Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology

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efforts to a new level. Tiny printed circuits can be afﬁxed

to labels and packages to carry signiﬁcant amounts of

information. Active RFID chips draw power from built-in

batteries to send a signal many meters; as battery tech-

nology becomes increasingly miniaturized and inexpen-

sive, active RFID will ﬁnd many new uses in packaging.

Passive RFID chips do not require a power source—a radio

query from an electronic reader provides enough energy to

allow the chip to report its data—so they can be extremely

small, thin and inexpensive. Users may write new infor-

mation to IC tags, adding ﬂexibility.

TAMPER EVIDENT FEATURES

Rather than try to reproduce a package, some counter-

feiters use a brand’s genuine packaging and reﬁll it or

adulterate the ingredients. Any tampering with a package

represents a signiﬁcant threat to both the brand and the

consumer, so anti-tampering features can be extremely

important elements of a brand protection campaign.

From the days of sealing wax, signet rings and signa-

tures across the folds of an envelope, tamper-evident

features have been employed. In many ways, the princi-

ples remain the same as they have been for centuries.

Induction Sealing

The familiar foil seals under the lids of products from pain

reliever to peanut butter utilize a technology called in-

duction sealing. A laminate consisting of a foil and poly-

mer on a paper backing is placed across the top of a plastic

or glass container. Passing the container and lidding

material under an electrical induction coil causes the foil

layer to heat up in response to the electromagnetic energy

supplied by the coil. The foil is released from the backing,

and the polymer (heated by the aluminum) fuses with the

lip of the container. The result is a tight seal. Any attempt

to access the contents of the container is immediately

apparent in the form of a torn or missing seal. Many

induction seals are designed to leave a residue on the lip of

the container, showing that the laminate has been

removed.

Tamper-Evident Films

Many polymer materials are employed as heat-sealed

wraps or capsules over lids to provide evidence of tamper-

ing. The materials are typically quite durable, but are

prone to ragged tearing or shattering when someone

applies force to them or attempts to slip them off of the

package. Many tamper-evident ﬁlms also include holo-

grams or other anti-counterfeiting features to establish

authenticity and to ensure that they are not replaced with

a simpler shrink ﬁlm after the package has been opened.

Tamper-Evident Labels

Some pressure-sensitive labels include a layer that re-

mains ﬁrmly adhered to the product, leaving behind

adhesive residue or displaying a message such as ‘‘void’’

if the label has been removed. Other labels are constructed

with perforations or built-in weak points to prevent their

intact removal. (This is often seen with price tags, which

are difﬁcult to remove intact and move to a more expen-

sive product. The same beneﬁts apply when preventing

the movement of wine or pharmaceutical labels to un-

authorized packages.)

RFID Chips

Radio-frequency identiﬁcation (RFID) chips are playing

an increasing role in tamper protection. Active RFID

chips, which include a power supply, can sound a radio-

frequency distress call, including speciﬁc product or pack-

age information, if they have been tampered with. Passive

RFID chips, which respond to electronic queries from

readers, may provide evidence of tampering when they

are deployed on destructible labels—tampering destroys

the antenna, so the chip’s non-performance can serve as a

warning that tampering has taken place.

BIBLIOGRAPHY

1. The Economic Impact of Counterfeiting and Piracy, Organiza-

tion for Economic Co-Operation and Development, Paris

(2008).

2. B. Jones, ‘‘First Line of Defense,’’ Manufacturing Today Europe

(April–May 2007).

3. M. Noach and E. Feder, The Tadbik Group, personal commu-

nication (2008).

4. U.S. Department of the Treasury, ‘‘U.S. Treasury and Federal

Reserve Issue a New $20 Bill’’ (May 20, 1998).

5. Web site www.UsingRFID.com.

6. Web site of the BP Council (www.bpcouncil.org).

ANTI-FOG COATING

CRAIG D. BOYD

Sun Chemical

One of the main purposes of a package is to facilitate

consumers to repeatedly purchase the product that

it contains. Inks and coatings are continually expected

to have a higher contribution to the overall performance

and/or aesthetics of the package. There is possibly no

coating that offers a more signiﬁcant effect on the

consumers’ acceptance of a package than the anti-fog

coating.

CONDENSATION PROBLEMS DEFINED

Whenever a sealed high-humidity environment is placed

through a temperature gradient, moisture condensation

will occur. This condensation will materialize as small

beads of water droplets forming on the inside of the

48 ANTI-FOG COATING

package. The droplets will begin to vaporize and then form

a fog on the inside of the package and transform a clear

package into an opaque one and thus conceal the contents

from the consumer. Most manufactures want the consu-

mer to see their product. This is normally achieved either

by packaging the product in a clear ﬁlm or by printing a

pictorial of the product on the outside of the package.

Therefore, it is obvious that when a manufacturer

packages a product in a clear package, they expect that

it will remain clear. The produce manufacturer wants the

consumers to see the multicolor mixture of the green

lettuce, orange carrots, red cabbage, and radishes.

CONVENIENT, HEALTHY EATING

In order to attract more consumers, produce manufactures

are marketing the convenience of prewashed produce.

These packages are an attractive way of quickly preparing

a healthy meal. Today, there are literally dozens of differ-

ent salad and vegetable blends sold in the produce depart-

ment in the grocery store. These packages are sealed in a

plastic bag and the produce contains a relatively large

amount of moisture.

REFRIGERATION UNIT TYPES

There are two different classiﬁcation of refrigeration units

used in the produce section of the grocery store. They are

either vertical or horizontal. Because cold air is denser

than warm air, the horizontal refrigeration units allow for

the entire package to maintain a consistent temperature

and therefore will not produce a great amount of conden-

sation. The main drawback of the horizontal unit is that it

conceals the packages from consumers as they navigate

through the produce section. Because of this, the horizon-

tal unit is not used very often any more. The vertical unit,

when positioned properly in the store, can allow consu-

mers to see products from virtually across the produce

section of the store. The largest problem with the vertical

unit is that it allows the refrigerated package to be in

direct contact with the warm ambient air in the store. This

conﬁguration is a perfect design to allow the outside of the

package, the side facing the consumer, to be exposed to a

rather drastic temperature gradient. Thus vertical units

create a perfect environment for the generation of a great

amount of moisture condensation. In the vertical refrig-

eration unit, only the most outside package will experi-

ence condensation. Therefore, the greater the popularity

of the product, the less time any one package will set on

the outside of the unit. Ironically, the less popular the

product, the more the package will require an anti-fog

coating.

