active pack

408 JOURNAL OF FOOD SCIENCE—Vol. 68, Nr. 2, 2003

Concise Reviews in Food Science

© 2003 Institute of Food TechnologistsFurther reproduction prohibited without permission

JFS: Concise Reviews and Hypotheses in Food Science

Active Packaging Technologieswith an Emphasis on AntimicrobialPackaging and its ApplicationsP. SUPPAKUL, J. MILTZ, K. SONNEVELD, AND S.W. BIGGER

ABSTRACT: In response to the dynamic changes in current consumer demand and market trends, the area ofActive Packaging (AP) is becoming increasingly significant. Principal AP systems include those that involveoxygen scavenging, moisture absorption and control, carbon dioxide and ethanol generation, and antimicrobial(AM) migrating and nonmigrating systems. Of these active packaging systems, the AM version is of great impor-tance. This article reviews: (1) the different categories of AP concepts with particular regard to the activity of AMpackaging and its effects on food products, (2) the development of AM and AP materials, and (3) the current andfuture applications of AM packaging.

Keywords: active packaging, antimicrobial packaging, antimicrobial additives

Introduction

IN RECENT YEARS, THE MAJOR DRIVING FORCES

for innovation in food packaging tech-nology have been the increase in consumerdemand for minimally processed foods,the change in retail and distribution prac-tices associated with globalization, newconsumer product logistics, new distribu-tion trends (such as Internet shopping),automatic handling systems at distributioncenters, and stricter requirements regard-ing consumer health and safety (Vermeir-en and others 1999; Sonneveld 2000). Ac-tive Packaging (AP) technologies are beingdeveloped as a result of these driving forc-es. Active Packaging is an innovative con-cept that can be defined as a mode ofpackaging in which the package, the prod-uct, and the environment interact to pro-long shelf life or enhance safety or sensoryproperties, while maintaining the qualityof the product. This is particularly impor-tant in the area of fresh and extendedshelf-life foods as originally described byLabuza and Breene (1989). Flores and oth-ers (1997) reviewed the products and pat-ents in the area of AP and identified anti-microbial (AM) packaging as one of themost promising versions of an AP system.Han (2000) and Vermeiren and others(2002) recently published articles focusedon AM systems, but without a detailed dis-cussion of some of the principal AP con-cepts. The present article reviews the gen-eral principles of AP and AM packagingconcepts including oxygen scavenging,moisture absorption and control, carbon

dioxide and ethanol generation, and it re-views in detail AM migrating and nonmi-grating systems.

Oxygen Scavenging Systems

THE PRESENCE OF O2 IN A PACKAGED FOOD

is often a key factor that limits the shelflife of a product. Oxidation can cause chang-es in flavor, color, and odor, as well as destroynutrients and facilitate the growth of aerobicbacteria, molds, and insects. Therefore, theremoval of O2 from the package headspaceand from the solution in liquid foods andbeverages, has long been a target of thefood-packaging scientists. The deteriorationin quality of O2-sensitive products can beminimized by recourse to O2 scavengersthat remove the residual O2 after packing.Existing O2 scavenging technologies arebased on oxidation of 1 or more of the follow-ing substances: iron powder, ascorbic acid,photo-sensitive dyes, enzymes (such as glu-cose oxidase and ethanol oxidase), unsatur-ated fatty acids (such as oleic, linoleic andlinolenic acids), rice extract, or immobilizedyeast on a solid substrate (Floros and others1997). These materials are normally con-tained in a sachet. Details on O2 scavengingcan be obtained from other reviews (Labu-za and Breen 1989; Miltz and others 1995;Miltz and Perry 2000; Floros and others1997; Vermeiren and others 1999).

Oxygen scavenging is an effective way toprevent growth of aerobic bacteria andmolds in dairy and bakery products. Oxygenconcentrations of 0.1% v/v or less in theheadspace are required for this purpose

(Rooney 1995). Packaging of crusty rolls in acombination of CO2 and N2 (60% CO2) hasshown to be an effective measure againstmold growth for 16 to 18 d at ambient tem-perature. However, the study also revealedthat such an “anaerobic environment” is nottotally effective without the incorporation ofan oxygen scavenger into the package toensure that the headspace O2 concentrationnever exceeds 0.05%. Under such condi-tions the rolls remain mold-free even after60 d (Smith and others 1986).

Many researchers have expressed con-cern about the safety of Modified Atmo-sphere Packaged (MAP) foods, especiallywith respect to the growth of psychrotrophicpathogens such as Listeria monocytogenesand anaerobic pathogens such as Clostridi-um botulinum (Farber 1991). Lyver and oth-ers (1998) monitored the physical, chemical,microbiological, textural, and sensorychanges in surimi nuggets inoculated withL. monocytogenes, packaged in either air or100% CO2 with and without an oxygen scav-enger and stored at 4 °C and 12 °C. Theyfound that MAP was not effective in con-trolling the growth of the pathogen in eitherraw or cooked nuggets and also that thepathogen overcame competitive inhibitionand pH reduction caused by lactic acid bac-teria. They concluded that nuggets pack-aged under these conditions and contami-nated with this pathogen could pose a riskto the consumer. More importantly, it wasfound that the product retained acceptableodor and appearance scores at the abovestorage temperatures, even though the lev-

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iencePackaging technologies . . .

el of the pathogen increased over the stor-age period. The latter is indeed a cause forconcern, since the contaminated productmay appear safe from the sensory point ofview (Lyver and others 1998).

Oxygen scavenging is advantageous forproducts that are sensitive to O2 and light.One important advantage of AP over MAP isthat the capital investment involved is sub-stantially lower; in some instances, only thesealing of the system that contains the oxy-gen absorbing sachet is required. This is ofextreme importance to small- and medium-sized food companies for which the packag-ing equipment is often the most expensiveitem (Ahvenainen and Hurme 1997).

An alternative to sachets involves the in-corporation of the O2 scavenger into thepackaging structure itself. This minimizesnegative consumer responses and offers apotential economic advantage through in-creased outputs. It also eliminates the riskof accidental rupture of the sachets and in-advertent consumption of their contents. Asummary of available O2 scavengers is givenin Table 1.

Since the share of polymers in primarypackages for foods and beverages increasesconstantly, they have become the mediumfor incorporation of active substances suchas antioxidants, O2 scavengers, flavor com-pounds, pigments, enzymes, and AMagents (Hotchkiss 1997). BP Amoco Chem-ical (U.S.A) is marketing Amosorb® 2000and 3000, which are polymer-concentratescontaining iron-based O2 scavengers. Thesecan be used in polyolefins and in certainpolyester packaging applications for wines,beers, sauces, juices, and other beverages.Other recent developments includeOS2000TM developed by Cryovac Div.,Sealed Air Corporation, U.S.A. (Butler 2002)and ZERO2™ developed by CSIRO, Div. ofFood Science Australia, in collaboration withSouthcorp Packaging (now VisyPak), Austra-lia (Brody and others 2001). Both of the latterare organic-based, UV light-activated O2

scavengers that can be tailored to allowthem to be bound into various layers of awide range of packaging structures. OxbarTM

is a system developed by Carnaud-MetalBox (now Crown Cork and Seal) that involvescobalt-catalyzed oxidation of a MXD6 nylonthat is blended into another polymer. Thissystem is used especially in the manufac-turing of rigid PET bottles for packaging ofwine, beer, flavored alcoholic beverages,and malt-based drinks (Brody and others2001).

Another O2 scavenging technology in-volves using directly the closure lining. Dar-ex® Container Products (now a unit of GracePerformance Chemicals) has announced an

ethylene vinyl alcohol with a proprietaryoxygen scavenger developed in conjunctionwith Kararay Co. Ltd. In dry forms, pelletscontaining unsaturated hydrocarbon poly-mers with a cobalt catalyst are used as oxy-gen scavengers in mechanical closures, plas-tic and metal caps, and steel crowns (bothPVC and non-PVC lined). They reportedlycan prolong the shelf life of beer by 25%(Brody and others 2001).

