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Antimicrobial Active Packaging for Food 105

Package Coating Food Coating Package Food

Package Food Package Food

Spray/coating before Packaging Spray/coating after Packaging

Incorporation in Package Chemical Immobilization

in Package

Active

Substance

Figure 6.2 Migration of Active Substances. Reproduced from J. Han, Food Technology 54, 3,

6.6.2 Surface modiﬁcation of packages with antimicrobials

Surface modiﬁcation includes not only the direct coating/casting of antimicrobial layer but

also the implementation of an immobilized layer of antimicrobials on the package sur-

face. This method brings the antimicrobials into direct contact with the food to inhibit the

bacterial growth. The mechanism is schematically indicated in Figure 2. Some antimicro-

bial packaging uses covalently immobilized antibiotics or fungicides. In this case surface

suppression of microbial growth by immobilization of the non-food grade antimicrobial

substance occurs without diffusional mass transfer. The antimicrobial activity of an im-

mobilized layer requires the presence of functional groups on both the antimicrobial and

the polymer. Examples of antimicrobials with functional groups are peptides, enzymes,

polyamines and organic acids. Figure 2 also shows how the immobilization method differs

in its mass transfer aspects from other mechanisms of antimicrobial activity.

6.6.3 Antimicrobial packaging using gas-based systems

Gas-based antimicrobial systems fall into two groups, one using sachet/pad and the other

relying on emitting/ﬂushing a selected gas to inhibit microorganism growth. These systems

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106 Smart Packaging Technologies for Fast Moving Consumer Goods

have been the most widely used and most successful antimicrobial packaging systems

to date. Sachets/pads modify the gas composition inside of the package. They may con-

tain oxygen scavengers, moisture absorbers, ethanol vapor generators, organic acids and

surfactants. These systems have been used in bakery, pasta, vegetables and meat product

packaging to inhibit oxidation and moisture condensation in the package. They may induce

the decrease of A

and O

thus decreasing bacteria growth inside of the package. Ellis et al

reported (2006) that chlorine dioxide sachets were very effective in controlling the quality

of fresh chicken breasts when combined with modiﬁed atmosphere technology. Additional

beneﬁts are the minimization of negative consumer responses and the potential economic

advantage of increased outputs. Gas-ﬂush systems eliminate the risk of accidental rupture

of sachets and inadvertent consumption of their contents. An example of a gas-ﬂush an-

timicrobial packaging system, is the use of a speciﬁc gas composition to control mold in the

storage of berries and grapes in produce boxes, which are palletized and stretch-wrapped,

then sulﬁte-ﬂushed to prevent fungal spoilage. It is easy to use these types of bulk gas

ﬂushing and controlled/modiﬁed atmosphere technologies.

6.6.4 Inherently antimicrobial polymers

Some polymers are inherently antimicrobial and have been used in ﬁlms and coatings. Some

of these polymers enhance barrier properties, as well. It was reported that the chitosans

having different molecular weight distributions showed different antimicrobial activity as

well as different antioxidant activity (Kim, KW and et al, 2004 and 2005). Other cationic

polymers such as poly-L-lysine promote cell adhesion (Goldberg, Doyle & Rosenberg,

1990) since charged amines interact with negative charges on the cell membrane, causing

leakage of intracellular constituents.

6.7 Design of antimicrobial packaging systems

Antimicrobial food packaging systems can offer the containment and protection function

simultaneously. Before manufacturing a package incorporating an antimicrobial packaging

system, several factors should be considered. First of all, the characteristics of not only the

food but also the antimicrobial agent which will affect the bacteria should be understood.

The physicochemical composition of the food (such as lipid, carbohydrate or protein con-

tent ratio) can directly affect the activity of an antimicrobial agent in terms of diffusion

rate or miscibility and the growth rate of speciﬁc bacteria. Second, the migration kinetics

of antimicrobial agents into foods may be important to quantify in order to control the

antimicrobial food packaging system and predict, for example, food and package shelf

life. Also, the organoleptic properties of the antimicrobial agents might be important in

the food application. During commercialization of an antimicrobial food packaging sys-

tem, the entire packaging dynamics from processing to distribution to consumer should be

considered as well to assess feasibility for mass production, cost and safety. Toxicity and

regulatory issues will be another factor for designing a successful antimicrobial packaging

system.