PRODUCE PACKAGE TYPES

Produce packages fall into two different categories. First is

the ‘‘pillow’’ pouch. These pouches are made from soft,

subtle ﬁlms that will contain loose packaged produce. This

is the most popular package for produce. Lettuce and cole

slaw blends as well as baby carrots and small pieces of

vegetables such as broccoli ﬂowerets are usually packaged

in the pillow pouch. These pouches have very little rigidity

and thus the package will contain many wrinkles to allow

for the water droplets to collect. The second type of

produce packages are vertical stand-up packages. These

vertical packages are made from very rigid ﬁlms and will

not allow any wrinkles to form. These packages usually

contain more rigid produce like romaine lettuce or celery

stalks. In order to work properly, these packages will

utilize different types of anti-fog coatings. The rigid

packages will be printed with an anti-fog that will cause

the condensation to bead up and then gravity will draw

the water beads to the bottom the pouch where they will

do no harm. The pillow pouch will use an anti-fog that will

allow the water vapor to easily wet out the wrapper. This

way the moisture will not gather and will not create any

fogging. This type of anti-fog is required for the pillow

pouch because the wrinkles will cause the water beads to

gather and will eventually cause fogging. The coatings for

rigid pouches are designed to produce a dried coating that

will have a very low surface energy, while the coatings for

the pillow pouches are designed to have a very high

surface energy.

NOT JUST PRODUCE PACKAGING

Anti-fog coatings are used not only in produce packaging,

but often also in raw and prepared meat and poultry

packaging. For example, meat may be packaged in rigid

trays using modiﬁed atmosphere packaging (MAP), where

the trays are ﬂushed with an optimum composition of

and then sealed with a shrink ﬁlm. These pack-

ages allow a greatly increased shelf life when compared to

the old-fashioned meat wrappers. However, these

packages can easily experience condensation and will

often need an anti-fog coating on the inside of the shrink

ﬁlm. Preprepared meats have become very popular at

grocery stores. Rotisserie chickens are available at most

grocery stores. These chickens are placed in an opaque

rigid tray and then covered with a clear rigid bubble. The

inside of the clear bubble will often contain an anti-fog

coating.

NOT ALL REFRIGERATED PACKAGES REQUIRE ANTI-FOG

COATINGS

Any package where the ﬁlm is in direct contact with

the product does not require an anti-fog coating no

matter how much moisture the package contains. When

the ﬁlm is in direct contact with the product, no matter

how the structure of the refrigeration unit, there is no

area of air space that will allow the formation of conden-

sation. For example, an unwashed head of lettuce with a

ﬁlm that is tightly wrapped around the lettuce will never

experience condensation and therefore will not require the

use of an anti-fog coating. Another example of a package

that will not contain an anti-fog coatings are meat

ANTI-FOG COATING 49

wrappers that are in direct contact with the meat. For

example, the old-fashioned styrofoam meat trays that are

tightly wrapped with a ﬂexible ﬁlm do not require an anti-

fog coating.

ANTI-FOG COATING APPLICATIONS AND

FORMULATIONS

Since anti-fog coatings are designed to deter condensation

formation on the inside of the package, these coatings are

always applied to the inside of the wrapper. Therefore, all

anti-fogs at a minimum have two things in common. They

must be FDA compliant for direct food contact and must be

designed to print and adhere to the untreated side of the

ﬁlm. Since the inks are applied to outside of the ﬁlm, the

treated side is always on the outside of the package. These

coatings are normally applied with at a very low coating

weight, resulting in a very thin ﬁlm of o1mm. Anti-fog

coatings are tested for smudge resistance, block resis-

tance, and offset (transferring to the back side of the

ﬁlm) resistance.

Some anti-fog coatings will affect packaging seal bond

strengths, while other will not. The coatings that do

interfere with seal bonds must be patterned out of the

heat seal areas. Anti-fog coatings can be difﬁcult to reach

correct register because they are absolutely clear. There-

fore, the coatings that do not interfere with heat seal

bonds are more popular. The problem with these coatings

is that they are much more prone to offsetting, so achiev-

ing the correct ﬁlm weight is essential with either coating.

Excessive coating applications can greatly interfere

with heat seals, while a lack of coating will not allow the

coating to reach its anti-fog potential.

Anti-fog coatings for ﬂexible ﬁlms are normally applied

using the ﬂexographic process; coatings for rigid dome lids

for the precooked poultry are normally spray applied.

CONCLUSION AND REVIEW

Some ﬂexible substrates are manufactured with anti-fog

agents added to them. These ﬁlms will only provide

marginal anti-fog properties because the active agents

are diffused throughout the entire thickness of the ﬁlm,

while the coatings are concentrated on the surface. There-

fore, the use of anti-fog coatings are typically required for

high-performance applications.

There is far more to anti-fog coatings than immediately

meets the eye. Whether a package receives an anti-fog

coating is always the decision of the manufacturer. This

decision is based on the type of the product, the type of

refrigeration unit, and the turnaround time of the pro-

duct. The requirements for the correct type of anti-fog are

mostly dependent on the type of product and package. The

purpose of anti-fog coating is to allow the clear ﬁlm to

remain clear so that the consumer can easily see the

colorful and wholesome product that the package con-

tains. The main use of anti-fog coatings is a matter of

manufacturers wanting to increase market share and

product differentiation.

ANTIMICROBIAL PACKAGING

S. Y. CHO

Institute of Life Sciences and

Biotechnology, Korea

University, Seoul, Korea

D. S. LEE

Department of Food Science

and Biotechnology, Kyungnam

University, Masan, Korea

J. H. HAN

PepsiCo Fruit and Vegetable

Research Center, Frito-Lay Inc.,

Plano, Texas

INTRODUCTION

In the past, the functions of packaging had been limited to

the roles of containment, protection of its content from

environmental effects, consumer convenience, and com-

munication of the product information. While the conven-

tional functions of packaging was considered as passive,

the new paradigm of packaging—called active packa-

ging—has been emerged. The active packaging may be

deﬁned as a packaging system in which the product, the

packaging, and the environment interact in a positive way

to extend shelf-life or to achieve some characteristics that

cannot be obtained otherwise (1). Antimicrobial packaging

is a form of active packaging that can control the growth of

microorganisms on the surfaces of foods and packaging

materials and eventually reduce cell counts in the

products.