Oxygen scavengers have opened newhorizons and opportunities in preservingthe quality and extending the shelf life offoodstuffs. However, much more informa-tion is needed on the action of O2 scaven-gers in different environments before opti-mal, safe, and cost-effective packages canbe designed. The need for such informa-tion is especially acute on O2 scavengingfilms, labels, sheets, and trays that havebegun to appear in recent years (Miltz andothers 1995; Miltz and Perry 2000).

Moisture-Absorbing andControlling Systems

IN SOLID FOODS, A CERTAIN AMOUNT OF MOIS-ture may be trapped during packaging or

may develop inside the package due to gen-eration or permeation. Unless it is eliminat-ed, it may form a condensate with the atten-dant spoilage and/or low consumer appeal.Moisture problems may arise in a variety ofcircumstances, including respiration in hor-ticultural produce, melting of ice, tempera-ture fluctuations in food packs with a highequilibrium relative humidity (ERH), or dripof tissue fluid from cut meats and produce(Rooney 1995). Their minimization via pack-aging can be achieved either by liquid waterabsorption or humidity buffering.

Liquid water absorptionThe main purpose of liquid water control

is to lower the water activity, aw, of the prod-uct, thereby suppressing the growth of mi-croorganisms on the foodstuff (Vermeirenand others 1999). Temperature cycling ofhigh aw foods has led to the use of plasticswith an antifog additive that lowers the in-terfacial tension between the condensateand the film. This contributes to the trans-parency of the films and enables the cus-tomer to see clearly the packaged food(Rooney 1995) although it does not affectthe amount of liquid water present insidethe package.

Several companies manufacture drip-absorbent sheets such as Thermarite® orPeaksorb® (Australia), or ToppanTM (Japan)for liquid water control in high aw foods suchas meat, fish, poultry and fresh produce.Basically, these systems consist of a super-absorbent polymer located between 2 lay-

ers of a micro-porous or nonwoven polymer.Such sheets are used as drip-absorbing padsplaced under whole chickens or chickencuts. Large sheets are also utilized for ab-sorption of melted ice during air transporta-tion of packaged seafood. The preferredpolymers used for this purpose are polyacry-late salts and graft copolymers of starch(Rooney 1995).

Humidity bufferingThis approach involves interception of

moisture in the vapor phase by reducing thein-pack relative humidity and thereby thesurface-water content of the food. It can beachieved by means of 1 or more humec-tants between 2 layers of a plastic film thatis highly permeable to water vapor or by amoisture-absorbing sachet. An example ofthis approach is the PichitTM film manufac-tured by Showa Denko (Japan). It is mar-keted in Japan for wrapping fish and chick-en and reduces the ERH in the vicinity ofthe product, but has not been evaluatedexperimentally. Pouches containing NaClhave also been used in the US tomato mar-ket (Rooney 1995).

Desiccants have been successfully usedfor moisture control in a wide range of foods,such as cheeses, meats, chips, nuts, pop-corn, candies, gums and spices. Silica gel,molecular sieves, calcium oxide (CaO) andnatural clays (such as montmorillonite) areoften provided in TyvekTM sachets (Brodyand others 2001). Other desiccant systemsinclude the MiniPax® and StripPax® pack-ets, the DesiMax® (United Desiccants,U.S.A.) and the DesiPak®, Sorb-it®, Tri-sorb® and 2-in-1TM sachets (Multisorb Tech-nologies Inc., U.S.A.).

Carbon Dioxide GeneratingSystems

CARBON DIOXIDE IS KNOWN TO SUPPRESS

microbial activity. Relatively high CO2

levels (60 to 80%) inhibit microbial growth onsurfaces and, in turn, prolong shelf life.Therefore, a complementary approach to O2

scavenging is the impregnation of a packag-ing structure with a CO2 generating systemor the addition of the latter in the form of asachet. Table 2 lists the main commercialCO2 generators. Since the permeability ofCO2 is 3 to 5 times higher than that of O2 inmost plastic films, it must be continuouslyproduced to maintain the desired concen-tration within the package. High CO2 levelsmay, however, cause changes in taste ofproducts and the development of undesir-able anaerobic glycosis in fruits. Conse-quently, a CO2 generator is only useful incertain applications such as fresh meat,poultry, fish and cheese packaging (Floros



Packaging technologies . . .

and others 1997). In food products for whichthe volume of the package and its appear-ance are critical, an O2 scavenger and CO2

generator could be used together (Smithand others 1995) in order to prevent pack-age collapse as a result of O2 absorption.

Nakamura and Hoshino (1983) reportedthat an oxygen-free environment alone isinsufficient to retard the growth of Staphy-lococcus aureus, Vibrio species, Escherichiacoli, Bacillus cereus and Enterococcus faecalisat ambient temperatures. For complete in-hibition of these microorganisms in foods,the authors recommended a combinedtreatment involving O2 scavenging withthermal processing, or storage under refrig-eration, or using a CO2 enriched atmo-sphere. They found that an O2 and CO2 ab-sorber inhibited the growth of Clostridium

sporogenes while an O2 absorber and a CO2

generator enhanced the growth of this mi-croorganism, which is quite a surprising re-sult. This result indicates the importance ofselecting the correct scavenger to control thegrowth of Clostridium species in MAP foods.

Ethanol Generating Systems

ETHANOL IS USED ROUTINELY IN MEDICAL

and pharmaceutical packaging applica-tions, indicating its potential as a vaporphase inhibitor (Smith and others 1987). Itprevents microbial spoilage of intermediatemoisture foods (IMFs), cheeses, and bakeryproducts. It also reduces the rate of stalingand oxidative changes (Seiler 1989). Ethanolhas been shown to extend the shelf life ofbread, cake and pizza when sprayed ontoproduct surfaces prior to packaging. Sa-

Table 1—Overview of commercial oxygen scavengers

Format Trade Name Manufacturer References

Card Ageless® Mitsubishi Gas Chemical Co. (Japan)Closure Liner Darex® Grace Performance Chemicals (U.S.A.) Teumac (1995), Brody and others (2001)

PureSeal® Advanced Oxygen Technologies Inc. (U.S.A.) Teumac (1995)Smartcap® Advanced Oxygen Technologies Inc. (U.S.A.) Teumac (1995)

Concentrate Amosorb®‚ 2000, 3000 BP Amoco Chemical (U.S.A.)Oxbar™ Crown Cork and Seal (U.S.A.) Brody and others (2001)Oxyguard™ Toyo Seikan Kaisha (Japan)Oxysorb® Pillsbery Co (U.S.A.)

Film Bioka® Bioka Ltd (Finland)OS2000® Sealed Air Corporation (U.S.A.) Butler (2002)ZERO2™ CSIRO and VisyPak (Australia) Brody and others (2001)

Label Ageless® Mitsubishi Gas Chemical Co. (Japan)ATCO® Standa Industrie (France)FreshMax® Multisorb Technologies Inc. (U.S.A.)

Sachet Ageless® Mitsubishi Gas Chemical Co. (Japan) Nakamura and Hoshino (1983), Smith andothers (1995), Lyver and others (1998)

ATCO® Standa Industrie (France) Hurme and Ahvenainen (1996)Bioka® Bioka Ltd (Finland) Ahvenainen and Hurme (1997)Freshilizer® Toppan Printing Co. (Japan) Smith and others (1995)FreshPax® Multisorb Technologies Inc (U.S.A.) Smith and others (1995)KeplonTM Keplon Co. (Japan) Brody and others (2001)ModulanTM Nippon Kayaku Co. (Japan) Brody and others (2001)Negamold®1 Freund Industrial Co. (Japan) Smith and others (1995)OxyeaterTM Ueno Seiyaku Co. (Japan) Brody and others (2001)Oxysorb® Pillsbury Co. (U.S.A.)Sanso-cut® Finetech Co. (Japan) Hurme and Ahvenainen (1996)SansolessTM Hakuyo Co. (Japan) Brody and others (2001)Secule® Nippon Soda Co. (Japan) Brody and others (2001)Sequl® Dai Nippon Co. (Japan) Brody and others (2001)TamotsuTM Oji Kako Co. (Japan) Brody and others (2001)Vitalon®2 Toagosei Chemical Co. (Japan) Hurme and Ahvenainen (1996)

Thermoformed Tray Oxycap® Standa Industrie (France)1Combined actions between O2 scavenging and ethanol generation2Combined actions between O2 scavenging and CO2 generation

Table 2—Commercial carbon dioxide generators

Trade Name Manufacturer References

Ageless® G1 Mitsubishi Gas Chemical Co. (Japan) Nakamura and Hoshino (1983), Smith and others (1995)Freshilizer® C1 and CW1 Toppan Printing Co. (Japan) Smith and others (1995)FreshPax® M1 Multisorb Technologies Inc. (U.S.A.)Vitalon® G1 Toagosei Chemical Co. (Japan) Vermeiren and others (1999)Verifrais® SARL Codimer (France) Vermeiren and others (1999)1Combined actions between CO2 generating and O2 scavenging

chets containing encapsulated ethanol re-lease its vapor into the packaging head-space thus maintaining the preservativeeffect (Labuza and Breene 1989).

