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142 COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETYVol. 2 (Supplement), 2003

Chapter IV

Microbiological Safetyof Controlled and

Modified AtmospherePackaging of Fresh andFresh-Cut Produce

J.N. Farber, L.J. Harris, M.E. Parish, L.R. Beuchat, T.V. Suslow, J.R. Gorney, E.H. Garrett, F.F. Busta

ScopeThis chapter addresses the use of modified atmosphere packag-

ing and controlled atmosphere packaging for the preservation offresh produce. There have been great technological advances inthis area of preservation, particularly as it refers to improving thequality and shelf-stability of highly perishable food products, such

as produce. However, when using these technologies, careful at-tention must be paid to the effect on the survival and growth ofpathogenic organisms. This chapter focuses on food safety as-pects of packaging technologies that are either commerciallyavailable or under investigation.

1. IntroductionOver the past 20 years, there has been an enormous increase in

the demand for fresh fruit and vegetable products that has requiredthe industry to develop new and improved methods for maintain-ing food quality and extending shelf life (see Chapter I). Due to thecomplexities involved with produce, that is, varying respirationrates which are product and temperature dependent, different opti-

mal storage temperatures for each commodity, water absorption,by-products, and so on, many considerations are involved inchoosing an acceptable packaging technology. One of the areas ofresearch that has shown promise, and had success, is that of modi-fied atmosphere packaging (MAP). This technique involves eitheractively or passively controlling or modifying the atmosphere sur-rounding the product within a package made of various types and/or combinations of films. In North America, one of the first applica-tions of this technology for fresh-cut produce was introduced byMcDonalds (Brody 1995), which used MAP of lettuce in bulk-sized packages to distribute the product to retail outlets.

The major factors responsible for extending the shelf life of fruitsand vegetables include: careful harvesting so as not to injure theproduct, harvesting at optimal horticultural maturity for intendeduse, and good sanitation (Moleyar and Narasimham 1994; Lee

and others 1996). When these are practiced, the implementationof optimum storage conditions through modified atmospherescan be quite effective at maximizing the shelf life and quality ofthe product.

A modified atmosphere can be defined as one that is created byaltering the normal composition of air (78% nitrogen, 21% oxy-gen, 0.03% carbon dioxide and traces of noble gases) to providean optimum atmosphere for increasing the storage length andquality of food/produce (Moleyar and Narasimham 1994; Phillips1996). This can be achieved by using controlled atmosphere stor-age (CAS) and/or active or passive modified atmosphere packag-ing (MAP). Under controlled atmospheric conditions, the atmo-sphere is modified from that of the ambient atmosphere, and

these conditions are maintained throughout storage. Examples ofthis type of storage and the commercial systems available are list-ed in Table IV-1. MAP uses the same principles as CAS; however,it is used on smaller quantities of produce and the atmosphere isonly initially modified. Active modification occurs by the dis-placement of gases in the package, which are then replaced by a

desired mixture of gases, while passive modification occurs whenthe product is packaged using a selected film type, and a desired at-mosphere develops naturally as a consequence of the productsrespiration and the diffusion of gases through the film (Moleyar andNarasimham 1994; Zagory 1995; Lee and others 1996). The nu-merous film types used in MAP are listed in Table IV-2, and somecommercially available MAP systems are listed in Table IV-3.

Oxygen, CO2, and N2, are most often used in MAP/CAS (Parry1993; Phillips 1996). Other gases such as nitrous and nitric oxides,sulphur dioxide, ethylene, chlorine (Phillips 1996), as well asozone and propylene oxide (Parry 1993) have been suggested andinvestigated experimentally. However, due to safety, regulatory andcost considerations, they have not been applied commercially.These gases are combined in three ways for use in modified atmo-

spheres: inert blanketing using N2, semi-reactive blanketing usingCO2/N2or O2/CO2/N2or fully reactive blanketing using CO2orCO2/O2(Parry 1993; Moleyar and Narasimham 1994).

Normally, the concentration of O2in a pack is kept very low (1-5%) to reduce the respiration rate of fruits and vegetables (Lee andothers 1995). Reducing the rate of respiration by limiting O2pro-longs the shelf life of fruits and vegetables by delaying the oxida-tive breakdown of the complex substrates which make up theproduct. Also, O2concentrations below 8% reduce the produc-tion of ethylene, a key component of the ripening and maturationprocess. However, at extremely low O2levels (that is,


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Vol. 2 (Supplement), 2003COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY 143

Chapter IV: Microbiological Safety of Controlled and Modified Atmosphere Packaging . . .

ers. Moreover, the elimination or significant inhibition of spoilageorganisms should not be practiced, as their interaction withpathogens may play an integral role in product safety. A numberof packers of fresh prepared green vegetables in the United King-dom have been experimenting with O2mixtures between 70 and100% (Day 1996). The treatment, referred to as oxygen shockorgas shock,has been found to be very effective in inhibiting en-zymatic discoloration, preventing anaerobic fermentation reac-tions, and inhibiting aerobic and anaerobic microbial growth.

High levels of O2can inhibit the growth of both anaerobic andaerobic microorganisms since the optimal O2 level for growth(21% for aerobes, 0-2% for anaerobes) is surpassed. However,there have also been reports of high O2(that is, 80-90%) stimulat-ing the growth of foodborne pathogens such asEscherichia coliand Listeria monocytogenes(Amanatidou and others 1999). Re-cent studies by Kader and Ben-Yehoshua (2000) and Wszelakiand Mitcham (2000) examining the use of superatmospheric O2levels to control microorganisms on produce, have found thatonly O2atmospheres close to 100 kPa or lower pressures (40 kPa9). in combination with CO2(15 kPa), are truly effective. These re-quirements may be difficult to achieve in industry since workingwith such high O2levels can be hazardous due to flammability is-sues. As with most MAP gases, superatmospheric O2has variedeffects depending on the commodity, and further research is re-quired in this area to elucidate the utility of this technique in thefresh-cut produce industry. A high O2 MAP group has beenformed in the United Kingdom and includes a number of industrygroups, notably Marks and Spencer plc, one of the first retailchains to distribute MAP foods. More recently, the high O2MAPclubhas provided a base for the new Novel Gases MAP Clubin the United Kingdom, a group that will investigate the use ofnovel high 9). argon and nitrous oxide MAP for extending shelflife and quality of fresh-cut produce. Their main focus is researchinto the commercial application of this process.

Nitrogen has three uses in MAP: displacement of O2to delayoxidation, retardation of the growth of aerobic spoilage organismsand action as a filler to maintain package conformity (Parry 1993).Of the three major gases used in MAP, CO2is the only one that

has significant and direct antimicrobial activity. A number of theo-ries have been suggested to explain this antimicrobial effect. Ingeneral, CO2in MAP results in an increased lag phase and gener-ation time during the logarithmic phase of growth of the organ-isms involved (Phillips 1996), with inhibition being concentrationand temperature dependent. Theories to explain the antimicrobialaction of CO2have been summarized by Farber (1991):

alteration of cell membrane function including effects on nu-trient uptake and absorption;

direct inhibition of enzymes or decreases in the rate of en-zyme reactions;

penetration of bacterial membranes leading to intracellularpH changes;

direct changes to the physicochemical properties of proteins.

The inhibitory action of CO2has differential effects on microor-ganisms. Thus, while aerobic bacteria such as the pseudomonadsare inhibited by moderate to high levels of CO2(10-20%), micro-organisms such as lactic acid bacteria can be stimulated by CO2(Carlin and others 1989; Amanatidou and others 1999). Further-more, pathogens such as Clostridium perfringens, C. botulinumand L. monocytogenesare minimally affected by CO2levels be-low 50%, and there is concern that by inhibiting spoilage micro-organisms, a food product may appear edible while containinghigh numbers of pathogens that may have multiplied due to alack of indigenous competition (Farber 1991; Zagory 1995; Phil-lips 1996). More research needs to be done on the interactions ofthe background microflora with foodborne pathogens in various

modified atmospheres used for produce, as well as on the effectsof different gaseous environments on the survival and growth ofbacterial foodborne pathogens on whole and fresh-cut produce.The optimal MAP conditions for produce quality and respirationfor a number of fruits and vegetables are listed in Table IV-4.

1.1. Types of CAS

There are a number of commercially available systems for CAS(Table IV-1). There are advantages and disadvantages to each, andgenerally the active control systems are most costly due to theneed for constant maintenance of gas levels. Since this type ofstorage is used for large quantities of product, and is not a type of

Table IV-1Commercially available controlled atmospheresystems

Oxygen Control Systems

System Description

External gas generator Oxygen is removed from incoming air byexternal gas generators which operate onthe open-flame or catalytic burner prin-ciples. Fuel as well as CO2scrubbers arerequired; however, the system operation is

very flexible and O2 is rapidly removed.Liquid nitrogen The controlled atmosphere is maintained byatmospheric generators flushing with sprayed liquid nitrogen placed

in front of the evaporator blowers. ExcessCO2 is absorbed by lime bags; a sensordetects rising O2 levels and corrects themby spraying more liquid nitrogen.

Gas separator systems Pressure-swing adsorption (PSA) systemThe absorption of O2 is mediated by afiltering system where it is contained in amembrane; N2rich gas is exported, and thebound O2 is flushed by depressurization ofthe vessel. Hollow Fibre Membrane (HFM)systemCompressed air is heated andforced through hollow fibers made ofsemipermeable membranes; the CO

2and

O2 are selectively removed by the mem-brane and the N

2continues into the storage

space.

Hypobaric storage This form of low pressure storage ismediated by a vacuum pump whichevacuates the container until the desiredpressure is reached. All gas levels arereduced and ethylene diffusion from theproduct is enhanced. Moisture loss is alsoreduced. Recommended for the curing ofonions.

Carbon Dioxide Control Systems

These systems are based on scrubbingaction where one of the following 5 reagentsis used: caustic soda, water, hydrated lime,activated charcoal, and molecular sieves.All involve the removal of CO2.

