3.1 Introduction
The best known and most widely used active packaging technologies for foods
today are those engineered to remove undesirable substances from the headspace
of a package through absorption, adsorption or scavenging. To achieve this goal
a physical or chemical absorbent or adsorbent is incorporated in the packaging
material or added to the package by means of a sachet. In most publications, the
term ‘absorption’ is used loosely to describe any system that removes a
substance from the headspace. However, there is a clear difference between
absorption and adsorption. Adsorption is a two-dimensional phenomenon while
absorption is three-dimensional. According to Mortimer (1993), absorption
involves a substance being taken into the bulk of a phase while adsorption
involves a substance being taken onto a surface. Both, absorption and adsorption
are physical phenomena while scavenging implies a chemical reaction (Brody et
al., 2001). This chapter focuses mainly on oxygen and ethylene scavenging and
finally also discusses carbon dioxide absorbers and odour removers.
3.2 Oxygen scavenging technology
3.2.1 Introduction
In many cases, food deterioration is caused by the presence of oxygen, as
oxygen is responsible for oxidation of food constituents and proliferation of
moulds, aerobic bacteria and insects. Modified atmosphere packaging (MAP)
and vacuum packaging have been widely adopted to exclude oxygen from the
headspace. However, these physical methods of oxygen elimination do not
3
Oxygen, ethylene and other scavengers
L. Vermeiren, L. Heirlings, F. Devlieghere and J. Debevere, Ghent
University, Belgium
always remove the oxygen completely. Some oxygen (0.1–2%) generally
remains in the package and even more when the food is porous. Moreover, the
oxygen that permeates through the packaging film during storage cannot be
removed by these techniques. In the presence of such amounts of oxygen, many
of the oxidation reactions and mould proliferation still proceed. Oxygen
scavengers are able to reduce the oxygen concentration to less than 0.01% and
can maintain those levels (Rooney, 1995; Hurme and Ahvenainen, 1998;
Vermeiren et al., 1999). An oxygen scavenger is a substance that scavenges
oxygen chemically or enzymatically and therefore, protects the packaged food
completely against deterioration and quality changes due to oxygen.
3.2.2 Role of oxygen scavengers
Preventing oxidation
Oxygen scavengers effectively prevent oxidative damage in a wide range of
food constituents such as (i) oils and fats to prevent rancidity, (ii) both plant and
muscle pigments and flavours to prevent discolouration (e.g. meat) and loss of
taste and (iii) nutritive elements, e.g., vitamins to prevent loss of the nutritional
value. Berenzon and Saguy (1998) investigated the effect of oxygen scavengers
on the shelf-life extension of crackers packaged in hermetically sealed tin cans
which were stored at 15, 25 and 35oC for up to 52 weeks. Oxygen scavengers
reduced the hexanol concentration significantly. Peroxide values were markedly
reduced by the presence of oxygen scavengers. In the presence of oxygen
scavengers, the lag period before the peroxides started to build up was prolonged
to, respectively, 17 and 10 weeks at 25 and 35oC. Sensory evaluations showed
that in the presence of oxygen scavengers and independently of storage
temperature, no oxidative rancid odours were observed for up to 44 weeks.
Preventing insect damage
Oxygen scavengers are effective for killing insects and worms or their eggs
growing in cereals such as rice, wheat and soybeans. Fumigation treatments
using gases such as bromides and methyl disulfide kill insects but their residues
can remain in the food. Additionally, insects in the egg or pupal stages can be
resistant against fumigation treatments. Oxygen scavengers are very effective
against insects because they remove the oxygen the insects need to survive.
Prevention of proliferation of moulds and strictly aerobic bacteria
Oxygen scavenging is effective in preventing growth of moulds and aerobic
bacteria. Mould spoilage is an important microbial problem limiting the shelf-
life of high and intermediate moisture products. Losses due to mould spoilage
are a serious economic concern in the bakery industry. Some moulds, such as
Aspergillus flavus and Aspergillus parasiticus, can also produce highly toxic
substances called mycotoxins. In gas packaging aerobic growth can still occur
depending on the residual oxygen level in the package headspace. It has been
demonstrated that moulds can proliferate in headspaces with oxygen
Oxygen, ethylene and other scavengers 23
concentrations as low as 1–2% (Smith, 1996). Oxygen levels of 0.1% or lower
are required to prevent the growth and mycotoxin production of many moulds
(Rooney, 1995). The effects of modified atmosphere packaging involving
oxygen scavengers, storage temperature and packaging film barrier
characteristics on the growth of and aflatoxin production by Aspergillus
parasiticus in packaged peanuts was investigated (Ellis et al., 1994). A slight
mould growth was visible in air-packaged peanuts using a high gas barrier film
(Oxygen Transmission Rate (OTR) of 3–6 cc. m
2
. day
1
at 23oC and dry
conditions) while extensive growth was observed in peanuts packaged under
similar air conditions using a low gas barrier film (OTR of 4000 cc m
2
day
1
).
When an oxygen scavenger (Ageless
type S) was incorporated, mould growth
was inhibited in peanuts packaged in a high gas barrier film and was reduced
when a low barrier film was used. Aflatoxin B
1
production was inhibited in
peanuts packaged in a high barrier film with an oxygen scavenger, while a
limited amount of aflatoxin less than the regulatory level of 20 ng. g
1
was
detected in absorbent packaged peanuts using a low barrier film. This study
showed that oxygen scavengers are effective for controlling the growth of and
aflatoxin production by Aspergillus parasiticus. However, the effectiveness of
the scavengers will be dependent on the gas barrier properties of the packaging
film.
Smith et al. (1986) showed that oxygen scavengers are three times more
effective than gas packaging for increasing the mould-free shelf-life of crusty
rolls. In gas packaged (40% N
2
/60% CO
2
) crusty rolls with Ageless
the
headspace oxygen never increased beyond 0.05% and the product remained
mould-free for over 60 days at ambient storage temperature. A similar mould-
free shelf-life was obtained in air and N
2
packaged crusty rolls with Ageless
.
The mould-free shelf-life of white bread packaged in a polypropylene film could
be extended from 4–5 days at room temperature to 45 days by using an Ageless
sachet. Pizza crust, which moulds in 2–3 days at 30oC was mould-free for over
10 days using an appropriate O
2
scavenger (Nakamura and Hoshino, 1983).
It is well known that an oxygen-free atmosphere at a water activity greater
than 0.92 can favour the growth of many microbial pathogens including
Clostridium botulinum (Labuza and Breene, 1989). Clostridium botulinum
mainly grows under anaerobic conditions but can also have a limited growth
under low O
2
conditions. The use of oxygen scavengers could be dangerous if
the temperature is not kept close to 0oC. Daifas et al. (1999) investigated the
growth and toxin production by Clostridium botulinum in English-style
crumpets, using an Ageless
FX
200
oxygen scavenger at room temperature.
All inoculated crumpets were toxic within 4 to 6 days and were organoleptically
acceptable at the time of toxigenesis. Counts of C. botulinum increased to
approximately 10
5
CFU/g at the time of toxin production. This study confirms
that C. botulinum could pose a public health hazard in high a
w
– high pH
crumpets using an oxygen scavenger when stored at non-chilled conditions.