Many applications of ethanol-generatingfilms or sachets have been patented (Florosand others 1997) and marketed (Smith andothers 1995), including an adhesive-backedfilm that can be taped on the inside of apackage to provide AM activity (Labuza andBreene 1989). Mitsubishi Gas Chemical Co.patented a sachet containing encapsulatedethanol, glucose, ascorbic acid, a phenoliccompound and an iron salt (Floros and oth-ers 1997), thereby achieving the combinedeffect of O2 scavenging and ethanol gener-ation. Table 3 lists examples of commercialethanol generators.

An ethanol-generating technology was


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originally developed in Japan wherebyfoodgrade ethanol is encapsulated in a fineinert powder inside a sachet. The rate of eth-anol vapor release can be tailored by con-trolling the permeability of the sachet. Sev-eral Japanese companies manufacture thistype of ethanol generator, the most widelyused being Ethicap® or Antimold Mild® pro-duced by the Freund Industrial Co. (Smithand others 1995). These systems, approvedfor use in Japan, extend the mold-free shelflife of various bakery products.

Smith and others (1987) demonstratedthe usefulness of ethanol vapor in extend-ing the shelf life of apple turnovers. Theshelf life was found to be 14 d for the prod-uct packaged in air or in a CO2/N2 gas mix-ture (60% CO2) and stored at ambient tem-perature. Afterwards, visible swellingoccurred as a result of Saccharomyces cerevi-siae growth and additional CO2 production.When encapsulated ethanol was incorpo-rated in the package, yeast growth was total-ly suppressed and the shelf life was ex-tended to 21 days. On the other hand, thissolution caused the packages to contain1.5% ethanol at the end of the storage peri-od as compared to only 0.2% when packedwithout ethanol. Consequently, the finalproducts may be unacceptable to the con-sumer due to elevated ethanol contents.This problem can be partially resolved byheating the contents of the package prior toconsumption, thereby evaporating the eth-anol.

Antimicrobial Migrating andNonmigrating Systems

ANTIMICROBIAL FOOD PACKAGING MATER-ials have to extend the lag phase and

reduce the growth rate of microorganisms inorder to extend shelf life and to maintainproduct quality and safety (Han 2000). Al-ternatives to direct additives for minimizingthe microbial load are canning, aseptic pro-cessing and MAP. However, canned foodscannot be marketed as “fresh”. Aseptic pro-cessing may be expensive and hydrogenperoxide, which is restricted in level by reg-ulatory agencies, is often used as a steriliz-ing agent. In certain cases, MAP can pro-mote the growth of pathogenic anaerobesand the germination of spores, or preventthe growth of spoilage organisms which in-dicate the presence of pathogens (Farber1991). If packaging materials have self-ster-ilizing abilities due to their own AM effec-tiveness, the need for chemical sterilizationof the packages may be obviated and theaseptic packaging process simplified(Hotchkiss 1997).

Food packages can be made AM active byincorporation and immobilization of AM

agents or by surface modification and sur-face coating. Present plans envisage the pos-sible use of naturally derived AM agents inpackaging systems for a variety of processedmeats, cheeses, and other foods, especiallythose with relatively smooth product surfac-es that come in contact with the inner sur-face of the package. This solution is becom-ing increasingly important, as it represents aperceived lower risk to the consumer(Nicholson 1998). Table 4 lists a number ofsubstances, which can be bound to polymersto impart AM properties. Such substancescan be used in AM films, containers andutensils (Ishitani 1995). Antimicrobial mate-rials have been known for many years. How-ever, antimicrobial packages have had rela-tively few commercial successes, except inJapan. Table 5 (Brody and others 2001) sum-marizes some of the antimicrobial systems.Antimicrobial films can be classified in 2types: (1) those that contain an AM agentthat migrates to the surface of the food, and(2) those that are effective against surfacegrowth of microorganisms without migration.

Gas emission or flushingGas emission or flushing controls the

growth of mold. Typical spoilage molds in-clude Botrytis cinerea, Penicillium, Aspergil-lus and Rhizopus species commonly found incitrus and berry fruits. To extend the storageperiod of these fruits, fungicides or antimy-cotic agents can be applied.

Sulfur dioxide (SO2) is known to be themost effective material in controlling thedecay of grapes and is superior to the gam-ma irradiation and heat-radiation combina-tion methods (Smilanick 1990). However, aSO2-releasing material entails a number ofproblems, including bleaching and SO2 res-idues.

Thomas and others (1995) studied theeffect of SO2 generating pads on the decayand quality of table grapes. In Australia, 2different SO2 release sheets were tested forpackaging of the white “Thompson Seed-less” and the purple “Red Globe” grapes(Christie and others1997). SO2 in the sur-rounding air is absorbed into the grapes andinitially converted to sulfite and then me-

Table 3—Commercial ethanol generators

Trade name Manufacturer Reference

Ethicap® Freund Industrial Co. (Japan) Smith and others (1995)Negamold®1 Freund Industrial Co. (Japan) Smith and others (1995)Oitech™ Nippon Kayaku Co. (Japan) Smith and others (1995)ET Pack Ueno Seiyaku Co. (Japan) Smith and others (1995)Ageless® SE1 Mitsubishi Gas Chemical Co. (Japan) Floros and others (1997)Fretek® Techno Intl. Inc. (U.S.A.)2 Brody and others (2001)1Combined actions between ethanol-generating and O2 scavenging2Under license from Freund Industrial Co (Japan)

tabolized into the sulfate form. At the end ofthe experiment (after 4 d at 21 °C), the sulfitelevels in the “Red Globe” were found to belower than those in the “Thompson Seed-less”, even though the former was subjectedto a higher SO2 level. This reflects the differ-ent metabolic rates of the 2 varieties(Christie and others 1997). The authors sug-gested development of a controlled releasepolymer that would apply the fungicide at asufficient level to retain satisfactory fungi-static action, while minimizing undesirableeffects.

Opperman and others (1999) consideredcontrolling the decay of table grapes withmonolithic-type polymer structures that re-lease SO2 at a constant rate over an extend-ed period. Two different systems containingeither 2 or 4 SO2-containing polymer discswere tested. In the 4-disc system, a disc wasplaced in the corner of each carton boxwhereas in the 2-disc system they wereplaced in a central location, approximately10 cm from the edges of the carton. In 50%of the monolithic device treatments, thediscs were placed directly on top of thegrapes, while in the other treatments, theywere placed on top of a corrugated paper lin-er. It was found that the liner acted as aphysical barrier between the grapes and theSO2 generator and that the carton absorbedmuch of the free SO2. The controlling effectwas vastly improved by raising the level ofsodium metabisulfite (Na2S2O5) impregnat-ed in the polymer structure, but the prod-uct suffered from SO2 damage. The opti-mum range for the Na2S2O5 concentrationwas found to be 10 to 20% w/w.