Ethylene Control Systems

Ethylene can be removed by means of ascrubber-heated catalyst system whereethylene is oxidized to yield CO2and watervapor, which is then removed from theroom, or by means of an absorbent beadscrubber where ethylene is bound toaluminum silicate spheres mixed withpotassium permanganate. In the latter, asbead saturation occurs, they turn frompurple (KMnO

4) to brown.

(Raghavan and others 1996).


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IFT/FDA Report on Task Order 3

packaging, it will not be discussed further.

1.2. Types of MAP

MAP is used mainly for wholesale/foodservice use and retaildisplay. There are many MAP systems currently in use (Table IV-3).The films used for MAP of fresh-cut produce (Table IV-2) will be

discussed briefly.1.2.1. Bulk packaging. Bulk packaging is similar to CAS, but re-

lies on a passively modified atmosphere (Lee and others 1996).This type of packaging is mainly used for pallet bags and paper-board containers used in the transportation and storage of com-modities. These films can be ecologically advantageous since

Table IV-2Polymers, film types and permeability available for packaging of MAP produce

Water vaportransmission, g/m2/day/atm

Permeability(cm3/m2.d.atm for 25 mu film at 25C)(38 C and 90%

Film Oxygen Nitrogen Carbon dioxide relative humidity)

Ethylene-vinyl alcohol (EVOH) 3-5 * 16-18Polyvinylidene chloride coated (PVdC) 9-15 20-30 -Polyethylene, LD 7800 2800 42000 18

Polyethylene, HD 2600 650 7600 7-10Polypropylene cast 3700 680 10000 10-12Polypropylene, oriented 2000 400 8000 6-7Polypropylene, oriented, PvdC coated 10-20 8-13 35-50 4-5Rigid PVC 150-350 60-150 450-1000 30-40Plasticized PVC 500-30000 300-10000 1500-46000 15-40Ethylene vinyl acetate (EVA) 12500 4900 50000 40-60Polystyrene, oriented 5000 800 18000 100-125Polyurethane (polyester) 800-1500 600-1200 7000-25000 400-600PvdC-PVC copolymer (Saran) 8-25 2-2.6 50-150 1.5-5.0Polyamide (Nylon-6) 40 14 150-190 84-3100Microperforated (MP) >15,0004 -Microporous, (MPOR) >15,0004 Variable

O2 permeability CO

2permeability

Edible Films (mL.mm/m2.d.atm) (mL.mm/m2.d.atm) Relative Humidity

Pectin 57.5 87Chitosan 91.4 1553 93Wheat (gluten) 190/250 4750/7100 91/94.5Na caseinate 77 462 77Gluten-DATEM 153 1705 94.5Gluten-beeswax 133 1282 91Na casenate/Myvacet 83 154 48MC/MPMC/fatty acids 46.6 180 52MC and beeswax 4 27 42Gluten-DATEM and beeswax


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Table IV-3Commercially available modified atmosphere packaging systems for small and large quantities of produce

Product1 Description Use

Pallet Package System Pallet box wrapped in heavy gauge polyethylene, with a silicone Apples, pears and other perishablesmembrane window to allow gas exchange regulation and acalibrated hole for pressure regulation.

Marcellin System For room storage: regulates the atmospheric composition via aparallel series of rectangular bags of silicone rubber; can beinstalled in or out of storage area and maintains a fairly consistent

atmosphere. Various perishablesAtmolysair System System of gas diffusion panels enclosed in an airtight container,

having two separate airflow paths and a control panel, allowing thepotential for automation. Cabbage in Canada, other perishables

Tectrol System Pallet box bulk unit-wrapped with a barrier plastic film; gases are Strawberries for short term transport(TransFRESH Co.) injected and the bag-sealed.

Tom-Ah-Toes Long, narrow box overwrapped with gas permeable film; Avocados, tomatoes, mangoes(Natural Pak Produce) contains a sachet containing calcium chloride and activated lime to

absorb CO2.

FreshSpanTM(Sun Consists of a breathable plastic membrane in the liner of the walls Fresh-cut asparagus, broccoli,Blush Technologies Inc) of a corrugated paperboard FreshSpanTMbox, which can be cauliflower, avocados, berries, stone

hermetically sealed. fruit

MaptekFreshTM(Sun Maptek Freshis a postharvest biotechnology where specific Fresh-cut produce: pineapple, fruitBlush Technologies Inc.) features and conditions are applied for each type of product to salad, cut tomatoes, mango, kiwi,

stabilize the produce and place it in a state of hibernation. melon, citrus fruitsFreshflexTM(Curwood) Curwood provides a variety of films for produce packaging and Produce

can add a variety of features to the package such as antifog,EZ Peel, Peel-Reseal, Integra Tearand Magic Cut.

MAPAX(AGA, Sweden) This system incorporates the optimal atmosphere by testing, to Fresh-cut produce, lettuce,choose the exact gas mixture and the best film for each product mushrooms, pre-peeled potatoesconsidering respiration rate, temperature, packaging film, packvolume, fill weight and light.

FreshHold Polypropylene label with calcium carbonate embedded in it. Broccoli, asparagus, cauliflower and(Hercules Chemical Co.) cherries

Cryovac(W.R. Grace 0.75, 1.25, 2.5 mm thick bag made of several layers of Cut lettuce, broccoli, cauliflower,and Co.) polyethylene related polymers. spinach, peeled potatoes and other

fresh fruits and vegetables

Propafilm CR and CK Polypropylene-based films. Fresh-cut lettuce and other(Imperial Chemical vegetablesIndustries PLC)

P-Plus films Spark perforated films which result in non-uniform perforations Brussels sprouts, lettuce, broccoli,(Courtaulds Packaging) throughout the film to facilitate gas exchange. fresh mushrooms, and bean sprouts

T-grade (CVP Systems) Films are coextruded bilayer films in 1.0, 1.25, 1.5 and1.75 mm thickness.

Clysar EHC, EH, ECL, Biaxially oriented, heat shrinkable polyethylene or polyolefin films.LLP(DuPont)

Laminated boxes(Georgia Cartons with films laminated within the cardboard or coated on Strawberries, broccoli, and otherPacific, Weyerhaeuser and the inside of the cardboard liner. Reduces moisture loss and perishablesTamfresh Ltd.) potentiates air flow.

Film Convertors The converters (companies) buy resin or film and adapt it to Variable/product specificattractive specifications. Converters are often more flexible with

respect to specific applications of the requested film.

Edible Films1

TAL Pro-Long Blend of sucrose esters of fatty acids and sodium carboxymethyl Pears(Courtaulds Group) cellulose; depresses internal O2 and is edible.

Nutri-Save N, O-carboxymethychitosan edible film. Pears, applesSemperfresh, Nu-Coat Fo, Sucrose ester based fruit coatings with sodium carboxymethyl Most fruits and vegetables, processedBan-seel, Brilloshine, cellulose products manufactured exclusively from food and whole potatoes (Snow-WhiteSnow-White and White ingredients available in dip or spray. and White-Wash)Wash products (SurfaceSystems Intl. Ltd.)

(continued on next page)


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Table IV-3Commercially available modified atmosphere packaging systems for small and large quantities of produce(continued from previous page)

Product1 Description Use

PacRite products (American Variety of products, water-based carnauba-shellac emulsions, Apples, citrus, tomatoes, cucumbers,Machinery Corp.) shellac and resin water emulsions, water-based mineral oil fatty green peppers, squash, peaches,

acid emulsions, and so forth. plums, nectarines

Fresh-Cote product line Variety of products including; shellac-based, carnauba-based and Apples, pears, eggplant, tomatoes,(Agri-Tech Inc.) oil emulsion edible films. cucumbers, stone fruits

Vector 7, Apl-Brite 300C, Vector 7 is a shellac-based film with morpholine; the Apl-Brite and Apples and citrus fruitsCitrus-Brite 300C Citrus-Brite are carnuba-based films.(Solutec Corp.)

Primafresh Wax Carnauba-based wax emulsion. Apples, citrus and other firm-(S.C. Johnson) surfaced fruit

Shield-Brite products Shellac, carnauba, natural wax and vegetable oil/wax and xanthan Citrus, pears, stone fruit(Pace Intl. Shield-Brite) gum products.

Sta-Fresh Products Natural, synthetic, and modified natural resin products and Citrus, apples, stone fruits, pome-(Food Machinery Corp.) combinations thereof. granates, tomatoes, pineapple, canta

loupes, and sweet potatoes

Fresh Wax products Shellac and wood resin, oxidized polyethylene wax, white Citrus, cantaloupes, pineapples,(Fresh Mark Corp.) oil/paraffin wax products. apples, sweet potatoes, cucumbers,

tomatoes and other vegetables

Brogdex Co. products Carnauba wax emulsions with or without fungicides, emulsion wax, Apples, melons, bananas, avocado,high shine wax, water-based emulsion wax, carnauba-based chayote, papaya, mango, pineapple,emulsion, vegetable oil, resin-based and concentrated polyethylene citrus, stone fruits.emulsion wax products.

FreshSealTM(Planet Polymer A patented coating that slows the ripening process by controlling Currently available for avocado,Technologies Inc. has the O2 and CO2and water vapor flowing in and out of the product. cantaloupe, mangoes and papaya.licensed CPG Technologies It can be tailored to the individual respiration rates of different fruit Use on limes, pineapples andof Agway, Inc. to produce) and vegetable varieties. bananas is currently under

investigation.

Nature-SealTM, AgriCoat Composite polysaccharide-based coating using cellulose derivatives Sliced apples, carrots, peppers,(Mantrose Bradshaw as film formers. onions, lettuce, pears, avocados,Zinsser Group) sliced bananas

Intelligent Systems

Activated Earth Films Typically polyethylene bags with powdered clay material made of Variable

powdered aluminum silicates, incorporated into the film matrix.Possibly reduces ethylene concentration by facilitating its diffusionout of the bag.

