Jung Han. Innovations in Food Packaging

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90 Innovations in Food Packaging

encourage the antimicrobial activity of the packaging system, such as refrigeration,

the antimicrobial effectiveness will be increased; however, generally refrigeration is

not necessary when all of

the

system factors satisfy the requirements. Refrigeration

may be very effective in inhibiting the growth of untargeted (unexpected) micro-

organisms. If the initial concentration of microbiocidal antimicrobial systems is lower

than the m.i.c. of the target micro-organisms, and the concentration has never been

above the m.i.c, the agent may show a microbiostatic instead of a microbiocidal

effect. Therefore, it is very important to maintain the antimicrobial concentration

above the

m.i.c.

for certain critical

periods,

to eliminate the target micro-organisms. If

the package has hermetically sealed, the packaged foods may not contain any live

micro-organisms even when the concentration decreases to below the

m.i.c.

due to the

migration or loss of the agent after the critical period.

Microbiostatic

Microbiostatic agents can inhibit the growth of micro-organisms above a certain crit-

ical concentration

(i.e.

m.i.c). However, when the concentration is lower than the crit-

ical concentration, or when the agent is removed from the packaging systems through

a seal defect, leakage, opening or any other means, the suppressed micro-organisms

can grow or their spores germinate. Therefore, it is critical to maintain the concentra-

tion of the antimicrobial agent above the

m.i.c.

during the entire shelf life of the pack-

aged foods. Chemical indicators that show the concentration or microbial growth

would be very beneficial in microstatic antimicrobial packaging systems, and this is a

concept of intelligent packaging (Rodrigues and Han, 2003).

Functioning modes and volatility

In most packaged solid or semi-solid foods, micro-organisms grow primarily at the

surfaces of the foods (Brody et

al.,

2001). Therefore, antimicrobial activity should be

exerted on these surfaces. The antimicrobial activity may exist in packaging materi-

als,

in the in-package atmosphere or in the headspace, varying the incorporation

methods. The antimicrobial activity should be transferred to the surface of foods to

suppress the microbial growth. Therefore, incorporation methods and transferring

techniques are critical in designing effective antimicrobial packaging systems. As

examples of incorporation methods, antimicrobial agents have been impregnated into

packaging materials before final extrusion (Han and Floros, 1997; Nam et

al.,

2002),

dissolved into coating solvents (An et al., 2000), added in edible coating materials

(Rodrigues and Han, 2000; Rodrigues et al., 2002), and mixed into sizing/filling

materials such as paper and cardboard (Nadarajah et al., 2002). Gaseous antimicro-

bial agents can also be added to the package atmosphere (Lanciotti et al.,

2003;

Krause era/., 2003).

The edible coating system has various benefits due to its edibility and biodegrad-

ability (Krochta and De Mulder-Johnston, 1997). The edible coating may be either a

dry coating or a wet battered coating. Dry coatings can incorporate chemical and nat-

ural antimicrobials, and play the role of physical and chemical barriers as well as a

Antimicrobial packaging systems 91

microbial barrier (Han,

2001,

2002). Wet coating systems may need another wrapper.

However, the wet system can carry many different types of functional agents as well

as probiotics and antimicrobials (Gill, 2000). Lactic acid bacteria can

incorporated

into the wet coating system and control the competing undesirable bacteria. This new

wet coating system may be very beneficial to the fresh produce, meats and poultry

industries.

Chemical immobilization covalently binds the agents into the chemical structures

of packaging materials when regulations do not permit the migration of agents into

foods (Miller 6^ a/.,

1984;

Halek and

Garg,

1989;

Appendini and

Hotchkiss,

1996,1997).

The immobilized antimicrobial agents will inhibit the growth of micro-organisms on

the contact surfaces of packaged products.

Non-volatile migration

The mass transfer of non-volatile antimicrobials is dominated by dififusional migra-

tion. Non-volatile agents will be positioned initially in the packaging materials or

between the package and the surface of the food. If the agent is sprayed onto the sur-

face of food, the initial surface concentration will be very high and starts to decrease

due to dissolution and diffusion of the agent towards the center of the food. Therefore,

the solubility (or partition coefficient) and diffusion coefficient (diffusivity) of the

agent in the food are very important characteristics to maintain the surface concen-

tration above the effective m.i.c. during the expected shelf

life.