Another volatile compound exhibitingAM effects is allyl isothiocyanate (AIT), themajor pungent component of black mus-tard (Brassica nigra), brown mustard (Bras-sica juncea) and wasabi (Eutrema wasabiMaxim.). Isshiki and others (1992) com-pared the minimum inhibitory concentra-tion (MIC) of AIT vapor against microor-ganisms on agar. In the experiments, amixture (500 mg) of AIT and beef fat (2:98,w/w) was placed on top of a perforated cel-lophane film, and packed in the bag withthe sample food. It was claimed that at such




Table 4—Examples of antimicrobial agents for potential use in food packaging materials

Class Examples References

Acid Anhydride Benzoic anhydride Weng and Hotchkiss (1993), Huang and others (1997), Dobiasand others (2000)

Sorbic anhydride Weng and Chen (1997)

Alcohol Ethanol Luck and Jager (1997)

Amine Hexamethylenetetramine (HMT) Luck and Jager (1997), Devlieghere and others (2000b)

Ammonium Compound Silicon quaternary ammonium salt

Antibiotic Natamycin Luck and Jager (1997)

Antimicrobial Attacin Dillon (1994) Peptide Cecropin Dillon (1994)

Defensin Dillon (1994)Magainin Abler and others (1995)

Antioxidant Butylated hydroxyanisole (BHA) Hotchkiss (1997) Phenolic1 Butylated hydroxytoluene (BHT) Hotchkiss (1997)

Tertiary butylhydroquinone (TBHQ) Hotchkiss (1997)

Bacteriocin Bavaricin Nettles and Barefoot (1993)Brevicin Nettles and Barefoot (1993)Carnocin Nettles and Barefoot (1993)Lacticin Nettles and Barefoot (1993), An and others (2000), Scannell

and others (2000)Mesenterocin Nettles and Barefoot (1993)Nisin Luck and Jager (1997), An and others (2000), Natrajan and Sheldon

(2000a, b), Scannell and others (2000)Pediocin Barnby-Smith (1992), Nettles and Barefoot (1993)Sakacin Nettles and Barefoot (1993)Subtilin Barnby-Smith (1992)

Chelator Citrate Hotchkiss (1997)Conalbumin Conner (1993)EDTA Luck and Jager (1997), Rodrigues and Han (2000)Lactoferrin Conner (1993)Polyphosphate Shelef and Seiter (1993)

Enzyme Chitinase Fuglsang and others (1995)Ethanol oxidase Fuglsang and others (1995)�-Glucanase Fuglsang and others (1995)Glucose oxidase Fuglsang and others (1995)Lactoperoxidase Conner (1993), Fuglsang and others (1995)Lysozyme Conner (1993), Fuglsang and others (1995), Appendini and Hotchkiss

(1997), Luck and Jager (1997), Rodrigues and Han (2000)Myeloperoxidase Fuglsang and others (1995)

Fatty Acid Lauric acid Ouattara and others (1997; 2000b)Palmitoleic acid Ouattara and others (1997)

Fatty Acid Ester Monolaurin (lauricidin®) Luck and Jager (1997)

Fungicide Benomyl Halek and Garg (1989)Imazalil Hale and others (1986), Weng and Hotchkiss (1992)Sulfur dioxide Thomas and others (1995), Christie and others (1997), Luck and Jager

(1997), Opperman and others (1999)Inorganic Acid Phosphoric acid Hotchkiss (1997)

Metal Copper Ishitani (1995)Silver Ishitani (1995), Luck and Jager (1997), An and others (1998), Chung

and others (1998)

Miscellaneous Reuterin Helander and others (1997)

Natural Phenol Catechin Walker (1994)p-Cresol Hotchkiss (1997)Hydroquinones Hotchkiss (1997)

(continued on next page)

low concentrations, only slight odors wereperceived, which suggests that AIT can beemployed in MAP. The shelf life of variousfoods (such as fresh beef, cured pork,sliced raw tuna, cheese, egg sandwich, noo-dles, and pasta) packaged in barrier plastic

bags was enhanced when the package wasflushed with AIT.

The AM effectiveness of AIT inside apackage depends on its interaction with theparticular packaging materials. Lim andTung (1997) determined the vapor pressure

of pure AIT and that of AIT above AIT-cano-la oil mixtures. Canola oil is effective in de-pressing the vapor pressure of AIT, and maybe used as a controlling diluent for this pur-pose in MAP applications. It was found thatthe diffusion, solubility and permeability


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coefficients of AIT in polyvinylidenechlo-ride (PVDC)/ polyvinylchloride (PVC) co-polymer films are concentration and tem-perature dependent. At a fixed vaporactivity, the diffusion and permeability co-efficients increased whereas the solubility

coefficient decreased with an increase intemperature.

Coating of films with antimicrobialagents

Appropriate coatings can sometimes im-

part AM effectiveness. An and others (2000)claimed that a polymer-based solutioncoating would be the most desirable meth-od in terms of stability and adhesiveness ofattaching a bacteriocin to a plastic film. Itwas found that low-density polyethylene

Table 4—continued

Class Examples References

Oligosaccharide Chitooligosaccharide Cho and others (2000), Hong and others (2000)

Organic Acid Acetic acid Doores (1993), Ouattara and others (2000a, b), Luck and Jager (1997)Benzoic acid Luck and Jager (1997), Weng and others (1997), Chen and others (1999),

Weng and others (1999)Citric acidLactic acid Doores (1993), Luck and Jager (1997)Malic acid Doores (1993)Propionic acid Doores (1993), Ouattara and others (2000a, b), Luck and Jager (1997)Sorbic acid Luck and Jager (1997), Weng and others (1999)Succinic acid Doores (1993)Tartaric acid Doores (1993)

Organic Acid Salt Potassium sorbate Chen and others (1996), Han and Floros (1997, 1999), Devlieghereand others (2000a)

Sodium benzoate Chen and others (1996)

Paraben Ethyl paraben Davidson (1993), Luck and Jager (1997), Dobias and others (2000)Methyl paraben Davidson (1993), Luck and Jager (1997)Propyl paraben Davidson (1993), Luck and Jager (1997), Dobias and others (2000)

Plant-Volatile Allyl isothiocyanate (AIT) Isshiki and others (1992), Luck and Jager (1997), Brody Component and others (2001)

Carvacrol Ouattara and others (1997), Scora and Scora (1998)Cineole Lis-Balchin and others (1998), Scora and Scora (1998)Cinnamaldehyde Ouattara and others (1997; 2000b)Citral Lis-Balchin and others (1998), Scora and Scora (1998)p-Cymene Scora and Scora (1998)Estragole (methyl chavicol) Scora and Scora (1998), Suppakul and others (2002)Eugenol Ouattara (1997), Scora and Scora (1998)Geraniol Scora and Scora (1998)Hinokitiol (�-thujaplicin) Fallik and Grinberg (1992), Brody and others (2001)Linalool Lis-Balchin and others (1998), Scora and Scora (1998), Suppakul

and others (2002)Terpineol Scora and Scora (1998)Thymol Ouattara and others (1997), Scora and Scora (1998)

Polysaccharide Chitosan Sudarshan and others (1992), Begin and Calsteren (1999), Hongand others (2000)

Konjac glucomannan Xiao and others (2000)1Although generally used as Antioxidants, they have shown also Antimicrobial activity (Hotchkiss,1997).

Table 5—Trade names and manufacturers of commercial antimicrobial materials

Format Trade Name Manufacturer References

Concentrate AgIONTM AgION Technologies LLC (USA) www.agion-tech.comApacider-A® Sangi Co. (Japan) Brody and others (2001)MicroFreeTM DuPont (U.S.A.) Brody and others (2001), Vermeiren and others (2002)Microban® Microban Products (U.S.A.) Brody and others (2001), Vermeiren and others (2002)Novaron® Milliken Co. (U.S.A.) Vermeiren and others (2002)Sanitized® Sanitized AG / Clariant (Switzerland) Vermeiren and others (2002)Surfacine® Surfacine Development Co. (U.S.A.) Vermeiren and others (2002)Ultra-Fresh® Thonson Research Associates (Canada) Vermeiren and others (2002)Zeomic® Shinanen New Ceramics Co. (Japan) Brody and others (2001)

Extract CitrexTM Quimica Natural Brasileira Ltd. (Brazil) Lee and others (1998) (Grapefruit seed)Nisaplin® (Nisin) Integrated Ingredients (U.S.A.) Scannell and others (2000), Brody and others (2001)Take Guard Takex Co. (Japan) Brody and others (2001)(Bamboo)

WasaOuro® Green Cross Co. (Japan) Brody and others (2001)(Mustard)

Film MicroGardTM Rhone-Poulenc (U.S.A.) Brody and others (2001)Piatech Daikoku Kasei Co. (Japan) Brody and others (2001)




(LDPE) films coated with a mixture of polya-mide resin in i-propanol/n-propanol and abacteriocin solution provided AM activityagainst Micrococcus flavus. The migration ofbacteriocins reached equilibrium within 3d, but the level attained was too low to af-fect several bacterial strains spread on anagar plate media. When the films were incontact with a phosphate buffer solutioncontaining strains of M. flavus and L. mono-cytogenes, a marked inhibition of microbialgrowth of both strains was observed.