Temperature Responsive Films increase their gas permeabilities in response to temperature Specific for each productFilms(Landec Labs) increases as well as increases in respiration. Stabilizes the modified

atmosphere so it remains the same under various temperatures.

CO2ScavengersFreshLock Sachet type product which is placed directly in the package and Fruits and vegetables, coffee(Mitsubishi Gas Chemical absorbs both carbon dioxide and oxygen.Co.), Verifrais (CodimerTournessi, Gujan-Mestras)

Ethylene absorbents Sachet type product which is placed directly in the package and Fruits and vegetablesEthysorb (StayFresh Ltd), absorbs ethylene. They are composed of a variety of productsAgeless C (Mitsubishi Gas such as aluminum oxide, potassium permanganate, activatedChemical Company), carbon, and silicon dioxide.

Freshkeep (Kurarey),Acepack (nippon Greener),Peakfresh (Klerk PlasticIndustries, ChantlerPackaging Inc.)

Antimicrobial Films

-unsure of commercial availability

(Church 1993; Baldwin 1994; Zagory 1995; Lee and others 1996; Raghavan and others 1996; Smith and Ramaswamy 1996; Padgett and others 1998; Han 2000).1Different film types discussed in Table IV-2.


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some are returnable, and thus reuse is possible in some cases. Anexample of this kind of packaging is the Marcellin System (TableIV-3).

1.2.2. Prepackaging. Following bulk packaging and arrival atthe retail outlet, produce can be prepackaged by the grocer or thecustomer using a passive MAP (Smith and Ramaswamy 1996).Prepackaging in the store usually involves the use of plastic filmpackaging such as low density polyethylene (LDPE), polyvinyl-chloride (PVC) or polypropylene (PP); films which help to mini-mize moisture loss and maintain produce quality (Lee and others1996). However, the films used often supply only a narrow rangeof gas selectivity and due to its imprecise nature, this type of pack-aging is only applicable to a few products.

In-store packaging has recently been applied to the new onlinegrocery shopping and delivery services. A number of online gro-cery stores,such as www.peapod.com and www.netgrocer.comin the United States, and www.grocerygateway.com andwww.onlinegrocer.ca/shop/home.asp in Canada, have recentlybeen established. The most comprehensive of these organizationswill ship everything from fresh fruits and vegetables and staples tofrozen and fresh meat and seafood products. It does not appearthat these services use any special packaging in addition to thatalready used in the grocery store. However, it is recommendedthat attention be paid to this growing online service, especially interms of the potential for cross-contamination in the warehouseand temperature abuse during storage and/or transportation.

Table IV-4Some characteristics and optimum storage conditions of whole fruits and vegetables for MAP

Tolerance Optimum

Respiration Rate Maximum Minimum CO2

O2

Recommended ApproximateCommodity (at 5 C, mg CO2/kg/h) CO2 (%) O2(%) (%) (%) storage temp. storage life

FruitApple 5-10 2-5 1-2 1-3 1-2 0-3 2-11mApricot 10-20 2 2 2-3 2-3 0-5 Avocado 5 3 3-10 2-5 5-13 8-10d

Banana 5 2 2-5 2-5 12-15 15dBlackberry 15-20 5-10 0-5 Blueberry 12-20 2.5 0-5 Cantaloupe 15 2 3-7 Cherry (sweet) 10-20 15 2 10-12 3-10 0-5 Cranberry 0-5 1-2 2-5 Fig 15-20 5-10 0-5 Grape 1-3 or 10-15 2-5 or 5-10 0-5 Grapefruit - 10 5 5-10 3-10 10-15 Kiwifruit 5 2 3-5 1-2 0-5 6mLemon 0-10 5-10 10-15 Lime 0-10 5-10 10-15 Mango 15a 5 5-8 3-7 10-15 Nectarine 3-5 or 15-17 1-2 or 4-6 0-5 Orange 0-5 5-10 5-10 Papaya 5 2 5-8 2-5 10-15 Peach 10-20 5 2 3-5 1-2 0-5

Pear 2 2 0-1 2-3 0-5 Persimmon 5-8 3-5 0-5 Pineapple 10 2 5-10 2-5 8-13 Pomegranate 5-10 3-5 5-10 Raspberry 15-20 5-10 0-5Strawberry 20-40 15 2 15-20 5-10 0-5

Vegetable

Artichoke 2 3 2-3 2-3 0-5 29dAsparagus >60 14 5 10-14 Air 1-5 21dBeans, snap 40-60 10? 2 5-10 2-3 5-10 7-10dBroccoli >60 10 1 5-10 1-2 0-5 2-3mBrussels sprouts 40-60 5 2 5-7 1-2 0-5 2-3mCabbage 10-20 5 2 3-6 2-3 0-5 6-12mCarrot 10-20 5 5 3-4 5 0-5 4-5mCauliflower 20-40 5 2 2-5 2-5 0-5 2-3mChili peppers 10-20 2 3 5 3 8-12

Corn, sweet >60 15 2 10-20 2-4 0-5 Cucumber 4b 10 3 0 3-5 8-12 14-21dLettuce (leaf) 10-20 2 2 0 1-3 0-5 3-4wksMushrooms >60 15 1 5-15 3-21 0-5 3-4dBell peppers 10-20 2 3 0 3-5 8-12 2-3wksSpinach >60 15 10-20 air 0-5 2-3wksTomatoes (mature) 10-20 2 3 0 3-5 12-20 2wksTomatoes (partly ripe) 10-20 2 3 3-5 3-5 10-15 Potato 5-10 none none 4-12 Onion 5-10 0 1-2 0-5 8m

(Adapted from Powrie and Skura 1991; Day 1993; Exama and others 1993; Moleyar and Narasimham 1994; Smith and Ramaswamy 1996).aAt 10C in air (Day 1993).bAt 10C in 3% O2 (Day 1993).


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1.3. Films used in MAP

The use of MAP for whole and fresh-cut produce involves care-ful selection of the film and package type for each specific prod-uct and package size (Tables IV-2 and VI-3). Effective MAP of pro-duce requires consideration of the optimal gas concentration,product respiration rate, gas diffusion through the film, as well asthe optimal storage temperature in order to achieve the most ben-efit for the product and consumer. In addition, when selecting anappropriate film, one has to take into account the protection pro-vided, as well as the strength, sealability and clarity, machineabili-ty, ability to label, and the gas gradient formed by the closed film(Zagory 1995).

Recently, the long list of films and commercially available MAPsystems has been augmented with the conception of both smart

and edible packaging systems (Guilbert and others 1996; Phillips1996). Smart or intelligent packaging is being used in thefresh-cut industry and includes indicators of time and tempera-ture, gas composition, seal leakage, and food safety and quality(Rooney 2000). Some intelligent systems alter package oxygenand /or carbon dioxide permeability by sensing and respondingto changes in temperature. Other smart films incorporate chemi-cals into packets placed in the packaging system, with no contactwith the product; an example would be the use of O2scavengers

with O2indicators. Another type of smart film, developed withfood safety in mind, is currently undergoing testing. This novelsystem, when incorporated into a packaging film, uses an anti-body detection system to detect pathogens, and expresses a posi-tive finding as a symbol on the surface of the package, therebyalerting food handlers to the presence of pathogens. Although thistechnology shows promise, it is still in its infancy and comprehen-sive assessments have yet to be performed. Several limitationshave been suggested with this technology; for example, it wouldnot likely be able to detect pathogens at concentrations below104CFU/g or cm2 and would not detect pathogens within theproduct.

Edible biodegradable coatings are yet another variant of thesmart film technology, where a film is used as a coating and ap-plied directly on the food (Guilbert and others 1996; Francis andothers 1999). Wax has been used in China since the 12th and13th centuries as an edible coating to retard desiccation of citrusfruits, and in the last 30 years, edible films and coatings madefrom a variety of compounds have been reported. Guilbert andothers (1996) and Baldwin (1994) have extensively reviewedsome of the newer edible films (see Tables IV-3 and VI-5). Thesefilms are gaining popularity due to both environmental pollutionand food safety concerns (Padgett and others 1998). However, anumber of problems have also been associated with edible coat-ings. For example, modification of the internal gas composition ofthe product due to high CO2 and low O2 can cause problemssuch as anaerobic fermentation of apples and bananas, rapidweight loss of tomatoes, elevated levels of core flush for apples,rapid decay in cucumbers, and so on (Park and others 1994).

Edible films may consist of four basic materials: lipids, resins,polysaccharides and proteins (Baldwin and others 1995). Plasti-cizers such as glycerol as well as cross-linking agents, antimicro-bials, antioxidants, and texture agents can be added to customizethe film for a specific use (Guilbert and others 1996). Plasticizershave the specific effect of increasing water vapor permeability.Therefore, their addition must be considered when calculating thedesired water vapor properties of each specific film, since toomuch moisture can create ideal growth conditions for some food-borne pathogens. The most common plasticizer used to cast edi-ble films is foodgrade polyethylene glycol, which is used to re-duce film brittleness (Koelsch 1994).

Lipids, or waxes and oils, and resins such as shellac and woodrosin have been widely used for intact fruits and vegetables in twodistinct forms, laminates and emulsions (Baldwin and others

1995). Lipid-based edible barriers are known for their low watervapor permeabilities. Koelsch (1994) found that the water vaporpermeability of a cellulose-based emulsion barrier is dependenton the lipid moiety used; a minimum permeability can beachieved when stearic acid is used as the lipid. This is due to theeffective barrier formed by stearic acid through an interlockingnetwork. However, lipid-based edible films also require a supportmatrix to reduce brittleness, and have difficulty adhering to thehydrophilic cut surfaces of fruits and vegetables (Koelsch 1994;Baldwin and others 1995). Some of the most common com-pounds used for support matrices are modified celluloses of hy-droxypropylmethyl, ethyl and methylcellulose, chitosan andwhey protein isolate (WPI; Koelsch 1994).

