7.1 Introduction
As we know from the definition, intelligent or smart packaging monitors and
gives information about the quality of the packed food. According to Huis in’t
Veld (1996) the changes taking place in the fresh food product can be
categorised as (i) microbiological growth and metabolism resulting in pH-
changes, formation of toxic compounds, off-odours, gas and slime formation,
(ii) oxidation of lipids and pigments resulting in undesirable flavours, formation
of compounds with adverse biological reactions or discoloration. The focus of
this chapter is on intelligent concepts indicating the changes mainly belonging to
the first category.
The intelligence of a package can be based on the package’s ability to give
information about the requirements of the product quality like package integrity
(leak indicators) and time-temperature history of the product (time-temperature
indicators). Intelligent packaging can also give information on product quality
directly (see Fig. 7.1). A freshness indicator indicates 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. Of the indicators mentioned, time-temperature
indicators and leak indicators are already commercially available and their use is
increasing constantly. An indicator that would show specifically the spoilage or the
lack of freshness of the product, in addition to temperature abuse or package leaks,
would be ideal for the quality control of packed products. The number of concepts
of package indicators for contamination or freshness detection of food is still very
low, however new concepts of freshness indicators are patented and new
commercially available products are likely to become available in the near future.
7
The use of freshness indicators in
packaging
M. Smolander, VTT Biotechnology, Finland
In this chapter the potential microbial metabolites and other compounds
indicating the quality of packaged food are presented. Subsequently, freshness
indicator concepts, which are commercially available or have been described in
literature are reviewed. Finally, the possibilities for the future are discussed.
7.2 Compounds indicating the quality of packaged food
products
An essential prerequisite in the development of freshness indicators is
knowledge about the quality indicating metabolites. These metabolites have
also been studied because they offer a possibility to replace time-consuming
sensory and microbiological analyses traditionally used in the quality evaluation
of food products (Dainty, 1996). The formation of the different metabolites
depends on the nature of the packaged food product, spoilage flora and the type
of packaging. The chemical detection of spoilage has been extensively reviewed
by Dainty (1996). Chemical changes in stored meat have been discussed by
Nychas et al. (1998). They propose that some chemical compounds do indeed
indicate the microbiological quality of food products but also that more
information is needed about the correlation between the sensory quality and the
concentration of the metabolites. In this chapter some of the quality-indicating
metabolites and other compounds representing potential target molecules for the
quality-indicating freshness indicators are discussed in detail.
Fig. 7.1 Quality indicators for packaged food products can be either on direct or indirect
freshness evaluation.
128 Novel food packaging techniques
7.2.1 Glucose
Glucose is an initial substrate for many spoilage bacteria in air, vacuum
packages and modified atmosphere packages (Dainty, 1996). As bacterial
growth takes place glucose is depleted from meat surface and it has been
proposed by Kress-Rogers (1993) that the measurement of the glucose gradient
could be utilised to predict the remaining shelf-life. However glucose is not
among the most promising quality-indicating compounds since the
concentration decreases during storage and it would be more beneficial to have
a quality-indicating compound with non-existent or low intitial concentration.
7.2.2 Organic acids
Organic acids like lactic acid and acetic acid are the major compounds having a
role in glucose fermentation by lactic acid bacteria. The amount of L-lactic acid
has generally been reported to decrease during storage of fish and meat (Kakouri
et al., 1997; Drosinos and Nychas, 1997; Nychas et al., 1998). On the contrary,
the concentration of D-lactate has been reported to increase during storage of
meat and therefore D-lactate seems to be a more promising freshness indicator
(Shu et al., 1993).
Acetate concentrations have been reported to increase during storage of fresh
fish (Kakouri et al., 1997). In our studies with modified atmosphere packaged
poultry meat (Smolander et al. in preparation) we have also found that the
concentration of acetic acid in the tissue fluid and homogenised meat increased
as a function of storage time and temperature. We also studied the formation of
formic acid. At the beginning of storage some decrease in the concentration in
meat was seen but later the concentration increased, however the increase was
not as clearly dependent on storage temperature as in the case of acetic acid.
