Jung Han. Innovations in Food Packaging
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130 Innovations in Food Packaging
Few polymers are compatible with PET, so this approach constituted a breakthrough
in the development of
PET
bottles for oxygen-sensitive beverages in general. It was
shown that around 200 ppm of cobalt is necessary in a 7% blend of MXD-6 nylon in
PET in order to generate a total barrier
to
oxygen permeation (Folland, 1990). Several
developments by competing companies have resulted in approaches that
use
this chem-
istry either in a PET matrix or in a separate MXD-6 nylon layer co-injected with two
layers of PET. One such patent involves use of
a
blend of MXD-6 nylon, polyester, and
a cobalt salt in the core layer of bottles (Collette, 1991). Other commercial approaches
have been to incorporate the cobalt into a thin (10
jjim)
layer of
MXD-6
sandwiched
between PET layers in bottles.
An alternative approach to dealing with the PET compatibility issue was devised in
Amoco Chemicals (Cahill and Chen, 1997). This approach involved making a block
copolymer of
a
polybutadiene with PET with
the
trade
name
Amosorb^^ 3000, sold
by
BP
Amoco.
The PET caused
the
compatibilization while the polybutadiene was the oxi-
dizable polymer. The process is catalyzed
by
means of
a
transition metal
salt.
This poly-
mer lent itself
to use in PET
bottle manufacture, since the catalyst can be added at a late
stage
in the
injection-molding process
and
premature oxidation
can be
minimized. Even
though the injection-molded preforms have been heated while containing the catalyst,
they have a substantial shelf life due to the
low
permeability of the thick layers of PET,
especially when the Amosorb^^ 3000 is in a buried layer. Perhaps an improvement
would be to include some form of triggering or activation closer to the time of filling
the bottle.
Triggering of oxygen-absorbing sachets was an essential feature present from the
time they
were
initially introduced commercially. In that case the trigger
was
the water
necessary for the rusting of iron by the oxygen. In general, this water came from the
food and the sachets were not prematurely activated unless exposed to the air for too
long.
The concept of triggering an otherwise unreactive plastic system
was
also demon-
strated in
the
1970s in the singlet oxygen approach
to
oxygen scavenging (Rooney and
Holland, 1979). Around the same time, Rabek and Ranby (1975) showed that the
oxidative degradation of
a
plastic in sunlight was substantial if
a
photosensitizer and
a transition metal salt were dispersed therein. Against this background, the break-
through concept of single-dose triggering has been developed and introduced commer-
cially. Speer et al. (1993) were the first to claim that films of unsaturated polymers,
such as poly(l,2-butadiene), could very effectively scavenge ground-state oxygen
provided they contained a transition metal catalyst and a photosensitizer. The use of
pendant C=C double bonds was designed
to
minimize rupture of the polymer backbone
during oxidation. This overcame one of the significant drawbacks of the process of
Rooney
(1982).
Speer's process has been developed with a large number of patents, and
has been marketed by the Cryovac division of Sealed Air Corporation under the trade
name OS 1000™.
The approach of using autoxidation of unsaturated groups on a polymer as a basis
for oxygen scavenging has been taken up by Chevron Chemical Company, with a
fur-
ther development of the Cryovac concept. In this case the oxidizable moity is a cyclo-
hexene side group bound to the backbone, for instance by transesterification (Ching
et
al.,
1994).
The novelty of this process lies in its apparent "tasteless" achievement of
Oxygen-scavenging packaging 131
oxygen removal.
The
earlier approaches involving autoxidation
of
non-cyclic side
groups are claimed to have imparted some taste to the food.
The chemistries employed in the oxidation of aromatic nylons and of hydrocarbon
polymers with various side groups have the common theme of light-triggering to pro-
duce enough free radicals
to
remove the antioxidants remaining after extrusion. The
transition metal catalysts then facilitate the rupture of the hydroperoxides formed, and
accelerate the ongoing chain reactions.