Table IV-4bControlled and modified atmosphere storagerecommendations for selected fresh-cut fruits and vegetables

Fresh-cut Vegetables

Temp.Atmosphere

Product (C) O2 (%) CO2(%) Efficacy

Beets (Red), Grated,Cubed or Peeled 0-5 5 5 Moderate

Broccoli, florets 0-5 2-3 6-7 Good

Cabbage, Shredded 0-5 5-7.5 15 GoodCabbage, (Chinese),

Shredded 0-5 5 5 Moderate

Carrots, Shredded,

Sticks or Sliced 0-5 2-5 15-20 Good

Leek, Sliced 0-5 5 5 Moderate

Lettuce (Butterhead),Chopped 0-5 1-3 5-10 Moderate

Lettuce (Green Leaf),Chopped 0-5 0.5-3 5-10 Good

Lettuce (Iceberg),Chopped or Shredded 0-5 0.5-3 10-15 Good

Lettuce (Red Leaf),Chopped 0-5 0.5-3 5-10 Good

Lettuce (Romaine),

Chopped 0-5 0.5-3 5-10 GoodMushrooms, Sliced 0-5 3 10 Not

recommended

Onion, Sliced or Diced 0-5 2-5 10-15 Good

Peppers, Diced 0-5 3 5-10 Moderate

Potato, Sliced orWhole-Peeled 0-5 1-3 6-9 Good

Rutabaga, Sliced 0-5 5 5 Moderate

Spinach, Cleaned 0-5 0.8-3 8-10 Moderate

Tomato, Sliced 0-5 3 3 Moderate

Zucchini, Sliced 5 0.25-1 Moderate

Fresh-Cut Fruits

Apple, Sliced 0-5


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In general, polysaccharides such as cellulose, pectin, starch,carrageenan, and chitosan, can adhere to cut surfaces of produceand effectively allow gas transfer; however, they are not effectivemoisture barriers. Due to their CO2 and O2 permeabilities,polysaccharide-based films allow the creation of desirable modi-fied atmospheres, an attractive advantage over plastic or shrinkwrap MAP which can be labor intensive, expensive and environ-mentally harmful (Baldwin and others 1995). A number of cellu-lose derived coatings are available commercially, most taking ad-

vantage of the modified atmosphere effect of the barriers. Pro-long(Courtaulds Group, London) and Semperfresh (Surface SystemsInternational, Ltd., Oxfordshire, U.K.) are examples of water-solu-ble composite coatings comprised of the sodium salt of car-boxymethyl cellulose (CMC) and sucrose fatty acid ester emulsifi-ers (Baldwin and others 1995). Their properties are discussed inTable IV-6. A newer product called Snow-White,based on su-crose esters of fatty acids, has also been used to combat oxidativebrowning in the potato industry. Nature-Seal is a polysaccharide-based surface treatment that uses cellulose derivatives as filmformers, but unlike Semperfresh and Pro-long, does not containsucrose fatty acid esters. Nature-Seal is a browning inhibitor thatis applied as a dip or spray and has been shown to delay ripeningof whole fruits and vegetables, and to retard discoloration ofpeeled carrots and cut mushrooms.

Finally, proteins such as casein, soy, and zein, can also adhereto hydrophilic cut produce surfaces and are easily modified toform films; however, they also allow water diffusion (Baldwin andothers 1995). Unlike lipid-based barriers, protein-based barriersdo not require the addition of a support matrix, since the proteinacts as both the water vapor barrier and structural component ofthe film (Koelsch 1994). Park and others (1994) reported the suc-cessful application of a corn-zein film to extend the shelf life of to-matoes. Color change, loss of firmness, and weight loss duringstorage were delayed, and shelf life was extended by 6 days incomparison to untreated tomatoes. The corn-zein product used inthe above study was a commercial product that was brushed ontothe tomatoes (Regular Grade F4000, INC Biomedicals, Inc.), andconsisted of 54 g of corn-zein, 14 g of glycerine, and 1 g of citric

acid dissolved in 260 g of ethanol. Park and others (1994) did notcomment on the use of citric acid in the film solution; however,others have found that edible films composed of zein were moresuccessful in preventing the rancidity of nuts when citric acid wasadded (Guilbert and others 1996).

In order to obtain an edible film that incorporates all the bestqualities of these four basic materials, as well as fulfilling the spe-cific conditions for each fruit or vegetable, manufacturers are nowproducing films comprised of different combinations. Some of theadvantages and disadvantages of the four basic edible film barri-ers, as well as combinations thereof, are listed in Table IV-5.

As with other MAP technologies, edible films can create a verylow O2environment where anaerobic pathogens such as C. botu-linummay thrive; however, antimicrobial compounds can be in-corporated into the coating in this scenario (Guilbert and others

1996). Since the antimicrobial or antioxidant can be incorporatedand applied directly to the surface of the product, only smallquantities are required. Not all films are equally amenable to theaddition of antimicrobials. Much of the current work on antimi-crobial films is taking place in Europe. Some of the incorporatedantimicrobial compounds include metal ions supported in zeo-lite, isothiocyanate in cyclodextrin with cobalt ion, chitosan, allylisothiocyanate, silver-based fungicide, quaternary ammoniumsalt, organic monoglycerides, copper and zinc (Padgett and others1998), benzoic acid, sodium benzoate, sorbic acid and potassi-um sorbate and propionic acid (Baldwin and others 1995). Re-searchers are also currently looking at the use of nisin, a bacterio-cin, in coatings to suppress L. monocytogenes, as well as other

bacteriocins for the control of C. botulinum. Successful applica-tions of this technology have been demonstrated using sodiumcaseinate/stearic acid to coat peeled carrots and caseinate/acety-lated monoglyceride to coat celery sticks (Guilbert and others1996). Zhuang and others (1996) investigated the ability of a hy-droxypropyl methylcellulose coating containing various antimi-crobials to inactivate SalmonellaMontevideo on the surface andin the core tissues of tomatoes. Citric or acetic acid (0.2, 0.4%)did not enhance inactivation; however, 0.4% sorbic acid signifi-

cantly enhanced the inactivation of S. Montevideo, although thetomatoes had a chalky and unappealing appearance. A study per-formed by Padgett and others (1998) did not specifically look atthe application of antimicrobial films to food products; however,the incorporation and behavior of antimicrobials in edible filmswere observed. Padgett and others (1998) examined the inhibitoryeffect of both lysozyme and nisin, incorporated directly into cornzein and soy protein films, against a gram-positive and gram-neg-ative indicator organism. They found that casting, rather than heatpressing during the processing of films, was more effective at pro-ducing an antimicrobial film when using corn and soy films. Also,the antimicrobial additives affected the film structure as fracturelines were noted at the microscopic level when lysozyme was in-corporated, potentially affecting the film integrity. Following incor-poration into the films, both nisin and lysozyme maintained theirantimicrobial capacity against the indicator organisms Lactobacil-lus plantarumand E. coli, which was augmented by the additionof a chelating agent such as EDTA (Padgett and others 1998).

In addition to the study performed by Padgett and others(1998), there have been many studies investigating the migrationof additives such as antimicrobials from coatings into food (Guil-bert and others 1996). Sodium benzoate, benzoic acid, propionicacid, and potassium sorbate are also generally recognized as safe(GRAS) food additives, and sorbic acid has become a model addi-tive for migration studies. In general, wheat gluten-glycerol filmscontaining lipid components, resulted in a 50% reduction in thediffusivity of sorbic acid out of the film. Films composed entirelyof lipids allowed even less diffusion of sorbic acid. Therefore, themost advantageous use of these films for antimicrobial properties

would be the formation of a monolayer lipid and sorbic acid film,or a bilayer film composed of a hydrophilic base layer coatedwith a thin layer of lipid containing sorbic acid (Guilbert and oth-ers 1996). Chen and others (1996) attempted the construction ofan antimicrobial film containing chitosan (water resistant) and me-thylcellulose (water susceptible), and either sodium benzoate orpotassium sorbate as antimicrobials. Although the film was foundto be inhibitory to fungi as judged by inhibitory zones on agarmedia, release of the antimicrobials from the film was too high tomaintain a continuous and effective concentration of the antimi-crobial in the film.

Antimicrobial compounds have also been used with traditionalfilms such as low-density polyethylene (LDPE); for example, thefungicide Imazalil (IM) and the antimicrobial grapefruit seed ex-tract (GFSE) have recently been used with bell peppers and let-

tuce, respectively (Miller and others 1984; Han 2000). In thestudy using IM, it was noted that the use of IM and IM impregnat-ed film was more effective than either treatment alone at control-ling fungal decay; however, IM impregnated film increased the in-cidence of bacterial soft rot (Miller and others 1984). The action ofthis fungicide on potential pathogens is unknown. Lee and others(1998) investigated the ability of GFSE with LDPE films to inhibitgrowth of E. coli, Staphylococcus aureus,molds, yeasts, and lacticacid bacteria, using the plate disk test. Films containing 1.0%GFSE in LDPE film inhibited E. coli andS. aureusas demonstratedby a clear zone; however, molds, yeasts and lactic acid bacteriawere unaffected. After testing the films using the plate disk test,Lee and others (1998) used the films for packaging of curled let-


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Table IV-5Properties and characteristics of edible films

Film Film Preparation Advantages Disadvantages

General Films

Natural biopolymer films: composed of Simple coacervationa Polysaccharide/Protein Polysaccharide/Proteinpolysaccharides, polyester proteins, Complex coacervationa biodegradable and renewable highly sensitive to moisturelipids and derivatives Gelatin or thermal coagulationa used to replace short shelf life and has poor water vapor

plastics barrier properties suitable overall mechanicaland optical properties Lipids/Polyesters

good for high-moisture foods reduction of moisture transportLipids/Polyesters opaque and relatively inflexible biodegradable and renewable can be fragile and unstable good water vapor barrierproperties

Lipid-Based Coatings (Koelsch 1994)