Antimicrobial function of packaging materials can be

achieved by providing unfavorable environmental condi-

tions to microorganisms by eliminating growth require-

ments, rendering direct contact of microorganisms to the

immobilized antimicrobials on the packaging material

surface, or transferring antimicrobial agents originally

incorporated into the packaging materials. With the above

actions, antimicrobial packaging extends the shelf life of

food and secure consumer safety by controlling spoilage

and pathogenic microorganisms in foods.

According to the Flexible Packaging Association (2), the

market size of ﬂexible packaging in the United States in

2007 is about $23,500 million, garnering 18% $130,000

million packaging market. The largest market for ﬂexible

packaging is food industry (retail and institutional) ac-

counting for over 57% of shipment. Active role of food

packaging has been empathized for sustainable develop-

ment of food packaging industry. Antimicrobial packaging

would make the food packaging industry possible to

achieve an innovative development with the aid of reg-

ulatory requirements such as food product liability and

HACCP. Therefore, research and development trends of

antimicrobial packaging systems may progress to achiev-

ing more effective antimicrobial activity with broader

spectrum, utilizing natural extracts and creating new

applications.

50 ANTIMICROBIAL PACKAGING

A BRIEF HISTORY OF ANTIMICROBIAL PACKAGING

Early Works on Antimicrobial Packaging

As an early stage application of antimicrobial packag-

ing, shelf-life extension of perishable product had been

achieved by applying modiﬁed atmosphere packaging

(MAP) technologies that provided adverse environments

of microbial growth. MAP eliminates oxygen level and

elevates the concentration of carbon dioxide to inhibit the

growth of aerobic microorganisms.

The antimicrobial polymeric materials were ﬁrst intro-

duced to protect biomedical devices from microbial con-

tamination in Japan (1). A considerable progress in

antimicrobial packaging technology has been made in

1990s, and various antimicrobial products was developed

and commercialized in household goods, textiles, surgical

implants, biomedical devices, and food packaging materi-

als. The progress could be attributed to the development

of inherently antimicrobial polymers and also to the

development of antimicrobial agent that was incorporated

into polymer matrix. For example, chitosan-based poly-

mers and copolymerized acrylic with protonated amine

co-monomer have been developed as antimicrobial packa-

ging materials (3). Preservatives with antimicrobial

activity play an important role in preventing microbial

contamination. Many of these agents such as silver sub-

stituted zeolite, potassium sorbates, sodium benzoate,

propionic acid, and acetic acid have been successfully

incorporated directly into packaging materials to control

the microbial contamination (4, 5).

Current Works on Antimicrobial Packaging

The use of chemical preservatives as antimicrobial agents

caused public concerns on the potential risks of chemical

preservatives that might migrate into food products.

These agents are categorized as food additives and con-

trolled by legislation.

Although the chemical preservatives in packaging ma-

terials had been carefully regulated by domestic autho-

rities, the increased consumer demand for preservative

free foods has rendered the development of antimicrobial

packaging with natural antimicrobial agents. The natural

antimicrobials and GRAS antimicrobials may include

bacteriocins, enzymes, plant extracts, and natural essen-

tial oils (5, 6). They hold a great potential and represent

excellent activities for controlling microbial contamina-

tion. With the effort of ﬁnding safe antimicrobial agents,

considerable studies have been exerted on developing

antimicrobial biopolymer matrix as a carrier for natural

antimicrobial agents (6).

ANTIMICROBIAL PACKAGING SYSTEM

Antimicrobial packaging is a system that is designed

to control the growth of microorganisms by extending

the microbial lag phase and by reducing the growth rate,

thereby extending the shelf life of perishable products

and enhance the safety of packaged products (4). Anti-

microbial packaging can be constructed using antimicro-

bial packaging materials and/or antimicrobial agents.

Antimicrobial packaging systems can be classiﬁed into

three types according to the mode of antimicrobial agent’s

action: absorption, release, and immobilization (5). The

ﬁrst type is the packaging materials containing antimi-

crobial agents that eliminate oxygen and moisture in the

packaging system by absorption. This type of packaging

controls the growth of microorganisms by providing

unfavorable conditions to cell growth. The second is the

packaging materials containing antimicrobial agents that

migrate to the surface of food materials. The antimicrobial

action is achieved by the release of the antimicrobial

agents from the packaging material. The third type is

those containing antimicrobial agents without migration.

This type of packaging needs direct contacts between

packaging materials and food product since the antimi-

crobial agents in the packaging material does not release

into foods.

The antimicrobial agents may be coated, incorporated,

immobilized, or surface modiﬁed onto the packaging mate-

rials according to the characteristics of the antimicrobials

and to the antimicrobial mechanisms how the agents are

working (6). Thermal polymer processing methods such as

extrusion and injection molding are used for heat-stable

antimicrobial agents like silver substituted zeolites. Mean-

while, solvent compounding methods may be a more sui-

table method to combine the antimicrobial agents and the

packaging materials for heat-sensitive antimicrobials such

as enzymes and volatile compounds (7).

Antimicrobial Packaging Containing Oxygen Absorbing

Agent

Modiﬁed atmosphere packaging (MAP) with the absence

of oxygen along with elevated concentration of carbon

dioxide has been used for controlling the aerobic micro-

organisms that are responsible for food spoilage. Gener-

ally, oxygen concentrations of 0.1% v/v or less in package

headspace are required to inhibit the growth of aerobes

(1). However, MAP does not guarantee this anaerobic

condition in the packaging system throughout the shelf

life since the ﬂexible packaging materials show consider-

able gas permeabilities. Introduction of oxygen absorbing

agent in the packaging system rendered active control of

oxygen level in the package headspace suitable for anti-

microbial purpose by removing oxygen molecules.