7.2.3 Ethanol
In addition to lactic and acetic acid, ethanol is another major end product of
fermentative metabolism of lactic acid bacteria. It has been postulated that an
increase in ethanol concentration in meat and fish indicates an increase of total
viable count of the product. For instance, Rehbein (1993) studied the formation
of ethanol in iced fish. He found that on an average the concentration of ethanol
was increased as a function of storage time. At sensory rejection point an
average of 1.77 mg ethanol was found in 100 g fish. Rehbein (1993) also studied
the formation of ethanol in smoked, vacuum-packed salmon. The concentrations
in stored fish samples were considerably higher than in fresh, iced fish. At the
end of shelf-life concentrations as high as 10 mg/100 g fish were observed.
Randell et al. (1995) studied the effect of storage time and package integrity on
the formation of ethanol in modified atmosphere packaged, marinated rainbow
trout slices. They found that the amount of ethanol in package headspace was
increased together with storage time and size of the package leakage. In our
unpublished studies analogous to Randell et al. (1995) we found also that
The use of freshness indicators in packaging 129
storage temperature had a remarkable effect on the ethanol concentration. The
higher the storage temperature was, the higher was the concentration of ethanol.
Randell et al. (1995) also studied the volatile compounds in packages
containing marinated chicken pieces in modified atmosphere (40%CO
2
+
60%N
2
). They found that ethanol concentration in the package headspace
increased as a function of storage time. In our own unpublished studies we also
found some correspondence between sensory quality of modified atmosphere
(40%CO
2
+ 60%N
2
) packaged, unmarinated poultry meat and ethanol
concentration in the package headspace. However, in unmarinated poultry meat
packaged in MAP with higher (80%) CO
2
concentration we did not observe a
clear trend in the formation of ethanol as a function of storage time and
temperature.
7.2.4 Volatile nitrogen compounds
It is well known that high levels of basic volatile nitrogen compounds like
ammonia, dimethylamine and trimethylamine give an indication about
microbiological spoilage of fish (Ohlenschla¨ger, 1997). The European
Commission has even fixed TVB-N (total volatile basic nitrogen contributed
by ammonia, dimethylamine and trimethylamine) limits for some fish species
(95/149/EEC). Trimethylamine, formed by microbial actions in fish muscle is
generally considered as a major metabolite responsible for the spoilage odours
of seafood. A drawback of using trimethylamine as a quality indicator for
seafood is the variation in the concentration of its precursor trimethylamine N-
oxide according to the species and season (Dainty, 1996; Rodr?′guez et al.,
1999).
7.2.5 Biogenic amines
Biogenic amines (e.g. tyramine, cadaverine, putrescine, histamine) are
especially widely considered as indicators of hygienic quality of meat products.
In addition to this indicative nature, they can have pharmacological,
physiological and toxic effects. Due to the health risks, a tolerance level of
100 mg/kg of fish has been established for histamine by FDA (Kaniou, et al.
2001). Even if biogenic amines indicate the quality of food products they do not
themself contribute to the sensory quality of the product.
Putrescine and cadaverine are formed from ornithine and lysine, respectively
in enzymatic decarboxylation. It has been widely suggested that these diamines
are indicators of the initial stage of decomposition of meat products. Okuma et
al. (2000) describe an increase in the diamine concentration together with the
increase of the total viable counts in aerobically stored chicken. Kaniou et al.
(2001) reported the formation of putrescine and cadaverine in unpacked beef. In
addition to putrescine and cadaverine, histamine was also produced during the
storage of vacuum-packed beef. Also in our studies we have found a clear
correspondence between the microbiological quality of modified atmosphere
130 Novel food packaging techniques
packaged poultry and the total amount of biogenic amines. Tyramine formation
took place evenly during the storage period, the formation being however
dependent on temperature. Storage temperature had a more striking effect on the
formation of putrescine and cadaverine which were accumulated especially at
the end of storage period (Rokka et al., submitted).
