Advances In Modified Atmosphere Packaging

(MAP) of Fresh Produce

by Devon Zagory, Devon Zagory & Associates, Davis, CA

The rapid expansion of what is often referred

to as the "fresh-cut revolution" has been made

possible, in part, by improvements in MAP. Sophis-ticated packaging has facilitated:

Extension of product shelf life to meet the de-mands of long distance distribution.

Maintenance of product quality through reductionof respiration rate, browning reactions, fruitsoftening and decay.

Added product convenience through portioncontrol and resealable bags.

Enhanced marketing through identification ofbrands and improved visibility of the product.Early advances in MAP of fresh produce

centered around matching appropriate plastic films tospecific products. Because achieving a favorableequilibrium modified atmosphere inside a packagedepends on product respiration rate, product mass,film surface area, film thickness and film gas trans-mission rates, a diversity of products require a

diversity of packaging films. Different bag sizes forthe same product often require different packagingfilms. The science describing the relationships of theappropriate variables has often been lost and producepackaging seen as an art mastered by few.

Produce packaging has progressed in the past

several years. Appropriate packaging materials havebeen developed for most of the more common fresh-cut products. There is consensus as to which filmsare appropriate for standard size packages of prod-ucts such as garden salad, broccoli, and peeledcarrots. Knowledge of how to effectively seal

packages and reduce incidence of leakers has devel-oped and printing capabilities have provided evermore attractive packages. Technical challenges stillexist in produce packaging. Some of the technolo-gies currently available to meet those challenges aredescribed below.

Tailored Oxygen Transmission Rate (OTR). Theflexible packaging industry has become increasingly

responsive to the specific gas requirements of freshproduce and are now providing films specificallydesigned for given produce items. Films for low,medium and high respiration rate commodities arenow available from many package vendors and theprocess of matching OTR to product is being con-stantly refined. This has allowed fresh-cut proces-sors to begin to provide a much greater diversity ofproducts which now includes artichoke hearts, babysalad greens, sliced strawberries, stir fry mixes andmany others. Very high respiration rate commoditiessuch as broccoli, asparagus and mushrooms havealways presented a challenge to packagers. Newtechnologies are now allowing the manufacture ofvery high OTR (> 1000 cc/100in2-day) films forthese applications.

Metallocene Technology. Technology developedindependently by Dow Chemical Co. and ExxonChemical Co. uses new single site catalysts toproduce desired polymer resins. These catalysts,when applied to the manufacture of polyethylene andother polymers, can provide a much narrower distri-bution of polymer chain length, molecular weight anddensity. This results in flexible plastic films withvery high OTR, low moisture vapor transmissionrate, enhanced clarity, superior strength, low sealinitiation temperature and very rapid bonding of theseal. These stronger films with stronger seals arefinding wide application in produce packaging.Microperforated And Microporous Films. Alter-native approaches to providing high OTR's, espe-cially in applications where there is limited packagesurface area for gas exchange, have included filmswith holes or pores. FreshHold, a microporous filmtechnology owned by Albert Fisher, Inc. and P-Plus,microperforated technology owned by Print Pak, arefinding applications in the rapidly emerging fresh-cutfruit market. Most cut fruit is packaged in rigid, gasimpermeable trays with a permeable film overwrapsealed to the tray. Because the tray is impermeableto gases, there is reduced surface area for gas ex-change. All the gas exchange must occur through thefilm overwrap. Until recently, few films had high