Emulsions non-lipid support matrix required lower water vapor permeability requires non-lipid supportto reduce brittleness than laminate barriers matrix lipid added to an emulsion barrierwhen cellulose within supportmatrix is dissolved when mixed (lipid/support matrix),the barrier is cast using impenetrable glass or metal levelplate water and ethanol are removed,

and the barrier dried to moisturecontent of 2-5%, and then peeledfrom plate

Laminates molten lipid is either painted, easier to apply than emulsions requires non-lipid supportsprayed, or poured to form a matrixdistinct layer on the dry supportmatrix laminate is then dried/cooled,peeled off and stored until use

Protein Barriers (Koelsch 1994; Baldwin and others 1995; Guilbert and others 1996)

Casein, collagen, corn zein, gelatin, soy obtained from aqueous or biodegradable more permeable to waterprotein, wheat gluten, gelatin, WPIb ethanolic solution reduces moisture loss vapor than lipid barriers

adds nutritional value does not require supportmatrix

Wheat (gluten) obtained from aqueous solution effective oxygen barrier at low vapor barrier ability limitedrelative humidity high gluten content may also* high gluten content be a disadvantage for those* increased puncture strength intolerant to glutenand extensibility

Polysaccharide Barriers (Baldwin and others 1995)

Pectin most effective on low moisture products generally made from low-methoxyl can retard water loss from food not adequate moisture

pectin, calcium chloride (cross-l can improve handling and bar riersinker), a plasticizer, and appearance of foods low oxygen permeabilitysometimes organic acids

Chitosan Nutri-Save (NovaChem) used for methylation of the chitosan natural preservative, inhibits * at 100% RH, permeabilitywhole apples and pears polymer results in increased growth of fungi to CO2and O2due to

resistance to CO2 permeability impermeable to gases at diffusion with water use of chitosan with lipids may 70% RHc

solve moisture barrier problemsDerivatives of cellulose used mainly for composite good film formers due to not good barriers to movement Tal Pro-long (Courtaulds Group) coatings comprised of the sodium linear structure of polymer of water; however, the film can Semperfresh (Surface salt of carboxymethyl cellulose backbone retain a moisture layer whichSystems Intl, Ltd.) (CMC) as the film former, with O2is limited in entering the fruit will delay moisture loss from

sucrose fatty acid ester as the more than CO2 is from escaping; the fruit by being the first layeremulsifiers limiting buildup of harmful CO2

and maintenance of reduced O2 of moisture lost

Carrageenan Coatings extracted from several species can reduce moisture loss, not yet approved by the FDA sucessfully used on cut grapefruit of red seaweeds and used in food oxidation or disintegration of the for food coatingshalves (Bryan 1972) systems as a gel product not yet approved by FDA for coatings

aSee glossary for definition of molding techniques.bWheat protein isolate.cRelative humidity.


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tuce and soybean sprouts. Although inhibition of E. coliand S.aureuswas not measured on the commodities, it was noted thatincorporation of 1.0% GFSE into the LDPE film decreased thegrowth rates of aerobic bacteria and yeasts (initial counts rangingfrom 103to 104 CFU/g) over 8 days for the curled lettuce stored at5 C (59 F). Soybean sprouts were found to have a higher initialload of aerobic bacteria and yeasts than the curled lettuce (10 6

CFU/g). Therefore, the only observed decrease in growth rates wasfor the lactic acid bacteria over a 12-day period at 5 C (41 F).Further tests need to be performed using this film technology toascertain the effects on pathogens as well as aerobic bacteria andyeasts when the film is used with a food product. Inhibition ofnonpathogenic organisms that can be indicators of organolepticquality may lengthen shelf life such that outgrowth of pathogens ispossible, while the product is still organoleptically acceptable.

Grapefruit seed extract is reported to be inhibitory to a number ofhuman pathogens. There has been evidence, however, that anyantibacterial activity of commercial preparations is due to the vari-ous preservative agents (triclosan, methyl parabene, benzethoni-um chloride) contained within the product. Researchers havefound that products not containing any preservatives and severalself-made preparations had no antimicrobial activity (Woedtkeand others 1999). In the aforementioned study by Lee and others(1998), the composition of the GFSE incorporated in the film wasnot discussed or examined. It is obvious that if pure GFSE is to beused, its antimicrobial properties will have to be fully investigated.If the active antimicrobial ingredients in commercial GFSE prepa-rations are preserving agents, they may be better targets for inves-

tigation.At present, the area of edible films and antimicrobial ediblefilms is not considered a priority by industry due to overall publicperception and hesitation about adding more chemicals, naturalor not, to fresh produce. Besides the waxing of fruits, edible filmsare not commonly used and presently, the main issue involves theproduction of coatings with good surface tension that will stick toproduce.

2. Factors affecting shelf lifeA main aim of MAP is extension of shelf life. It must be reiterat-

ed here that extension of product shelf life may allow outgrowthand/or growth of pathogens to higher levels as compared to air-stored samples. Since fruits and vegetables are still alive and

therefore respiring when harvested and processed, there aremany factors that affect the postharvest shelf life extension of freshproduce and the success of MAP.

The rate of respiration of a fruit or vegetable is inversely propor-tional to the shelf life of the product; a higher rate decreases shelflife (Day 1993; Lee and others 1995). In general, those productswith increased wounding, as in the case of fresh-cut produce, willhave a high degree of perishability due to increased respirationrates. Respiration can be measured by the oxygen uptake or byproduction of CO2and also results in the production of heat andwater vapor (Zagory 1995). Therefore, a goal of MAP is to de-crease the produce respiration rate, which can be successfullyachieved with decreased O2levels (1-5%) and refrigeration. How-

Table IV-6Edible coating applications and functions1

Type of edible coating

Polysaccharide coatings Function Reference

I. CelluloseCarboxymethyl celluloseBananas O2and CO2 barrier Banks 1984Apples O

2and CO

2barrier Banks 1985;

Fresh fruits and vegetables O2and CO2barrier Drake and others 1987Freshly-cut celery Moisture barrier Lowings and Curts 1982

Pears O2and CO2 barrier Mason 1969Tomatoes O2and CO2barrier Meheriuk and Lau 1988Oranges O2and CO2barrier Nisperos and Baldwin 1988

Nisperos-Carriedo and others 1990II. StarchDextrins (starch hydrolysates)Freshly sliced apples O2barrier Murray and Luft 1973

III. Seaweed ExtractsCarrageenanCut grape-fruit halves Moisture barrier Bryan 1972

IV. Chitin/ChitosanApples, pears, peaches, plums O2and CO2barrier Davies and others 1989; Elson and Hayes 1985Fresh strawberries Postharvest decay control El Ghaouth and others 1991aFresh cucumbers, bell peppers Postharvest decay control El Ghaouth and others 1991b

Protein CoatingsI. Corn ZeinZeinTomatoes Moisture and O2 barrier Park and others 1994II. CaseinCasein-acetylated monoglycerideZucchini Moisture barrier Avena-Bustillos, Krochta, and others 1994Apples and celery sticks Moisture barrier Avena-Bustillos and others 1997

Casein-stearic acid, beeswax, or acetylated monoglyceridePeeled carrots Moisture retention Avena-Bustillos and others 1993, Avena-Bustillos,

Cisneros-Zevallos and others 1994

1 (Adapted from Table IV-3 and Table IV-4 in Krochta and De Mulder-Johnston 1997).


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ever, O2concentrations below 1-2% can lead to anaerobic respi-ration and the production of off-odors, as well as create ideal con-ditions for pathogens such as C. botulinum. As previously dis-cussed, high O2 (70-100%) combined with CO2 for MAP hasbeen tested and shown to have beneficial effects on product qual-ity (Amanatidou and others 1999); however, more research is re-quired to support and explain this concept (Wszelaki and Mit-cham 2000; Kader and Ben-Yehoshua 2000).

The delay of senescence, the natural form of deterioration, is the

main goal in the preservation of fresh produce, as senescence ac-counts for the majority of postharvest losses (Lee and others 1995).Senescence is endogenously controlled and is the stage when ex-tensive catabolic reactions occur, resulting in dissolution of plantmembranes. It is marked by chlorophyll loss, decreases in RNA andprotein content and tissue softening. Plants, for example, senesce toreroute materials into seeds representing the next generation; it istherefore a predestined apoptosis process that can only be delayed,not completely inhibited. It is driven by an increase in respiration,as well by an increase in ethylene production in some products, aprocess referred to as climacteric. It is therefore reasonable to as-sume that maintaining and reducing ethylene perception and pro-duction may effectively delay senescence.

As mentioned above, ethylene, a plant hormone, plays a largerole in shelf life and can cause a marked increase in respirationrates and enhance ripening and senescence (Nguyen-the andCarlin 1994; Day 1993). In some commodities, accelerated age-ing and the initiation of ripening can occur following exposure toethylene concentrations as low as 0.1 ml/l (Lee and others1995). As senescence begins, spoilage due to indigenous bacteriacan be augmented. Ethylene is also a by-product of the aerobiccombustion of hydrocarbons, and it is therefore important duringthe handling of produce to maintain low levels of environmentalethylene, which are often increased by fork lifts and other ma-chinery (Zagory 1995). Different biological structures of assortedproduce varieties contribute to the products sensitivity responseto ethylene, as well as the response to O2andCO2. Furthermore,different stages of maturity, cultivar and postharvest storage condi-tions also influence sensitivity to ethylene (Lee and others 1995).

Control measures taken to minimize perception and productionof ethylene following harvest include storage in a modified atmo-sphere at optimal low temperatures (just above the chilling orfreezing injury threshold) and oxidizing the ethylene by variouschemical and physical means. Part of the success of MAP, and thequality attributed to MAP products, depends on preventing thedamaging effects of exposure to ethylene. To this end, CO2can in-hibit ethylene action as well as autocatalytic production of ethyl-ene by climacteric products such as apples and tomatoes. How-ever, increased damage to whole leaf plants has been observed atCO2levels above 15-20%, thus reinforcing the importance of de-signing a specific MAP for each product (Lee and others 1995).

