, samples stored in oxygen-enriched atmospheres had higher O₂ uptake than samples stored in air. Microbial growth was similar in both atmospheres. Under conditions of this study, head space enrichment to about 90% oxygen prolonged acceptable meat color when compared with samples stored in an air atmosphere.     

MODIFIED ATMOSPHERE PACKAGING of SWEET CORN ON COB

Respiration rates (RR) of two varieties of sweet corn on cob were determined at O₂ concentrations: 5, 10, 15, and 21% and CO₂: 0, 5, and 10%, and temperatures: 2, 12, and 25C. Temperature and O₂ had strong influence on RR. Activation energies for effect of temperature on RR(O₂) and RR(CO₂) were, 44.6 and 104.4 kJ/mole, respectively. At 12C, to maintain 4% O₂ and 6% CO₂ in a package 10.8 cm² area, with 1.12 kg of corn, the estimated film permeabilities were 14 ml O₂/h.cm² and 65 ml CO₂/h.cm², respectively. Experimental and theoretical transient gas concentrations using microporous films were in reasonable agreement, but the desired O₂ and CO₂ levels were not achieved.     

Microbiological Benefits of Removing Foam Formed After UV-Enhanced Ozonation of Poultry-Processing Chiller Water for Recycling

ABSTRACT: Prior experiments using 250 mL samples of unscreened poultry overflow chiller water evaluated the beneficial bactericidal and oxidative effects of 4 different treatments (namely, O₂/O₃,O₂/UV, O₂/O₃/UV, and O₂ as the control) for improving microbiological safety, turbidity, and water-use efficiency allowing its reconditioning for reuse. When excluding foam as in this present study, synergistic reductions > 1.5 log CFU/mL for aerobic plate counts (APC) were additionally achieved after 4 min for all O₃/UV treatment combinations as compared to serially applied treatments of O₃ and UV acting separately. With foam present, 16-min O₃/UV treatments were required to achieve similar results. We now report these additional benefits achieved by removing the foam formed by the advanced oxidation process of ultraviolet-photon enhanced ozonation. Furthermore, foam microbial and general physical content were analyzed to determine suitability as an additive in rendering-type processes. Treatment of the wastewater resulted in total plate counts between 2 to 4 Log CFU/mL in the foam after 8 min. Fat and protein constituted 89% of the solids collected (384 mg/L or 14% of the foam) with trace amounts of metal elements (for example, Ca, Na, K, Fe, Cu) present. Irradiating had negligible effect on foam characteristics yet decreased the amount of solids collected.     

Controlled atmosphere storage to decrease physiological disorders in nectarines

'Fantasia', 'Flavortop', and 'Flamekist' nectarines were examined for their response to controlled atmosphere (CA) storage. All three cultivars stored well for up to 6 weeks at 0°C in an atmosphere of 10% O₂+ 10% CO₂, while some but not all the cultivars also stored well in 2% O₂+ 5% CO₂ or 10% O₂+ 5% CO₂. The physiological storage disorders of internal breakdown and reddening were almost completely absent in nectarines kept in 10% O₂+ 10% CO₂. When 'Flamekist' nectarines from two harvests were stored in 10% O₂+ 10% CO₂ atmosphere for 6 or 8 weeks at 0°C, the fruit from the first harvest was of better quality after post-storage ripening. Although this controlled atmosphere prevented internal breakdown and reddening, after extended storage fruit did not develop the increased soluble solids content or extractable juice during post-storage ripening that occurred in non-stored fruit. Therefore, while preventing storage disorders, CA does not reduce the loss of ripening ability occurring during nectarine storage.     