Lyver et al. (1998) have done challenge studies on raw surimi nuggets, which
were inoculated with 10
4
spores/g of Clostridium botulinum type E spores. All
24 Novel food packaging techniques
products were packaged in air and air with an Ageless
SS oxygen absorber and
stored at 4, 12 and 25oC. Toxin was not detected in any raw product throughout
storage (28 days). The absence of toxigenesis was attributed to the low pH (4.1–
4.3) due mainly to the growth of lactic acid bacteria. Whiting and Naftulin
(1992) showed that controlling the pH and NaCl concentration of the food
product is an important factor in controlling growth of C. botulinum under low
oxygen concentrations. When oxygen absorbers are used, challenge studies
should be done to investigate if C. botulinum is able to grow. An overview of the
effects of oxygen scavengers and their most important food applications is
shown in Table 3.1.
3.3 Selecting the right type of oxygen scavenger
Oxygen scavengers must satisfy several requirements: they must
1. be harmless to the human body. Though the oxygen scavengers themselves
are neither food nor food additives, they are placed together with food in a
package, and there is therefore the possibility of accidental intake by
consumers.
2. absorb oxygen at an appropriate rate. If the reaction is too fast, there will be
a loss of oxygen absorption capacity during introduction into the package. If
it is too slow, the food will not be adequately protected from oxygen
damage.
3. not produce toxic substances or unfavourable gas or odour.
4. be compact in size and are expected to show a constant quality and
performance.
5. absorb a large amount of oxygen.
6. be economically priced (Nakamura and Hoshino, 1983; Abe, 1994; Rooney,
1995).
An appropriate oxygen scavenger is chosen depending on the O
2
-level in the
headspace, how much oxygen is trapped in the food initially and the amount of
Table 3.1 Effects of oxygen scavengers on foods (Abe, 1994; Smith et al., 1990)
Effect Typical application
Fresh taste and aroma Various food items, coffee, tea
$ Mould growth Bakery products, cheese, processed
seafood, pasta
$ Rancidity Nuts, fried foods, processed meat, whole
milk powder product
$ Discolouration Processed meat, green noodle, herbs, tea,
dried vegetables
$ Insect damage Beans, grain, herbs, spices
Maintaining nutritional value All kinds of foods
Oxygen, ethylene and other scavengers 25
oxygen that will be transported from the surrounding air into the package during
storage. The nature of the food (e.g. size, shape, weight), water activity and desired
shelf-life are also important factors influencing the choice of oxygen absorbents.
For an oxygen scavenger (sachet) to be effective, some conditions have to be
fulfilled (Nakamura and Hoshino, 1983; Abe, 1994; Smith, 1996). First of all,
packaging containers or films with a high oxygen barrier must be used, otherwise
the scavenger will rapidly become saturated and lose its ability to trap O
2
. Films
with an oxygen permeability not exceeding 20 ml/m
2
.d.atm are recommended for
packages in which an oxygen scavenger will be used. Examples of barrier layers
used with oxygen scavengers are EVOH (ethylene vinyl alcohol) and PVDC
(polyvinylidene chloride) (Nakamura and Hoshino, 1983; Rooney, 1995). If films
with high O
2
permeabilities are used (> 100 ml/m
2
.d.atm), the O
2
concentration
will reach zero within a week but after some days, it will return to ambient air level
because the absorbent is saturated. If high-barrier films (e.g. < 10 ml/m
2
.d.atm) are
used, the headspace O
2
will be reduced to 100 ppm within 1–2 days and remain at
this level for the duration of the storage period provided that package integrity is
maintained (Rooney, 1995). Secondly, for flexible packaging heat sealing should
be complete so that no air invades the package through the sealed part. A rapid,
inexpensive and efficient method of monitoring package integrity and ensuring low
residual headspace oxygen throughout the storage period is through the
incorporation of a redox indicator, e.g. Ageless
Eye
. Ageless
Eye
is a tablet
which indicates the presence of oxygen by a colour change. When placed inside the
package, the colour changes from blue to pink when the O
2
concentration
approaches zero. If the indicator reverts to its blue colour, this is an indication of
poor packaging integrity (Smith et al., 1990; Nakamura and Hoshino, 1983;
Rooney, 1995). Finally, an oxygen scavenger of the appropriate type and size must
be selected. The appropriate size of the scavenger can be calculated using the
following formulae (Roussel, 1999; ATCO
technical information, 2002). The
volume of oxygen present at the time of packaging (A) can be calculated using the
formula:
A V P O
2
=100
V volume of the finished pack determined by submersion in
water and expressed in ml;
P weight of the finished pack in g;
O
2
initial O
2
concentration in package ( 21% if air).
In addition, it is necessary to calculate the volume of oxygen likely to
permeate through the packaging during the shelf-life of the product (B). This
quantity in ml may be calculated as follows:
B S P D
26 Novel food packaging techniques
S surface area of the pack in m
2
;
P permeability of the packaging in ml/m
2
=24h/atm;
D the shelf-life of the product in days.
The volume of oxygen to be absorbed is obtained by adding A and B. Based on
these calculations, the size of the scavenger and the number of sachets can be
determined.
3.3.1 Oxygen scavenging sachets
In general, O
2
scavenging technologies are based on one of the following
concepts: iron powder oxidation, ascorbic acid oxidation, catechol oxidation,
photosensitive dye oxidation, enzymatic oxidation (e.g. glucose oxidase and
alcohol oxidase), unsaturated fatty acids (e.g. oleic acid or linolenic acid) or
immobilised yeast on a solid material (Floros et al., 1997). A summary of the
most important trademarks of oxygen scavenger systems and their
manufacturers is shown in Table 3.2.
The majority of presently available oxygen scavengers are based on the
principle of iron oxidation (Nakamura and Hoshino, 1983; Rooney, 1995;
Vermeiren et al., 1999)
Fe!Fe
2
2e
1
2
O
2
H
2
O 2e
!2OH
Fe
2
2OH
!Fe (OH)
2
Fe (OH)
2
1
4
O
2
1
2
H
2
O!Fe (OH)
3
The principle behind oxygen absorption is iron rust formation. To prevent the
iron powder from imparting colour to the food, the iron is contained in a sachet.
The sachet material is highly permeable to oxygen and water vapour. A rule of
thumb is that 1 g of iron will react with 300 ml of O
2
(Labuza, 1987; Nielsen,
1997; Vermeiren et al., 1999). The LD
50
(lethal dose that kills 50% of the
population) for iron is 16 g/kg body weight. The largest commercially available
sachet contains 7 grams of iron so this would amount to only 0.1 g/kg for a
person of 70 kg, or 160 times less than the lethal dose (Labuza and Breene,
1989). Iron-based oxygen scavengers have one disadvantage: they cannot pass
the metal detectors usually installed on the packaging line. This problem can be
avoided, e.g. by ascorbic acid or enzyme based O
2
scavengers (Hurme and
Ahvenainen, 1998).
Some important iron-based O
2
absorbent sachets are Ageless
(Mitsubishi
Gas Chemical Co., Japan), ATCO
O
2
scavenger (Standa Industrie, France),
Freshilizer
Series (Toppan Printing Co., Japan), Vitalon (Toagosei Chem.