Successful control of both product respiration and ethyleneproduction and perception by MAP can result in a fruit or vegeta-ble product of high organoleptic quality; however, control of

these processes is dependent on temperature control. Along thewhole food continuum, that is, processing, storage, transportationand retailing, one needs to maintain optimum temperatures.Maintaining proper storage temperatures is often most difficult atthe retail level, due to the increased handling and the need tomake the product visually appealing. A study by LeBlanc and oth-ers (1996) revealed the extent of temperature abuse of produce inthe retail setting. Of 746 and 745 produce samples examined dur-ing the winter and summer, 87% and 93% of samples, respective-ly, that should have been stored at 4 C (39.2 F), were being heldabove 4 C (39.2 F) and as high as 8.4 C (47.1 F). Furthermore,temperature fluctuations between items stored in different parts ofthe cabinet were observed. The authors stated that MAP products

should probably not be stored with fresh fruit and vegetables. Forsome products, the success and microbiological safety of MAP isdependent on controlled low temperature storage and the prod-ucts characteristics. Many MAP fresh-cut products overtly spoilbefore becoming microbiological safety concerns and thus, therisk factors, that is, outgrowth of pathogens, for both the upperand lower limits of recommended storage temperatures for MAPproduce, should be carefully considered when designing a MAPsystem. Hintlain and Hotchkiss (1987) presented the concept of a

safety index where products that result in an increasing ratio ofspoilage organisms to pathogenic organisms can be consideredless hazardous than products that show a decrease in spoilage or-ganisms with respect to pathogens. This concept could be usedwhen designing MAP systems, with a better understanding of theinteraction between spoilage organisms and fresh-cut produce.State of the art temperature control cabinets are currently beingused at the retail level; however, it is a matter of recovery on in-vested capital and managing the system. Recent advances in thecold-storage industry show promise for improved temperaturecontrol of produce during transport as well as at the retail level.Freshloc Technologies, Inc. recently revealed a state-of-the-art,wireless, Internet-based data collection system for the transporta-tion of temperature sensitive products. This system automaticallymonitors and alerts grocery industry personnel to fluctuations instorage temperature and can be adapted to the grocery, restaurantor transport industry. This system should help in maintaining con-sistent storage temperatures; however, it cannot resolve the prob-lems associated with cabinet design (temperature fluctuations), orthe efforts of grocery personnel to make displays as attractive aspossible, while neglecting recommended storage temperatures.Mild abuse temperatures will not only shorten product shelf life,but will also allow for the more rapid growth of psychrotrophicpathogens in some products.

3. Influence of MAP/CAS on growth and survival oforganisms on produce

3.1. Spoilage organismsThe commonly encountered microflora of fruits and vegetablesare Pseudomonasspp., Erwiniaherbicola, Flavobacterium, Xanth-omonas, Enterobacter agglomerans, lactic acid bacteria such asLeuconostoc mesenteroides and Lactobacillus spp., and moldsand yeasts (Nguyen-the and Carlin 1994; Zagory 1999). Althoughthis microflora is largely responsible for the spoilage of fresh pro-duce, it can vary greatly for each product and storage conditions.Temperature can play a large role in determining the outcome ofthe final microflora found on refrigerated fruits and vegetables,leading to a selection for psychrotrophs and a decrease in thenumber of mesophilic microorganisms. Previous studies haveshown that cabbage (in coleslaw) deteriorated at the same rate at7 C (44.6 F) and 14 C (57.2 F); however, at 7 C (44.6 F), thereduction in the total microbial load was significant (King and oth-

ers 1976). Similar phenomena have been reported for shreddedchicory salads (Nguyen-the and Prunier 1989) and shredded car-rots (Carlin and others 1989), where the total counts of the meso-philic flora decreased with temperature. Low temperature storagenot only decreases the growth rate of foodborne pathogens butalso increases the inhibitory effects of MAP by increasing the sol-ubility of CO2in the liquid phase surrounding a food.

The effect of MAP on lactic acid bacteria can vary dependingon the type of produce packaged. The increased CO2 and de-creased O2 concentrations used in MAP generally favor thegrowth of lactic acid bacteria. This can expedite the spoilage ofproduce sensitive to lactic acid bacteria, such as lettuce, chicoryleaves and carrots (Nguyen-the and Carlin 1994). The effect of


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MAP on yeasts is negligible, however, molds are aerobic microor-ganisms and therefore CO2can cause growth inhibition at con-centrations as low as 10% (Molin 2000), although the effect is notfungicidal (Littlefield and others 1996). Beuchat and Brackett(1990a) examined the effects of cutting, chlorine dip and modifiedatmospheres on the growth of yeasts and molds on lettuce. At10 C (50 F), in both air and a modified atmosphere (3% O2and97% CO2), and with or without chlorine treatment, the organismsgrew slowly regardless of the conditions and at 5 C (41 F), the

growth over a 15-day period was erratic. However, no specific in-hibitory effects of the modified atmosphere were noted.

The concern when using MAP for fruit and vegetables arisesfrom the potential for foodborne pathogens, which may be resis-tant to moderate to high levels of CO2 (50%), to outgrow spoil-age microorganisms, which may be susceptible to the modifiedatmosphere (Bennik and others 1998). The interaction of thepathogenic and resident (saprophytic) microflora has been exten-sively reviewed for meat and milk products; however, data are stillrequired for MAP fruits and vegetables (Nguyen-the and Carlin1994). This interaction of the resident microflora and pathogenicorganisms on MAP produce needs to be studied more extensively(Francis and OBeirne 1998).

3.2. Pathogenic organisms

There are many steps involved along the whole farm to forkproduce chain and, therefore, many points for potential microbialcontamination (NACMCF 1999). Preharvest contamination offresh produce can occur through the use of non-pasteurized ma-nure for fertilization, fecal contamination by indigenous or do-mestic animal species as well as agricultural workers, contaminat-ed irrigation water, and general human handling (see Chapter I).During harvest and postharvest, critical points for contaminationinclude contaminated wash water or ice, human handling, ani-mals, contaminated equipment or transportation vehicles, cross-contamination, and inefficient processing of the product that failsto remove substantial levels of bacteria (NACMCF 1999).

Therefore, MAP produce is vulnerable from a safety standpointbecause modified atmospheres may inhibit organisms that usually

warn consumers of spoilage, while the growth of pathogens maybe encouraged. Also, slow growing pathogens may further in-crease in numbers due to the extension of shelf life. Currently,there is concern with the psychrotrophic foodborne pathogenssuch as L. monocytogenes, Yersinia enterocoliticaand Aeromo-nashydrophila, as well as nonproteolytic C. botulinum,althoughclearly a number of other microorganisms, especially Salmonellaspp., E. coliO157:H7 and Shigellaspp., can be potential healthrisks when present on MAP produce.

3.3. Clostridium botulinum

The spores of C. botulinumare commonly found in agriculturalsoils and on the surfaces of fruits and vegetables. Proteolytic C.botulinumhas difficulty growing and producing toxin at tempera-tures below 12 C (53.6 F), pH below 4.6, a water activity below

0.95 and NaCl concentrations above 10% (Lund and Peck 2000).Nonproteolytic C. botulinum can grow at a minimum of 3 C(37.4 F), pH above 5.0, water activity above 0.97 and NaCl con-centrations above 4%. Therefore, there is some concern about theuse of MAP with respect to this organism (Zagory 1995). Depend-ing on the product in a MA package, the level of O2can decreaserapidly if the product is temperature abused and product respira-tion increases, leaving a highly anaerobic environment ideal forthe growth and toxin production of C. botulinum (Francis andothers 1999). In a study looking at this potential in lettuce, cab-bage, broccoli, carrots, and green beans packaged under vacuumor in air, Larson and others (1997) found that most often the prod-uct was grossly spoiled before significant toxin production was

detected (Table IV-7). The probability of botulinal toxin being pro-duced before the product was obviously spoiled was less than 1in 105in the foods examined using the standard mouse assay fordetection of botulinal toxin. Hao and others (1998) found similarresults for shredded carrots and green beans packaged under 4different films allowing for different oxygen transmission rates.Similar results were obtained by Petran and others (1995) for ro-maine lettuce and shredded cabbage; that is, all toxin-positivesamples were grossly spoiled prior to toxin detection. Larson and

Johnson (1999) obtained the same results in a similar study whenlooking at the incidence of botulinal toxin production on artifi-cially inoculated cantaloupe and honeydew. At abusive tempera-tures, with the exception of UV-treated samples, samples were ob-viously spoiled, although they were also considered marginallyorganoleptically unacceptable when toxin was detected. Thesefindings were supported by the results of Hao and others (1998),which showed that packaged lettuce and cabbage becamespoiled before becoming toxic. The study by Larson and Johnson(1999) demonstrated the ability of the spoilage flora to protectagainst pathogen overgrowth. It is likely, however, that productcharacteristics such as water activity, pH, respiration rate, initialspore levels, and indigenous microflora play a role in the survivaland persistence of the pathogen on MAP produce. For example,in 1987, four circus performers in Sarasota, FL became ill withsymptoms of botulism after consuming coleslaw prepared frompackaged shredded cabbage purchased three weeks earlier inNew Orleans (Solomon and others 1990). Researchers suspectedthat the cabbage had been packaged using MAP and that con-taminated cabbage further contaminated the dressing, leading tothe recovery of C. botulinum type A toxin and spores from thedressing. A follow-up study done to determine the possibility of C.botulinumsurviving on cabbage in MAP was undertaken, and re-sults indicated that only C. botulinumtype A grew and producedtoxin in the modified environment when stored at room tempera-ture (Solomon and others 1990). Two isolates used in the follow-up study were obtained when the outer leaves of 88 cabbageswere surveyed; 12 of them (13.6%) were found to contain toxintype A strains. However, this high incidence of type A spores may

have been due to the origin of this particular product and type ofsoil. For example, Lilly and others (1996) found that only 0.3% (1of 337) of sampled shredded cabbage obtained from retail suppli-ers in the United States contained C. botulinum. However, theproducts tested had all been stored at 4 C (39.2 F), below theminimum for growth of proteolytic C. botulinum.