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Antimicrobial Active Packaging for Food 107

6.8 Prognosis for commercialization

In many food products, the driving force for commercialization has focused on the con-

venience and health issues. To ensure the food safety, these technologies used in active

packaging systems should meet the convenience criterion for both consumer and manufac-

turer. Based on market research done by Business Insights Ltd (Eaton and Sadler, 2005), of

all the convenient products launched between January 2002 and January 2005, 50.5% were

classed innovative. Among the innovative products, 77.3% were innovative in formulation

and 20.4% were innovative because of convenience packaging. There are several trends in

convenience packaging innovation such as active packaging, antimicrobial packaging or

smart packaging. These technologies contribute to the fulﬁllment of such demands as food

safety, product freshness sustainability and elements of food service entering the home. Si-

multaneously they support convenience trends such as the evolution of sports caps closures

and the evolution of the can. Active packaging technology is therefore a very hot topic in

all over the world both in the current and future food marketplaces.

On the other hand, some active packaging technologies are looked upon negatively

when considering the difﬁculty of commercialization, in spite of the growing commercial

success for such alternatives as sachets/pads and controlled atmosphere packaging. A major

technical difﬁculty with the introduction of active packaging agents into ﬁlms and moldings

is the process temperatures that haveto be sustained for these package forming technologies.

In addition, equivalent functionality to antimicrobial packages might be easily achieved by

incorporating an agent into the food or by coating the food surface with the agent. Another

challenge is posed by the global growth of sustainability targets and awareness, since many

active packaging systems may not be compatible with sustainability objectives.

6.9 The future of antimicrobial packaging systems

Packaging technology innovation is well-positioned to respond to consumer demands for

higher performance food. Innovation should address concepts such as food safety from

potentially fatal bacteria and environmentally toxic hormones, nutritional quality and fresh-

ness, the package convenience and recyclability or sustainability. Antimicrobial packaging

systems can change the condition of packaged food to extend shelf life or improve the safety

and sensory properties. These systems are attracting the interest of researchers and industry

due to their potential to provide quality and safety beneﬁts. Antimicrobial packaging tech-

nologies have been successfully used in many commercial food products especially in the

US and Japanese markets. Moreover, they may be combined with other active packaging

technologies such as modiﬁed atmosphere packaging (MAP), radio frequency identiﬁcation

(RFID) systems, fresh indicator packaging or tamper resistance systems in order to increase

the degree of success in verifying, preserving and enhancing food product quality in the

eyes consumers. The combination of various active packaging technologies with antimi-

crobial packaging has not been fully used in industry yet. Nevertheless, the development of

such combination systems in response to consumers’ increasing demands can be foreseen

in the not-to-distant future. In addition, the increasing attention on renewable sources of

energy and more sustainable forms of packaging will also drive higher commitments of

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108 Smart Packaging Technologies for Fast Moving Consumer Goods

industry and government to support R&D and commercialization of antimicrobial packag-

ing systems based on natural products.

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Freshness Indicators

for Food Packaging

Maria Smolander

7.1 Introduction

The idea of freshness indicators is that they monitor the quality of the packed food by

reacting in one way or another to changes taking place in the fresh food product as a result

of microbiological growthand metabolism. Contrary to concepts reﬂecting the requirements

of the product quality, like package integrity and time–temperature history of the product,

the freshness indicators indicate directly the quality of the product. The indication of

microbiological quality is, for example, based on a reaction between the indicator and the

metabolites produced during growth of microorganisms in the product. The general idea of

a freshness indicator is not new, since as early as in the 1940s Clark (1949) ﬁled a patent

application describing an indicator for food product that ‘exhibits an irreversible change in

visual appearance upon an appreciable multiplication of bacteria in the indicator’. A direct

determination of a volatile metabolite, namely CO

from the microbiologically spoiling

product itself with pH-dye based indicator was proposed by Lawdermilt (1962). Recent

publications reviewing freshness indicators have been compiled by Smolander (2003) and

Kerry et al. (2006).