Oxygen, ethylene and other scavengers 27
Table 3.2 Some manufacturers and trade names of oxygen scavengers (Ahvenainen and Hurme, 1997; Day, 1998; Vermeiren et al., 1999)
Company Trade name Type Principle/Active substances
Mitsubishi Gas Chemical Co., Ltd. (Japan) Ageless Sachets and labels Iron based
Toppan Printing Co., Ltd. (Japan) Freshilizer Sachets Iron based
Toagosei Chem. Ind. Co. (Japan) Vitalon Sachets Iron based
Nippon Soda Co., Ltd. (Japan) Seaqul Sachets Iron based
Finetec Co., Ltd. (Japan) Sanso-cut Sachets Iron based
Toyo Pulp Co. (Japan) Tamotsu Sachets Catechol
Toyo Seikan Kaisha Ltd. (Japan) Oxyguard Plastic trays Iron based
Dessicare Ltd. (US) O-Buster Sachets Iron based
Multisorb technologies Inc. (US) FreshMax Labels Iron based
FreshPax Sachets Iron based
Amoco Chemicals (US) Amosorb Plastic film unknown
Ciba Specialty chemicals (Switzerland) Shelfplus O
2
Plastic film Iron based
W.R. Grace and Co. (US) PureSeal Bottle crowns Ascorbate/metallic salts
Darex Bottle crowns, bottles Ascorbate/sulphite
CSIRO/Southcorp Packaging (Australia) Zero
2
Plastic film Photosensitive dye/
organic compound
Cryovac Sealed Air Co. (US) OS1000 Plastic film Light activated scavenger
CMB Technologies (UK) Oxbar Plastic bottles Cobalt catalyst/ nylon polymer
Standa Industrie (France) ATCO Sachets Iron based
Oxycap Bottle crowns Iron based
ATCO Labels Iron based
Bioka Ltd. (Finland) Bioka Sachets Enzyme based
Industry Co., Japan), Sanso-cut (Finetec Co., Japan), Seaqul (Nippon Soda Co.,
Japan), FreshPax
(Multisorb technologies Inc., USA) and O-Buster
(Dessicare Ltd., USA). Some of them will be discussed in detail.
Ageless
can reduce the oxygen in an airtight container down to 0.01% (100
ppm) or less to prolong shelf-life of food products. Several types of Ageless
are
commercially available and applicable to many types of foods (Labuza and
Breene, 1989; Smith et al., 1990; Abe, 1994; Ageless
technical information,
1994; Rooney, 1995; Smith, 1996). The different types and properties of
Ageless
oxygen scavenging sachets are shown in Table 3.3.
A self-reacting type contains moisture in the sachet and as soon as the sachet
is exposed to air, the reaction starts. In moisture-dependent types, oxygen
scavenging takes place only after moisture has been taken up from the food.
These sachets are stable in open air before use because they do not react
immediately upon exposure to air therefore they are easy to handle if kept dry.
Toppan Printing Co. developed another type of oxygen scavenging sachet,
named Freshilizer
. Two series are commercially available, the F series and C
series. Sachets of the F series contain ferrous metal and scavenge oxygen
without generating another gas. The C series contain non-ferrous particles and
are able to sorb oxygen and generate an equal volume of carbon dioxide to
prevent package collapse.
FreshPax
TM
is a patented oxygen scavenger developed by Multisorb
technologies. Four main types of FreshPax are commonly available: type B,
D, R and M. Type B is used for moist or semi-moist foods with a water activity
above 0.7. Type D is recommended for use with dehydrated and dried foods. To
scavenge oxygen at refrigerated or frozen storage temperatures, type R should
Table 3.3 Types and properties of Ageless oxygen scavenging sachets (Rooney, 1995;
Ageless technical information, 2002)
Type Function Moisture status Water activity Absorption
speed
a
(day)
ZP/ZPT Decreases [O
2
] Self-reacting < 0.95 1–3
SA Decreases [O
2
] Self-reacting 0.65–0.95 0.5–1.0
SS Decreases [O
2
] Self-reacting 0.65–0.95 2–3 (0–4oC)
10 ( 25oC)
FX Decreases [O
2
] Moisture > 0.85 0.5–1.0
dependent
FM Decreases [O
2
] Moisture dependent > 0.80 1.0
also microwaveable
products
E Decreases [O
2
] Self-reacting < 0.3 3–8
Decreases [CO
2
]
G Decreases [O
2
] Self-reacting 0.3–0.5 1–4
increases [CO
2
]
GL Decreases [O2] Self-reacting 0.3–0.95 2–4
a
number of days to reduce the oxygen level to less than 0.01% (measured at room temperature)
Oxygen, ethylene and other scavengers 29
be used. Type M can be used for moist or semi-moist foods, which are packaged
under modified atmospheres containing carbon dioxide.
Another scavenging technology is based on catechol oxidation. As catechol is
an organic compound, it passes metal detectors. Tamotsu is the only commercial
product in Japan based on this technology (Abe, 1994). Tamotsu type D is used
for dry products such as spices, freeze-dried foods, tea. These sachets do not
require moisture for their oxygen scavenging reaction.
Another way of controlling the oxygen level in a food package is by using
enzyme technology. A combination of two enzymes, glucose oxidase and
catalase, has been applied for oxygen removal. In the presence of water, glucose
oxidase oxidises glucose, that can be originally present or added to the product,
to gluconic acid and hydrogen peroxide (Greenfield and Laurence, 1975; Labuza
and Breene, 1989; Nielsen, 1997). The reaction is:
2 glucose + 2 O
2
+ 2 H
2
O ! 2 gluconic acid + 2 H
2
O
2
where glucose is the substrate.
Since H
2
O
2
is an objectionable end product, catalase is introduced to break
down the peroxide (Rooney, 1995; Vermeiren et al., 1999):
2 H
2
O
2
catalase ! 2 H
2
O O
2
catalase
Enzymatic systems are usually very sensitive to changes in pH, water
activity, temperature and availability of solvents. Most systems require water for
their action, and therefore, they cannot be effectively used with low-water
content foods (Floros et al., 1997). The enzyme can either be part of the
packaging structure or put in an independent sachet. Both polypropylene (PP)
and polyethylene (PE) are good substrates for immobilising enzymes (Labuza
and Breene, 1989). A commercially available enzyme-based oxygen absorbent
sachet is Bioka (Bioka Ltd., Finland). It is claimed that all components of the
reactive powder and the generated reaction products are food-grade substances
safe for both the user and the environment (Bioka technical information, 1999).
The oxygen scavenger eliminates the oxygen in the headspace of a package and
in the actual product in 12–48 hours at 20oC and in 24–96 hours at 2–6oC. With
certain restrictions, the scavenger can also be used in various frozen products.
When introducing the sachet into a package, temperature may not exceed 60oC
because of the heat sensitivity of the enzymes (Bioka technical information,
1999). An advantage is that it contains no iron powder, so it presents no
problems for microwave applications and for metal detectors in the production
line.
Besides glucose oxidase, other enzymes are able to scavenge oxygen. One
such enzyme is alcohol oxidase, which oxidises ethanol to acetaldehyde. It could
be used for food products in a wide a
w
range since it does not require water to
operate. If a lot of oxygen has to be absorbed from the package, a great amount
of ethanol would be required, which could cause an off-odour in the package. In
addition, considerable aldehyde would be produced which could give the food a
yoghurt-like odour (Labuza and Breene, 1989).
30 Novel food packaging techniques
The Pillsbury Company holds a 1994 patent that utilises ascorbic acid as
reducing agent (Graf, 1994). The product, also referred to as Oxysorb, comprises
a combination of a reducing agent, ascorbic acid, and a small amount of a
transition metal, such as copper. The oxygen removing system may be added in
a small oxygen permeable pouch.