Growth and toxin production of C. botulinumbefore obviousproduct spoilage has also been observed on Agaricus bisporusmushrooms (Sugiyama and Yang 1975) and potato slices (Dignan1985). As well, Austin and others (1998) performed challengestudies using both nonproteolytic and proteolytic strains of C.botulinumon MAP fresh-cut vegetables and found that samplesof butternut squash (5 C [41 F], 21 days) and onion (25 C [77F], 6 days) appeared organoleptically acceptable when toxin wasdetected. It was also demonstrated that toxin production by C.

botulinumvaried with the vegetables tested. Only nonproteolyticstrains growing on butternut squash were capable of producingneurotoxin at temperatures as low as 5 C (41 F ) in 21 days,whereas proteolytic strains were able to produce toxin on all veg-etables tested (onion, butternut squash, rutabaga, romaine lettuce,stir-fry and mixed salad), except coleslaw at 15 C (59 F). andhigher (Austin and others 1998).

A mixture of proteolytic strains were able to produce botulinumneurotoxin on MAP broccoli, stored at 13 C (55.4 F) and 21 C(69.8 F), however the product was obviously spoiled by the timetoxin was produced (Hao and others 1999). During a study of un-inoculated vacuum packaged minimally processed green bellpeppers, Senesi and others (2000) found that after 7 days at refrig-


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eration temperatures, the environment within the package had be-come anaerobic and high in CO2, stressing the importance ofcareful selection of a MAP film and initial gas atmosphere.

Fresh mushrooms and tomatoes have also been shown to con-tain spores of Clostridiumspp., and therefore the possibility of bot-ulism associated with these MAP products must not be ignored(Zagory 1995). However, it is thought that the acidic nature of toma-toes (pH


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find that at increased CO2levels (20%), the growth of the lactic acidbacteria increased, inhibiting the growth of the pathogen, possiblydue to the production of well-known antilisterial agents.Pseudomonads had no effect on the growth rate of L. monocytoge-nes in this study, although the fluorescent pseudomonads havebeen previously shown to activate the growth of L. monocytogenesin various foods, a phenomenon related to the release of potential

nutrients by the pseudomonads (Liao and Sapers, 1999; Nguy-en-the and Carlin, 1994). Alternatively, Liao and Sapers (1999)

also reported that P. fluorescensstrains inhibited the growth of L.monocytogeneson endive leaves and spinach, possibly due tothe production of a fluorescent siderophore by thepseudomonads. In general, at 3% 9). a level often reached incommercial MAP packages, it appeared that growth of the inocu-lated mixed natural population was decreased, whereas L. mono-cytogenesproliferated.

Reports of L. monocytogenesgrowing on sliced apples in con-trolled atmosphere (Conway and others 1998) and peeled pota-toes in vacuum-packages (Juneja and others 1998) at abusivetemperatures provide further evidence that this organism maypose a safety risk with respect to certain MAP fruit and vegetableproducts, and reiterates the importance of Good Agriculture Prac-tices (GAP), Good Manufacturing Practices (GMP) and HACCP forproduce postharvest handling and processing.

More research needs to be done to examine the influence ofdifferent atmospheres, background microflora and storage tem-peratures on the survival and growth of L. monocytogenes onMAP fresh-cut produce.

3.5.Aeromonas hydrophila

Aeromonasspp. can be found on a wide variety of foods, aswell as in most aquatic environments and most often causes gas-troenteritis, and occasionally septicemia (Kirov 1997). Additionalinformation regarding pathogenesis may be found in Chapter III.Similar to L. monocytogenes, A. hydrophilacan grow at refrigera-tion temperatures, and several studies have shown that growth isnot affected by low O2levels (1.5%) and CO2levels up to 50%(Francis and others 1999). A survey of 97 prepared salads found

A. hydrophila to be present in 21.6% of them, significantly lowerthan in meat products tested (Fricker and Tompsett 1989). Hud-son and De Lacy (1991) also did a small survey of 30 salads andfound A. hydrophila in only one salad package not containingmayonnaise. They surmised that the mayonnaise lowered the pHof the food, thereby inhibiting the growth of or inactivating theaeromonads present. Differences in recovery rates between thestudies of Fricker and Tompsett (1989) and Hudson and De Lacy(1991) may be due to methodology. Fricker and Tompsett (1989)tested three solid media for recovery of Aeromonasspp. and mayhave subsequently achieved better recovery, as compared toHudson and De Lacy (1991) who only used one plating medium.Garcia-Gimeno and others (1996) observed a decline in bacterialnumbers paralleled by a decrease in pH and increase in CO2, forA. hydrophilainoculated vegetable salads stored at 15 C (59 F).

At 4 C (39.2 F), the bacteria survived, but did not grow. The ac-tual significance of finding A. hydrophilaon foods is unclear atthe present time.

Berrang and others (1989b) determined that although at both4 C (39.2 F) and 15 C (59 F), the shelf life of broccoli, aspara-gus and cauliflower was prolonged by MAP (that is, 11-18% 9).3-10% CO2, 97% N2), it did not negatively affect the growth ofresident or inoculated A. hydrophila.Interestingly, the organismwas detected on most lots obtained from the commercial produc-er. Therefore, for storage periods of 8-21 days, depending on theproduct, A. hydrophilaincreased from roughly 104to 108or 109

CFU/g, and product that appeared suitable for consumption washeavily contaminated with the pathogen. As with L. monocytoge-

nes, the CO2levels that were inhibitory to A. hydrophila(that is,>50%) also damaged the product (Bennik and others 1995). Aspreviously discussed, the challenge study performed by Jacxensand others (1999) demonstrated that Aeromonasgrew faster thanL. monocytogeneson minimally processed vegetables in air andMAP and that a decline in the populations of both organisms wasobserved on Brussels sprouts . A recent study has proposed theuse of a Lactobacillus caseiinoculum combined with MAP andchill temperatures to reduce the survival and/or growth of A. hy-

drophilain ready-to-use vegetables such as fresh-cut lettuce (Ves-covo and others 1997). Previous studies have shown that an in-crease in lactic acid bacteria combined with high levels of CO 2(33%) decreases product pH and, therefore, populations of Aero-monas spp. on vegetable salads (Garcia-Gimeno and others1996). However, the increased level of CO2could damage theproduct.

3.6. Other pathogens of concern with respect to MAP

produce

Organisms such as Salmonella, Shigella, E. coli, and various en-teric viruses, such as hepatitis A, have been implicated in produceoutbreaks, and, therefore, there is concern about their behaviorunder modified atmosphere conditions (Zagory 1995; Amanatid-ou and others 1999). A 1986 outbreak of shigellosis was traced

back to commercially distributed MAP shredded lettuce; 347people were affected in two west Texas counties (Davis and others1988). Fernandez-Escartin and others (1989) tested the ability ofthree strains of Shigellato grow on the surface of fresh-cut papa-ya, jicama, and watermelon and reported that populations in-creased significantly when the inoculated product was left atroom temperature for 4 to 6 hours. Shigellais not part of the nor-mal flora associated with produce, but can be passed on as con-taminants by infected food handlers and contaminated manureand irrigation water.

More recently, an outbreak of SalmonellaNewport was reportedin the U.K., associated with the consumption of ready-to-eat saladvegetables (PHLS 2001). To date, nine human cases have been iden-tified with the isolated strain from the implicated salad vegetables

having an identical PFGE pattern to three of the human isolates.In an agar-based study to investigate the effects of high (80-90%) O2and moderate (10-20%) CO2concentrations on food-borne pathogens at 8 C (46.4 F), Amanatidou and others (1999)noted little inhibitory action against a number of pathogens. Allpathogens were able to grow in air; however, S. Typhimuriumgrew slowly, at a rate of 0.011 m/h. Ten to 20% CO2was inhibito-ry to S. Enteritidis; however, S. Typhimurium, L. monocytogenesand nonpathogenic E. coliwere unaffected or stimulated. Onlywhen high O2 (90%) and moderate CO2 levels (10-20%) wereused, did consistently strong inhibition of S. Enteritidis and E. colioccur. Kakiomenou and others (1998) however, found that S. En-teritidis numbers decreased on both carrots and lettuce whenstored under 5% CO2, 5.2% O2and 89.9% N2. Salmonella Typh-imurium and L. monocytogenesactually had an increased growth

rate at these concentrations; growth increased from 0.011 and0.031 m/h to 0.023 and 0.041 m/h for S. Typhimurium and L.monocytogenes,respectively. In general, E. coliO157:H7, S. Ha-dar and S. Typhimurium were only inhibited by CO2levels thatcaused damage and spoilage to the produce (Piagentini and oth-ers 1997; Amanatidou and others 1999; Francis and others1999). A modified atmosphere of 3% O2and 97% N2also hadno significant effect on E. coliO157:H7 inoculated onto shreddedlettuce, sliced cucumber, and shredded carrot and incubated at12 and 21 C (21.6 and 69.8 F) (Abdul-Raouf and others 1993).At 5 C (41 F), populations of viable E. coliO157:H7 declinedon stored vegetables; however, at 12 and 21 C (53.6 and 69.8F), populations increased, demonstrating the importance of re-


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frigeration temperatures in maintaining product safety. Richert andothers (2000) who, although not studying MAP, reported that E.coli O157:H7 could survive on produce (broccoli, cucumbersand green peppers) stored at 4 C (39.2 F) and proliferate rapidlywhen stored at 15 C (59 F). In 1993, there were two foodborneoutbreaks of enterotoxigenic E. coli(ETEC) linked to carrots in atabouleh salad served in New Hampshire and to an airline saladon a flight from North Carolina to Rhode Island (CDC 1994). Al-though these carrots were of U.S. origin, ETEC is a common cause

of diarrheal illness in Mexico and developing countries that im-port fresh product to North America. Research on the behavior ofthis pathogen on fresh and fresh-cut product, both under MAPand without MAP, seems warranted.

