Modified atmosphere packaging of shredded lettuce

A retail package system was used to study the atmosphere modification which developed within packages of shredded Iceberg lettuce, sealed in trays with a range of polymer films of different gas permeabilities (oxygen permeability of 3000 to 10,000 ml/m²/day/atm. at 25°C). Modified atmospheres were produced both naturally by respiration, and by application of gas flushing techniques.
The effects of these modified atmosphere conditions on visual and sensory quality of shredded lettuce was observed by monitoring colour change and development of off-odours. An equilibrated modified atmosphere containing 1–3% O₂ and 5–6% CO₂was established with 35 um low density polyethylene film after flushing with 5% O2, 5% CO₂ in N₂. This resulted in a shelf-life of approximately 14 days at 5°C, almost double that of the controls.     

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.     

Modified atmosphere packaging of broccoli florets

A retail packaging system was used to study the atmosphere modification which developed within sealed packages of prepared broccoli florets with a range of polymer films of different gas permeabilities (oxygen permeability 3000–32,500 ml/m²/day/atm). Three methods of sealing were investigated and modified atmospheres (MA) were produced both naturally by respiration and by application of gas flushing techniques. The effects of these MA conditions on sensory quality were observed by monitoring colour change and development of off-odours. A 2–3% O₂, 2–3% CO₂ equilibrium MA was established using LF film to package broccoli florets when stored at 5°C. This, the only consistently aerobic MA attained, did not markedly improve retention of quality of broccoli florets when compared with broccoli stored in air. When broccoli florets were packaged with films which resulted in very low O₂ atmospheres (1% or less) foul of-odours shortened broccoli storage life.     

Effects of storage atmosphere on Listeria monocytogenes and competing microflora using a surface model system

A solid-surface model system was used to study the effects of gas atmospheres encountered in modified atmosphere packaging of vegetables on the survival and growth of Listeria monocytogenes and competing micro-organisms. The effects of increasing CO₂ levels (from 5% to 20%), 100% N₂ and 3% O₂ were determined. The model system allowed for estimation of the growth of L. monocytogenes alone or in the presence of competing microflora. CO₂ concentrations of 5–10% (with 5% O₂ in N₂) had no inhibitory effect, by comparison with air, on the growth and survival of pure cultures of L. monocytogenes . At 20% CO₂ population densities were reduced up to day 8, but the final population densities reached were not. An atmosphere of 100% N₂ allowed survival of pure cultures of L. monocytogenes , but populations did not significantly change ( P  > 0.05) during storage, whereas a low O₂ (3%, balance N2) atmosphere allowed significant growth ( P  < 0.05) of L. monocytogenes . Growth and inhibitory activities of Enterobacter cloacae and E. agglomerans were inversely related to the concentration of CO₂. By contrast, the growth and anti-listerial activities of Leuconostoc citreum increased with elevated CO₂ concentrations. In the low O₂ atmosphere, L. monocytogenes grew considerably better in the presence of populations from the indigenous microflora of lettuce than when in pure culture. The results indicate that the gas atmospheres present within modified atmosphere packages of minimally processed vegetables may affect the interactions between the pathogen and the natural competitive microflora sufficiently to indirectly enhance L. monocytogenes growth.     

Quality changes during refrigerated storage of MA-packaged pre-rigor fillets of farmed Atlantic cod (Gadus morhua L.) using traditional MAP, CO2 emitter, and vacuum

ABSTRACT:  Quality changes during 3 wk of refrigerated storage (1.3 °C) were studied on pre -rigor filleted farmed Atlantic cod packed in modified atmosphere (MAP, 60% CO₂ and 40% O₂) or vacuum. The packages of MAP contained either a CO₂ emitter and low gas volume to product volume (g/p ratio) of 1.3, or a 3.9 g/p ratio and no emitter. The CO₂ level remained stable or increased in the packages with CO₂ emitter, whereas the CO₂ level in the packages with no CO₂ emitter decreased to 40% after 4 d of refrigerated storage. High levels of oxygen in the gas mixture prevented formation of trimethyl amine (TMA) during storage of the MA-packed fish, whereas the TMA content increased significantly after 10-d storage in vacuum. MA-packed samples had the highest values of 1-penten-3-ol. Sensory scores of sour, sulfur, and pungent odors were significantly higher for vacuum-packed cod compared to the 2 MA-packaging methods measured 14 d after slaughtering. No differences in sensory scores were observed between the 2 methods of MAP, and shelf life of these samples seemed to be 14 to 21 d. Cod samples packaged in vacuum packages had higher pH values compared to ordinary MAP and packages containing a CO₂ emitter. Bacterial growth was inhibited by MAP and resulted at the end of the storage period in dominance of Carnobacterium and some Photobacterium . In MA packages with high O₂ levels the Photobacterium was inhibited. It is concluded that CO₂ emitters are well suited for reduction of transport volume for MA-packaged farmed cod.     

