Modified atmosphere/modified humidity packaging

Nitrogen generator for modified atmosphere packaging

Modified atmosphere/modified humidity (MA/MH) packaging is a technology used to preserve the quality of fresh produce so that it can be sold to markets far away from where it is grown, extend the marketing period, and to help suppliers reduce food waste within the cold chain. Commercial examples of MA/MH include sea freight of Galia and cantaloupe melons from Central and South America to Europe (a 21-day journey) and North America (a 7-day journey); transport of white asparagus from fields in Peru to markets in Western Europe (a 20-day journey by land and sea); and trucking of cherries from orchards in Turkey to supermarkets in the UK (a 7-day journey).

Scientific terms

EMAP: Equilibrium modified atmosphere packaging
MA/MH: Modified atmosphere/modified humidity
MAP: Modified atmosphere packaging
RH: Relative humidity
MVTR: Moisture vapor transmission rate

History

Modified atmosphere/modified humidity (MA/MH) packaging is a type of equilibrium modified atmosphere packaging (EMAP), which evolved due to the need for more control of humidity in the packaging. Most of the polymers that are commercially used in EMAP are polyolefin-based, characterized by low moisture vapor transmission rate (MVTR). Temperature fluctuations during the various links in the cold logistics chain are unavoidable and will result in condensation forming on the inner surface of the package. The accumulation of condensed water in packages with low MVTR is conducive for pathological and physiological disorders. Not only does excess moisture enhance fungal and bacterial decay and the formation of off odors, it also encourages leaf sprouting in topped root vegetables, regrowth of leaves and physiological disorders such as tissue discoloration and peel blemishes. Certain produce items are more sensitive to excess moisture than others.

In 1995, StePac LA. Ltd., with the assistance of the Agricultural Research Organization – The Volcani Center, began developing plastic films with higher MVTR than most commercially available EMAP products then on the market. The aim was to provide more humidity control in EMAP products and alleviate problems associated with excess moisture.

Since this original research and development work, StePac LA Ltd. has developed MA/MH films and bags for over 50 different fruits, vegetables and herbs in a product line commercially known as Xtend.

Technology

MA/MH technology is achieved by combining proprietary blends of polymers to obtain the desired MVTR and then manipulating the oxygen (O
2) and carbon dioxide (CO₂) transmission rates of the polymer by laser and/or mechanical microperforations. The result is a film which is tailored to provide the optimum modified atmosphere and modified humidity for the produce to be packaged. “Film composition and extent of microperforation are tailored in accordance with the respiratory activity and weight of the produce packaged, anticipated temperature fluctuations during storage and shipment, and expected physiological and pathological responses of the produce to CO₂/O
2 concentrations and humidity levels inside the package. . . . [MA/MH] packaging allow[s] the formation of a desirable modified atmosphere, retarding ripening and senescence of the produce. Additional beneficial effects . . . include reduction of decay, chilling injury, leaf elongation, leaf sprouting, tissue discoloration, peel blemishes, and formation of off-odors, and inhibition of bacterial growth on the produce surface.”^[1]

Benefits to fresh produce

Modifying the atmosphere inside fresh produce packaging to provide lowered levels of O
2 and elevated levels of CO₂ is beneficial for many fresh produce items and “can reduce respiration, decrease ethylene production and action, retard tissue ripening and softening, retard chlorophyll degradation and biosynthesis of carotenoids and anthocyanins, reduce enzymatic browning, alleviate physiological disorders and chilling injury, retard development of decay, and maintain nutritional quality of produce. The effect of decreased O
2 and increased CO₂ on senescence and ripening process are additive and can be synergistic.”^[2]

“In vegetative tissues MAP can also reduce leaf regrowth (green onion and leek), stem toughening (asparagus),and leaf sprouting and rooting in root vegetables (parsnip, radishes). The delay of ripening and senescence of fruits and vegetables also reduces their susceptibility to pathogens.”^[3]

The importance of tightly controlled relative humidity

Maintaining high relative humidity (RH) in modified atmosphere packaging is important because it “results in reduced transpiration of water from the produce, thereby reducing wilting, shriveling, and loss of firmness. The accumulation of vapor in the packaging depends on the rate of water loss from the product, its surface area, the water vapor transmission rate (WVTR) of the film, and the external environment temperature.”^[4]

“The RH in most sealed packaging is near the saturation level. Therefore, even very small fluctuations in temperature during storage or shipment may result in water condensation on the surface of both film and produce. Condensed water on the produce surface may adversely affect the gas exchange, leading to an unfavorable internal atmosphere.”^[5] Even more detrimental may be the enhancement of produce decay, and physiological processes such as regrowth. In addition, certain human pathogens may proliferate when in-pack atmosphere contains high humidity and low O
2.

Hazards associated with MAP

Successful delivery of fresh produce in MAP is not without potential hazards due to incompatibility of MAP film to the fruit or vegetable it is intended to keep fresh and high dependence on good temperature management. Undesirable consequences of incompatible film and/or high temperatures may be “anaerobic respiration with the accumulation of acetaldehyde, ethanol, ethyl acetate, and lactic acid, all of fermentation, contributing to the development of off odors, off flavors, and disuse deterioration.”^[6]

Extreme changes in O
2 and CO₂ to intolerable levels often occur when fresh produce packed in improper MAP is exposed to higher than recommended temperatures during shipment and distribution. Other undesirable effects of improper MAP are initiation or aggravation of certain physiological disorders, irregular fruit ripening, and increased susceptibility to decay following physiological damage.”^[7]

Products

Several types of products, including retail bags, carton liners, bin bags, lidding films and flow pack have been developed from MA/MH films and are commercially available. Each product type is uniquely engineered for the specific produce type (and in some cases, the produce variety) to be packaged. This is done through a rigorous process of developing, testing, adjusting and retesting each MA\MH product both in the lab and in commercial trials.