LDPE film was successfully coated withnisin using methylcellulose (MC)/ hydrox-ypropyl methylcellulose (HPMC) as a carri-er. Nisin was found to be effective in sup-pressing S. aureus and L. monocytogenesrespectively (Cooksey 2000). Natrajan andSheldon (2000a) studied the efficacy of ni-sin-coated polymeric films such as PVC, lin-ear low-density polyethylene (LLDPE), andnylon, in inhibiting Salmonella typhimuri-um on fresh broiler drumstick skin. As antic-ipated, the more hydrophobic LLDPE filmrepelled the aqueous nisin formulations toa greater extent than the other films andcaused coalescence of the treatment solu-tion droplets. The repulsion between theLLDPE film and the treatment solution mayhave affected the overall inhibitory activityof the formulations by causing more local-ized inactivation of the target. An agar-based film containing nisin was also stud-ied. It was found that in this film, thedegree of cross-linking depends on the agarconcentration, which may affect the migra-tion of nisin to the surface of a broiler drum-stick skin (Natrajan and Sheldon 2000b).Thus, 0.75% w/w compared with 1.25% w/wgels formed a more open and elastic net-work, allowing greater migration of thetreatment components over time. The re-spective levels of bacterial inhibition exhib-ited by the films, especially after 96 h, ap-peared to support this postulation.

Incorporation of antimicrobialadditives

The direct incorporation of AM additivesin packaging films is a convenient means bywhich AM activity can be achieved. Severalcompounds have been proposed and/ortested for AM packaging using this method.Han and Flores (1997) studied the incorpo-ration of 1.0% w/w potassium sorbate inLDPE films. A 0.1-mm thick film was used forphysical measurements, while a 0.4-mmthick film was used for AM effectivenesstests. It was found that potassium sorbatelowered the growth rate and maximumgrowth of yeast, and lengthened the lagperiod before mold growth became appar-ent. The results of this study, however, con-

tradict those obtained by Weng and Hotch-kiss (1993) with LDPE films (0.05-mm thick)containing 1.0 % w/w sorbic acid. In the lat-ter case, the films failed to suppress moldgrowth when brought into contact with in-oculated media. Devlieghere and others(2000a) studied these contradicting results.Their results confirm that ethylene vinyl al-cohol/linear low-density polyethylene(EVA/LLDPE) film (70-�m thick) impregnat-ed with 5.0% w/w potassium sorbate is un-able to inhibit the growth of microorganismson cheese and to extend its shelf life. As sug-gested by Weng and Hotchkiss (1993), verylimited migration of potassium sorbate intowater as well as into cheese cubes occurs,probably because of the incompatibility ofthe polar salt with the nonpolar LDPE. Thechoice of an AM agent is often restricted bythe incompatibility of that agent with thepackaging material or by its heat instabilityduring extrusion (Weng and Hotchkiss1993; Han and Floros 1997).

While polyethylene (PE) has been widelyemployed as the heat-sealing layer in pack-ages, in some cases the copolymer polyeth-ylene-co-methacrylic acid (PEMA) wasfound to be preferable for this purpose.Weng and others (1999) reported a simplemethod for fabricating PEMA films (0.008-to 0.010-mm thick) with AM properties bythe incorporation of benzoic or sorbic acids.The experimental results suggest that sodi-um hydroxide and preservative-treatedfilms exhibit dominantly AM properties forfungal growth, presumably due to the high-er amount of preservatives released fromthe films (75 mg benzoic acid or 55 mg sorbicacid per g of film) than hydrochloric acidand preservative-treated films. Chen andothers (1996) found that chitosan filmsmade from dilute acetic acid solutions blockthe growth of Rhodotorula rubra and Penicil-lium notatum if the film is applied directlyto the colony-forming organism. Since chi-tosan is soluble only in slightly acidic solu-tions, production of such films containingthe salt of an organic acid (such as benzoicacid, sorbic acid) that is an AM agent isstraightforward. However, the interactionbetween the AM agent and the film-formingmaterial may affect the casting process, therelease of the AM agent and the mechanicalproperties of the film.

Begin and Calsteren (1999) showed thatfilms containing AM agents with a molecularweight larger than that of acetic acid are softand can be used in multi-layer systems or asa coating. Acetic acid diffusion was, howev-er, not as complete as that of propionic acidwhen chitosan-containing films were usedin contact with processed meats (Ouattaraand others 2000a) in spite of the fact that in

an aqueous medium, acetic acid diffusedout of chitosan more rapidly than propion-ic acid (Ouattara and others 2000b). Theseresults suggest that the release of organicacids from chitosan is a complex phenome-non that involves many factors such as elec-trostatic interactions, ionic osmosis, andstructural changes in the polymer inducedby the presence of the acids.

According to Weng and Hotchkiss (1993),anhydrides are more compatible with PEthan their corresponding free acids or salts,due to the lower polarity and higher molec-ular weight of the former compared to thelatter. Hence, anhydrides may serve as ap-propriate additives to plastic materials forfood packaging. LDPE films impregnatedwith benzoic anhydride completely sup-pressed the growth of Rhizopus stolonifer,Penicillium species and Aspergillus toxicari-us on potato dextrose agar (PDA). Similarly,LDPE films that contained benzoic anhy-dride delayed mold growth on cheese (Wengand Hotchkiss 1993). PE films (0.010- to0.015-mm thick) containing benzoic anhy-dride (20 mg benzoic anhydride per g of PEin the initial preparation) alone or in combi-nation with minimal microwave heating,were effective in controlling microbialgrowth of tilapia fillets during a 14-d stor-age at 4 °C (Huang and others 1997). Shelf-life studies of packaged cheese and toastedbread demonstrated the efficiency of LDPEfilm containing benzoic anhydride againstmold growth on the food surface during stor-age at 6 °C (Dobias and others 2000). Dobiasand others (2000) also studied the migra-tion of benzoic anhydride, ethyl paraben(ETP) and propyl paraben (PRP) in LDPEfilms. It was found that the incorporation ofthese parabens in the polymer was moredifficult than that of benzoic anhydride dueto their higher volatilities.

No single AM agent can cover all the re-quirements for food preservation. Weng andChen (1997) investigated a range of anhy-drides for use in food packaging. It is knownthat for mold growth inhibition, the effec-tiveness of sorbic anhydride (10 mg sorbicanhydride per g of PE initial concentration)incorporated in PE films (0.10- to 0.12-mmthick) is much better with slow-growing(Penicillium species) than with fast-growingmold (Aspergillus niger). This is due to thetime required for the PE to release sorbicacid to an inhibitory concentration.

Apart from organic acids and anhydrides,Imazalil has also been used with LDPEfilm. Weng and Hotchkiss (1992) showedthat an Imazalil concentration of 2000 mg/kg LDPE film (5.1 �m thick) delayed A. toxi-carius growth on potato dextrose agar, whileLDPE film containing 1000 mg/kg Imazalil


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substantially inhibited Penicillium sp.growth and the growth of both of thesemolds on cheddar cheese.