Maintaining Quality of Fresh-cut Tomato Slices through Modified Atmosphere Packaging and Low Temperature Storage

ABSTRACT: Quality of fresh-cut tomato slices was compared during cold storage under various modified atmosphere packaging conditions. Chilling injury of slices in containers sealed with Film A was higher than with Film B; these films had oxygen transmission rates of 87.4 and 60.0 ml · h^-1· m^-2· atm^-1 at 5 °C and 99% RH, respectively. While slices in containers with an initial atmospheric composition of air, 4% CO₂+ 1 or 20% O₂, 8% CO₂+ 1 or 20% O₂, or 12% CO₂+ 20% O₂ showed fungal growth, slices in containers with 12% CO₂+ 1% O₂ did not. Low ethylene in containers enhanced chilling injury. Modified atmosphere packaging provided good quality tomato slices with a shelf life of 2 w or more at 5 °C.     

Colour stability of six beef muscles stored in a modified atmosphere mother pack system with oxygen scavengers

Summary The effect of O₂ scavengers on the colour stability of beef in retail overwrap trays within a modified atmosphere mother pack (CO₂/N₂) was assessed. Steaks from six muscles, namely Longissimus dorsi, Psoas major, Semimembranosus, Gluteus medius, Semitendinosus and Biceps femoris were examined. After storage for 2, 4 or 6 weeks mother packs were opened and steak colour was monitored during 96 h of retail display. Redness of all muscles stored with O₂ scavengers was superior to that of steaks stored without O₂ scavengers at all storage times. Hue angle results indicated some metmyoglobin formation in all muscles during storage. Comparisons were made between steaks stored with O₂ scavengers and fresh steaks. Shelf-life values were calculated using the reflectance difference method (R₆₃₀–R₅₈₀). O₂ scavengers did not affect weight loss from the stored steaks.     

MODIFIED ATMOSPHERE PACKAGING of HEAD LETTUCE

Magnitudes of respiration rates of lettuce heads at O₂ levels: 5, 10, 15, and 21%, and three temperatures: 2, 12, and 25C ranged between 3 to 30 ml O₂/kg.h. Oxygen concentration (O₂). temperature (T), storage time (t), and the interactions between temperature and O₂ (T*O₂) and temperature and time (T*t), affected respiration rates. Predicted and experimental O₂ and CO₂ concentrations in packages using two plastic films were in good agreement with each other. However, steady state gas concentrations were achieved after about 90 h.     

Shelf-life of chicken liver/egg paté in modified atmosphere packages

Shelf-life of paté (salad in Israel) made by blending fried chicken liver and onions with hard-boiled eggs was extended, from 6 days in air to 14 days by Modified Atmosphere Packaging (MAP), using high CO₂/low O₂ mixtures. Aerobic microbial growth, mainly B. subtilis , and lipid oxidation (as TBA values) were largely inhibited, during 14 days, and odour up to 8 days (not tested beyond). the microbial growth inhibition was due to high CO₂ levels. Oxidation was prevented due to microbial inhibition and not due to reduced O₂.     

Changes of glucosinolates in mixed fresh-cut broccoli and cauliflower florets in modified atmosphere packaging

ABSTRACT:  Glucosinolates of broccoli and cauliflower florets were assessed to determine the effect of modified-atmosphere packaging on postharvest glucosinolate dynamics in mixed florets of Brassica vegetables. Mixed-packaged broccoli and cauliflower florets stored in food trays sealed with 2 different microperforated biaxial-oriented polypropylene films for up to 7 d at 8 °C were analyzed. Both applied modified atmospheres (1% O₂+ 21% CO₂; 8% O₂+ 14% CO₂) maintained aliphatic glucosinolates in cauliflower florets, whereas in broccoli florets, the aliphatic glucosinolate concentration decreased slightly in each modified atmosphere. In addition, total indole glucosinolate concentration for both broccoli and cauliflower florets was maintained, and even increased in cauliflower florets at 1% O₂+ 21% CO₂ due to rising neoglucobrassicin concentration. Thus, to simultaneously maintain glucosinolates and external appearance as well as to prevent off-odor, a modified atmosphere of 1% O₂+ 21% CO₂ provides a suitable environment for storage of this Brassica floret medley for up to 7 d at 8°C.     