Ruiz-Capillas and Moral (2002) studied the effect of controlled and modified
atmosphere on the production of biogenic amines during storage of hake. They
found that controlled and modified atmosphere generally restricted the
formation of biogenic amines and that cadaverine was a major biogenic amine
formed in most of the studied atmospheres. Rodr?′guez et al. (1999) proposed
that biogenic amines cadaverine and putrescine could indicate the freshness of
freshwater rainbow trout either stored in air or in a vacuum package.
7.2.6 Carbon dioxide
Carbon dioxide (CO
2
) is generally known to be produced during microbial
growth. CO
2
is also typically added as a protecting gas to modified atmosphere
packages, together with inert nitrogen, since it has bacteriostatic effects. A
modified atmosphere package for non-respiring food typically has a CO
2
concentration as high as 20–80 % and, e.g., Fu et al. (1992) reported a further
increase of CO
2
during storage in modified atmosphere packages containing
beef. Even if the indication of microbial growth by CO
2
may be difficult in these
modified atmosphere packages already containing a high concentration of CO
2
,
it is possible to use the increase in CO
2
concentration as a means of determining
microbial contamination in other types of product. For instance Mattila et al.
(1990) found a correlation between CO
2
concentration and the growth of
microbes in pea and tomato soup which were packaged aseptically either in air
or in a mixture of O
2
(5%) and nitrogen.
7.2.7 ATP degradation products
K-value is defined as the ratio of the sum of hypoxanthine and inosine and the
total concentration of ATP-related compounds (Henehan et al., 1997). This
value, indicating the extent of ATP-degradation, correlates with the sensory
quality of fish and also other types of meat and has been used as a freshness
indicating parameter (Watanabe et al., 1989; Yano et al., 1995a). For fresh meat
the value is low since the concentration of ATP-degradation products is low as
compared to the concentration of all ATP-related compounds. The correlation
between ATP-degradation products and fish quality has been extensively
studied, e.g., by Hattula (1997).
7.2.8 Sulphuric compounds
Some sulphuric compounds have a remarkable effect on the sensory quality of
meat products due to their typical odour and low odour threshold. Hydrogen
The use of freshness indicators in packaging 131
sulphide (H
2
S) is produced from cysteine and triggered by glucose limitation
(Borch et al., 1996). H
2
S forms a green pigment, sulphmyoglobin, when it is
bound to myoglobin (Paine and Paine, 1992, Egan et al., 1989). However,
sulphmyoglobin is not formed in anaerobic conditions.
H
2
S and other sulphuric compounds have been found to be produced during
the spoilage of poultry by pseudomonas, Alteromonas sp. and psycrotrophic
anaerobic clostridia (Freeman et al., 1976; Lea et al., 1969; Russell et al., 1997,
Vieshweg et al., 1989; Arnaut-Rollier et al., 1999; Kalinowski and Tompkin,
1999). According to Dainty (1996), production of H
2
S can be used as an
indication of Enterobacteriacae and hence also of hygienic problems in
aerobically stored meat. H
2
S production by Alteromonas putrefaciens,
Enterobacter liquefaciens and pseudomonas was discovered in high ultimate
pH beef from stressed animals (Gill and Newton, 1979; Nicol et al., 1970). It has
also been found that in vacuum packed meat H
2
S indicates the growth of
particular strains of lactic acid bacteria (Egan et al., 1989). Also in fish the
volatile sulphuric compounds have been suggested as the main cause of putrid
spoilage aromas (Olafsdottir and Fleurence, 1997).
7.3 Freshness indicators
A variety of different concepts for freshness indicators have been presented in
the scientific literature. 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. Smolander et al., 2002; Wallach and Novikov, 1998; Kahn, 1996;
Namiki, 1996), but also concepts for indicators relying on more advanced
technology have been presented. For instance, a miniaturised gas detector based
on conducting polymers has been patented by Aromascan, a manufacturer of
electronic nose equipment (Payne and Persaud, 1995). Fibre optics can also be
used to construct indicators for the volatile compounds produced in microbial
spoilage (Honeybourne, 1993; Wolfbeis and List, 1995). Freshness indicator or
detector concepts have been proposed, for example, for CO
2
, diacetyl, amines,
ammonia and hydrogen sulphide (see Table 7.1). These concepts are discussed
in detail in following chapters.