The oxidation of polyunsaturated fatty acids (PUFAs) is another technique to
scavenge oxygen. It is an excellent oxygen scavenger for dry foods. Most known
oxygen scavengers have a serious disadvantage: when water is absent, their
oxygen scavenging reaction does not progress. In the presence of an oxygen
scavenging system, the quality of the dry food products may decline rapidly
because of the migration of water from the oxygen scavenger into the food.
Mitsubishi Gas Chemical Co. holds a patent that uses PUFAs as a reactive agent.
The PUFAs, preferably oleic, linoleic or linolenic, are contained in carrier oil
such as soybean, sesame or cottonseed oil. The oil and/or PUFA are
compounded with a transition metal catalyst and a carrier substance (for
example calcium carbonate) to solidify the oxygen scavenger composition. In
this way the scavenger can be made into a granule or powder and can be
packaged in sachets (Floros et al., 1997).
3.3.2 Oxygen scavenging films
It should be noted that the introduction of oxygen scavenger sachets into the
food package suffers from the disadvantage of possible accidental ingestion of
the contents by the consumer. Another concern is that the sachet could leak out
and contaminate the product. When sachets are used, there also needs to be a
free flow of air surrounding the sachet in order to scavenge headspace oxygen
(Rooney, 1995). To eliminate this problem, oxygen removing agents can be
incorporated into the packaging material such as polymer films, labels, crown
corks, liners in closures. These oxygen scavenging materials have the additional
advantage that they can be used for all products, including liquid products. The
oxygen consuming substrate can be either the polymer itself or some easily
oxidisable compound dispersed or dissolved in the packaging material (Nielsen,
1997; Hurme and Ahvenainen, 1998).
A problem related to the use of O
2
scavenging films is that the films should
not react with atmospheric oxygen prior to use. This problem has been solved by
inclusion of an activation system triggering the O
2
consuming capabilities of the
film in the packaging system. Activation by illumination or catalysts or reagents,
supplied at the time of filling, may be required to start the reaction.
Illumination of a package that contains a photosensitising dye and a singlet
oxygen acceptor results in rapid scavenging of oxygen from the headspace.
Australian researchers have reported that reaction of iron with ground state O
2
is
too slow for shelf-life extension (Hurme and Ahvenainen, 1998). The singlet-
excited state of oxygen, which is obtained by dye sensitisation of ground state
oxygen using near infra-red, visible or ultraviolet radiation, is highly reactive
and so its chemical reaction with scavengers is rapid (Rooney, 1981). The
Oxygen, ethylene and other scavengers 31
technique involves sealing of a small coil of ethyl cellulose film, containing a
dissolved photosensitising dye and a singlet oxygen acceptor, in the headspace
of a transparent package. When the film is illuminated with light of the
appropriate wavelength, excited dye molecules sensitise oxygen molecules,
which have diffused into the polymer, to the singlet state. These singlet oxygen
molecules react with acceptor molecules and are thereby consumed. The
photochemical reaction can be presented as follows (Rooney, 1981; Vermeiren
et al., 1999):
photon + dye ! dye
*
dye
*
+ O
2
! dye + O
2
*
O
2
*
+ acceptor ! acceptor oxide
O
2
*
! O
2
This scavenging technique does not require water as an activator, so it is
effective for wet and dry products. Its scavenging action is initiated on the
processor’s packaging line by an illumination-triggering process. Examples of
light-activated oxygen scavenger films are OS1000, developed by Cryovac
Sealed air corporation and Zero
2
TM
developed by CSIRO and marketed by
Southcorp Packaging (Australia). Cryovac OS1000 is a multi-layer flexible film
with a coextruded sealant. The invisible, oxygen scavenging polymer is a
component of the sealant. UV lights are used to trigger the scavenging reaction
through a patented activation process. These films are activated on the
packaging line just before filling and sealing, so light never comes in contact
with the food. The active ingredient in the Southcorp technology, named Zero
2
,
is integrated into the polymer backbones of such common packaging materials
as PET, polyethylene, polypropylene and EVA. The active ingredient is non-
metallic and is activated by UV light once it is incorporated into packaging
material (Graff, 1998).
Amoco Chemicals has developed Amosorb
oxygen scavenger, a plastic
concentrate that sorbs oxygen in food and beverage packages. Amosorb
concentrate is a polymer-based oxygen scavenger that can be incorporated as an
inner layer within a multi-layer packaging structure during co-extrusion or
lamination. The oxygen scavenger is activated by moisture and can reduce
headspace oxygen levels to less than 0.01%. It can be incorporated into several
packaging structures such as the sidewall or lid of rigid containers, flexible film
and closure liners (Edwards, 1998; Amoco Chemicals bulletin AS-1, 1999a;
Amoco Chemicals bulletin AS-3, 1999b). In June 2000, the Amosorb 2000
oxygen absorber technology was acquired by Ciba Specialty Chemicals
Corporation. The trade name was changed to Ciba Shelfplus O2-2400
(polyethylene application) and Shelfplus O2-2500 (polypropylene application)
(Brody et al., 2001).
Oxyguard, from Toyo Seikan Group, is an oxygen scavenger that uses an iron
salt-based additive and is available in the form of a flexible or rigid plastic. It is
a multi-layer that consists of an outer layer, a barrier layer, an oxygen
32 Novel food packaging techniques
scavenging layer and an inner layer. The oxygen sorption is initiated by water
(Vermeiren et al., 1999; Oxyguard technical information, 2002).
Oxbar
TM
is a system developed by Carnaud-Metal Box (UK) and is
composed of a PET/MXD6/Co film where the PET serves as the structural
material and the active ingredients are MXD6 nylon (polymetaxylylene
adipamide or polymetaxylylene diamine-hexanoic acid) and cobalt salt. Cobalt
catalyses the oxidation of the nylon polymer (Miltz et al., 1995). It can be used
for plastic packaging of beer, wine, sauces and other beverages.
3.3.3 Other scavenging devices
Labels
Other layouts for oxygen scavengers are cards and sheets in or labels on the
packaging. In 1991, Multisorb technologies introduced the iron-based oxygen
scavenging label FreshMax. FreshMax is designed for adhesion within packages
and so the risk for ingestion is minimised. The technology has a printed surface
and is acceptable for food contact. It is resistant to fat and moisture and can be
used for several food products (Anon., 1991; Rooney, 1995; Silgelac technical
information, 1998; Caldic technical information, 2002). Standa Industrie has
also developed a self-adhesive oxygen scavenging label, named ATCO
and
Ageless
also has a label type and a card type.
Bottle closures
Removal of oxygen from a bottle by a closure requires that a component reacts
with gaseous oxygen in the headspace of the bottle. Darex oxygen scavenging
technology utilises a material that can be incorporated into barrier packaging
such as crowns, cans and a broad variety of plastic and metal closures. The basic
reaction of their oxygen scavenging technique is ascorbate oxidising to
dehydroascorbic acid and sulphite to sulphate. Darex DarExtend is designed
to be incorporated as an integral part of traditional barrier packaging such as the
aluminium roll-on closures as well as in plastic closures and crowns. Darex
DarEval is an EVOH-based oxygen scavenging barrier resin used as an inner
layer in multi-layer PET. DarEval enables multi-layer PET bottles to have a
glass-like performance (Rooney, 1995; Vermeiren et al., 1999; Darex Technical
Information, 2002). The major use is in crown caps to protect beer from
oxidation. Other examples of oxygen scavenging crowns caps are Pure Seal caps
(W.R. Grace Co., USA) and Oxycap (Standa Industrie, France).