Little published data exist on the incor-poration of bacteriocins into packagingfilms. Siragusa and others (1999) highlight-ed the potential of incorporating Nisin di-rectly into LDPE film for controlling foodspoilage and enhancing product safety.Devlieghere and others (2000b) were prob-ably the first to use hexamethylene-tetra-mine (HMT) as an AM packaging agent. TheAM activity of the latter is believed to be dueto the formation of formaldehyde when thefilm comes into contact with an acidic medi-um (Luck and Jager 1997). It was found thata LDPE film containing 0.5% w/w HMT ex-hibited AM activity in packaged cookedham and therefore this agent is a promisingmaterial for food packaging applications.

In Japan, the ions of silver and copper,quaternary ammonium salts, and naturalcompounds such as Hinokitiol are generallyconsidered safe AM agents. Silver-substitut-ed zeolite (Ag-zeolite) is the most commonagent with which plastics are impregnated.It retards a range of metabolic enzymes andhas a uniquely broad microbial spectrum. Asan excessive amount of the agent may af-fect the heat-seal strength and other phys-ical properties such as transparency, thenormal incorporation level used is 1 to 3%w/w. Application to the film surface (that isincreasing the surface area in contact withthe food) is another approach that could beinvestigated in the future (Ishitani 1995).

Another interesting commercial devel-opment is Triclosan-based antimicrobialagents such as Microban®, Sanitized® andUltra-Fresh®. Vermeiren and others(2002)reported that LDPE films containing 0.5 and1.0% w/w triclosan exhibited antimicrobialactivity against S. aureus, L. monocytogenes,E. coli O157:H7, Salmonella enteritidis andBrocothrix thermosphacta in agar diffusionassay. The 1.0% w/w Triclosan film had astrong antimicrobal effect in in vitro simu-lated vacuum-packaged conditions againstthe psychrotrophic food pathogen L. mono-cytogenes. However, it did not effectively re-duce spoilage bacteria and growth of L.monocytogenes on refrigerated vacuum-packaged chicken breasts stored at 7 °C.This is because of ineffectiveness towardsmicrobial growth.

Other compounds with AM effects arenatural plant extracts. Recently, Korean re-searchers developed certain AM films im-pregnated with naturally-derived AM agents(An and others 1998; Chung and others1998; Lee and others 1998; Hong and others2000; Ha and others 2001; Suppakul and oth-ers 2002). These compounds are perceived to

be safer and were claimed to alleviate safetyconcerns (Lee and others 1998). It was report-ed that the incorporation of 1% w/w grape-fruit seed extract (GFSE) in LDPE film (30 ìmthick) used for packaging of curled lettucereduced the growth rate of aerobic bacteriaand yeast. In contrast, a level of 0.1% GFSEyielded no significant effect on the rate ofmicrobial growth in packaged vegetables,except for lactic acid bacteria on soybeansprouts (Lee and others 1998). Ha and others(2001) studied GFSE incorporated (by co-ex-trusion or a solution-coating process) in mul-tilayered PE films and assessed the feasibil-ity of their use for ground beef. They foundthat coating with the aid of a polyamidebinder resulted in a higher level of AM activ-ity than when incorporated by co-extrusion.A co-extruded film (15 �m thick) with 1.0% w/w GFSE showed AM activity against M. flavusonly, whereas a coated film (43 �m of LDPEwith 3 �m of coating layer) with 1.0% w/wGFSE showed activity also against E. coli, S.aureus, and Bacillus subtilis. Both types re-duced the growth rates of bacteria onground beef stored at 3 °C, as compared withplain PE film. The 2 investigated GFSE levels(0.5 and 1.0% w/w) did not differ significantlyin the efficacy of the film in terms of its abil-ity to preserve the quality of beef.

Chung and others (1998) found thatLDPE films (48 to 55 �m thick) impregnatedwith either 1.0% w/w Rheum palmatum andCoptis chinensis extracts or silver-substitutedinorganic zirconium retarded the growth oftotal aerobic bacteria, lactic acid bacteria andyeast on fresh strawberries. However, thestudy of An and others (1998) showed thatLDPE films (48 to 55 �m thick) containing1.0% w/w R. palmatum and C. chinensis ex-tracts or Ag-substituted inorganic zirconiumdid not exhibit any AM activity in a disk test(Davidson and Parish 1989) against E. coli, S.aureus, Leuconostoc mesenteroides, S. cerevi-siae, A. niger, Aspergillus oryzae, Penicilliumchrysogenum. A film containing sorbic acidshowed activity against E. coli, S. aureus, andL. mesenteroides. The reasons for this unusu-al result are not clear. During diffusion as-says, the AM agent is contained in a well orapplied to a paper disc placed in the center ofan agar plate seeded with the test microor-ganism. This arrangement may not be ap-propriate for essential oils, as their compo-nents are partitioned through the agar due totheir affinity for water (Davidson and Parish1989). Accordingly, broth and agar dilutionmethods are widely used to determine theAM effectiveness of essential oils (Davidsonand Parish 1989). According to Hong andothers (2000), the AM activity of 5.0% w/wPropolis extract, Chitosan polymer and oligo-mer, or Clove extract in LDPE films (0.030- to


0.040-mm thick) against Lactobacillus plan-tarum, E. coli, S. cerevisiae, and Fusarium ox-ysporum is best determined through viablecell counts. Overall, LDPE films with incor-porated natural compounds show a positiveAM effect against L. plantarum and F. ox-ysporum. Preliminarily studies by Suppakuland others (2002) with LLDPE films (45 to 50�m thick) containing 0.05% w/w linalool ormethyl chavicol showed a positive activityagainst E. coli.

Edible films and various AM compoundsincorporated in edible food packages havealso been investigated recently (Rodriguesand Han 2000; Coma and others 2001). Ro-drigues and Han (2000) investigated edibleAM materials produced by incorporatingLysozyme, Nisin and Ethylenediamine tet-racetic acid (EDTA) in whey protein isolate(WPI) films. Such Lysozyme or Nisin-con-taining films are effective in inhibiting Bro-chothrix thermosphacta but fail to suppressL. Monocytogenes. The incorporation ofEDTA in WPI films improved the inhibitoryeffect on L. monocytogenes but had a mar-ginal effect only on E. coli O157:H7.

Coma and others (2001) studied themoisture barrier and the AM properties ofHPMC-fatty acid films (30-50 ìm thick) con-taining Nisin (105 IU/mL) as the AM agentand its efficacy against Listeria innocua andS. aureus growth in food products. Stearicacid was chosen as the fatty acid because ofits ability to reduce the rate of water vaportransmission. However, it impaired the ef-fectiveness of the film against both strains.This may be explained by electrostatic inter-action between the cationic Nisin and theanionic stearic acid.

ImmobilizationBesides diffusion and sorption, some AM

packaging systems utilize covalently immo-bilized AM substances that suppress micro-bial growth. Appendini and Hotchkiss(1997) investigated the efficiency ofLysozyme immobilized on different poly-mers. It is known that cellulose triacetate(CTA) containing Lysozyme yields the high-est AM activity. The viability of Micrococcuslysodeikticus was reduced in the presence ofimmobilized Lysozyme on CTA film (Appen-dini and Hotchkiss 1997). Scannell and oth-ers (2000) showed that PE/polyamide(70:30) film formed a stable bond with Nisinin contrast to Lacticin 3147. Nisin-adsorbedbioactive inserts reduced the level of L. in-nocua and S. aureus in sliced cheese and inham.

Surface modificationOzdemir and others (1999) introduced

(by chemical methods) functional groups



possessing AM activity into polymer filmswith the purpose of preventing the transferof the AM agents from the polymer to thefood. Cho and others (2000) synthesized anew biopolymer containing a chito-oligosac-charide (COS) side chain. The COS was in-troduced on polyvinylacetate (PVA) bycross-linking with the bifunctional com-pound, N-methylolacrylamide (NMA). Itwas found that the growth of S. aureus wasalmost completely suppressed by thismeans.