7.3.1 Indicators sensitive to pH change
The majority of concepts described in the literature are based on the use of pH-
dyes, which change colour in the presence of volatile compounds produced
during spoilage. As early as the 1940s Clark (1949) filed a patent application
describing ‘an indicator which exhibits an irreversible change in visual
appearance upon an appreciable multiplication of bacteria in the indicator’.
The idea was that if microbiological growth inducing a pH change has been
possible in the indicator, the conditions might have been such that the food
product itself may also have been subject to deterioration. A direct
132 Novel food packaging techniques
Table 7.1 Examples of freshness and contamination indicator systems for food
packages
Author/ Patent applicant or
holder/Trade name
Metabolite
detected
Principle of the indicator
Freshness indicators
Holte (1993) CO
2
Colour change of e.g.
bromothymol blue
Visual Spoilage Indicator
Company (Eaton et al. 1977)
CO
2
Colour change
Mattila et al. (1990) CO
2
Colour change of
bromothymol blue
Horan (1998, 2000) E.g. CO
2
, SO
2
,
NH
4
Colour change of the
indicator (e.g. xylenol blue,
bromocresol purple,
bromocresol green, cresol
red, phenolphalein,
bromothymol blue, neutral
red) incorporated in the
packaging material
Neary (1981) CO
2
, H
2
, NH
4
Colour change of liquid
crystal/liquid crystal +
indicator
AVL Medical Instruments
(Wolfbeis and List, 1995)
CO
2
, NH
4
,
amines, H
2
S
Colour change of CO
2
,
NH
4
, and amine-sensitive
dyes, formation of colour of
heavy-metal sulfides (H
2
S)
Biodetect Corporation
(Wallach and Novikov, 1998)
E.g. acetic acid,
lactic acid,
acetaldehyde,
ammonia,
amines
Visually detectable colour
change of a pH-dye (e.g.
phenol red, cresol red, m-
cresol purple)
Mattila and Auvinen
(1990a, b)
Not specified Colour change of methylene
blue or 2,6-dichlorophenol
indophenol
Miller et al. (1999) Volatile amines Colour change of a food dye
Loughran and Diamond
(2000)
Volatile amines Colour change of
calix[4]arene-based dye
VTT Biotechnology
(Ahvenainen et al., 1997)
H
2
S Colour change of myoglobin
Cameron and Talasila (1995) Ethanol Alcohol oxidase-peroxidase-
chromogenic substrate
system
Honeybourne (1993) Diacetyl Detection of optical changes
in aromatic orthodiamine
DeCicco and Keeven (1995) Microbial
enzymes
Colour change of
chromogenic substrates of the
microbial enzymes
The use of freshness indicators in packaging 133
determination of CO
2
from the microbiologically spoiling product itself with a
pH-dye (e.g. fuchsine acid) based indicator was proposed by Lawdermilt (1962).
The use of the pH-dye bromothymol blue as an indicator for the formation of
CO
2
by microbial growth has been suggested in many studies (Holte, 1993;
Mattila et al., 1990). As mentioned before, an increase in CO
2
can be used to
determine microbial contamination in certain types of products. On the other
hand, Balderson and Whitwood (1994) proposed a CO
2
-sensitive packaging
indicator for correct filling and subsequent opening of the package. In addition
to the detection of spoilage and package filling, pH-dyes reacting to the presence
of CO
2
have also been used to construct intelligent packaging concepts
indicating the ripeness of traditional fermented vegetable foods in Korea
(kimchi) (Hong and Park, 2000).
In addition to the most frequently used pH-dye bromothymol blue, many other
reagents e.g. xylenol blue, bromocresol purple, bromocresol green, cresol red,
phenol red, methyl red and alizarin, among others, have been proposed for the same
purpose (Horan 2000). Besides CO
2
, other metabolites like SO
2
, NH
4
, volatile
amines and organic acids have been proposed to be suitable target molecules for
pH-sensitive indicators (Mattila and Auvinen, 1990a, b; Horan, 2000).