A crucial prerequisite in the successful development of freshness indicators is knowledge

about the quality-indicating metabolites. Evidently, the developed indicator concept has to

be able to react to the presence of these compounds with the required sensitivity. Moreover,

the indicator system should comply with legislation since the indicator needs to be brought

into contact either directly with the food product or with the package headspace. Hence

the indicator generally needs to be placed inside the food package unless the packaging

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112 Smart Packaging Technologies for Fast Moving Consumer Goods

material is a breathable or gas-permeable wrap like that described by Williams et al. (2006).

It is also essential to avoid false negatives, which are likely to dissuade producers from

adopting indicators in real use (Kerry et al., 2006).

7.2 Freshness Indicators for Quality Indicating Metabolites

Quality indicating metabolites have been widely studied since they offer the possibility of

replacing the time-consuming sensory and microbiological analyses traditionally used in

the quality evaluation of food products (Dainty, 1996). There are several potential quality

indicating metabolites that could be utilised as target molecules of the freshness indicators.

However, it should be kept in mind that the formation of the different metabolites depends

on the nature of the packaged food product, spoilage ﬂora and the type of packaging,

and the indicating capacity of a particular metabolite should always be veriﬁed case by

case. It is also beneﬁcial from the point of freshness indicator development to trace a

compound with non-existent or low initial concentrations. A wide variety of freshness

indicators reacting to the presence of quality indicating metabolites has been presented in

the scientiﬁc literature (Table 7.1). Most of these concepts are based on a colour change

of the indicator tag due to the presence of microbial metabolites produced during spoilage

(e.g. Williams et al., 2006; Smolander et al., 2002, 2004b; Miller et al., 1999; Wallach

and Novikov, 1998; Kahn, 1996; Namiki, 1996). Concepts based on optical or electronic

measurement have also been presented (e.g. Pacquit et al., 2006, 2007; VanVeen, 2004;

Smolander et al., 2003; Byrne et al., 2002; Payne and Persaud, 1995; Wolfbeis and List,

1995; Honeybourne, 1993) and existing technologies like biosensors and electronic nose are

likely to serve as the technological basis for the development of new, even more advanced,

freshness indicator concepts in the future. The utilisation of biomolecules as the metabolite

recognising elements can be expected to expand. The different types of biomolecule as

well as examples of their potential utilisation for functional purposes, e.g. in diagnostics

and packaging, were recently reviewed by Aikio et al. (2006).

7.2.1 Metabolites Related to Glucose Fermentation

Ethanol, in addition to lactic and acetic acids, is a major end product of fermentative

metabolism of lactic acid bacteria and it has been proposed that an increase in ethanol

concentration in meat and ﬁsh indicates an increase of total viable count of the product.

Concentration of ethanol has been found to increase as a function of storage time, e.g. in

studies by Rehbein (1993) who studied the formation of ethanol in iced ﬁsh and smoked

vacuum-packed salmon, and by Randell et al. (1995) who studied modiﬁed-atmosphere

packaged, marinated salmon trout slices and chicken pieces. In our unpublished studies

analogous to Randell et al. (1995) we have also seen an effect of storage temperature on

the ethanol concentration.