In general, oxygen scavenging technologies are con-

structed by the oxidation of oxygen absorbing agents: iron

powder, ascorbic acid, photosensitive dyes, enzymes (e.g.,

glucose oxidase and alcohol oxidase), unsaturated fatty

acids (e.g., oleic acid or linoleic acid), and immobilized

yeast on a solid substrate (8). Iron-based material is

known to the most effective oxygen scavenging system

among the above substances. It has been reported that 1 g

of iron will react with 300 ml of oxygen (8). The oxygen-

absorbing antimicrobial packaging has been successfully

commercialized in bakery, pasta, and meat products by

applying the agents enclosed in sachets or incorporated in

polymer matrix. Recently, diversiﬁed matrices for oxygen

absorbents are available in ﬁlm, tray, label, and closure

liner as well as sachet (8). In spite of the strong anti-

microbial activity of the oxygen scavenging system

ANTIMICROBIAL PACKAGING 51

against aerobic microorganisms, this system does not

possess the effective activity against anaerobic micro-

organisms.

Antimicrobial Packaging Containing Antimicrobial Agent

that Migrate into Food

The packaging materials may act as a carrier for anti-

microbial agents to perform their active role to control

microorganisms. Some of the antimicrobial agents may

be coated or directly incorporated into the packaging

materials and subsequently migrate to the food system.

The antimicrobial action is achieved by release of the

antimicrobial agents from the packaging material. The

released antimicrobial agents control the growth of micro-

organisms by altering cell membrane properties or by

inhibiting essential metabolic pathways of the microor-

ganisms (4–6).

Most spoilage incidents occur primarily at food surface

by the contamination of aerobic microorganisms. The

concentration of the antimicrobial agents above their

minimal inhibitory concentration (MIC) is required to

impart antimicrobial function. Without the antimicrobial

packaging concept, the excess amount of preservatives

such as benzoates and sorbates should be included in foods

to control the spoilage microorganisms. Thus, releasing

antimicrobial additives to the food surface conveniently

increases the additives concentration in the food surface

above the MIC while maintains the preservative concen-

tration inside the food at sufﬁciently low level (4). Con-

sidering that the use of preservatives for shelf-life

extension has been strictly controlled by food safety

authorities, antimicrobial packaging is advantageous in

reducing potential risks of consuming excess amount of

food preservatives.

An additional advantage of antimicrobial packaging is

the sustainable antimicrobial activity. The antimicrobial

agents initially included in food ingredients might be

inactivated by interacting with other food components.

For example, bacteriocins and enzymatic antimicrobial

agent applied in the foods or onto the food surface may

interact with proteolytic enzymes in food and may cause

the loss of antimicrobial activities. On the contrary, in-

corporation of the above substances in packaging ﬁlms did

not cause the loss of antimicrobial activity, controlled the

release of the antimicrobial agents, and maintained anti-

microbial activity for fairly long periods.

Nonvolatile Migration. The incorporated antimicrobials

are migrated to the food surface in either solute or gas

states. The migrating solutes are nonvolatile materials

such as organic acids and their salts, enzymes, bacterio-

cins, fungicides and some of natural extracts, while the

gases are volatiles such as alcohols, small phenolics,

aldehydes, and others (4–6, 8). They moved from the

ﬁlm matrix to the food surface and diffused or dissolved

into the food. Diffusion is a primary mechanism of non-

volatile solute transfer in the ﬁlm matrix, in which relates

to the release rate. The migration kinetics of nonvolatile

solute followed the Fick’s second law of diffusion, where

diffusion coefﬁcient depends on the type of ﬁlm materials,

microstructural voids in ﬁlm matrix, and environmental

temperature (9, 10). The migration of the antimicrobial

agents in the ﬁlm to the food surface requires directly

contact. The contact between the ﬁlm matrix and the food

surface throughout the shelf life should be assured for

their migration and, consequently, their antimicrobial

action. For this, the food should be a continuous matrix

without any factors that interfere with the diffusional

migration. This food matrix could be a liquid solution,

a semisolid paste, or a smooth solid matrix without

signiﬁcant pores, holes, or heterogeneous particles.

The antimicrobial agents in the food surface will move

into the center of the food by diffusion or dissolution. The

solubility and diffusion coefﬁcients of the agent in the food

are very important factors that govern the rate of agent

removal in the food surface. The antimicrobial concentra-

tion in the food surface could be maintained above the

MIC for their effectiveness in controlling the microbial

growth when the agent transfer in the food and ﬁlms are

balanced (5).

Volatile Migration. The migrating antimicrobials could

be gaseous compounds released from a gas emitting

material. The gaseous antimicrobials can be migrated

into the food surface and its packaging headspace or into

the air gap between the package and the solid food (4).

The migrating volatile gases include SO

, ethanol,

essential oils, and a component of natural herb and spice

extracts. The advantage of using volatile antimicrobial

agents is that the packaging ﬁlm does not need to contact

directly to the food surface. Therefore, food matrix in this

system could be highly porous foods, powdered foods,

particulate foods, or shredded and irregularly shaped

foods. Sometimes, however, the use of volatile antimicro-

bial is limited by the incompatibility of the agent with the

packaging materials, or by the loss of volatile antimicro-

bials during incorporation into packaging by extrusion or

coating (5).

The volatile antimicrobial agent initially incorporated

in the packaging ﬁlm or sachet material is transferred to

the ﬁlm surface and subsequently evaporated to the

packaging headspace. The vaporized agent in the head-

space is then absorbed to the food surface. Eventually, the

agent concentration in the food surface is equilibrated

with the volatilized antimicrobials in the headspace (4).

For the antimicrobial efﬁcacy of the agent, the agent

concentration in the food surface should be maintained

above the MIC of target microorganisms. The concentra-

tion of migrated agent in the food surface is determined by

the release rate of the volatile agent from the packaging

material and by the absorption rate of headspace volatile

agents into the food. The release rate of the agent from the

packaging material to the headspace depends on the

volatility of the agent which represents the partitioning

behavior between packaging material and headspace. The

absorption rate of the agent into food depends on the

solubility of the agent into the food ingredient. Therefore,

the composition of the food is a very important factor of the

agent’s solubility to the food materials. In general, the

volatile agents are more soluble in lipid foods than in

hydrophilic food materials.

52 ANTIMICROBIAL PACKAGING

The desired antimicrobial concentration of a food sur-

face can be attained by controlling the release rate of

antimicrobial agent from the packaging material surface.

When we use an appropriately selected ﬁlm layer that has

a speciﬁc permeability of the volatile substance, the anti-

microbial’s release rate could be controlled efﬁciently. The

microencapsulation of the volatile substance with appro-

priate wall materials may control the release of antimi-

crobials. This encapsulation method can also provide a

solution against the loss of volatile antimicrobials during

packaging material fabrication processes.