Table 7.1 (continued)
Author/ Patent applicant or
holder/Trade name
Metabolite
detected
Principle of the indicator
Namiki (1996) Micro-
organisms
Degradation of lipid
membrane by micro-
organisms and subsequent
diffusion of coloured
compound
Aromascan (Payne and
Persaud, 1995)
Not specified Miniaturised electronic
component with electrical
properties affected by volatile
compound associated with
spoilage
Pathogen indicators
Food Sentinel System (Sira
Technologies); Goldsmith
(1994)
Various
microbial toxins
Bar code detector comprising
a toxin printed onto a
substrate and indicator colour
irreversibly bound to the
toxin, in the presence of toxin
the bar code is illegible
Toxin Guard (Toxin Alert);
Bodenhamer (2000)
Various
pathogens
Formation of a coloured
pattern when a target analyte
is first bound to labelled
antibody and subsequently to
capture antibody
Lawrence Berkeley National
Laboratory (Quan and
Stevens, 1998)
E. coli 0157
enterotoxin
Colour change of
polydiacetylene-based
polymer
134 Novel food packaging techniques
7.3.2 Indicators sensitive to volatile nitrogen compounds
A concept reacting to volatile amines with a colour change, hence indicating
freshness of seafood, has been proposed by Miller et al. (1999). This concept
was marketed by COX Recorders (USA) with the trade name FreshTag
. The
concept consisted of a plastic chip incorporating a reagent-containing wick. As
the label was attached to the package the sharp barb on the back of the label
penetrated the packaging film thus enabling contact between the package
headspace gases and the reagent. As volatile amines passed through the wick a
bright pink colour was developed along the wick.
Loughran and Diamond (2000) propose a simple method for the
determination of volatile nitrogen compounds (NH
3
, DMA, TMA) with the
aid of chromogenic dye calix[4]arene which has been impregnated on a paper
disc. They show that the reflectance spectrum of the indicator disc is changed
due to the volatile compounds emitted from cod stored on ice. They also propose
that the system could form a base for an intelligent packaging concept.
7.3.3 Indicators sensitive to hydrogen sulphide
In our own studies we have utilised a reaction between hydrogen sulphide and
myoglobin in a freshness indicator for the quality control of modified-
atmosphere-packed poultry meat (Ahvenainen et al., 1997; Smolander et al.,
2002). Freshness indication is based on the colour change of myoglobin by
hydrogen sulphide (H
2
S), which is produced in considerable amounts during the
ageing of packaged poultry during storage. The indicators were prepared by
applying commercial myoglobin dissolved in a sodium phosphate buffer on
small squares of agarose. These indicators were tested in the quality control of
MA-packaged fresh, unmarinated broiler cuts. It was found that the colour
change of the myoglobin-based indicators corresponded with the deterioration of
the product quality, hence it could be concluded that the myoglobin-based
indicators seem to be promising for the quality control of packaged poultry
products.
7.3.4 Indicators sensitive to miscellaneous microbial metabolites
Cameron and Talasila (1995) have explored the potential of detecting the
unacceptability of packaged, respiring products by measuring ethanol in the
package headspace with the aid of alcohol oxidase, peroxidase and a
chromogenic substrate. Honeybourne and co-workers (Honeybourne, 1993;
Shiers and Honeybourne, 1993) have developed a diamine dye-based sensor
system responding to the presence of diacetyl vapour. Diacetyl is a volatile
compound evolving from meat as spoilage takes place and Honeybourne and co-
workers have proposed that the dye could be printed onto the surface of a gas
permeable meat package. Diacetyl migrating through the packaging material
would react with the dye and induce a colour change.
The use of freshness indicators in packaging 135
7.3.5 Other principles for freshness indicating systems
In addition to indicators based on reactions caused by microbial metabolites,
other concepts for contamination indicators have been proposed. DeCicco and
Keeven (1995) describe an indicator based on a colour change of chromogenic
substrates of enzymes produced by contaminating microbes. The indicator can
be applied for contamination detection in liquid health care products.