This meticulous process is repeated for each combination of produce and packaging type because of the many factors involved in developing a successful MA/MH packaging. These factors are “storage and shipment temperature, product respiration rate and quotient, response to levels of CO₂, O
2 and humidity, and product weight. Hence, film packaging that is adequate for consumer packages in not always suitable for bulk packaging and vice versa.”^[1]

Sources

1 2 Aharoni, Nehemia, et al.; Intelligent and Active Packaging for Fruits and Vegetables; Chapter Five: Modified atmosphere packaging for vegetable crops using high-water-vapor-permeable films; [date]
↑ Kadar et al., 1989; kader and Saltveit, 2003; Zagory and Kader, 1988
↑ Barkai-Golan, 1990; El-Goorani and Sommer, 1981
↑ Geeson, 1989
↑ Burton and Wigginton, 1970; Cameron et al., 1995
↑ Kays, 1997; Mattheis and Felman, 2000
↑ Kadar and Saltveit, 2003

References

Fonseca, Jorge M.; High Relative Humidity; Fresh Americas, #1, 2008 Series, Master Media Worldwide Publishing
Devon Zagory, Devon Zagory & Associates, University of California, Davis,; Advances In Modified Atmosphere Packaging (MAP) of Fresh Produce; Perishables Handling Newsletter Issue No. 90, May 1997, pages 2–3
N. Aharoni, V. Rodov, E. Fallik, R. Porat, E. Pesis and S. Lurie; Department of Postharvest Science of Fresh Produce, ARO, The Volcani Center; Humidity Improves Efficacy of Modified Atmosphere Packaging of Fruits and Vegetables
Adel A. Kader, Dept. of Pomology University of California, Davis; Modified Atmosphere Packaging of Fresh Produce; Outlook Second Quarter, Volume 13, No. 2, 1986
Stephen R. Harris; Storage of fresh produce Food and Agriculture Organization of the United Nations; Production is only Half the Battle – A training manual in fresh produce marketing for the Eastern Caribbean, Chapter 8: Storage of fresh produce; Bridgetown, Barbados, December 1988

Packaging

General topics	Active packaging Child-resistant packaging Disposable food packaging Food packaging Luxury packaging Modified atmosphere/modified humidity packaging Package pilferage Package testing Packaging engineering Pharmaceutical packaging Reusable packaging Shelf life Sustainable packaging Tamper-evident Tamper resistance Wrap rage

Containers	Aerosol Container Aluminium bottle Aluminum can Ampoule Antistatic bag Bag-in-box Bags and flexible containers Barrel Beer bottle Biodegradable bag Blister pack Boil-in-Bag Bottle Box Bulk box Carboy Carton Chub Clamshell Corrugated box design Crate Disposable cup Drum Envelope Flexible intermediate bulk container Foam food container Folding carton Growler Insulated shipping container Intermediate bulk container Jar Jerrycan Jug Juicebox Keg Multi-pack Oyster pail Packet (container) Padded mailer Pail Paper bag Paper sack Plastic bag Plastic bottle Popcorn bag Retort pouch Sachet Security bag Self-heating can Self-heating food packaging Shaker-style pantry box Shipping container Skin pack Spray bottle Tin can Tube Unit load Vial Wooden box

Materials and components	Adhesive Aluminium foil Bioplastic Biodegradable plastic BoPET Bubble wrap Bung Cellophane Closure Coated paper Coating Corrugated fiberboard Corrugated plastic Cushioning Desiccant Double seam Foam peanut Glass Hot-melt adhesive Kraft paper Label Linear low-density polyethylene Liquid packaging board Low-density polyethylene Metallised film Modified atmosphere Molded pulp Nonwoven fabric Overwrap Oxygen scavenger Packaging gas Pallet Paper Paper pallet Paperboard Plastic film Plastic pallet Plastic wrap Polyester Polyethylene Polypropylene Pressure-sensitive tape Screw cap Screw cap (wine) Security printing Security seal Shock detector Shock and vibration data logger Shrink wrap Slip sheet Staple (fastener) Strapping Stretch wrap Susceptor Tear tape Temperature data logger Time temperature indicator Tinplate Velostat

Processes	Aseptic processing Authentication Automatic identification and data capture Blow fill seal Blow molding Calendering Canning Coating Containerization Curtain Coating Die cutting Die forming (plastics) Electronic article surveillance Extrusion Extrusion coating Glass production Graphic design HACCP Hermetic seal Induction sealing Injection molding Laminating Laser cutting Molding Papermaking Plastic welding Plastics extrusion Printing Quality assurance Radio-frequency identification Roll slitting Shearing (manufacturing) Thermoforming Track and trace Vacuum forming Ultrasonic welding Vacuum packaging Verification and validation

Machinery	Barcode printer Barcode reader Bottling line Calender Can seamer Cartoning machine Case sealer Check weigher Conveyor system Extended core stretch wrapper Filler Heat gun Heat sealer Industrial robot Injection molding machine Label printer applicator Lineshaft roller conveyor Logistics automation Material handling equipment Mechanical brake stretch wrapper Multihead weigher Orbital stretch wrapping Palletizer Rotary wheel blow molding systems Shrink tunnel Staple gun Tape dispenser Turntable stretch wrapper Vertical form fill sealing machine

Environment, post-use	Biodegradation Environmental engineering Glass recycling Industrial ecology Life-cycle assessment Litter Paper recycling Plastic recycling Recycling Reusable packaging Reverse logistics Source reduction Sustainable packaging Waste management

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