Influence of Storage Atmosphere and Temperature on Quality Evolution of Cut Belgian Endives

ABSTRACT: An optimal combination of O₂, CO₂, and N₂ for storage of cut Belgian Endive was defined, investigating visual quality aspects. In the experimental design, principles of mixture theory were used. The acceptability of cut endives stored under different gas combinations, selected in the range where both CO₂ and O₂ were varied between 2% and 18%, was evaluated by a consumer panel at different time intervals during storage. The response was modeled with a second-degree polynomial, the response surface pointed in the direction of a gas mixture 10% CO₂, 10% O₂, and 80% N₂ for maximum acceptability or best quality during storage. Repeated experiments, including different varieties from 2 different growers, confirmed the optimal gas concentration, (10% CO₂, 10% O₂, and 80% N₂). In a second step, the effect of temperature on quality degradation of cut endives stored under optimal atmosphere conditions, was quantified using the Arrhenius equation. An activation energy of 16.3 kcal/mol was obtained.     

THE EFFECT OF OXYGEN SCAVENGERS ON THE COLOR STABILITY AND SHELF-LIFE OF CO, MASTER PACKAGED PORK

Pork chops were stored with and without O₂ scavengers in a modified atmosphere (50% CO₂/50% N, or 100% CO₂) master pack system at 0C for up to 21 days, At 7-day intervals, the chops were displayed at ca. 4.5C for 96 h. Color (L, a, b, hue and chroma); panelist assessments of color and odor; and drip losses were recorded. Oxygen scavengers reduced O₂ levels, resulting in chops that were generally as red as flesh, but tended to have higher hue angles at 0 h, and towards the end of display (P<0.05). Visually, chops packaged in 50% CO₂/50% N₂ were less acceptable than flesh (P<0.05). There were no odor differences between flesh and packaged chops. Fresh chops had lower drip losses than packaged (P<0.05). An acceptable display life was obtained for pork chops stored for up to 21 days in a modified atmosphere CO₂ master pack containing O₂ scavengers.     

Chemical and sensory changes in haddock and herring stored under modified atmosphere

The effectiveness of storage in atmospheres with increased proportions of CO₂ to extend the shelf-life of haddock and herring was examined. Using a 40: 30: 30/CO₂: O₂: N₂ atmosphere with haddock no useful extension of shelf-life was achieved at +5°C and only limited extension at 0°C. A more useful extension of shelf-life at 0°C was obtained by storing haddock in a 60: 20: 2O/CO₂: O₂: N₂ atmosphere and with herring in a 60:40/CO₂::N₂: atmosphere. Total volatile bases (TVB) and hypoxanthine values (Hx) correlated with the cooked flavour. There were no significant differences in drip-loss between the modified atmosphere packaging (MAP) stored samples and the controls. Peroxide values (PV) in herring were lower in MAP stored samples. Whole haddock and whole herring were found to have a longer shelf-life when stored in MAP at 0°C than when stored as fillets.     

Light and copper catalysed oxidized flavours in stored milk

Oxidized flavour results from milk lipid oxidization which, in practice, is catalysed by either light (Λ around 450 nm) or Cu. Damaging levels of Cu may be present naturally in some milks but are usually due to contamination. Of the two defects. light-induced flavour is today the more important by far, especially where milk is exposed to light in containers that transmit the damaging wavelengths and are, in addition, highly permeable to O₂. Thus, in the UK. sterilized milk in blow-moulded polyethylene bottles is especially at risk. The level of O₂ required to produce the development of Cu-induced oxidized flavour is negligible compared with that in milk saturated with air. In contrast, light-induced oxidized flavour develops only after considerable O₂ uptake has occurred in the milk due to ascorbic acid and other oxidations. In sterile milks exposed to fluorescent light with only the dissolved O₂ present, oxidized flavour did not develop. It did. however, develop where there was an additional supply of O₂ during storage. from a headspace or through an O₂-_-permeable container.