Surface amine groups formed in poly-mers by electron irradiation were alsoshown to impart AM effectiveness (Cohenand others 1995; Ozdemir and others 1999).Another AM film has recently been devel-oped using a UV excimer laser. Nylon 6,6films irradiated in air by a laser at 193 nmexhibited AM activity, apparently due to a10% conversion of the amide groups on thenylon surface to amines bound to the poly-mer chain (Cohen and others 1995). Bycontrast, irradiation at 248 nm did notchange the surface chemistry or initiateconversion of the amide (Ozdemir and oth-ers 1999).

Paik and others (1998) and Shearer andothers (2000) observed a decrease in all bac-terial cells, including S. aureus, Pseudomonasfluorescens, and E. faecalis in bulk fluidwhen using an AM nylon film. The resultsindicate that this decrease is more probablyto be due to the bactericidal action than tosurface adsorption (Paik and others 1998).Although the mechanism of the reductionin the bacteria population remained uncer-tain, electrostatic attractive forces betweenthe positively charged film surface and thenegatively charged E. coli and S. aureuswere presumed to be the reason for this ef-fect (Shearer and others 2000). Further re-search is needed to characterize the AM ac-tive groups on the irradiated film surfaceand the mechanism of AM action.

Ionomers, with their unique propertiessuch as a high degree of transparency,strength, flexibility, stiffness and tough-ness, as well as inertness to organic solventsand oils, have also drawn much attention asfood packaging materials. Halek and Garg(1989) successfully incorporated theBenomyl fungicide into ionomer films viaits carboxyl groups. Unfortunately, Benom-yl is not an approved food preservative.

Weng and others (1997) investigated ap-plication of AM ionomers combined withapproved food preservatives. Anhydridelinkages in the modified films were formedby reaction of acid/or base-treated filmswith benzoyl chloride. The AM activity wascharacterized in terms of the release of ben-zoic acid, which was higher in the base-

treated version indicating the superiority ofthe latter. The AM effect of modified iono-mer films was further demonstrated by theirability to inhibit the growth of Penicilliumspecies and A. niger.

Factors to Consider inthe Manufacturing ofAntimicrobial Films

IT IS CLEAR THAT THE SELECTION OF BOTH THE

substrate and the AM substance is impor-tant in developing an AM packaging sys-tem. Furthermore, when an AM agent isadded to a packaging material, it may affectthe inherent physico-mechanical propertiesof the latter.

Process conditions and residualantimicrobial activity

The effectiveness of an AM agent ap-plied by impregnation may deteriorate dur-ing film fabrication, distribution and storage(Han 2000). The chemical stability of an in-corporated AM substance is likely to be af-fected by the extrusion conditions, namely,the high temperatures, shearing forces andpressures involved (Han and Floros 1999).To minimize this problem, Han (2000) rec-ommended using master batches of the AMagent in the resin for preparation of AMpackages. Also, all operations such as lami-nation, printing and drying as well as thechemicals used (adhesives and solvents) inthe process may affect the AM activity of thepackage. In addition, some of the volatileAM compounds may be lost during storage.All these parameters should be evaluated.

Characteristics of antimicrobialsubstances and foods

The mechanism and kinetics of growthinhibition are generally studied in order topermit mathematical modeling of microbi-al growth (Han 2000). Foods with differentbiological and chemical characteristics arestored under different environmental con-ditions, which, in turn, may cause differentpatterns of microflora growth. Aerobic micro-organisms can exploit headspace O2 for theirgrowth. The pH of a product affects thegrowth rate of target microorganisms andchanges the degree of ionization of the mostactive chemicals, as well as the activity ofthe AM agents (Han 2000). Weng and Hotch-kiss (1993) reported that LDPE film contain-ing benzoic anhydride was more effective ininhibiting molds at low pH values. Rico-Pena and Torres (1991) found that the diffu-sion of sorbic acid decreased with an in-crease in pH. The food aw may alter themicroflora, AM activity, and chemical stabil-ity of active ingredients applied by impreg-nation. Vojdani and Torres (1989a) showed


that the diffusion of potassium sorbatethrough polysaccharide films increases withaw; this has a negative impact on theamount available for protection. Rico-Penaand Torres (1991) found that potassium sor-bate diffusion rates in MC/HPMC film con-taining palmitic acid were much higher athigher values of aw.

Chemical interaction of additiveswith film matrix

During incorporation of additives into apolymer, the polarity and molecular weightof the additive have to be taken into con-sideration. Since LDPE itself is nonpolar,additives with a high molecular weight andlow polarity are more compatible with thispolymer (Weng and Hotchkiss 1993). Fur-thermore, the molecular weight, ionic chargeand solubility of different additives affecttheir rates of diffusion in the polymer(Cooksey 2000). Wong and others (1996)compared the diffusion of ascorbic acid,potassium sorbate, and sodium ascorbatein calcium-alginate films at 8, 15, and 23 °C.They found that ascorbic acid had the high-est and sodium ascorbate the lowest diffu-sion rate at all studied temperatures. Thesefindings were attributed to the different ion-ic states of the additives.

Storage temperatureThe storage temperature may also affect

the activity of AM packages. Several re-searchers found that the protective actionof AM films deteriorated at higher tempera-tures, due to high diffusion rates in the poly-mer (Vojdani and Torres 1989a, b; Wong andothers 1996). The diffusion rate of the AMagent and its concentration in the film mustbe sufficient to remain effective throughoutthe shelf life of the product (Cooksey 2000).Weng and Hotchkiss (1993) stated that lowamounts of benzoic anhydrides in LDPEmight be as effective at refrigeration tem-peratures as high levels at room tempera-ture.

Mass transfer coefficients andmodeling

Mathematical modeling of the diffusionprocess could permit prediction of the AMagent release profile and the time duringwhich the agent remains above the criticalinhibiting concentration. With a higher dif-fusivity and much larger volume of the foodcomponent compared to the packagingmaterial, a semi-infinite model in which thepackaging component has a finite thicknessand the food component has infinite vol-ume could be practical (Han 2000). The ini-tial and boundary conditions that could be


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used in mass transfer modeling have beenidentified.

Physical properties of packagingmaterials

AM agents may affect the physical prop-erties, processability or machinability of thepackaging material. Han and Flores (1997)reported no significant differences in thetensile properties before and after the incor-poration of potassium sorbate in LDPEfilms, but the transparency of the films de-teriorated as the sorbate concentration in-creased. Weng and Hotchkiss (1993) report-ed no noticeable differences in clarity andstrength of LDPE film containing 0.5 and1.0% benzoic anhydride. Similar resultswere reported for naturally-derived plantextracts such as propolis at 5.0% (Hong andothers 2000), clove at 5.0% (Hong and oth-ers 2000), R. palmatum at 1.0% (An and oth-ers 1998; Chung and others 1998), and C.chinensis at 1.0% (An and others 1998;Chung and others 1998). On the other hand,LDPE film coated with MC/HPMC contain-ing Nisin was difficult to heat-seal (Cooksey2000).

Dobias and others (2000) found statisti-cally significant differences between thephysical properties of films without AMagents and with different agents at concen-trations of 5 g/kg and 10 g/kg . It was foundthat the tensile and sealing strengths werelower in all samples containing AM agentsincluding benzoic anhydride, ethyl paraben(ETP) or propyl paraben (PRP). In all stud-ied cases, the coefficient of friction increasedwith the addition of AM substances, watervapor permeability declined by the incorpo-ration of PRP, and oxygen permeability de-creased by the impregnation of benzoic an-hydride or PRP.

CostThere are no published data on the cost

of films impregnated with AM agents, butthey can be expected to be more expensivethan their basic counterparts. Commercial-ization of such films could therefore be-come viable for high-value food productsonly (Cooksey 2000).