the

agent is incor-

porated into packaging material initially, it should escape from the packaging material

and dissolve into the food before diffusing into the food core. Therefore, the signifi-

cant characteristic constants of the mass transfer profile are the diffusivity of the agent

in the packaging material, the solubility (or partition coefficient) of

the

agent in the

food at the surface, and the diffusivity of the agent in the food. It is important for the

food/packaging/antimicrobial agent system to have mass transfer kinetics appropriate

to the microbial growth kinetics in order to provide efficient antimicrobial activity. To

understand the concentration distribution profile, it is necessary to simulate mass

transfer models which have more than two-layer diffusion and interface partitioning

(or dissolution). Since the migrating agent is non-volatile, this system requires intact

contacting between the packaging materials and the food surface. The food should be

a continuous matrix form without significant pores, holes, air gaps or heterogeneous

particles, due their interference with the diffusion. One-piece solid, semi-solid (soft

solid) foods and liquid products are good examples of the products that can use this

non-volatile migrating antimicrobial packaging system.

Practical examples of this system may include cured or fermented meats and

sausages battered with antimicrobial agents, natural cheeses sprayed with potassium

sorbate before packaging, antimicrobial plastic films for deli products, antimicrobial

wax coatings on fruits, and antimicrobial cleansing of fruits/vegetables before pack-

aging. The advantages of this non-volatile migrating system are the simplicity of the

system design, which could be installed ahead of the currently existing packaging

process without high investment load, and the easy maintenance required to control

the effectiveness.

92 Innovations in Food Packaging

Volatile migration

Many researchers have claimed that it

necessary

have intact contact of the antimi-

crobial material with the food surface to facilitate the migration of the active agent

for maximal effectiveness (Vermeiren et ai, 2002; Suppakul et al, 2003

a).

However,

this is not necessary when using volatile antimicrobial agents.

maintain the surface

concentration above a certain m.i.c. it is very important to control the headspace

gas concentration, since the volatile agent's concentration in the headspace has

been equilibrated with the concentration on the food surface and in the packaging

materials. Initially the volatile agent is placed in the packaging material, whether it is

a film, container, sachet or

tray.

After packaging the food, the volatile agent is vapor-

ized into the headspace, reaches the surface of the food and is absorbed by the food.

The mass transfer of a volatile agent in the packaging system is more dynamically

balanced. The release rate of

the

volatile agent from the packaging system is highly

dependent on the volatility, which relates to the chemical interaction between the

volatile agent and the packaging materials. There are ways to control the volatility of

the agent in the packaging system, including the use of

oil,

cyclodextrin or microen-

capsulation. These techniques can control the volatility of

the

agent and, eventually,

the headspace concentration. The absorption rate of headspace volatiles into the food

surface is related to the composition of

the

foods, as the ingredients undergo chemi-

cal interactions with the gaseous agents. Since most volatile agents are generally

lipophilic, the lipid content of the food is an important factor of the headspace

concentration.

The use of volatile antimicrobial agents has many advantages. This system can be

used effectively for highly porous foods, powdered, shredded, irregularly shaped, and

particulate foods, such as ground

beef,

shredded cheese, small fruits, mixed vegeta-

bles,

etc. Because natural herb and spice extracts provide the majority of volatile

antimicrobial agents, this system is linked to the nutraceutical research and develop-

ment area as well as being easily accepted

consumers and governmental regulatory

agencies.

Non-migration and absorption

The non-migration system uses non-migratory antimicrobial polymers, where the

antimicrobial agent does not migrate out of the polymer due to its covalent attachment

to the polymer backbone (Steven and Hotchkiss, 2003). Besides the antimicrobial

agents, other

bioactive

agents (such

enzymes, proteins and other organic compounds)

can

attached

the polymer through covalent cross-linkers. Since the agents are not

mobile, their activity

limited

the contact surface

only.

This limitation

more crit-

ical in solid or semi-solid foods. However, in liquid foods the disadvantages of this

non-migration characteristic may be minimized. This system could be designed for

large-size membrane reactors or processing units to convert any pre-existing sub-

strates into valuable compounds using immobilized enzymes.

For the

fiiture,

impor-

tant that

this

packaging system

evaluated

assess whether it can

used effectively

unit-operation substituting reaction process during any necessary timed processes

such as aging, chilling, tank-holding, etc.

Antimicrobial packaging systems 93

As a food packaging system, this non-migration system has unique advantages in

marketing and

regulation.