Antimicrobial Packaging without Antimicrobial Agent

Migration

Antimicrobial packaging can also use agents that are not

migrated into the food. The nonmigrating antimicrobial

packaging system can be achieved using inherently bioac-

tive polymers or developing novel packaging materials

where the antimicrobials are attached to the nonactive

ﬁlms by either covalent bond or ionic immobilizations (4).

In this antimicrobial packaging system, many antimicro-

bials are enzymes or chemicals that are directly and

indirectly participated in the microbial inactivation func-

tion. They participate in the biological reactions that lead

to the microbial inactivation or produce biologically active

radicals, ions, and reactive singlet oxygen that may induce

antimicrobial effects.

Since the biologically active compounds are not mobile,

the incorporation of the antimicrobials in the matrix

during ﬁlm fabrication processes is not considered neces-

sary. Although the incorporated antimicrobials uniformly

distributed in the ﬁlm matrix, their activity is limited to

the ﬁlm surface only. Therefore, imparting a biologically

active ingredient to the ﬁlm surface would be sufﬁcient to

exhibit the antimicrobial efﬁcacy of the nonmigrating

antimicrobial packaging ﬁlm. Therefore, assigning an

antimicrobial activity without migration of antimicrobials

can be performed by immobilizing nonmigrating antimi-

crobials on the polymer ﬁlm surface, by coating a very thin

layer of active matrix on to the packaging ﬁlm, or by

attaching antimicrobial compounds covalently on the ﬁlm

surface with the aid of multifunctional ligands (11).

The active materials in the ﬁlm surface may catalyze

antimicrobial action or provide sufﬁcient energies to form

ions and radicals on the food surface which are capable to

control microbial growth. Therefore, this type of antimi-

crobial ﬁlm is particularly effective for the packaging with

liquid food and is advantageous for regulatory com-

pliances. Since antimicrobial agents do not migrate into

the food system, the antimicrobial agents that are not

permitted as food ingredient and food additives may be

used for this purpose as food contact substances.

Inherently Antimicrobial Packaging Materials. Some

polymers are inherently antimicrobial, and they have

been utilized in many ﬁelds currently such as biomedical

instruments, ﬁlters, membranes, and packaging materi-

als. Cationic polymers such as chitosan, poly

L-lysine,

lysozyme, and numerous synthetic polymers that have

quaternary ammonium, phosphonium, and biguanide

compounds have exhibited to be effective antimicrobial

polymers.

It has been well known that chitosan (a natural poly-

saccharide), and its derivatives have an antimicrobial

effect due to the presence of a positively charged ammo-

nium group. Besides the natural antimicrobial polymers,

antimicrobial synthetic polymers have been produced by

polymerizing biologically active monomers. The widely

used biologically active materials for synthetic polymers

are the cationic compounds including quaternary ammo-

nium compounds (QACs), biguanide groups, quaternary

pyridinium compounds, phosphonium compounds, sulfo-

nium compounds, and 2-(4u-thiazolyl) benzimidazol (TBZ)

(Table 1). The functional groups are linked to reactive

groups of monomers and, in turn, have been polymerized

to form synthetic antimicrobial polymers (Figure 1).

Therefore, most synthetic antimicrobial polymers can be

understood as polymerized biocides, and the polymer

backbone has the multiplied activity of the antimicrobial

functions of attached biocides. Many of these polymers are

amphiphilic and positively charged.

The antimicrobial action of polycationic compound has

been considered as the disruption of cytoplasmic mem-

brane of bacterial cell (13). Polycationic antimicrobial

polymers are absorbed onto the negatively charged bacter-

ial cell surface at physiological pH by electrostatic inter-

action. The absorbed polycations are bound to cytoplasmic

membrane, and disrupt it. The consequent leakage of

potassium ions and other cytoplasmic constituents lead

to cell death. In particular, the mode of antimicrobial

action of QACs is the damage of cytoplasmic membrane

of bacteria through surfactant-like interaction resulting in

the loss of permeability properties of the membrane (14).

This means that the functional groups of the antimicrobial

polymer must diffuse through the microbial cell wall, be

water soluble, and have no interaction with the microbial

cell wall. For this, spacer molecules that link the biologi-

cally active agents to the polymer backbone are required to

allow the agent to have sufﬁcient freedom of motion when

the polymer backbone does not act as the spacer (11).

Physical modiﬁcation of polymers often produces biolo-

gically active packaging ﬁlms. Ultraviolet or electron beam

irradiation on polyamide ﬁlms increases positively charged

amine concentration on the ﬁlm’s surface, resulting in

enhanced cell adhesion potential. However, this type of

ﬁlm has limited microcidal effect, and microbial adsorption

on the ﬁlm surface diminishes antimicrobial activity. In-

corporation of antimicrobial agents into this ﬁlm matrix

may overcome these drawbacks successfully (7).

Immobilized Antimicrobial Agents in the Packaging Film

Matrix. The immobilized antimicrobial agents are not

removed from polymer surfaces. Various immobilization

techniques have been developed to overcome the contact

problems of antimicrobial residues to food surfaces.

The antimicrobial materials used for immobilization

include the hydrolysis product of a quaternary amine-

containing organosilicon salt, hexachlorophene, acriﬂa-

vine, antibiotics such as streptomycins and gentamycins,

and antimicrobial enzymes including lactoferrin, sulfhy-

dril oxidase, and bile-salt- stimulated lipase. The changes

ANTIMICROBIAL PACKAGING 53

in conformation and denaturation of proteins and peptides

may result in reduced antimicrobial activities of antimi-

crobial enzymes. The active site should be protected

during the ﬁlm formation.

INGREDIENT OF ANTIMICROBIAL PACKAGING

Film Matrix

The antimicrobial packaging system is comprised of ﬁlm

matrix and antimicrobial agents. In considering the

biologically active role of the antimicrobial agent in the

ﬁlm, the relationships between the ﬁlm matrix and the

antimicrobial agent would be critical, since thermal de-

gradation of the antimicrobial agent during ﬁlm fabrica-

tion and its chemical compatibility with the ﬁlm material

may limit the antimicrobial activity. Synthetic polymeric

packaging materials are produced by thermal processing

method such as extrusion. Thermally stable antimicrobial

agents should be incorporated. In general, synthetic ﬂex-

ible ﬁlms consist of many layers of different ﬁlms. Low-

density polyethylene (LDPE) has been used for the ﬁlm

layer that is in direct contact with the food. Therefore,

LDPE has been most widely used packaging materials

among the synthetic polymers for antimicrobial agent

carriers. For further modiﬁcation of the contact ﬁlm layer,

poly(ethylene-co-methacrylic acid) (PEMA) has also been

explored as a ﬁlm matrix (15).