Food contact approvalSome organic acids, bacteriocins and vol-

atile compounds derived from plants haveFDA approval as additives for certain foods(see Table 6). AIT is currently not approvedby the FDA for use in the U.S.A. (Brody andothers 2001) due to a safety concern thatthis synthetic compound may be contami-nated with traces of the toxic allyl chlorideused in the manufacturing process (Clark1992). In Japan, the use of AIT is allowed

only when this compound is extracted froma natural source (Isshiki and others 1992).Weng and Hotchkiss (1993) pointed out thatthe rapid hydrolysis of benzoic anhydride tobenzoic acid should not pose a safety con-cern, although at the time of their studybenzoic anhydride did not have FDA ap-proval. The use of Ag-zeolite as an accept-able food additive in Europe has not beenclarified (Brody and others 2001). However,recently, Ag-zeolites such as AgIONTM andZeomic® received the approval of the FDAfor use in food-contact materials. Triclosan isalso not accepted by US regulatory author-ities for food contact materials (Brody andothers 2001). In Europe, the legislative sta-tus of Triclosan is unclear. Triclosan does not


appear on the EU directive list of approvedfood additives that may be used in the man-ufacturing of plastics intended for food con-tact materials (Vermeiren and others 2002).

No European regulations exist currentlyon the use of active and intelligent packag-ing. Packages intended for food contact ap-plications are required to belong to a positivelist of approved compounds, and an overallmigration limit from the material into thefood or food simulant was set at 60 mg/kg.This is incompatible with the aim of activepackaging, especially when the system isdesigned to release active ingredients intothe foods. Consequently, as was also statedby van Beest (2001), a new approach in foodpackaging regulations is needed. The cur-

Table 6—List of permitted food additives that could be used as antimicrobialagents in packaging materials.

Code Assigned by Legislative AuthorityAdditive Australia/New Zealand1 Europe2 U.S.A.3

Acetic acid 260 E260 GRASBenzoic acid 210 E210 GRASButylated hydroxyanisole (BHA) 320 E320 GRASButylated hydroxytoluene (BHT) 321 E321 GRASCarvarcol FACitral GRASCitric acid 330 E330 GRASp-Cresol FAEDTA FAEstragole (methyl chavicol) GRASEthanol E1510 GRASEthyl paraben E214 GRASEugenol GRASGeraniol GRASGlucose oxidase 1102 GRASHexamethylenetetramine (HMT) E239Konjac glucomannan E425 GRASLactic acid 270 E270 GRASLauric acid FALinalool GRASLysozyme 1105 E1105 GRASMalic acid 296 E296 GRASMethyl paraben 218 E218Natamycin 235 E235 FANisin 234 E234 GRASPhosphoric acid 338 E338 GRASPolyphosphate E452 GRASPotassium sorbate 202 E202 GRASPropionic acid 280 E280 GRASPropyl paraben 216 E216 GRASSodium benzoate 211 E211 GRASSorbic acid 200 E200 GRASSuccinic acid E363 GRASSulfur dioxide 220 E220 GRASTartaric acid 334 E334 GRASTertiary butylhydroquinone (TBHQ) 319 FA�-Terpineol FAThymol FA

Source: CFR (1988); Davidson and Branen (1993); Maga and Tu (1995); Lück and Jager(1997);Saltmarsh (2000); Taubert (2000).

1Assignment of a number signifies that additive is approved by the Australian and New Zealand FoodAuthority (ANZFA) and The Australian New Zealand Food Standards Council (ANZFSC) as being safe forfood use.

2Assignment of an “E” number signifies that additive has been approved by the European Communities(EC) Scientific Committee on Food (SCF).

3Classification in accordance with Food and Drug Administration (FDA) Title 21 of the Code of FederalRegulations (21 CFR) wherein substances intended for use in the manufacture of foodstuffs for humanconsumption are classified into 3 categories: food additives (FA), prior-sanctioned food ingredients andsubstances generally recognised as safe (GRAS).



rent applications of AM food packaging arerather limited, although promising. This isbecause of the legal status of the tested ad-ditives (Vermeiren and others 2002). Themajor potential food applications of AMfilms include meat, fish, poultry, bakerygoods, cheese, fruits and vegetables (Labu-za and Breene 1989). Table 7 lists the currentand potential future applications of AMpackaging technologies.

The Future

AM PACKAGING IS A RAPIDLY EMERGING TECH-nology. The need to package foods in

a versatile manner for transportation andstorage, along with the increasing consumerdemand for fresh, convenient, and safefood products presages a bright future forAM Packaging (Floros and others 1997).However, more information is required onthe chemical, microbiological and physio-logical effects of these systems on thepackaged food especially on the issues ofnutritional quality and human safety (Flo-ros and others 1997). So far, research on AMpackaging has focused primarily on the de-velopment of various methods and modelsystems, whereas little attention has beenpaid to its preservation efficacy in actualfoods (Han 2000). Research is essential toidentify the types of food that can benefitmost from AM packaging materials. It islikely that future research into a combina-tion of naturally-derived AM agents, bio-preservatives and biodegradable packag-ing materials will highlight a range of themerits of AM packaging in terms of foodsafety, shelf-life and environmentalfriendliness (Nicholson 1998; Rodriguesand Han 2000; Coma and others 2001). Thereported effectiveness of natural plant ex-tracts suggests that further research isneeded in order to evaluate their antimi-crobial activity and potential side effects in

packaged foods. An additional challenge isin the area of odor/flavor transfer by natu-ral plant extracts to packaged food prod-ucts. Thus, research is needed to determinewhether natural plant extracts could act asboth an antimicrobial agent and as anodor/flavor enhancer. Moreover, in order tosecure safe food, amendments to regula-tions might require toxicological and othertesting of compounds prior to their ap-proval for use (Vermeiren and others 2002).

AbbreviationsAIT Allyl isothiocyanateAM AntimicrobialAP Active Packagingaw Water activityBHA Butylated hydroxyanisoleBHT Butylated hydroxytolueneCOS Chito-oligosaccharideCTA Cellulose triacetateEDTA Ethylenediaminetetraacetic acidERH Equilibrium relative humidityEVA Ethylene vinyl alcoholETP Ethyl parabenFDA Food and Drug AdministrationGFSE Grapefruit seed extractGRAS Generally recognised as safeHDPE High density polyethyleneHMT HexamethylenetetramineHPMC Hydroxypropyl methylcelluloseIMF Intermediate moisture foodsLDPE Low density polyethyleneLLDPE Linear low density polyethyleneMAP Modified atmosphere packagingMC MethylcelluloseMIC Minimum inhibitory concentrationNMA N-methylol acrylamideOSP Oxygen scavenging packetOTR Oxygen transmission ratePDA Potato dextrose agarPE PolyethylenePEMA Polyethylene-co-methacrylic acidPRP Propyl paraben


PVA PolyvinylacetatePVC PolyvinylchloridePVDC PolyvinylidenechlorideTBHQ Tertiary-butyl-hydroquinoneWPI Whey protein isolate

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Table 7—Current and future applications of antimicrobial packaging

Minimally Food groupSystem Beverage Processed Meat/Poultry Seafood Dairy Bakery Produce

O2 Scavenging Wine Fresh meat Cheese Bread VegetablesBeer Processed meat

Fruit juice SausagesH2O absorb/control Meat Fish Vegetables

Chicken FruitCO2 generating Fresh meat Fish Cheese

PoultryEthanol generating Fish Cheese Bread

CakeAntimicrobial1 Fruit juice2 Noodles2 Meat Fish Cheese Bread Vegetables

Tea Pasta2 Ham Cake2 FruitSandwiches2 Pastrami

BolognaChicken

1Including both migrating and nonmigrating systems.2Possible future applications.


Conc

ise Re

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in Fo

od Sc


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On behalf of the Royal Thai Government, author Suppakulwould like to acknowledge the Australian Agency for Intl.Development (AusAid) for providing financial support. Thiswork was partially supported by a fund for the promotionof research at the Technion. Author Miltz would like to ex-press his thanks and appreciation for this support.

Authors Suppakul and Sonneveld are with theCenter for Packaging, Transportation and Stor-age, Victoria Univ. of Technology, POB 14428,Melbourne City, MS, Melbourne 8001, Australia.Author Miltz is with the Dept. of Food Engineeringand Biotechnology, Technion-Israel Inst. of Tech-nology, Haifa, 32000, Israel. Author Bigger is withthe School of Life Sciences and Technology, VictoriaUniv. of Technology, P.O. Box 14428, MelbourneCity Mail Centre, Melbourne, 8001, Australia.Direct inquiries to author Miltz (E-mail:[email protected]).

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