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1、Perishables Handling Newsletter Issue No. 90May 1997Page 2The 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 d
2、istance distribution. Maintenance of product quality through reduction of respiration rate, browning reactions, fruit softening and decay. Added product convenience through portion control and resealable bags. Enhanced marketing through identification of brands and improved visibility of the product
3、.Early advances in MAP of fresh produce centered around matching appropriate plastic films to specific products. Because achieving a favorable equilibrium modified atmosphere inside a package depends on product respiration rate, product mass, film surface area, film thickness and film gas trans- mis
4、sion rates, a diversity of products require a diversity of packaging films. Different bag sizes for the same product often require different packaging films. The science describing the relationships of the appropriate variables has often been lost and produce packaging seen as an art mastered by few
5、.Produce packaging has progressed in the past several years. Appropriate packaging materials have been developed for most of the more common fresh- cut products. There is consensus as to which films are appropriate for standard size packages of prod- ucts such as garden salad, broccoli, and peeled c
6、arrots. Knowledge of how to effectively seal packages and reduce incidence of leakers has devel- oped and printing capabilities have provided ever more attractive packages. Technical challenges still exist in produce packaging. Some of the technolo- gies currently available to meet those challenges
7、are described below.Tailored Oxygen Transmission Rate (OTR). The flexible packaging industry has become increasinglyresponsive to the specific gas requirements of fresh produce and are now providing films specifically designed for given produce items. Films for low, medium and high respiration rate
8、commodities are now available from many package vendors and the process 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 of products which now includes artichoke hearts, baby salad greens, sliced strawberri
9、es, stir fry mixes and many others. Very high respiration rate commodities such as broccoli, asparagus and mushrooms have always presented a challenge to packagers. New technologies are now allowing the manufacture of very high OTR ( 1000 cc/100in2-day) films for these applications.Metallocene Techn
10、ology. Technology developed independently by Dow Chemical Co. and Exxon Chemical Co. uses new single site catalysts to produce desired polymer resins. These catalysts, when applied to the manufacture of polyethylene and other polymers, can provide a much narrower distri- bution of polymer chain leng
11、th, molecular weight and density. This results in flexible plastic films with very high OTR, low moisture vapor transmission rate, enhanced clarity, superior strength, low seal initiation temperature and very rapid bonding of the seal. These stronger films with stronger seals are finding wide applic
12、ation in produce packaging.Microperforated And Microporous Films. Alter- native approaches to providing high OTRs, espe- cially in applications where there is limited package surface area for gas exchange, have included films with holes or pores. FreshHold, a microporous film technology owned by Alb
13、ert Fisher, Inc. and P-Plus, microperforated technology owned by Print Pak, are finding applications in the rapidly emerging fresh-cut fruit market. Most cut fruit is packaged in rigid, gas impermeable trays with a permeable film overwrap sealed to the tray. Because the tray is impermeable to gases,
14、 there is reduced surface area for gas ex- change. All the gas exchange must occur through the film overwrap. Until recently, few films had highAdvances In Modified Atmosphere Packaging (MAP) of Fresh Produceby Devon Zagory, Devon Zagory & Associates, Davis, CAPage 3Perishables Handling Newsletter I
15、ssue No. 90May 1997enough OTRs to be useful in these applications. Those films that had high OTRs often would not seal to the trays. Microporous and microperforated films allow much more rapid gas exchange than would normally be possible through plastic films.Films with pores or small holes have som
16、e physical limitations. Carbon dioxide (CO2) diffuses through plastic films 2-6 times faster than oxygen (O2). Therefore, CO2 exits a package much faster than O2 enters. This results in equilibrium atmo- spheres of low O2 and relatively low CO2. A range of CO2/O2 permeability ratios among plastic films can provide a range of CO2/O2 concentrations inside packages. Because fruits and vegetables vary in their tolerance to elevated CO2, this range of gas pro