Besides the products of microbial metabolism, the consumption of certain
nutrients could also be used as a measure of freshness. Kress-Rogers (1993)
has developed a knife-type freshness probe for meat. Freshness detection is
based on the formation of a glucose gradient as glucose from the surface of
meat is consumed during microbial growth and the bulk concentration of
glucose remains stable. The detection of microorganisms as such was
proposed by Namiki (1996). The principle of the indicator is the degradation
of lipid membrane by microorganisms and subsequent diffusion of coloured
compound.
7.4 Pathogen indicators
In addition to the above-mentioned indicators reacting to the normal spoilage
of food products, systems for the detection of a certain contaminant in the
food product have also been presented. Commercially available Toxin
Guard
TM
by Toxin Alert Inc. (Ontario, Canada) is a system to build
polyethylene-based packaging material, which is able to detect the presence of
pathogenic bacteria (Salmonella, Campylobacter, Escherichia coli O157 and
Listeria) with the aid of immobilised antibodies. As the analyte (toxin, micro-
organism) is in contact with the material it will be bound first to a specific,
labelled antibody and then to a capturing antibody printed as a certain pattern
(Bodenhamer, 2000). The method could also be applied for the detection of
pesticide residues or proteins resulting from genetic modifications. Another
commercial system for the detection of specific microorganisms like
Salmonella sp., Listeria sp. and E. coli is Food Sentinel System
TM
. This
system is also based on immunochemical reaction, the reaction taking place in
a bar code (Goldsmith, 1994). If the particular microorganism is present the
bar code is converted unreadable.
Specific indicator material for the detection of Escherichia coli O157
enterotoxin has been developed at Lawrence Berkeley National Laboratory
(Kahn, 1996; Quan and Stevens, 1998). This sensor material, which can be
incorporated in the packaging material, is composed of cross-polymerised
polydiacetylene molecules and has a deep blue colour. The molecules
specifically binding the toxin are trapped in this polydiacetylene matrix and
as the toxin is bound to the film, the colour of the film changes from blue to
red.
136 Novel food packaging techniques
7.5 Other methods for spoilage detection
In addition to the indicators undergoing a visual colour change it can be
expected that in the future intelligent packaging concepts will resemble more
and more small analytical tools that are incorporated in the package. Some
existing technologies like biosensors and electronic noses are likely to serve as a
technological basis for the development of new miniaturised concepts. These
technologies and their application in the determination of food quality and
freshness are described in the following chapters.
7.5.1 Biosensors
A biosensor is an analytical device consisting of a biological component specific
to the analyte and a physical component, which is able to transduce the
biological signal to a physical one (Turner et al., 1987). For instance enzymes,
antibodies and cells can be used as the biological component of biosensors. The
signal can also be detected in many ways e.g. with amperometric,
potentiometric, optic and calorimetric methods.
Several types of enzymatic biosensors have been developed for the detection of
biogenic amines. The increase in the amount of diamines (putrescine, cadaverine
and spermidine) in poultry meat was detected with a putrescine oxidase reactor
combined with amperometric hydrogen peroxide electrode by Okuma et al. (2000).
Niculescu et al. (2000) constructed an amperometric bienzyme (grass pea amine
oxidase, horseradish peroxidase) electrode and used it for the determination of
biogenic amines from fish muscle. Fre′bort et al. (2000) presented a flow system
based on spectrophotometric detection of hydrogen peroxide generated in the
oxidation of biogenic amines by amine oxidase. They applied their system for the
determination of histamine in rainbow trout meat. Yano et al. (1995b) developed a
tyramine oxidase based sensor for the quality control of beef. ATP degradation
products have also been measured with biosensors. For instance, Yano et al. (1995a)
and Mulchandani et al. (1990) developed an enzyme based electrochemical sensor
for ATP degradation products and applied it for the quality control of beef.
7.5.2 Electronic nose
Electronic nose is an analytical tool composed of an array of sensors (e.g. metal
oxide, polymer) responding to volatile compounds with changes in their
electrical properties. The combined pattern of these changes from all the sensors
forms a fingerprint for the sample. Individual compounds are not separated/
identified with electronic nose, but the samples can be classified to acceptable or
unacceptable according to the fingerprint of the volatile compounds and the
results obtained with a reference method (e.g. sensory evaluation or
microbiological analysis). On the basis of existing data on the correlation
between sensor responses and the quality of the sample the system can be
adjusted to classify samples of unknown quality.