3.3.4 Economic aspects
Oxygen scavengers have several economic advantages for the food processor
(Nakamura and Hoshino, 1983; Rooney, 1995; Smith, 1996):
? increased product shelf-life and distribution radius
? a longer time between deliveries enabling larger deliveries
Oxygen, ethylene and other scavengers 33
? increased length of time product can stay in the distribution pipeline
? reduced distribution losses
? reduced evacuation/gas flushing times in gas packaged products thereby
increasing product throughput
? reduced costs required for gas flushing equipments.
To save time and labour, oxygen scavenging sachets can be inserted
automatically (Ageless
technical information, 1994). Also labels can be
applied automatically at conventional line speeds. An iron-based sachet with a
capacity of 100 ml O
2
would cost 5.03 euro for 3000 pieces. The same sachet
with a capacity of 1000 ml O
2
would cost 20.4 euro for 500 pieces. The price of
another iron-based sachet of another trademark, which absorbs 100 ml O
2
, is
about 40 euro for 300 pieces.
3.4 Ethylene scavenging technology
3.4.1 Introduction
Ethylene acts as a plant hormone that has different physiological effects on fresh
fruit and vegetables. It accelerates respiration, leading to maturity and
senescence, and also softening and ripening of many kinds of fruit. Furthermore,
ethylene accumulation can cause yellowing of green vegetables and may be
responsible for a number of specific post-harvest disorders in fresh fruits and
vegetables. Although some effects of ethylene are positive, such as degreening
of citrus fruit, ethylene is often detrimental to the quality and shelf-life of fruits
and vegetables. To prolong shelf-life and maintain an acceptable visual and
organoleptical quality, accumulation of ethylene in the packaging of fruits and
vegetables should be avoided. A number of ethylene sorbing substances are
described. Most of these are supplied as sachets or integrated into films. Many of
the claims for ethylene adsorbing or absorbing capacity have been poorly
documented so the efficacy of these materials is difficult to substantiate
(Vermeiren et al., 1999; Zagory, 1995).
3.4.2 The role of ethylene scavengers
Ethylene is a naturally occurring, chemically simple molecule of the alkene type
that regulates numerous aspects of growth, development and senescence of
many fruits and vegetables. As it is effective at part-per-million to part-per-
billion concentrations and its effects are very dose-dependent, it is considered as
a plant hormone (Saltveit, 1999). Environmental ethylene can be produced both
biologically and non-biologically. Non-biological sources of ethylene are
incomplete combustion of fossil fuels, burning of agricultural wastes and
leakage from industrial polyethylene plants (Sawada and Totsuka, 1986).
Ethylene is thus a common air pollutant and ambient atmospheric levels are
normally in the range of 0,001–0,005 ppm (Abeles et al., 1992). Biological
34 Novel food packaging techniques
sources of ethylene include higher plant tissues, several species of bacteria and
fungi, some algae and mosses (Zagory, 1995).
In higher vascular plants, a relatively simple biosynthetic pathway produces
ethylene:
The amino acid methionine (MET) is converted to S-adenosyl methionine (SAM)
which is then converted in the next step to 1-amino-cyclopropane carboxylic acid
(ACC) by the enzyme ACC synthase. The production of ACC is often the
controlling step for ethylene synthesis. A number of intrinsic (e.g. developmental
stage) and extrinsic (e.g. wounding) factors influence this pathway. In the final
step, ACC is oxidised by the enzyme ACC oxidase to form ethylene. This last step
requires the presence of oxygen and low levels of CO
2
to activate ACC oxidase.
The ACC oxidase activity can show a dramatic increase in ripening of fruit in
response to ethylene exposure (Saltveit, 1999). As in the case of other hormones,
ethylene is thought to bind to a receptor, forming an activated complex that in turn
triggers a primary reaction. This primary reaction then initiates a chain of
reactions leading to a wide variety of physiological responses (Yang, 1985).
Ethylene has since long been recognised as a problem in post-harvest
handling of horticultural products (fruits, vegetables and flowers). The diverse
physiological effects of ethylene have been extensively reviewed by many
authors (Abeles et al., 1992; Hopkins, 1995 and Saltveit, 1999). Some of the
effects of ethylene are beneficial and economically useful, such as flowering of
pineapples, de-greening of citrus fruits and ripening of tomatoes. However,
ethylene is often involved in the decline of the quality and shelf-life of many
fruits and vegetables. Only those effects that are deleterious to packaged plant
produce will be discussed here.
First of all, ethylene accelerates the respiration of fruits and vegetables.
Respiration rate generally is well correlated with perishability of produce.
Commodities such as asparagus, broccoli, mushrooms, and raspberries with high
respiration rates have short shelf-lives. At the end of growth, climacteric fruit
(e.g. banana, avocado) undergoes a large increase in respiration accompanied by
marked changes in composition and texture. The ripening of climacteric fruit is
associated with a large increase in ethylene production. The increases in
respiration and ethylene production can be induced prematurely in climacteric
fruit by treating them with a suitable concentration of ethylene. The ripening
process is irreversible once endogenous ethylene production increases to a
certain level (McGlasson, 1985). As climacteric fruit starts to ripen, this
negative feedback inhibition of ethylene on ethylene synthesis changes into a
positive feedback promotion in which ethylene stimulates its own synthesis (i.e.
autocatalytic ethylene production) and copious amounts of ethylene are
ACC synthase ACC oxidase (O
2,
CO
2
)
Methionine ! S-adenosylmethionine ! 1-amino-cyclopropane- ! CH
2
=CH
2
(SAM) carboxylic acid (ACC)
" "
fruit ripening, wounding ripening, ethylene
Oxygen, ethylene and other scavengers 35
produced. Reducing the external concentration of ethylene around bulky
ripening climacteric fruit (e.g. apples, bananas, melons, tomatoes) has almost no
effect on reducing the internal concentration in these fruit. Internal concentra-
tions of ethylene can exceed 100 l/l, even when the external concentration is
zero. Therefore, reducing the external ethylene concentration generally has no
effect on the ripening of fruit that has progressed a few days into its climacteric
stage. However, at the initial stages of ripening, when the internal levels are still
low, inhibiting the synthesis of ethylene and removal of ethylene can
significantly retard ripening (Saltveit, 1999). Non-climacteric fruit show no
increase in respiration and ethylene production during ripening. In contrast, an
unnaturally climacteric-like respiratory increase can be induced in non-
climacteric fruit by treating them with ethylene. Yet this increased respiration
is not accompanied by an increase in endogenous ethylene production and is still
reversible upon removal of the exogenous ethylene (McGlasson, 1985). In most
cases, exposure to a few parts per million of ethylene leads to increased
respiration and consequently increased perishability (Zagory, 1995).
Ethylene is often referred to as the ripening hormone because it can accelerate
softening and ripening of many kinds of fruit by the direct or indirect stimulation
of the synthesis and activity of many enzymes such as pectinases, cellulases,
esterases and polygalacturonase. Examples are a reduced firmness of watermelons
through ethylene exposure and an increased toughness of asparagus spears after
exposure to 100 ppm ethylene for 1 hour, which was associated with increased
activity of peroxidases and accelerated lignin biosynthesis. In most cases, for
packaged fruits it would be desirable to prevent exposure to ethylene and thereby
preventing rapid ripening (Zagory, 1995; Kader, 1985). Ethylene accelerates
chlorophyll degradation and induces yellowing of green tissues, thus reducing
market quality of leafy green vegetables such as spinach, floral vegetables such as
broccoli and immature fruits such as cucumbers (Kader, 1985) and promotes
changes that are important to flavour such as starch to sugar conversion, loss of
acidity and formation of aroma volatiles in climacteric fruit. Furthermore,
ethylene can be responsible for a number of specific post-harvest disorders of
fruits and vegetables such as russet spotting of lettuce, sprouting of potatoes and
formation of bitter-tasting isocoumarins in carrots (Zagory, 1995; Kader, 1985).