Thermally unstable antimicrobial agents cannot be

used with extruded synthetic polymer ﬁlms, but they

can be applied to the biopolymeric ﬁlm matrix instead.

In general, biopolymer ﬁlms are formed by removing the

solvent from the ﬁlm solution in the cast plate. Therefore,

they do not require high temperature for polymer melting.

Examples of biopolymers are hydrocolloids including poly-

saccharide and protein, lipid, and the composite of hydro-

colloid and lipid. For antimicrobial purposes, the use of

biopolymeric ﬁlms such as chitosan, soy protein, whey

protein, corn zein, methyl cellulose (MC), and hydroxy-

propyl methyl cellulose (HPMC) ﬁlms with various anti-

microbial agents have been reported (16).

Antimicrobial Agent

The widely used method to inhibit the growth of undesir-

able microorganisms is the use of chemical agents exhibit-

ing antimicrobial activity. These chemicals may be either

synthetic compounds intentionally added to foods or natu-

rally occurring, biologically derived substances. The selec-

tion of an antimicrobial agent depends primarily on its

activity against the target microorganisms, compatibility

with the packaging material, and the heat stability during

the thermal process (4–6).

Table 1. A List of Synthetic Antimicrobial Polymers with Their Active Compounds (12)

Active Compound Biologically Active Polymer

Quaternary ammonium

compounds (QACs)

Poly[{dimethylalkyl-3-(and -4-)vinylbenzyl}alkylammonium chlorides]

Polyionenes (in-chain QAC of p-xylene spacer, in-chain QAC of hexamethylene spacer)

Hydroxyterechelic polybutadienes carrying covalently-bonded QAC

Polysiloxanes with pendant primary alcohol groups

Biguanide group Poly(hexamethylene biguanide hydrochloride)s

Polymer of methacrylate containing biguanide units

Quaternary pyridinium salt 4-[2,29-Bis(ethoxycarbonyl)ethyl]-1-alkylpyridinium bromide

Poly[iminoethyleneimino-2-[(1-butyl)pyridine-4-ylmethyl]malonyliminoethyleneiminoadipoyl bromide]

Phosponium salt Poly{trialkyl-3-[(and-4-)vinylbenzyl]phosphonium chloride}

Poly([ethylenebis(diphenylphosphonio)]ethylene dibromide)

Poly{[4-(2-tributylphosphonioethyl)styrene chloride]-co-4-(2-chloroethyl)styreme}

Poly{[4-(3-tributylphosphoniopropyl)styrene chloride]-co-4-(3-chloropropyl)styreme}

Sulfonium salt Poly[p-vinylbenzyltetramethlenesulfonium tetraﬂuoroborate]

2-(4u-Thiazolyl) benzimidazol

(TBZ)

Poly[N-Acryloyl-2-(4u-thiazolyl)benzimidazol]

Poly[2,4,4u-trichloro-2u-acryloyloxydiphenyl ether]

−

CH=CH

−

(CH

)

(CH

)

NH C NH

NHC

HCl

(a)

(b)

(c)

(d)

Figure 1. Monomers with antimicrobial activities. (a) Dimethy-

lalkyl-3-(and -4-)vinylbenzyl ammonium chlorides, (b and c)

polyionenes, and (d) poly(hexamethylene biguinide hydrochlor-

ide) (12).

54 ANTIMICROBIAL PACKAGING

Currently, synthesized chemical preservatives have

been widely employed to control the number of micro-

organisms in the packaged food, but increasing consumer

awareness of potential health risk associated with the

synthetic agent requires a substituent that is available in

the nature. The natural antimicrobial agents such as

bacteriocins and spice extract have long been used as

constituents of foods and showed negligible toxicity.

Therefore, natural antimicrobial agents are on the way

of replacing the synthetic antimicrobial agents as food

preservatives for direct deposition and also as ingredients

of packaging materials for migration into food.

Organic Acid. Sorbic acid, benzoic acid, propionic acid,

and their salts have been widely used for preventing

microbial deterioration of food. They are on the food

additive list in many countries and have been used under

the control of regulation for their potential health risk.

High polarity of organic acids causes them to be incompa-

tible with the apolar LDPE. Acid anhydrides were thought

to be more compatible than free acids and their salts

because of their lower polarity. Organic acid antimicro-

bials could be incorporated into the biopolymeric ﬁlm for

their compatibility.

Inorganic Metallic Ion.

Silver Ion. Silver ions in the microbial cell inhibit

metabolic enzymes and have strong antimicrobial activity.

Silver ions are generally incorporated into polymer ﬁlms

in the form of silver substituted zeolite, an ionic bonded

metallic compound in which the sodium ions present has

been substituted with the silver ions. Silver-substituted

zeolite is thermo-stable and can be applied to the thermal

process of synthetic polymers like polyethylene, polypro-

pylene, and nylon as well as biopolymeric ﬁlms (11, 17,

18). Silver ions are released from the silver-substituted

zeolite incorporated in the ﬁlm matrix to the food materi-

als for antimicrobial action (18).

Titanium Ion. Titanium dioxide (TiO

) is nontoxic and

has been approved by the U.S. Food and Drug Adminis-

tration for the use in foods and food contact materials (19).

Ultraviolet energy shifts the energy level of TiO

to the

excited state. On its way back to ground state, TiO

releases absorbed energy to the food material (20). The

released energy may form very reactive radicals and

singlet oxygen which have antimicrobial function. In this

system titanium ion is not a migrating agent but trapped

in the ﬁlm structure (20). Currently there is considerable

interest in the self-disinfecting property of TiO

to satisfy

hygienic design requirements in food processing equip-

ment surfaces (21, 22).

Natural Compounds. The naturally occurring antimi-

crobials are enzymes, peptides, oils, and other materials

that have been present self-defense functions against

microbial contamination. Typical examples are bacterio-

cins in lactic acid bacteria, lysozymes in egg white,

ﬂavonoids in plant extracts, and essential oils.