Since the active agents are not

migrating,

this system requires

a very small amount of attached agents. It may reduce the overall cost of packaging

systems that use very expensive antimicrobial agents. The non-migrating system can

include agents that are not permitted as food ingredients or food additives. With the

verification of non-migration, the packaging material may contain any food contact

substances. From the marketing aspect this system is attractive because the food does

not contain any chemical antimicrobial agent throughout its shelf life. However, in

contrast to the benefits, this system may have a very limited selection of antimicrobial

agents and may also be limited in application to certain types of

foods.

Shapes and compositions of systems

Packaging is a system used to contain and protect enclosed products, which consists

of a product, a

package,

and the in-package atmosphere. Antimicrobial agents may be

incorporated in the non-food parts of the packaging system, which are the package or

the in-package atmosphere. Antimicrobial agents can be incorporated directly in

packaging materials in the form of

films,

over-coating on

films,

sheets, trays, and con-

tainers, or in the in-package space in the form of inserts, sachets or

pads.

Edible coat-

ings also can contain edible antimicrobial agents, protecting the coated foods from

microbial quality degradation (Han, 2001). Figure 6.1 illustrates the possible forms of

antimicrobial packaging systems (Han, 2003

a).

Food

1 1

1—^r~

1—•v-

Food 1

JA—1

Figure 6.1 Possible ways to construct antimicrobial food packaging systems. A, the use of antimicrobial

packaging materials; B, antimicrobial coating on conventional packaging materials; C, immobilization of

antimicrobial agents in polymeric packaging materials; D, the use of antimicrobial trays or pads; E, the use

ofsachet/insert containing volatile antimicrobial agents; F, antimicrobial edible coating on foods (adapted

from Han, 2003b).

94 Innovations in Food Packaging

Commercialization

Some commercial antimicrobial packaging systems are listed in Table 6.3. Most sys-

tems consist of silver-containing active agents. Table 6.4 lists potential applications

of antimicrobial packaging and food groups. Since foods are complex systems with

respect to their composition, there are many factors to be considered in commercial-

izing antimicrobial packaging systems.

Technical factors

Compatibility of process conditions and material characteristics

Film/container casting methods, i.e. extrusion and solvent casting, are important to

maintain antimicrobial effectiveness. In the case of extrusion, the critical variables

related to the residual antimicrobial activity are extrusion temperature and specific

Table 6.3 Examples of commercial antimicrobial packaging products and manufacturers

Trade name

Piatech

Silvi Film

Okamoto Super

Wrap

Apacider

Zeomic

Bactekiller

Zeomix

AglON

MicroFree

Novaron

Surfacine

lonpure

Microban

Sanitized,

Actigard,

Saniprot

Ultra-Fresh

WasaOuro

MicroGarde

Take Guard

Acticap

Biocleanact

Microatmosphere

Active compounds

Ag oxide

Ag zeolite and others

Ag zeolite

Ag,

copper oxide, zinc

silicate

Ag zirconium

phosphate

Ag-halide

Ag/glass

Triclosan

Triclosan and others

Allyl isothiocyanate

Clove and others

Bamboo extract

Ethanol

Antibiotics

Chlorine dioxide

Manufacturer

Daikoku Kasei Co. (Japan)

Nimiko Co. (Japan)

Okamoto Industries,

Inc. (Japan)

Sangi Co. (Japan)

Shinanen New Ceramics

Co.

(Japan)

Kanebo Co. (Japan)

Mitsubishi Int. Corp. (Japan)

AglON Technologies LLC

(USA)

DuPont(USA)

Milliken Co. (USA)

Surfacine Development Co.

(USA)

Ishizuka Glass Co. (Japan)

Microban Products Co. (USA)

Sanitized AG/Clariant

(Switzerland)

Thomson Research Assoc.

(Canada)

Green Cross Co. (Japan)

Rhone-Poulenc (USA)

TakexCo. (Japan)

Freund Industrial Co. (Japan)

Micro Science Tech Co. (Korea)

Southwest Research Institute

(USA), Bernard Technologies

Inc. (USA)

References

Brody

etal.,

2001

BrodyetaL, 2001

Brody

etal.,

2001

Brody

etal.,

2001

Brody

etal.,

2001

Brody et^/., 2001

Brody

etal.,

2001

Suppakul

etal.,

2003a;

www.agion-tech.com

Vermeirenet^/., 2002;

Brody

etal.,200^

VermeWer}

etal.,

2002

Vermeiren

etal.,

2002

Vermeiren

etal.,

2002

Brody

etal.,

2001

Vermeiren et^/., 2002;