One of the major problems in the post-harvest storage of fruits and
vegetables is the proliferation of opportunistic microorganisms that thrive on
injured or senescent tissues. By stimulating ripening and senescence, ethylene
also enhances the opportunities for pathogenesis. Fruits and vegetables have an
epidermal layer that provides a protective barrier against infections but plant
pathogenic moulds and bacteria possess mechanisms to penetrate into external
tissues (Jacxsens, 2000). The growth of a number of post-harvest pathogens
e.g. the development and sporulation of the decay-causing fungi Penicillium
and Botrytis cinerea is directly stimulated by ethylene. In addition, several
post-harvest plant pathogens produce ethylene and this ethylene may
compromise the natural defences of the plant tissues (Barkai-Golan, 1990;
Saltveit, 1999).
36 Novel food packaging techniques
Plant organs like stems, roots and leafy parts that are consumed as vegetables
are less sensitive to ethylene exposure compared to fruits, but some vegetables
such as tomato, cucumber and broccoli are from a morphological point of view
‘fruits’ and responsive to ethylene (Jacxsens, 2000). These vegetables can
benefit from the removal of ethylene as ethylene detrimentally affects their
colour by yellowing and texture by promoting unwanted softening in cucumbers
and peppers or toughening in asparagus and sweet potatoes (Saltveit, 1999).
Strategies for protecting harvested horticultural products from the detrimental
effects of ethylene can be placed into three major categories: avoidance, e.g.,
through temperature control, removal and inhibition. In the category ‘removal’,
adsorption of ethylene will be discussed below.
3.4.3 Principle of ethylene adsorption
The double bond of ethylene makes it a very reactive compound that can be
altered or degraded in many ways. This creates a diversity of opportunities for
commercial methodologies for the removal of ethylene. Ethylene can be
absorbed or adsorbed by a number of substances, reviewed by Zagory (1995),
including activated charcoal, molecular sieves of crystalline aluminosilicates,
Kieselguhr, bentonite, Fuller’s earth, brick dust, silica gel and aluminium oxide.
A number of clay materials such as cristobalite, Oya stone and zeolite have been
reported to have ethylene sorbing capacity. Some regenerable sorbents have
been shown to have ethylene adsorbing capacity and have the benefit of being
reusable after purging. Examples are propylene glycol, hexylene glycol,
squalene, phenylmethylsilicone, polyethylene and polystyrene. Some sorbents
have been combined with catalysts or chemical agents that modify or destroy the
ethylene after adsorption. For example, activated charcoal, used to adsorb
ethylene, has been impregnated with bromine or with 15% KBrO
3
and 0,5 M
H
2
SO
4
to eliminate the activity of ethylene. A number of catalytic oxidisers
have been combined with adsorbents to remove the adsorbed ethylene such as
potassium dichromate, potassium permanganate (KMnO4), iodine pentoxide and
silver nitrate, each respectively embedded on silica gel. Electron-deficient
dienes or trienes such as benzenes, pyridines, diazines, triazines and tetrazines,
having electron-withdrawing substitutes such as fluorinated alkyl groups,
sulphones and esters, will react rapidly and irreversibly with ethylene. Such
compounds can be embedded in permeable plastic bags or printing inks to
remove ethylene from packages of plant produce (Holland, 1992). Metal
catalysts immobilised on absorbents such as powdered cupric oxide, will
effectively oxidise ethylene, but in many cases the reactions require high
temperatures (>180oC). Clearly such systems would be inappropriate for food
packaging applications (Zagory, 1995).
Most suppliers offer ethylene adsorbers based on KMnO4. To be effective,
KMnO4 must be adsorbed on a suitable inert carrier with a large surface area
such as celite, vermiculite, silica gel, alumina pellets, activated carbon, perlite or
glass. Typically, such products contain about 4–6% KMnO4. The oxidation of
Oxygen, ethylene and other scavengers 37
ethylene with potassium permanganate can be thought of as a two-step process.
Ethylene (CH
2
CH
2
) is initially oxidised to acetaldehyde (CH
3
CHO), which in
turn is oxidised to acetic acid (CH
3
COOH). Acetic acid can be further oxidised
to carbon dioxide and water:
3CH
2
CH
2
2KMnO
4
H
2
O!2MnO
2
3CH
3
CHO 2KOH 1
3CH
3
CHO 2KMnO
4
H
2
O!3CH
3
COOH 2MnO
2
2KOH 2
3CH
3
COOH 8KMnO
4
!6CO
2
8MnO
2
8KOH 2H
2
O 3
Combining eq. 1–3, we get:
3CH
2
CH
2
12KMnO
4
!12MnO
2
12KOH 6CO
2
Potassium permanganate adsorbers change from purple to brown as the MnO
4
is reduced to MnO
2
, indicating the remaining adsorbing capacity. Adsorbent
materials containing KMnO
4
cannot be integrated into food-contact packaging
but are supplied only as sachets because of their toxicity and purple colour
(Sherman, 1985; Zagory, 1995). Different studies have shown that these sachets
effectively remove ethylene from packages of pears (Scott and Wills, 1974),
bananas (Liu, 1970; Jayaraman and Raju, 1992; Chamara et al., 2000), kiwifruit
(Ben-arie and Sonego, 1980), diced onions (Howard et al., 1994), apples
(Shorter et al., 1992), grapes (Don and Koo, 1996), mango, tomato and other
fruits (Jayaraman and Raju, 1992). Examples of suppliers of potassium
permanganate based ethylene scavengers are given in Table 3.4. Not only
sachets are commercialised but the technique has been transferred to household
refrigerators e.g. Mrs. Green’s Extra Life cartridges from Dennis Green Ltd. and
Fridge Friend box. A special case is the paper Frisspack (Dunapack, Hungary),
for manufacture into corrugated fibreboard cases. This paper contains a
chemosorbent to bond with ethylene, which is then oxidised by KMnO
4
(Brody
et al., 2001).
Another type of ethylene scavenger is based on the adsorption of ethylene on
activated carbon and subsequent breakdown by a metal catalyst. Use of charcoal
with palladium chloride prevented the accumulation of ethylene and was
effective in reducing the rate of softening in kiwifruits and bananas and
chlorophyll loss in spinach leaves, but not in broccoli (Abe and Watada, 1991).
Some Japanese concepts such as Neupalon, Hatofresh System and Sendomate
(Table 3.4) are also based on the adsorption of ethylene by activated carbon that
is impregnated with different types of substances (palladium catalyst or
bromine-type inorganic chemicals) to help the breakdown of ethylene (Zagory,
1995).