A radically different process also triggered by light has been developed without the
use of photo-initiation. This process involves the light excitation
of
a
photoreducible
component, such
as a
quinone, followed
by its
photoreduction. This
new
photo-
reduced species is then oxidized by the oxygen that it scavenges. In this case the poly-
mer was inactive until exposure
to, for
example, ultraviolet light
-
something that
might
not be
applied until immediately before package filling (Rooney, 1993).
The
species reactive towards oxygen
is
therefore
not
present during thermal processes
such as extrusion and blow molding.
There have been other approaches
to
scavenging oxygen from food packs
or to
enhancing the barrier of packs such as
bottles.
These have generally included variants
on those mentioned here,
and
some have been reviewed elsewhere (Rooney,
1995;
Brody
et al,
2001). The processes that have progressed
to
the market
or
which
are
undergoing commercial development
are
described
in
ever increasing detail
in the
forest
of
patent applications that have been published. Despite
the
density
of
this
forest,
it is
clear that several different food distribution problems can
be
solved
by
using these scavengers. These problems have their genesis in the nature of the newer
packages as well as the requirements of high-speed filling and the use of distribution
temperatures that impose demands upon the packaging. Perhaps the greatest demand
has been made by the shift from glass and metal cans to substantially plastic packs.
The requirements of foods that impact
on
package selection involving oxygen scav-
enging can basically be subdivided into enhancement of barrier and headspace scaveng-
ing (Figure 8.2). Frequently both requirements are present, but the most economical
approach to package selection may be made by using oxygen scavenging
to
address
one problem or the other.
Barrier enhancement
is
commonly needed where
the
product
is
packaged
in an
impermeable package with
a
closure allowing oxygen entry, or when the product has
a very low headspace and the oxygen ingress needs to be prevented while maintaining
Packaging problem
1
1
Barrier enhancement
1
Thin films
bottles
closures
1
Headspace scavenging
1
Gaseous
dissolved
trapped
Figure
8.2
Roles
for
oxygen-scavenging packaging plastics.
132 Innovations in Food Packaging
a thin barrier
layer.
The latter limitation may
be a
requirement of the package for other
reasons, such as in aseptic brick packs or with close-fitting thermoformed films used
for vacuum
packaging.
The most recent need for barrier enhancement is found in PET
bottles for beer, where beer is packaged with a very low oxygen concentration but
is
degraded by oxygen permeating the PET.
Headspace scavenging is beneficial when, even though the package may provide
a
high barrier, the residual oxygen is not readily removed to the necessary level by con-
ventional
means.
This is typically the case with beverages and products with a porous
structure not economically deoxygenated by evacuation
or
gas flushing. Such prod-
ucts include bakery items, and spray-dried and
fi-eeze-dried
foods. Beverages that are
not readily deoxygenated include those that froth readily yet contain air bubbles due
to the presence of fruit pulp.
Application
to
food
and
beverage packaging
The interest in, and adoption
of,
oxygen-scavenging systems has been driven by the
wide range
of
mechanisms by which oxygen can contribute
to
loss
of
food quality.
These mechanisms include:
nutrient loss
discoloration
microbial spoilage
rancidity
organoleptic deterioration
infestation by insects and vermin.
Pathogen growth is not included in the above list, as measures to prevent their growth
should already
be in
place.
Each one of these mechanisms has its
own
kinetics and level
of sensitivity at which the effect on the food becomes unacceptable. Table 8.2 shows
a
selection of foods that benefit from oxygen scavenging, and indicates the importance of
the speed at which quality deterioration occurs. Hence, although a pack of full-cream
milk powder which has been nitrogen
flushed
may have an oxygen content of around
5%
after desorption from the pores, the oxidation occurs sufficiently slowly to present
Table
8.2
Oxygen sensitivity
of
sdme foods
Food/beverage
Substrate
Rate
Milk powder
Cheese
Beer
Wine
Juice
Fish
Fat
Mold
Flavors
Preservatives
Vitamin
C
Oil
Slow
Slow
Moderate
Moderate
Fast
Fast
Oxygen-scavenging packaging 133
only
a
minor
problem.