Information on the survival of the enteric pathogens Y. entero-coliticaand Campylobacterspp.on MAP produce is extremelylimited, and mainly consists of data involving meat products.These organisms can be recovered from animal reservoirs as wellas water sources and theoretically, produce may occasionally be-come contaminated by the application of natural fertilizers, ma-nure, by wild animal feces, or by contaminated surface or irriga-tion water (Barton and others 1997; Wallace 1997). There is someevidence that mushrooms may be a source of Campylobacter je-

juni; it was isolated from 1.5% of retail, polyvinyl chloride film-wrapped, and fresh mushrooms in 1984 (Doyle and Schoeni1986). It has been suggested that the mushrooms may becomecontaminated by harvesters. Two separate studies looking at storebought lettuce (Park and Sanders 1992; Little and others 1999) aswell as spinach, radish, green onions, parsley and potatoes (Parkand Sanders 1992) did not find any evidence of Campylobacterspp., indicating that there may be minimal risk, regardless of thepackaging technology used. Interestingly, Park and Sanders (1992)found evidence of gross contamination by Campylobacterspp. ofproduce at farmersmarkets, suggesting that industrial processingmay be effective in removing certain pathogens from fresh producebefore retail sale. Alternately, contamination may have occurred atthe market. A Canadian study detected no Campylobacterin any of65 unprocessed or 296 fresh-cut and packaged ready-to-use vege-tables such as lettuce, carrot, cauliflower, celery, broccoli, or sliced

green peppers (Odomeru and others 1997). A more recent study,investigating the survival of C. jejunion MAP fresh-cut cilantro andlettuce, found that refrigeration temperatures in combination with amodified atmosphere of 2% O2, 18% CO2and 80% N2can be fa-vorable for bacteria (Tran and others 2000). Due to the microaero-philic nature of Campylobacterspp., which require 5% O2, 10%CO2and 85% N2for optimal growth, the investigators suspectedthat a low O2modified atmosphere may provide an environmentconducive to survival of the pathogen. Campylobacter jejuni(initiallevel 106CFU/g) was able to survive on cilantro, green pepper, andromaine lettuce packaged under normal air, modified atmosphere,and vacuum, for 15 days of storage at 4 C (39.2 F). After 9 days ofstorage at 4 C (39.2 F) C. jejunilevels decreased to approximately104CFU/g on all three vegetables stored under the modified atmo-sphere. In contrast, C. jejunidecreased to levels of approximately

102and 103CFU/g for all vegetables packaged under normal airand vacuum, respectively.

Studies to determine the behavior of Y. entercoliticaon MAPproduce have not been published, however data obtained withmeat products indicate that 40-50% CO2has minimal inhibitoryeffects on its growth (Francis and others 1999).

Enteric viruses such as Norwalk and hepatitis A (HAV) are oftenthe cause of very large foodborne outbreaks, yet none have beenlinked specifically to MAP produce, and only HAV has beenlinked to outbreaks involving fresh produce (Beuchat 1996). Of14 reports of viral gastroenteritis cited by Hedberg and Oster-holm, salad was implicated as the vehicle in 36% (Beuchat 1996).One of the HAV outbreaks was linked to the consumption of

commercially distributed lettuce that was washed, sliced andbagged before being distributed to restaurants in Kentucky(Rosenblum and others 1990). A total of 202 people were affect-ed, and the investigation suggested that contamination occurredbefore distribution to the restaurants. Most often these viruses aretransmitted by an infected food handler, through the fecal-oralroute. In a survival study, lettuce inoculated with HAV was storedin normal air as well as various MAP conditions at both 4 C(39.2 F) and room temperature (Bidawid and others 2001). The

highest rate of virus survival on washed lettuce stored at 4 C(39.2 F) for 12 days, was observed for product stored under 70%CO2:30% N2and 100% CO2, (that is, 83.6 and 71.6%, respec-tively). Virus survival was significantly lower at room temperature,which was decreased slightly by the addition of CO2(that is, >70%), and the lowest virus survival rate (47.5%) was on lettucestored in a petri dish under air. It should be noted that these CO 2concentrations would be harmful to the product and are not usedin retail. These results are consistent with those of Bagdasaryan(1964), who studied the survival of enteroviruses on radishes, to-matoes, and lettuce stored at 6 to 10 C (42.8-50 F) for periodsexceeding the normal shelf life of these products, as well as withthose of Badawy and others (1985), who studied the survival ofrotavirus on lettuce, radishes, and carrots stored at 4 C (39.2 F)and room temperature. In all these studies, the greatest survivalrates were observed at refrigeration temperatures. Studies to deter-mine the role of the competitive bacterial microflora on virus sur-vival may be beneficial.

The protozoan parasites Cyclosporacayatenensis,Cryptospo-ridium parvum and Giardia lamblia have been the etiologicagents in serious foodborne outbreaks involving berries (Herwaldt2000), apple cider (Millard and others 1994; CDC 1997), and rawsliced vegetables (Mintz and others 1993), respectively. The be-havior of these organisms under MAP is not known. However, theincrease in incidence of produce-linked outbreaks due to theseorganisms indicates that research in this area is necessary. Re-search is needed to examine the behavior of both foodborne vi-ruses and protozoan parasites on MAP produce.

To date, only two MAP produce products, coleslaw mix (So-

lomon and others 1990) and ready-to- eat salad vegetables (PHLS2001), have been implicated in foodborne illness outbreaks ofbotulism and SalmonellaNewport, respectively. As well, althoughit is unclear how the product was packaged, commercially distrib-uted shredded lettuce caused an outbreak of shigellosis in theUnited States in 1986 (Davis and others 1988). There has been anoticeable increase in the consumption of fresh fruit and vegeta-bles in the last two decades, and more consumers are choosingthe less labor-intensive fresh-cut produce. There has been a paral-lel rise in the number of produce linked foodborne outbreaks, butnot linked to fresh-cut produce packaged under MAP. However,vigilance with respect to the safety of these products must bemaintained.

4. Conclusions Oxygen, CO2, and N2, are most often used in MAP/CAS.

Among them, CO2is the only one with a direct antimicrobial ef-fect, resulting in an increased lag phase and generation time dur-ing the logarithmic phase of growth. Although other gases such asnitrous and nitric oxides, sulphur dioxide, ethylene, chlorine, aswell as ozone and propylene oxide have been investigated, theyhave not been applied commercially due to safety, regulatory, andcost considerations.

The recommended percentage of O2 in a modified atmo-sphere for fruits and vegetables for both safety and quality falls be-tween 1 and 5%, although the oxygen level will realistically reachlevels below 1% in MAP produce.


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The concern when using MAP for fruit and vegetables arisesfrom the potential for foodborne pathogens, which may be resis-tant to moderate to high levels of CO2 (< 50%), to outgrow spoil-age microorganisms, which may be susceptible to the modifiedatmosphere.

It is generally believed that with the use of permeable films,spoilage will occur before toxin production is an issue; MAP ofproduce, however, should always incorporate packaging materi-als that will not lead to an anoxic package environment when the

product is stored at the intended temperature. The background microflora is largely responsible for the

spoilage of fresh produce and can vary greatly for each productand storage conditions. The elimination or significant inhibition ofspoilage organisms should not be practiced, as their interactionwith pathogens may play an integral role in product safety.

Edible films for use in MAP systems is an active area of re-search. However, as with other MAP, they can create a very lowO2environment where anaerobic pathogens such as C. botuli-nummay thrive. Antimicrobial compounds that can be incorpo-rated into the coating are also being currently investigated.

There have been many studies investigating the migration ofantimicrobials such as sodium benzoate, benzoic acid, propionicacid, and potassium sorbate from coatings into food. It appearsthat the most advantageous use of these films for antimicrobialproperties would be the formation of a monolayer lipid and sor-bic acid film, or a bilayer film composed of a hydrophilic baselayer coated with a thin layer of lipid containing sorbic acid. Themain issue involves the production of coatings with good surfacetension that will stick to produce.

Successful control of both product respiration and ethyleneproduction and perception by MAP can result in a fruit or vegeta-ble product of high organoleptic quality; however, control ofthese processes is dependent on temperature control. Along thewhole food continuum, that is, processing, storage, transportationand retailing, one needs to maintain optimum temperatures.Maintaining proper storage temperatures is often most difficult atretail level.

Currently, there is concern with psychrotrophic foodborne

pathogens such as L. monocytogenes, Y. enterocoliticaand A.hy-drophila, as well as nonproteolytic C. botulinum,although clearlya number of other microorganisms, especially Salmonellaspp., E.coli O157:H7 and Shigella spp., can be potential health riskswhen present on MAP produce.

The success and microbiological safety of MAP is dependenton controlled low temperature storage and the products charac-teristics.

Only two MAP produce products, coleslaw mix and ready-to-eat salad vegetables, have been implicated in foodborne illnessoutbreaks of botulism and SalmonellaNewport, respectively.

5. Research Needs

Investigate the antimicrobial effect of superatmospheric O2inthe fresh-cut produce safety.

Study the interactions of the background microflora withfoodborne pathogens in various modified atmospheres used forproduce, as well as the effects of different gaseous environmentson the survival and growth of bacterial foodborne pathogens onwhole and fresh-cut produce.

Examine the potential for growth of C. botulinumin a widevariety of modified atmosphere packaging (MAP) produce storedat mildly abusive temperatures such as 7-12 C. In addition, otherhurdles besides temperature need to be examined to prevent bot-ulinum toxin production.

Examine the influence of different atmospheres, backgroundmicroflora, and storage temperatures on the survival and growth

of L. monocytogeneson MAP fresh-cut produce. Investigate the behavior of verotoxin-producing E. coli on

fresh and fresh-cut product, both under MAP and without MAP. Explore the survival of the enteric pathogens Y. enterocolitica

and Campylobacterspp.and the behavior of foodborne virusesand protozoan parasites on MAP produce.

Hurdle technology or the combination of novel methods offood treatment and packaging need to be exa

atmosfera modificada artigo (2)

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