Accumulation of ethanol from fresh produce due to low oxygen concentration and ele-

vated carbon dioxide concentration is generally considered to be a measure of anaerobic

metabolism and a remarkable cause for quality deterioration (Gonzalez-Aguilar et al.,

2004). Some trials to utilise ethanol for quality indication of packaged products have been

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Table 7.1 Summary of the freshness indicating metabolites and indicator concepts available for their detection

Potential indicator and Commercial freshness

Quality indicating metabolite Corresponding food types sensor priciples indicating products

Ethanol Seafood (Rehbein, 1993; Randell

et al., 1995)

Fresh produce (Gonzalez-Aguilar

et al., 2004)

Enzymatic determination for package

head-space (Smyth et al., 1999 ;

Cameron and Talasila, 1995)

Organic acids Fresh ﬁsh (Kakouri et al., 1997;

Drosinos and Nychas, 1997)

Meat (Nychas et al., 1998)

Poultry (Smolander, unpublished)

Published methods applicable as

package integrated concepts not

available

Glucose Meat (Dainty, 1996) DTN by knife-type probe (inside the

product) (Kress-Rogers et al., 1993)

Volatile nitrogen compounds

(e.g. ammonia, dimethylamine,

trimethylamine)

Seafood (depending on species

and season) (e.g. Dainty, 1996)

DTN of volatile sulfur compounds

from the package head-space,

reaction based on pH sensitive dyes

as a visual colour change (e.g.

Williams et al., 2005, 2006; Miller

et al., 1999) or with optical sensor

(e.g. Oberg et al., 2006; Pacquit

et al., 2006; Byrne et al., 2002)

FreshTag (Cox Recorders,

USA) (previously

available)

freshQ (Food Quality

Sensor International,

Inc., USA)

Biogenic amines (e.g. tyramine,

cadaverine, putrescine,

histamine)

Poultry (Rokka et al., 2004;

Schmitt and Schmidt-Lorenz,

1992)

Beef (Smith et al., 1993; Edwards

et al., 1987; Yano et al., 1995b)

Pork (Ordonez et al., 1991)

Electrochemical biosensors or

spectrophotometric assay based on

enzymatic determination, direct

contact with food required (e.g.

Yano et al., 1995b; Okuma et al.,

2000; Niculescu et al., 2000; Frebort

et al., 2000; Punakivi et al., 2006)

(Continued )

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Table 7.1 (Continued )

Potential indicator and Commercial freshness

Quality indicating metabolite Corresponding food types sensor priciples indicating products

Carbon dioxide Indication of microbial growth

in several food types (Fu et

al., 1992; Mattila et al.,

1990) Indication of product

ripeness (Korean kimchi)

(Hong & Park, 2000)

DTN of CO

from package head-space,

reaction based on pH sensitive dyes (e.g.

Morris, 2006; Horan, 2000; Hong & Park,

2000)

For appropriate level of

in MA-packages

(Sealed Air, USA

Previously available)

ATP degradation products Meat, especially seafood

(Hattula et al, 1997)

Test strips and electrochemical biosensors

based on enzymatic determination, direct

contact with food required (e.g. Yano

et al., 1995a; Mulchandani et al., 1990)

Transia GmbH (Germany)

test strips

Sulfuric compounds Poultry meat (e.g. Lea et al.,

1969; Rajam

aki et al., 2006)

Seafood (Olafsdottir and

Fleurence, 1997)

DTN of volatile sulfur compounds from the

package head-space, reaction based on

colour change of myoglobin (Smolander

et al., 2002), colour change of nano-scale

silver layer (Smolander et al., 2004b) or

conductivity change of package

intergrated, RF readable silver layer based

tag (Smolander et al., 2003)

Freshness Guard Indicator

(UPM Raﬂatac, Finland)

Undeﬁned volatiles Meat (deli, cooked, raw) DTN of volatile compounds from the

head-space of a storage bag or container,

reaction based on visual colour change of

a dye

It’s Fresh

(It’s Fresh! Inc.)

(concept for consumers

own use)

Microbial enzymes Not speciﬁcally deﬁned,

several

DTN of substrate conversion due to the

enzymatic activity, reaction requiring a

direct contact with the food (Van Veen,

2004)

Pathogenic bacteria Not speciﬁcally deﬁned,

several

Immunochemical DTN requiring a direct

contact with the food product

(Bodenhamer, 2000; Goldsmith, 1994;

Woodaman, 2002)

Toxin Guard

(Toxin Alert

Inc., Canada)

Food Sentinel System

(Sira Technologies, USA)