Beer,
on the
other
hand,
is similarly sensitive to oxidation of oils
which cause off-flavor development. However, the damage done by the initial oxygen
uptake results in flattening of the flavor and can take some months off the potential
shelf
life.
This is crucial to the introduction of PET packaging for this beverage.
The choice of packaging for preserved
fish
products is severely limited by the rapid
oxidation of the polyunsaturated oils present. Indeed, a variety of fish oil products
cannot be packaged in glass jars because the residual oxygen present is sufficient to
cause unacceptable levels of both discoloration and rancid odor. Packaging that scav-
enges oxygen at a rate much greater than the food oxidation calls for rapid scaveng-
ing coupled with package design that maximizes the area of scavenger available.
Prevention of mold growth is a major role for oxygen scavenging (Smith et ah,
1995).
Although mold is one of the major causes of food quality
loss,
the slow rate of
growth in many foods provides an opportunity for oxygen scavenging to reduce oxygen
levels to around
0.1%,
which inhibits such growth. The capacity of oxygen scavenging
to
prevent mold growth
on
processed meat
was
addressed
by
Randell
et
al
(1995).
They
demonstrated that even in
the
presence of
a
pinhole in the seal of packages, an oxygen
absorber sachet could suppress growth for useful
periods.
They found that the concur-
rent degradation of the meat color
by
the action of the
fluorescent
display lights on the
oxidation reaction was also prevented.
Color loss due to photo-oxidation is not limited
to
processed
meats.
It
has
also been
shown that the
flavor
and color degradation of Havarti cheese is strongly enhanced by
fluorescent display lights. Randell et al (1995). These authors showed that by reduc-
ing the headspace oxygen in these packs to
0.1%,
the formation of pentanol (the indi-
cator of quality loss) could be essentially eliminated, regardless of the illumination
conditions tested. The benefit demonstrated by such work is that oxygen scavenging
can contribute not just to the package properties but also to the conditions under
which a food might be distributed.
The oxidation of vitamin C in orange juice occurs rapidly, and this reaction usually
results in substantial deoxygenation of the juice in ambient barrier packaging in asep-
tic brick
packs.
The result is the loss of the vitamin, coupled with the consequent gen-
eration of browning products several months later. Beverages do not lend themselves
to protection by oxygen absorber sachets or labels, so overcoming this problem has
been delayed pending the development of plastics with scavenging capability.
The development of these plastics has been described largely in
patents,
so there are
very few peer-reviewed research results published. One such investigation, from the
author's laboratory, involved the measurement of dissolved oxygen concentrations,
ascorbic acid, and total vitamin C assays, and browning of
the
juice when stored in an
oxygen-scavenging laminate under refi"igerated and ambient conditions (Zerdin et al.,
2003).
The laminate (OS) pouches consisted of EVOH/oxygen-scavenger film/EVA,
and the pouches contained orange juice
fi*om
freshly backed aseptic brick
packs.
The
juice was re-sterilized with dimethyldicarbonate on repacking in the pouches in order
to avoid microbial oxygen
uptake.
The scavenger
film
was an improved version of one
that involved photoreduction of
a
polymer-bound reducible compound and described
previously (Rooney and Horsham, 1998). It was found that the oxygen
was
scavenged
in less than three days at ambient temperature, and that the quantity of ascorbic acid
134 Innovations in Food Packaging
400-
350
^
300
E
Reference
OS
t
^
250
4t4
o
200
150
100
50
-KJ
--e-—
-^.
«^
—~^.^.^.
T:
~'"^-~-..