Suppakul

etal.,

2003a

Vermeiren

etal.,

2002

Brody et^/., 2001

Brody

etal.,

2001

Brody

etal.,

2001

Smith

etal.,

1987

Han and Moon, 2002;

www.biocleanact.com

Brody

etal.,

2001

Antimicrobial packaging systems 95

mechanical energy input. The extrusion temperature is related to the thermal degra-

dation of the antimicrobial agent, and the specific mechanical energy indicates the

severity of the process conditions that also induce the degradation of the agents. Nam

et al. (2002) showed the severe decrease in the activity of lysozyme in an extruded

starch container as the extrusion temperature increased. In the case of the wet casting

method (that is, using solvent to cast films and containers such as cellulose films and

Table 6.4 Potential applications of antimicrobial food packaging

Antimicrobials Meat/poultry Dairy Seafood

Produce

Bakery

Minimally

processed

Organic acids Fresh meat, Cheese

and their salts sausage, ham,

chicken

Ethanol

Fruits,

vegetables,

jam/jelly

Nuts

Fruit

juice,

wine

Bread,

cakes,

Precut salad,

noodle, pasta,

steamed rice,

sauce/dressing

Noodles,

pasta,

sandwiches

Bacteriocins

Enzymes

Chelating

agents

Fungicides

Sanitizers

Volatile

essential oils

Spices

Probiotics

Oxygen

scavengers

Fresh meat,

sausage,

ham,

chicken

Fresh meat,

sausage, ham,

chicken

Fresh meat.

sausage, ham,

chicken

Fresh meat,

chicken

Fresh and

processed

meats, ground

beef,

chicken

nuggets

Fresh and

processed

meats, fresh

and cooked

chicken

Fresh and

processed

meats, cured

meats

Fresh and

processed

meats, ground

beef,

dried

meats, chicken

Cheese

Shredded

cheese

Cheese

Cheese, yogurt

Shredded

cheese

Fish,

shellfish

Fish,

shellfish

Fish,

shellfish

Fish,

shellfish

Fish,

shellfish.

dried fish

Fish,

shellfish,

dried fish

Dried fish

Fruits,

Jam/jelly

Citrus, berries,

nuts

Fruits,

vegetables

Berries, nuts.

jam/jelly

Fermented

vegetables

Nuts,

jam/jelly

Bread,

cakes.

Bread,

cakes,

Fruit juice

Fruit juice,

wine

Ham/egg

sandwiches

Ham/egg

sand wiches,

meatball pasta

Precut fruits,

sauce/dressing

Precut salad

Noodles,

pasta,

steamed rice,

sandwiches,

hamburgers,

precut salad,

sauce/dressing

Noodles,

pasta,

steamed rice,

sandwiches,

sauce/dressing

Deli mix

Noodles,

pasta,

steamed rice,

sandwiches,

hamburgers,

sauce/dressing

96 Innovations in Food Packaging

collagen casing), the solubility and reactivity of the antimicrobial agents and poly-

mers to the solvents are the critical factors. The solubility relates to the homogeneous

distribution of the agents in the polymeric materials, while the reactivity relates to the

activity loss of the reactive antimicrobial agents.

The chemical properties of the antimicrobial agent, such

solubility, are also impor-

tant factors. For example, when water-soluble agents are mixed into plastic resins to

produce antimicrobial films, the plastic extrusion process may be beset with various

problems including crevice hole creation in the films, powder-blooming, the loss of

physical integrity, and/or the loss of transparency due to the heterogeneous blending

of the hydrophilic agents with the hydrophobic plastics. Therefore, the compatibility

of antimicrobial agent and packaging material is an important factor. The pH of the

system is also important. Most antimicrobial chemicals alter their activity with differ-

ent pH. The pH of

the

packaging system mostly depends on the pH of

the

packaged

foods,

and therefore consideration of

the

food composition along with the chemical

nature of the antimicrobial agent is important, as well as consideration of the packag-

ing material reaction with the chemical nature of the agents (Han, 2003b).

Storage and distribution conditions are further significant factors, including the

storage temperature and

time.

This time-temperature integration affects the microbial

growth profile, chemical reaction kinetics, and the distribution profile of antimicro-

bial agents in the food.

prevent microbial growth, storage at the temperature range

favorable for microbial growth should be avoided or minimized for the whole period

of storage and distribution.

In the

case of modified atmosphere packaging with antimicrobial

gas,

the active gas

permeation through the packaging materials may be changed by the temperature and

time profile during the whole period of storage and distribution. When the gas com-

position is altered through active gas permeation, unexpected gas invasion or a seal

defect, micro-organisms that are not considered as target micro-organisms may spoil

the packaged foods.