Other ethylene absorbing technologies are based on the inclusion of finely
dispersed minerals. Typically these minerals are zeolites or local kinds of
clays that are embedded in polyethylene (PE) bags that are then used to
package fresh produce (Zagory, 1995). The fine pores of these minerals serve
to absorb gases such as ethylene. Most of these films are opaque and not
38 Novel food packaging techniques
Table 3.4 Some commercialised ethylene scavengers
Company Trade name Type Principle/active substances
Purafil (Georgia, US) Purafil Pellets to be used in e.g. Potassium permanganate-
sachets impregnated alumina pellet
DeltaTRAK (US) Air Repair Sachets for shipments Potassium permanganate
Ethylene Control (US) Fridge Friend Sachets, box for consumer’s Potassium permanganate
refrigerator
International Ripening Company (US) No specific name Sachets for shipping boxes Potassium permanganate
Dennis Green Ltd. (US) Mrs. Green’s Extra Life Cartridges for consumer’s Potassium permanganate
refrigerator
Grofit plastics (Israel) Biofresh Zipper bags, bags and films -
Nippon Container Corporation (Japan) FAIN Films for inner surface of
cardboard -
Sekisui Jushi (Japan) Neupalon Sachet Activated carbon
Mitsubishi Chemical Co. (Japan) Sendomate Sachet Activated carbon + Pd-catalyst
Honshu Paper (Japan) Hatofresh System Paper bag or corrugated box Activated carbon + bromine type
inorganic chemical
E-I-A Warenhandels GmbH (Austria) Profresh Film Minerals
Evert-fresh Co. (US) Evert-Fresh Green-Bags Bags for consumer use Minerals
Peakfresh products (Australia) Peakfresh Film Minerals
Odja Shoji C. (Japan) BO film Film Crysburite ceramics
Cho Yang Heung San Co. (Korea) Orega bag Bags for consumer use Minerals
OhE Chemicals (Japan) Crisper SL Film -
Marathon products (US) Ethylene Filter products Sachet -
Dessicare (US) Ethylene EliminatorPak Sachet Zeolites
Pacific Agriscience (Singapore) BI-ON - -
capable of sufficiently absorbing ethylene (Suslow, 1997). Although the
incorporated minerals may absorb ethylene, they also alter the permeability of
the films, both ethylene and CO
2
diffuse more rapidly and oxygen will enter
more rapidly than through pure PE. These changes in permeability can reduce
headspace ethylene concentrations and consequently improve shelf-life
independently of any ethylene absorption. In fact, any powdered material
can be used to reach these effects. However, even if the minerals do absorb
ethylene, this capacity is often lost when incorporating these minerals into a
polymer matrix (Zagory, 1995). Japanese or Korean companies marketed
many of these bags for their internal markets and some of them are now also
sold in the USA and Australia but fewer in Europe. The Orega bag based on
the US patent of Dr Matsui (Matsui, 1989) contains fine porous material
consisting of pumice-tuff, zeolite, active carbon, cristobalite and clinoptilolite
mixed with a metal oxide. A similar concept is a sheet, described in the US
patent assigned to Nissho and Co. (Japan) (Someyo and Nobuo, 1992),
consisting of a synthetic resin film or a fibrous material and containing
crushed coral, a stony substance formed from the massed skeletons of marine
organisms that has calcium carbonate as the main ingredient. Others are
Evert-Fresh Green-Bags, Peakresh
TM
, BO film and Profresh
. An overview of
some commercially available ethylene scavengers is given in Table 3.4.
3.4.4 Measuring ethylene sorption
There are many bags and films being sold offering improved post-harvest life of
fresh produce due to the sorption of ethylene by minerals finely dispersed into
polyethylene bags. The evidence offered in support of this claim is generally
based on shelf-life experiments comparing common polyethylene bags with the
so-called ethylene sorbing films. Such studies generally show an extension of
the shelf-life and/or reduction of the headspace ethylene. However, such data do
not support claims of ethylene sorbing capacity as the improved shelf-life and
reduced ethylene level could also result from the increased gas permeabilities of
these types of films. To evaluate the ethylene sorbing capacity of any ethylene
sorbing substance, a direct measurement of ethylene depletion in closed systems
containing samples of the bags without any produce is necessary. Furthermore,
such studies should be done at low temperature and high relative humidity to
mimic the conditions of performance (Zagory, 1995).
A possible method to determine the ethylene sorbing capacity uses closed
recipients which include the film in their screw top. These recipients are flushed
with ethylene and stored at a low temperature. At regular times the ethylene
concentration in the recipients is measured by using a gas chromatograph. As the
permeability is influenced by the relative humidity, water is brought in each
recipient to reach a high relative humidity.
40 Novel food packaging techniques
3.4.5 Economic aspects
It is extremely difficult to assess the economic importance of protecting
harvested horticultural products from ethylene. Detrimental effects of ethylene
during the normal short-term marketing of fruit and vegetables are not well
defined and certainly are secondary to considerations regarding the maintenance
of optimum temperature and humidity. However, costs to the individual shippers
involved can easily run into tens of thousands of dollars when losses do occur
from problems like russet sprouting of lettuce. Losses caused by ethylene are
known to occur, but they are usually quantitatively undefined. A conservative
estimate for the US would be in the tens of millions of dollars annually
(Sherman, 1985). The ethylene sorbing packaging concepts could possibly
contribute to an increase in the export of fresh produce.
In the US, ethylene control within packages of fresh and minimally
processed fruit and vegetable products remains almost exclusively a reaction
of KMnO
4
on a porous mineral structure (Brody et al., 2001). The major
disadvantage of permanganate scavengers seems to be their expense e.g. 0.33
euro for a 27g sachet, 0.39 euro for a 28g sachet, 0.26 euro for an 8g sachet,
6.25 euro for a Mrs. Green’s Extra Life cartridge and 2.2 euro for a Fridge
friend box. Prices of mineral-containing bags for consumer use range, e.g.,
from 1.96 euro to 4.26 euro depending of the size of the sachets. Despite the
many Asian claims for the effectiveness of activated carbon and minerals,
little proof has been offered to convince packagers to use them. For this
reason, there are no strong commercial applications of ethylene-removing
films in the US. On the other hand, sachets based on KMnO
4
are in
widespread commercial use.
3.5 Carbon dioxide and other scavengers
3.5.1 Carbon dioxide scavengers
Role
Carbon dioxide is formed in some foods due to deterioration and respiration
reactions. The produced CO
2
has to be removed from the package to avoid food
deterioration and/or package destruction. Fresh roasted coffee can release
considerable amounts of CO
2
due to the Strecker degradation reaction between
sugars and amines (Labuza and Breene, 1989). Unless removed, the generated
CO
2
can cause the packaging to burst due to the increasing internal pressure.
Another CO
2
-producing food product is kimchi, a general term for fermented
vegetables such as oriental cabbage, radish, green onion and leaf mustard mixed
with salt and spices. Because kimchi cannot be pasteurised for its sensory
quality, the fermentation process still continues with the concomitant production
of CO
2
. The accumulation of CO
2
in the packages causes ballooning or even
bursting. Scavengers might therefore be useful.
Oxygen, ethylene and other scavengers 41
Principle
The reactant commonly used to scavenge CO
2
is calcium hydroxide, which, at a
high enough water activity, reacts with CO
2
to form calcium carbonate:
Ca(OH)
2
CO
2
!CaCO
3
H
2
O
A disadvantage of this CO
2
scavenging substance is that it scavenges carbon
dioxide from the package headspace irreversibly and results in depletion of CO
2,
which is not always desired. In the case of packaged kimchi, depletion of CO
2
in
the kimchi juices causes loss of the product’s characteristic fresh carbonic taste.