The use of freshness indicators in packaging 137
We have obtained very promising data on the determination of the quality of
broiler chicken cuts with electronic nose. The response of electronic nose was
found to be consistent with sensory and microbiological quality of the products
as well as with the concentration of volatile compounds in the package
headspace (Rajama¨ki et al., submitted). Also Boothe and Arnold (2002)
evaluated electronic nose as a promising tool for the quality evaluation of
poultry meat. Electronic noses have also been successfully used for the quality
evaluation of other products like fresh yellowfin tuna (Du et al., 2001) and
vacuum packaged beef (Blixt and Borch, 1999).
An interesting system working analogously with electronic nose has been
developed by Suslick and co-workers (Suslick and Rakow, 2001; Rakow and
Suslick, 2000). The system is a simple optical chemical sensing method
(colorimetric nose) that utilises the colour change taking place in an array of
metalloporphyrin dyes upon ligand binding. The liganding vapours (alcohols,
amines, ethers, phospines, phosphites, thioethers, thiols, arenes, halocarbons and
ketones) can be visually identified. Food quality control has been identified as
one of the potential applications of the system.
7.6 Future trends
Today the commercially available intelligent concepts are labels responding
with a visible change to time and temperature (TTI) or the presence of certain
chemical compounds (leak indicators, freshness indicators). It will however be
very likely that the visible labels will be replaced with more developed types of
indicator. The replacement of traditional barcodes by electronic tags in a supply
chain is becoming more and more common. Security tags, already in use today,
are the first examples of electronic labelling. However, it can be expected that in
future the tags will be used not only as information carriers but also as
miniaturised analytical tools. These quality indicating electronic labels could be
introduced, e.g., as chips. The advances in ink technology might enable the use
of intelligent printed circuits as well. The advantages of printed structures
include a low price and disposability. It is very likely that the advances in
electronics and biotechnology (e.g., biosensors, immunodiagnostics) would be
followed by the emergence of new concepts of intelligent packaging. However,
one has to bear in mind that the basic principles underlying all the indicators are
common and knowledge about food quality and safety is required in the
development work of all types of freshness indicators. Profound understanding
is needed about the formation of quality indicating compounds (both volatile and
non-volatile) and also about their correlation with product quality. On the basis
of this information new intelligent concepts, e.g., reacting to more than one
quality indicating compound could be developed.
138 Novel food packaging techniques
7.7 References
AHVENAINEN R, PULLINEN T, HURME E, SMOLANDER M. and SIIKA-AHO M. (VTT
BIOTECHNOLOGY AND FOOD RESEARCH, ESPOO, FINLAND) (1997) ‘Package
for decayable foodstuffs’ PCT International patent application WO
9821120.
ARNAUT-ROLLIER I., DE ZUTTER L and VAN HOOF L (1999) ‘Identities of
Pseudomonas spp. in flora from chilled chicken’, International Journal of
Food Microbiology 48, 87–96.
BALDERSON S N and WHITWOOD R J (TRIGON INDUSTRIES LIMITED, AUCKLAND,
NEW ZEALAND) (1994) ‘Gas Indicator for a Package’ EP 0627363 A1.
BLIXT Y and BORCH E (1999) ‘Using an electronic nose for determining the
spoilage of vacuum-packaged beef’, International Journal of Food
Microbiology 46, 123–34.
BODENHAMER W T (TOXIN ALERT, INC., CANADA) (2000) ‘Method and apparatus
for selective biological material detection’, US Patent 6051388.
BOOTHE D D H and ARNOLD J W (2002) ‘Electronic nose analysis of volatile
compounds from poultry meat samples, fresh and after refrigerated
storage’, Journal of the Science of Food and Agriculture 82, 315–22.
BORCH E, KANT-MUERMANS M-L and BLIXT Y (1996) ‘Bacterial spoilage of meat
and cured meat products’ International Journal of Food Microbiology 33,
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