--^
50 100 150 200 250
Storage time (days)
300 350
400
i;j f '^-^
Concentration
of
ascorbic acid
in
orange juice packed
in
oxygen scavenging and reference
pouches stored
at
25°C.
lost during that time was reduced compared with that in the control pouches. The loss
of ascorbic acid from the juice packed
in
the scavenger pouch was consistently less
than that in the reference over
a
period
of
one year (Figure 8.3). The extent of brown-
ing
of
the juice was reduced
by
around 33% when the juice was packaged with
the
scavenger laminate. Results broadly similar to these were reported by Rodgers (2000),
whose results were obtained from
an
independent laboratory and using the metal cat-
alyzed and photoinitiated polymer bearing cyclohexenyl groups.
The results obtained
at
refrigerator temperature
by
Zerdin
et al
(2003) were simi-
lar to those obtained under ambient conditions. The oxygen concentration was similar
after three days. The browning was suppressed
at
low temperature
in
both the control
and test pouches. Thus oxygen scavenging may be significantly more necessary where
aseptic packs
are
distributed under ambient conditions than where short shelf-life
juices are distributed chilled.
Besides the direct effects on the food
of
suppressing oxidation or microbial growth,
there
are
other aspects
of
food quality that can be influenced by use
of
oxygen scav-
engers. Chilled beef is conventionally distributed at the wholesale level as primal cuts
weighing several kilograms, vacuum-packaged
in
shrink bags with low oxygen per-
meability at 0°C. The drip, or liquid exudates, lost under these circumstances has been
minimized, but recent research into the use
of
non-vacuum packaging with the pres-
ence
of
an oxygen scavenger sachet has revealed
a
ftirther improvement (Payne
et al,
1998).
These investigators found that drip loss could
be
substantially reduced
by
avoiding
the
compression effect
of
evacuation and removing
the
residual oxygen
by
using an oxygen absorber sachet (Ageless'^^ Z50). Results like these are indicative
of
the potential
for
oxygen scavenging
to
contribute
to
quality
and
logistic parameters
associated with food distribution
in
the wider sense.
The application
of
oxygen scavenging
has not
been limited
to
plastics packages.
The shelf life of cracker biscuits in metal cans, as measured by hexanal formation and
Oxygen-scavenging packaging 135
peroxide value development, was almost doubled at 25°C (Berenzon and Saguy,
1998).
It was found that with the addition of oxygen-absorber sachets, no oxidative
odors were observed after 44 weeks at 25°C and 35°C. Results such as these support
the view that the method of oxygen scavenging will vary with the food/package com-
bination, and that no one approach is likely to satisfy the varying demands of food and
beverage packaging.
Future opportunities
The field of oxygen scavenging using plastics is still largely under development, even
though the use of sachets, labels, and closure liners is well established. The introduc-
tion of new technologies will depend upon the drivers revealed in the food and pack-
aging industries. The major driver should be the curiosity of food technologists
interested in seeking better outcomes when they introduce new or modified products.
This in turn may be expected to be a result of the education process. Another driver of
importance will be the need to achieve current (or better) quality levels as packaging
is changed, especially when newer materials are used. This is being observed already
with the introduction of PET bottles and jars in place of rigid metals and glass. Even
in the latter packaging there are ample opportunities to enhance the product quality
for the consumer by scavenging of the headspace already present therein. The poten-
tial impact on canned foods can only be guessed at currently.
Regulation by both food authorities and those caring for the environment will also
have major impacts. A variety of scavenging systems have already been approved in
Japan, the USA and European countries, among others. The expected amendment of
the Food Packaging Directive by the European Commission in late 2004/5 to address
active packaging will make the future paths to introduction clearer, even though oxy-
gen removal is not really the main thrust of the expected changes. The potential for
reduction in the complexity of multilayer plastics structures and the reduction in rigid
packaging use following the use of oxygen scavenging may be expected to have favor-
able outcomes for the environment, as long as there are not adverse impacts in the
manufacturing process.