Physical properties of packaging materials

The physical and mechanical properties of packaging materials are affected by the

incorporated antimicrobial agents. If the antimicrobial agent is compatible with the

packaging materials, a significant amount of the agent may be impregnated into

the

packaging material without any deterioration of

its

physical and mechanical integrity

(Han and Floros, 1997). However, excess antimicrobial agent that is not capable of

being blended with packaging materials will decrease physical strength and mechan-

ical integrity (Cooksey, 2000). Polymer morphological studies are very helpfiil in pre-

dicting the possible loss of physical integrity when the antimicrobial agent is added to

the packaging material, in the case of polymeric packaging materials. Small-size

antimicrobial agents can

blended with

polymers,

and may be positioned at the amor-

phous region of the polymeric structure without significant interference with polymer -

polymer interactions. If

high level of antimicrobial agent is mixed into the packag-

ing

materials,

the space provided by the amorphous region will be

filled

and the mixed

agent will start to interfere with the polymer-polymer interactions at the crystalline

Antimicrobial packaging systems 97

region.

Although there is no damage to the physical integrity after low levels of antimi-

crobial agent addition, optical properties can be changed - for example, there may be

a loss of transparency or a change in the color of

the

packaging materials (Han and

Floros, 1997).

Controlled release technology

The design of an antimicrobial packaging system requires the balanced consideration

of controlled release technology and microbial growth

kinetics.

When the mass trans-

fer rate of an antimicrobial agent is faster than the growth rate of the target micro-

organism, loaded antimicrobial agent will be diluted to less than the effective critical

concentration (i.e. minimum inhibitory concentration,

m.i.c.)

before the expected

storage period is complete, and the packaging system will lose its antimicrobial activ-

ity because the packaged food has almost infinite volume compared to the volume of

packaging material and the amount of antimicrobial agent. Consequently, the micro-

organism will start to grow following depletion of the antimicrobial agent. On the

contrary, when the migration rate is too slow to maintain the concentration above the

m.i.c,

the

micro-organism can grow

instantly,

before

the

antimicrobial agent

released.

Therefore, the release rate of

the

antimicrobial agent from the packaging material to

the food must

controlled specifically to match

the

mass transfer

rate

with

the

growth

kinetics of the target micro-organism. Controversially, in the case of antimicrobial

edible coating systems the mass transfer of antimicrobial agents is not desirable, since

the migration of the incorporated antimicrobial agents

fi*om

the coating layer into the

food product dilutes the concentration in the coating layer. Compared to the volume

of the coating layer, the coated food

has

almost infinitive

volume.

Therefore, the migra-

tion will deplete the antimicrobial agent in the coating layer, decrease the concentra-

tion below the m.i.c, and thus reduce the antimicrobial activity of the coating system.

The migration of incorporated antimicrobial agents contributes to antimicrobial effec-

tiveness in the case of packaging systems; on the contrary, no migration is beneficial

in the coating system.

The solubility of the antimicrobial agents in the foods is a critical factor of antimi-

crobial release. If the antimicrobial agent is highly soluble in the food, the migration

profile will follow unconstrained free diffusion, while the very low solubility creates

the dissolution-dependent monolithic system. For

example,

when highly soluble potas-

sium sorbate was incorporated in packaging materials (e.g. plastic films or papers)

and the antimicrobial packaging materials were used for semi-solid or high-moisture

foods,

such as paste, yogurt, fruit jelly, soft cheese and sliced ham, the potassium sor-

bate dissolved in the food immediately after packaging. The potassium sorbate con-

centration increased very fast on the surface of the foods and the surface concentration

decreased slowly as the potassium sorbate diffused into the food. Fast diffusion of the

antimicrobial agents in the food decreased the surface concentration rapidly. The

maintenance of the surface concentration is highly dependent on the release rate fi:om

the packaging materials (diffiisivity of packaging materials) and the migration rate of

the foods (diffusivity of

the

foods). Since the flux of

the

release from the packaging

materials decreases as the amount of antimicrobials in the packaging materials reduces

98 Innovations in Food Packagi

ging

U.w,.^,.,kl'.l.,.,iiVIV

o o

( ) o ©

O oO 03

o[t::i

O ^ a

Storage time

Figure 6.2 Release profiles of antimicrobial agents from various systems. A, unconstrained free

diffusion from packaging materials, or fast dissolution from antimicrobial tablets; B, slow diffusion of very

low solubility agents from monolithic packaging materials; C, membrane (reservoir) system with constant

flux of permeation, slow dissolution from antimicrobial powder/tablets or gaseous agent release from

concentrated antimicrobial sachets/tab lets with constant volatility in a closed packaging system. Dashed

lines and arrows indicate the minimum inhibitory concentration (m.i.c.) of

target micro-organism, and

the period of shelf life maintaining the surface concentration over the

m.i.c,

respectively.

with release time, the period when the surface concentration is maintained above the

m.i.c.

is carefully estimated, considering its rapid decay profile (Figure 6.2A).