Bacteriocins. Bacteriocins are small bacterial peptides

that show strong antimicrobial activity against closely

related bacteria. Antimicrobial effectiveness of bacterio-

cins in food is related to speciﬁc antimicrobial activity of

the bacteriocin, amount of the bacteriocin used, number of

microorganisms, process conditions, interaction with food

components, and pH and temperature of the product (23).

Nisin is a polypeptide produced by Lactococcus lactis

spp. It has been approved as a food additive with GRAS

status in over 50 countries worldwide. It has a relatively

broad spectrum of antimicrobial activity against various

lactic acid bacteria and other Gram-positive bacteria (24).

It is particularly effective against heat-resistant bacterial

spores of Clostridium botulinum (25). It is not effective

against gram-negative bacteria because it cannot pene-

trate outer lipid membrane of cell to the cytoplasm (24).

Use of nisin in conjunction with ethylenediamine tetra-

acetic acid (EDTA) may increase the antimicrobial effec-

tiveness against Gram-negative bacteria (26). Nisin has

been incorporated into biopolymer ﬁlms such as soy

protein, corn zein, chitosan, and methylcellulose ﬁlms

for antimicrobial edible coating applications (27, 28). The

thermal processing in ﬁlm production may reduce anti-

microbial activity of nisin (28).

Lysozyme. Lysozyme, also known as muramidase or N-

acetylmuramichydrolase, is a relatively small enzyme

from hen egg white. Lysozyme is effective against spoilage

and pathogenic microorganisms by disintegrating the cell

wall structure. Antimicrobial activity of lysozyme is at-

tributed to the function that catalyzes the hydrolysis of

the b-1, 4 glycosidic bond between N-acetylmuramic acid

and 2-cetyl-amino-2-deoxy-

D-glucose residues in the bac-

terial cell wall (29, 30). Lysozyme demonstrates a strong

antibacterial potential against Gram-positive bacteria

such as Listeria monocytogenes (30). Lysozyme has been

applied to biopolymer ﬁlms such as chitosan, whey pro-

tein, ﬁsh gelatin, corn zein, and sodium alginate ﬁlms in

either puriﬁed or unpuriﬁed forms alone and in combina-

tion with EDTA and other bacteriocins (31, 32). Antimi-

crobial activity of immobilized lysozyme in polyvinyl

alcohol ﬁlm also has been reported against various spoi-

lage and pathogenic bacteria (33).

Plant Extracts. Antimicrobial activity of phytochemicals

in the extracts of spices and herbs has been demonstrated

by many researchers (5, 6, 31). In many cases, the

concentration of biologically active component in spices

and herbs and their essential oils are too low to be

effectively used for packaging applications due to their

limited sensory acceptance at high concentration level

(23). They may be used in junction with other biologically

active agents and contribute to total hurdle technology

system for microbial control. Many phytochemical com-

pounds in essential oils and extracts responsible for anti-

microbial activity are phenolic compounds.

1. Essential Oils. Plant extracts of coffee, green tea,

spices, and herbs (i.e., cinnamon, cloves, mustard

seed, oregano, rosemary, thyme and vanillin) have

been evidenced for their antimicrobial activity

against a wide spectrum of microorganisms (5, 34).

The antimicrobial activities of the spices are

ANTIMICROBIAL PACKAGING 55

associated with phenolic compounds in their essen-

tial oil fraction. The antimicrobial essential oil com-

ponents of cinnamon and cloves are eugenol and

cinnamaldehyde, respectively. Terpenes such as car-

vacrol, p-cymene, and thymol are the major volatile

components of oregano and thyme (23). Many essen-

tial oils are volatile and can be applied to volatile

migration when they are incorporated into the

packaging ﬁlm (31).

2. Allyl Isothiocyanate (AIT). Allyl isothiocyanate is a

naturally occurring nonphenolic volatile compound

responsible for the ﬂavor of horseradish, wasabi,

and mustard. Volatilized AIT has an effective anti-

microbial activity against variety of pathogens when

used at low concentration. AIT causes metabolite

leakage by affecting cell membranes (35). Antimi-

crobial activity of AIT-incorporated gelatin ﬁlm,

nylon 6,6 ﬁlm, and PVDC/PVC copolymer ﬁlm has

been reported against spoilage and pathogenic mi-

croorganisms (36).

COMMERCIAL APPLICATIONS

Commercialized Antimicrobial Packaging

Even though many research works have been conducted

all over the world, there are only a few commercialized

products of antimicrobial food packaging materials. This

is because of strict hygienic regulation on food packaging,

high price, and limited consumer perception and accep-

tance on their effectiveness. The area of food preparation

and utensil products has less strict regulation in applying

the antimicrobial materials into real practices and has

seen a higher number of commercial products—for exam-

ple, kitchen board and gloves. Table 2 lists some examples

of commercial products available in market. The list is not

exclusive and covers only those observed in the writers’

eye for the last 20 years. Some products available in a

country or area may not be allowed for sale in other

countries because of the difference in food safety

regulation.

In a practical sense, ethanol emitter and plant extracts

have acquired wider acceptance, depending on people’s

attitude and corresponding country’s legislation. Some

ethanol emitters combine the oxygen-scavenging capacity

to inhibit aerobic spoilage organisms. Ag-containing cera-

mic materials have been applied in plastic ﬁlms and

containers where people generally recognize silver as

hygiene-improving and antitoxic material. SO

generator

may be used in postharvest handling and storage of

agricultural products, where agricultural safety practices

are applied. A ClO

-generating plastic tube, Knick’n’-

clean

, which is activated by bending to mix two ﬂuids

in it, is marketed for the use in refrigerators for a limited

time period of about 30 days. A ClO

-emitting ﬁlm (Micro-

Gardet) claimed to produce antimicrobial microatmo-

sphere for 10 days keeping freshness of foods and

breaking down ethylene gas. Until 2008, ready-to-eat

food applications of this system await FDA clearance in

the United States. Triclosan is not approved as a food

additive and is incorporated into a plastic master batch,

which is converted into food-contact household equip-

ments such as cutting board and hand gloves.