Some effects of modified-atmosphere packaging and vacuum packaging in combination with antioxidants on quality and storage life of chilled potato strips

A modified-atmosphere packaging system for chilled fresh potato strips, which rapidly produced oxygen levels < 3%, was identified. This system enclosed the strips within 25 μ low density polyethylene film heat sealed to a fibre tray lined with Surlyn-PVdC-Surlyn, and the package flushed with an initial atmosphere of 5% O₂, 10% CO₂. An equilibrium-modified atmosphere of 3–4% CO₂, 1–2% O₂ was established after 3 days' storage at 5°C. This modified-atmosphere package, used in combination with dipping of potato strips in a 10% ascorbic acid solution, inhibited enzymatic discoloration for 1 week at 5°C. Vacuum packaging within a Surlyn/PVdC-coated polyester film, with or without dipping in ascorbic acid solution, inhibited discoloration of chilled potato strips stored at 5°C for at least 2 weeks.     

Influence of Oxygen, Carbon Dioxide, and Degree of Cutting on the Respiration Rate of Rutabaga

ABSTRACT: Both the O₂-consumption and CO₂-production rates of uncut and cut rutabaga were measured in a closed system. Compared to enzymatic and 1st-order linear models, a 2nd-order expression was found to best predict respiration rates under the conditions typically found in modified atmosphere packages. The concept of degree of cutting was introduced to quantitatively analyze the effect of wounding on respiration rates. A linear relationship was observed between the respiration rates at a fixed pO₂ and pCO₂ and the quantified degree of cutting injury. Mathematical expressions were developed that accurately describe the relationship between respiration rates, O₂ and CO₂ partial pressures, and the degree of cutting.     

Mathematical modelling of O2 consumption and CO2 production rates of whole mushrooms accounting for the effect of temperature and gas composition

Investigation of respiration rate of fresh produce, under different gas composition and temperatures, and respective mathematical modelling is central for the modified atmosphere packaging design. This work investigates the effect of temperature (4, 8, 12, 16, 20 °C) and gas composition (O₂ between 3 to 21% and CO₂ between 0 to 15%) on respiration rate of whole mushrooms. Oxygen and carbon dioxide respiration rates increased significantly (3–4 fold) as the temperature elevated from 4 to 20 °C and were in the range of 13.23 ± 3.12 to 102.41 ± 2.132 mL kg⁻¹ h⁻¹) and 14.33 ± 1.56 to 97.02 ± 2.51 mL kg⁻¹ h⁻¹) respectively. Low O₂ and high CO₂ levels reduced O₂ consumption and CO₂ production rates of whole mushrooms on average by a circa 47–60% at all temperatures as compared to the respiration rate at ambient air. Mathematical models were developed for RO₂ and RCO₂, by combining the Arrhenius and Michaelis–Menten uncompetitive equations. These models predicted well, O₂ consumption and CO₂ production rates of whole mushrooms as a function of both temperature and gas composition.     

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%).     

EFFECT of MODIFIED ATMOSPHERE PACKAGING ON GLUTATHIONE and ASCORBIC ACID CONTENT of ASPARAGUS SPEARS

Asparagus (Asparagus Officinalis L.) spears were packaged in ordinary and microperforated oriented polypropylene (OPP) films and were stored at 15C and 75% RH for up to 10 days. CO₂ concentrations ranged from 15.5 to 23% at 10 days of storage. Weight loss was less than 1.2% in microperforated film packages compared with 15% in air storage under similar conditions. Ascorbic acid content was found to be adversely affected at all the O₂ levels (1–6%) prevailing in microperforated film packages, but it was retained to the extent of 45–55% of its original concentration in ordinary OPP film packaged asparagus. the O₂ concentrations in microperforated film packages were also associated with higher glutathione concentrations in packed asparagus spears. Results of the study indicated that to preserve ascorbic acid and glutathione simultaneously in stored asparagus through MAP under high CO₂ and low O₂ conditions, O₂ concentration levels must be selected between 1 and 6% in such a way so as to get acceptable retention levels of ascorbic acid and glutathione.     

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.     

Predicting Oxygen and Carbon Dioxide Partial Pressures within Modified Atmosphere Packages of Cut Rutabaga

ABSTRACT: A model was developed to predict pO₂ and pCO₂ surrounding cut rutabaga sealed in rigid packages fitted with 2 different polymeric films. The O₂ consumption and CO₂ production rates were calculated using several respiration models fitted using nonlinear least squares or response surface regression analysis. These functions were used in conjunction with variables such as O₂ and CO₂film permeability, film surface area, package free volume, and cut rutabaga weight to predict pO₂ and pCO₂ changes. A first-order polynomial model with parameters calculated via response surface analysis gave the best predictions, particularly at partial pressures that were far removed from those used to determine equation constants.     