When the solubility of antimicrobial agents in the packaged food is very low, the

antimicrobial concentration on the contact food surface is at its maximum solubility.

Since the release rate is relatively slower than unconstrained fi'ee diffusion, which

occurs in high solubility, the period of maintaining the concentration above the m.i.c.

in this slow-release system is generally longer than in the free diffusion system. If the

antimicrobial agents are impregnated into the polymeric packaging materials, the dif-

fusivity of the agent in the polymeric matrix will control the release rate significantly.

This system, shown in Figure 6.2B, may include, for example, sorbic acid anhydride

propyl para benzoic acid

plastic films that wrap high-moisture foods such as fruit

jelly or soft

cheese.

Since the antimicrobial agents are less soluble in

water,

the release

of these agents

fi*om

hydrophobic plastic will be very

slow.

takes

more time to reach

the maximum peak concentration, and there will be a longer period above the m.i.c.

than in the system shown in Figure 6.2A. After the agents initially located on the sur-

face of plastic films have migrated into the food, the release

flux

will decrease because

the agents positioned inside the plastic film should diffuse to the surface of the plas-

tic film. Because of this internal diffusion, the release kinetics do not show a zero-

order profile which has a constant release

flux.

The concentration on the food surface

will decrease due to the migration of the agent into the contained food products as

well as the reduction of release flux.

Antimicrobial packaging systems 99

Figure 6.2C illustrates the greater period of concentration above the m.i.c. given by

membrane systems, which consist of a permeable membrane that controls the release

rate.

In the case of liquid pharmaceuticals, the release rate will be controlled by the

permeability of the liquid agents through the control layer. Until the liquid agent is

depleted, the system maintains a zero order of release with a constant permeation flux.

This system may include volatile agent concentrates, such as horseradish

oil.

Horseradish

oil contains allyl isothiocyanate, which is a strong volatile flavoring and antimicrobial

agent. The volatile agent will split between the oil and the headspace of

packages.

there is enough oil in the package, the headspace concentration will be equilibrated

and maintained above the m.i.c. until the oil has disappeared. The equilibrated parti-

tioning is an important factor in controlling the release rate as well as the headspace

concentration.

Extra advantages

Traditional preservation methods sometimes include antimicrobial packaging

concepts - for example, the sausage casings of cured/salted/smoked meats, smoked

pottery/oak barrels for fermentation, and brine-filled pickle jars. The basic principle

of these traditional preservation methods and antimicrobial packaging is one of hur-

dle technology applications. The extra antimicrobial function of the packaging system

is another hurdle to prevent the degradation of quality and improve the safety of pack-

aged foods, in addition to the conventional protective functions of providing moisture

and oxygen barriers as well as physical protection. The microbial hurdle provides the

extra function of protection against micro-organisms, which has never been achieved

by conventional moisture- and oxygen-barrier packaging materials. Therefore, antimi-

crobial packaging is one of active packaging and hurdle technology applications. The

hurdle technology concept of antimicrobial packaging systems can enhance the effi-

ciency of other sterilization processes, such as aseptic processes, non-thermal processes

and the conventional thermal process, where the sterile foods are packaged in the

antimicrobial packaging systems.

Since the antimicrobial packaging system can incorporate natural antimicrobial agents

such as plant and herb extracts or probiotics, it is considered that natural antimicrobial

packaging design development has a connection to nutraceutical research and phar-

macognosy. This relationship may be helpful in transferring food packaging knowl-

edge to the area of nutraceutical and pharmaceutical research because of the studies

on the barrier properties of materials to volatile active ingredients, and the studies on

the clinical effectiveness of natural active agents.

Regulatory, marketing and political factors

The use of antimicrobials should follow the guidelines of regulatory agencies (Meroni,

2000;

Brody et al, 2001; Vermeiren et al, 2002; Han, 2003a, 2003b). Antimicrobial

agents are additives of packaging material, not food ingredients; however, when the

antimicrobial agents migrate into foods, they also require food ingredient approval -

as for food contact substances and packaging additives. Therefore, the use of natural