Edible coating being a component of food may be

applied for antimicrobial function when it contains safe

Table 2. Some Commercialized Antimicrobial Packaging or Food-Contact Materials in Food Storage, Packaging,

and Preparation

Active Compound or Releasing

Compound Matrix or Form Application Trade Name and/or Producer

Ag-substituted zeolite or

zirconium

PVC, LLDPE, PE, rubber Wrap, ﬁlm, kitchen board,

kitchen glove

Agion

(Agion Technologies,

USA), Zeomict (Sinanen

Zeomic Co., Japan),

Cleanaidt (Gyunghyang

Industrial Co., Korea)

Chlorine dioxide Polyoleﬁn Film, compartmented stick for

refrigerator

MicroGardet (BarrierSafe

Solutions International Inc.,

USA), Knick’n’clean

(Helrik Bobke, Germany)

Ethanol Silicon dioxide Sachet Ethicapt (Freund Corp.,

Japan), Agelesst type SE

(Mitsubishi Gas Chemical.,

Japan)

Sulfur dioxide Laminated plastic sheet with

Sheet or pad for postharvest

storage of grape fruits

Uvasyt (Grapetek, South

Africa)

Triclosan Polymer, rubber, etc. Food preparation equipment

and supplies, kitchen sponge

and gloves

Microban

(Microban

International Ltd., USA),

Ultra-Fresh

(Thomson

Research Associates,

Canada)

Wasabi (Japanese horseradish)

extract

Encapsulation in cyclodextrin Coated PET ﬁlm, tablet Wasapowert (Sekisui Plastics

Co., Japan)

56 ANTIMICROBIAL PACKAGING

bioactive compounds, organic acids, or edible essential oils

of plant or spice origins. Because the coating may be

understood as a food component, there would be no barrier

of application in the regulations if all active/inactive

ingredients are food grade. The potential edible coating

matrices include chitosan, hydroxy propyl methyl cellu-

lose, and alginate gels (29).

Effectiveness of Antimicrobial Food Packaging

Many studies showed potential beneﬁts of antimicrobial

packaging for fresh fruits and vegetables, milk, beverages,

cheese, ham, meat and ﬁsh (37, 38). Packaging materials

with nisin, chitosan, or acids typically resulted in mar-

ginal microbial count reduction of 1.5–2.5 log10 compared

to control (37). The reduction or suppression of microbial

growth by the antimicrobial packaging is varied too much

to conclude that any speciﬁc system or condition is uni-

versally optimal or better than others. It is generally

accepted that the results in microbial media or buffer

solutions cannot be directly applied to the real food

applications. Conducting test with real food sample is

needed for practical or commercial application.

The effectiveness of microbial inhibition by antimicro-

bial packaging is generally improved when combined with

other preservation hurdles such as modiﬁed atmosphere,

low pH, high-pressure treatment, and low temperature

(38–40). Analysis of microbial spoilage kinetics with anti-

microbial packaging showed that the microbial growth was

suppressed more with lower storage temperature (41). The

microbial inhibition of antimicrobial packaging at the low

temperature could be represented by low cell concentra-

tion, extended lag time, and reduced growth rate.

When the temperature dependence of microbial lag

time was analyzed by square root kinetic model [equation

(1)], antimicrobial packaging showed higher temperature

dependence (increased b value) with increase of hypothe-

tical minimum growth temperature (increased T

min

) (41):

ﬃﬃﬃﬃﬃﬃﬃ

lag

¼ b ðT  T

min

Þð1Þ

where T is the temperature (in 1C), b is slope parameter

representing temperature effect, and T

min

is respective

theoretical minimum temperatures for growth estimated

by extrapolation of the regression line to the temperature

axis (Figure 2).

The effectiveness of antimicrobial packaging may vary

with food type, release kinetics of antimicrobial agents,

and environmental factors. Many antimicrobial packaging

systems that show effective activity with microbial culture

media may not work with real foods. Some food compo-

nents such as fatty acids, amino acids, sulfates, and/or

enzymes may diminish the activity of the antimicrobial

packaging ﬁlms (11, 42). Food–package interaction may

change the mechanism and effectiveness of microbial

inhibition of the antimicrobial packaging system (29).

There are possibilities that the incorporation of antimi-

crobials into the plastic material may change its mechan-

ical, barrier, and optical properties. Sensory properties of

food may also be affected by food–package interaction. For

example, ﬁlm with plant extract such wasabi essential oil

may alter ﬂavor of the contained food. The antimicrobial

packaging may have to be designed, selected, and custo-

mized for each food type (43). The packaging system has to

be selected after consideration on the primarily concerned

target microorganism, spoilage organisms, its activity

spectrum, microbial inhibition mode, food properties, re-

lease of active agent, and storage conditions.

Regulations

Antimicrobial packaging to be marketed in the United

States is subject to the food additive approval process if its

components are reasonably expected to migrate to foods

for effective microbial inhibition (4). There are two pro-

cesses of food contact substance approval in FDA: food

contact notiﬁcation process and food additive petition

process. Packaging material that has no intended techni-

cal effect on the food may be approved by the former

process, in which a manufacturer should notify the FDA to

market a new product at least 120 days before its intro-

duction and can sell it unless the FDA objects to the

notiﬁcation. However, the material that exerts antimicro-

bial effect on the food through migration or controlled

release needs to be processed through the food additive

petition process. Food contact substance notiﬁcation is

speciﬁc only to the manufacturer named in the notiﬁca-

tion, and it does not apply generically to the product

category. Due to complicated and strict regulation on

approval of antimicrobial food packaging materials, their

applications in food packaging is very limited in the

United States. Chlorine-dioxide-releasing material seems

to reach the commercial stage (42). Some silver incorpo-

rated materials are approved for food-contact purpose (6).

Until 2004, plastic packaging regulations in the EU did

not allow any speciﬁc provisions for antimicrobial packa-

ging and, thus, required that any potential antimicrobial

component in the antimicrobial food packaging should be

covered by ‘‘positive lists,’’ which would have speciﬁc

0.2

0.4

0.6

0.8

1.2

1.4

0 5 10 15 20 25

Temperature (°C)

(1/tlag)

1/2

Figure 2. Effect of antimicrobial packaging (incorporated with

chitosan and nisin) on temperature dependence of microbial lag

time. (&) Yeasts of orange juice in plain package; (’) yeasts of

orange juice in the antimicrobial package; (



) aerobic bacteria of

milk in plain package; (



) aerobic bacteria of milk in the anti-

microbial package. (From data of Ref. (41)).

ANTIMICROBIAL PACKAGING 57