EFFECT OF HEADSPACE OXYGEN AND FILMS OF DIFFERENT OXYGEN TRANSMISSION RATE ON TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM TYPE E IN RAINBOW TROUT FILLETS STORED UNDER MODIFIED ATMOSPHERES

Studies were conducted to determine the effect of various levels of headspace oxygen (0–100%, balance CO₂) or film oxygen transmission rate (OTR) on the time to toxicity in modified atmosphere packaged (MAP) fresh trout fillets challenged with C. botulinum type E (10² spore/g) and stored under moderate temperature abuse conditions (12C). In all cases, trout were toxic within 5 days, irrespective of the initial levels of oxygen in the package headspace. However, spoilage preceded toxigenesis. Packaging of trout fillets in low gas barrier films, with OTRs ranging from 4,000 to 10,000 cc/m²/day at 24C and 0% relative humidity, also had no effect on time to toxicity in all MAP trout fillets. All fillets were toxic within 4–5 days and spoilage again preceded toxigenesis. This study has shown that the addition of headspace O₂, either directly to a package or indirectly by using a low gas barrier film, had no influence on the time to toxigenesis or spoilage. Additional barriers, other than headspace O₂ or film transmission rate, need to be considered to ensure the safety of MAP trout fillets, particularty at moderate temperature abuse conditions.     

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.     

Respiratory rate and quality changes in fresh-cut pears as affected by superatmospheric oxygen

ABSTRACT:  Changes in the respiration rate of fresh-cut "Flor de Invierno" pears stored under superatmospheric oxygen concentrations were studied and compared to those observed under traditional modified atmosphere packaging conditions. Changes in package headspace O₂ and CO₂ concentrations throughout storage were curve-fitted to nonlinear equations, calculating respiration rates by combining the derivatives of the equations and the gas permeations throughout storage. Moreover, relationships between respiratory activity and quality parameters of fresh-cut Flor de Invierno pears dipped into an antioxidant solution (0.75% N-acetylcysteine and 0.75% glutathione) were assessed. CO₂ production of fresh-cut Flor de Invierno pears stored under 70 kPa O₂ atmospheres was successfully estimated with the proposed mathematical procedure. This method also proved to describe well CO₂ production rates of fresh-cut pears stored under initial 2.5 kPa O₂+ 7 kPa CO₂ or 21 kPa O₂. In addition, a modification of Michaelis–Menten enzyme kinetics was adequate to describe the changes in estimated CO₂ production due to fermentative processes occurring under low oxygen concentrations. Superatmospheric O₂ concentrations seem to promote oxidative processes, which result into a dramatical modification of some quality attributes of fresh-cut pears.     

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.     

The Effects of Residual Oxygen on the Storage Life of Retail-Ready Fresh Beef Steaks Masterpackaged Under a CO2 Atmosphere

ABSTRACT:  Retail-packed rump ( Gluteus medius , GM) and striploins ( Longissiumus dorsi, LD) steaks were masterpackaged under carbon dioxide (CO₂) and stored at 1 °C ± 1 °C for 14, 28, 35, and 42 d. A commercial oxygen (O₂) scavenger (ATCO HV1000®, Standa Industrie, Caen, France) was used in the masterpacks to achieve an O₂-free atmosphere. Similar packages without the O₂ scavengers were also prepared. At each storage time, 2 masterpacks of each treatment were opened and the retail trays were placed in a display case at 4 °C ± 2 °C for 1 and 48 h for microbiological and sensorial evaluations. The low growth rate of aerobic psychrotrophic flora on the stored beefsteaks demonstrated the bacteriostatic effect of CO₂ during storage. The maximum level of psychrotrophic aerobic bacteria reached during storage was approximately 10⁶ CFU/g. The steaks stored in masterpacks with scavengers bloomed to the desirable red color associated with freshly cut meat in the display case for all of the storage periods, except in the case of GM steaks, which showed a cycle of transient discoloration. GM and LD steaks were well accepted (65% and 82%, respectively) after 42 d under CO₂ at 1 °C ± 1 °C. The GM and LD steaks stored without the O₂ scavenger showed variable fractions of discoloration that significantly detracted from the appearance of the samples.     

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.     

Modified Atmosphere Packaging of Cut Belgian Endives

ABSTRACT: Modified atmosphere packaging of cut Belgian endives was simulated based on experimentally determined package and product parameters. Permeability of commercial packaging films was determined at 3 temperatures. The film permeability ratio for CO₂ and O₂ varied between 1.6 and 6. Respiration rate of cut Belgian endives stored under 10%O₂-10%CO₂-80%N₂ (optimal gas conditions) was measured at different temperatures. Initially, the activation energy for respiration rate was higher compared to the one for film permeability. After 3 d of storage, the E_a-value for respiration rate was similar to the E_a-value for film permeability. Simulations at constant temperature proved that none of the packaging films tested was suitable to maintain optimal gas conditions.     

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.