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Intelligent packaging
Jung H, Han, Colin H, L Ho and Evangelina T. Rodrigues
introduction 138
Intelligent packaging applications and technologies 141
Consumer acceptance and legislative issues 151
Conclusions 152
Disclaimer 153
References 153
Introduction
The
primary function of packaging is to secure the food content against physical dam-
age,
moisture gain or loss, oxidation, and biological deterioration. The secondary
function is to facilitate the distribution of the product (containing the proper informa-
tion) to the consumer (Side, 2002). Packaging also fosters effective marketing of the
food through distribution and sale channels. It is of the utmost importance to optimize
the protection of the food product by selecting the right packaging materials, designs,
and distribution
methods.
Other purposes of food packaging are to fulfil changing con-
sumer
needs,
as well as the customers' desire for quality and convenience. Nowadays,
consumers are willing
to
pay more for better quality foods and for convenient packaged
foods with little preparation required. Such foods are "quality convenience foods"
that offer the consumer great quality and appearance - better than typical packaged
foods (Fito et al., 1997). In recent years, active packaging has evolved due to the
growing tendency to develop substances that are incorporated into the package and are
active in protecting the foodstuff against contamination.
New packaging systems
Terms such as active, smart, interactive, clever or intelligent are used to describe new
packaging
methods.
These terms lack clear definition, and are interchangeable in some
literature. Therefore, it is important to differentiate their meanings. Active packaging
Innovations in Food Packaging Copyright © 2005 Elsevier Ltd
ISBN:
0-12-311632-5
All rights of reproduction in any form reserved
Intelligent packaging 139
changes the condition of the packed foods with the use of the incorporation of certain
additives into the packaging films or inside the packaging headspaces so as to extend
the product's shelf hfe (Day, 1989). In some cases, it also changes the package's perme-
ation properties and/or
the
concentration of different volatiles and gases in
the
package
headspace during storage. Moreover, this packaging technique actively adds, in small
amounts, antimicrobial, antioxidative or other quality improving agents via the pack-
aging materials into the packed food. Active packaging also plays a role in food preser-
vation other than just providing
an
inert barrier
to the
external conditions (Rooney, 1995).
Active packaging techniques can
be
divided into two categories (Ahvenainen, 2003).
The first category is absorbers or scavengers, where the systems remove undesired
compounds such as oxygen, carbon dioxide, ethylene, and excessive water. The sec-
ond category is the releasing systems, which actively adds or emits compounds to the
packaged foods or into the headspace of
the
package - such as carbon dioxide, anti-
oxidants and preservatives.
Intelligent packaging
Intelligent packaging refers to a package that can sense environmental changes, and
in turn informs the changes to the users (Summers, 1992a). Rodrigues and Han (2003)
defined intelligent packaging as having two categories: simple intelligent packaging (as
defined by Summers, 1992a), and interactive or responsive intelligent
packaging.
In the
later,
the
packaging contains sensors that notify consumers that
the
product
is
impaired,
and they may begin to undo the harmful changes that
have
occurred in
the
food product
(Karel, 2000; Rodrigues and
Han,
2003). Such packaging systems contain devices that
are capable of sensing and providing information about the functions and properties
of the packaged foods (Day, 2001), and/or contain an external or internal indicator for
the active product history and quality determination (Ohlsson and Bengtsson, 2002).
These types of devices can be divided into three groups. The first type is the exter-
nal indicators. These indicators are attached outside the package, and include time-
temperature indicators and physical shock indicators. The second type is the internal
indicators, which are placed inside the
package.
They are either placed in the headspace
of the package or attached to the lid - for example, oxygen leak indicators, carbon
dioxide, microbial, and pathogen indicators (Ahvenainen, 2003). The third type of
devices is the indicators that increase the efficiency of information flow and effective
communication between the product and the consumer. These products include spe-
cial bar codes that store food product information such as use, and consumption date
expiration. Product traceability, anti-theft, anti-counterfeiting, and tamperproof devices
are also included in this category (Coles et a/., 2003).
This chapter will review intelligent packaging technologies and describe different
types of
devices.
Their principal food applications and recent developments will also
be highlighted. The intelligent packaging application systems will be discussed in the
following categorical order:
1.
Those that provide more convenience (quality, distribution and preparation
methods)