Therefore reversible absorption or adsorption by physical sorbents such as
zeolites and active carbon may be an alternative (Lee et al., 2001).
Commercially available technologies
Carbon dioxide scavengers are often commercialised as a sachet with a dual
function, both O
2
and CO
2
scavenging. The O
2
and CO
2
scavenging sachet
FreshLock or Ageless
E (Mitsubishi Gas Chemical Company, Japan),
containing Ca(OH)
2
(Natawa et al., 1982) is used for storing coffee. A similar
sachet is Frehilizer type CV of Toppan printing Co. (Japan) (Smith et al., 1995).
Multiform Desiccants patented (US 5322701) a CO
2
-absorbent sachet including
a porous envelope containing CaO and a hydrating agent such as silica gel on
which water is adsorbed. The water given off by the supersaturated silica gel
combines with the calcium oxide to form calcium hydroxide (Cullen and
Vaylen, 1994). Furthermore, a whole range of freshness-retaining mineral-based
ethylene scavengers, mentioned in Table 3.4 also claim to scavenge carbon
dioxide.
3.5.2 Odour scavengers
Role
As far as food aromas are concerned, plastics are usually considered to have a
negative impact on food quality. Flavour scalping, i.e., sorption of food flavours
by polymeric packaging materials, may result in loss of flavour and taste
intensities and changes in the organoleptic profile of foods. However, flavour
sorption could be used in a positive way to selectively absorb unwanted odours
or flavours. Odour removers have the potential to scavenge the malodorous
constituents of both oxidative and nonoxidative biochemical deterioration. Many
foods such as fresh poultry and cereal products develop during product
distribution very slight but nevertheless detectable deterioration odours such as
sulphurous compounds and amines from protein/amino acid breakdown or
aldehydes and ketons from lipid oxidation or anaerobic glycolysis. These odours
are trapped within gas-barrier packaging so that, when the package is opened,
they are released and detected by consumers. Another reason for incorporating
odour removers into packages is to obviate the effect of odours developed in the
package materials themselves (Vermeiren et al., 1999; Brody et al., 2001).
Although removal of these undesired odours may be attractive from a
42 Novel food packaging techniques
commercial point of view, care must be taken as in some cases these odours may
be a signal indicating that the products are exceeding the microbial or chemical
limits.
Principle and commercial applications
An active packaging to reduce bitterness in grapefruit juices has been described.
The causes of the bitter taste are glycosidic flavanone naringin and triterpenoid
lactone limonin. Naringin is the bitter component found in most fresh citrus
fruits and therefore in freshly processed citrus juices. Limonin is formed as a
result of heat treatment of the juice during processing and a chemical reaction in
the acidic juice medium. To counteract this, an active thin cellulose acetate (CA)
layer for application on the inside of the packaging has been developed. This
layer contains the fungal-derived enzyme naringinase, consisting of a-
rhamnosidase and b-glucosidase, which hydrolyses naringin to naringenin and
prunin, both non-bitter compounds. Food-contact approved CA films, which
contained immobilised naringinase showed a 60% naringin hydrolysis in
grapefruit juice in 15 days at 7oC and a reduction in the limonin content due to
adsorption on the CA film (Soares and Hotchkiss, 1998a,b, Vermeiren et al.,
1999).
Malodorous amines, resulting from protein breakdown in fish muscle, include
strongly alkaline compounds (Rooney, 1995). A Japanese patent based on the
interactions between acidic compounds, e.g., citric acid, incorporated in
polymers and the alkaline off-odours, claims amine-removing capabilities.
Hence the earliest work involved incorporation of such acids in heat-seal
polymers such as polyethylene and extruding them as layers in packaging
(Rooney, 1995; Hoshino and Osanai, 1986). Another approach to remove amine
odours has been provided by the ANICO Co. (Japan). The ANICO bags made from a
film containing ferrous salt and an organic acid such as citric or ascorbic acid are
claimed to oxidise the amine or other oxidisable odour-causing compounds as
they are absorbed by the polymer (Rooney, 1995).
Aldehydes, formed from the breakdown of peroxides produced during the
initial stages of auto-oxidation of fats and oils, can make a wide variety of fat-
containing foods, such as potato crisps, biscuits and cereal products,
organoleptically unacceptable. Removal of aldehydes such as hexanal and
heptanal from package headspaces by means of the layer Bynel IXP101, a
HDPE master batch, is claimed by Dupont Polymers (Rooney, 1995). Brody
et al. (2001) described laboratory tests on peanut butter, coffee and a snack
product demonstrating the effectiveness of the aldehyde scavenger. DuPont’s
materials are compositions of polyalkylene imine (PAI), particularly
polyethylene imine and polyolefin polymer. The invention comprises a
discontinuous PAI phase and an olefinic polymer continuous phase in a
weight ratio of PAI to olefinic polymer of about 0.001 to 30:100 (Brody et al.,
2001). DuPont also developed a scavenger for the removal of hydrogen
sulphide that could be incorporated into the lid of packaged processed cured
poultry (Brody et al., 2001).
Oxygen, ethylene and other scavengers 43
Some commercialised odour-absorbing sachets, e.g., MINIPAX
and
STRIPPAX
(Multisorb technologies, USA) absorb the odours mercaptanes
and H
2
S developing in certain packaged foods during distribution (Vermeiren et
al.,1999).
2-in-1
TM
from United Desiccants (USA) is a combination of silica gel and
activated carbon packaged together for use in controlling moisture, gas and
odour within packaged products. Furthermore, a whole range of freshness-
retaining mineral-based ethylene scavengers, mentioned in Table 3.4 also claim
to absorb ammonia, hydrogen sulphide and other unpleasant odours. Ecofresh
and Profresh
(E-I-A Warenhandels GmbH, Vienna) are claimed to be fresh
keeping and malodour control master batches (Vermeiren et al., 1999; Brody et
al., 2001).
UOP Corporation reported on the odour absorbing properties of a molecular-
sieve technology ‘Smellrite/Abscents’. This material, a crystalline zeolite, has
molecular sized pores that trap odour within its structure (Brody et al., 2001).
Vitamin E or alpha-tocopherol has been marketed as a food-grade odour
remover in packaging materials. Michigan State University researchers
concluded that alpha-tocopherol should be considered for incorporation into
package materials for food products such as crackers or potato chips (crisps) in
which lipid oxidation is a major concern (Brody et al., 2001).
Flavour incorporation in packaging material might be used to minimise
flavour scalping. Flavour release might also provide a means to mask off-odours
coming from the food or the packaging. It is of importance that this technology
is not misused to mask the development of microbial off-odours thereby
concealing the marketing of products that are below standard or even dangerous
for the consumer (Nielsen, 1997).
3.6 Future trends
Although more successfully applied in the US, Japan and Australia than in
Europe, active packaging is still in its early stages and has a distance to travel
before being applied on a large scale. However, the group of the scavengers
seems to have the best chance to become popular. The effectiveness of these
types of active systems has been studied profoundly and a whole range of
scavenging technologies has been patented and/or commercialised. However,
consumers are not always very keen on the use of sachets in food packaging.
This centres around fear of ingestion of the sachet even though the content is
safe. Precautions to minimise the risk have been taken by clearly stating ‘Do not
eat’ on the label and by legislating a minimum size of the sachets. Another
concern is that the content of the sachet could leak out and adulterate the product
(Smith et al., 1995; Nielsen, 1997; Hurme and Ahvenainen, 1998). To avoid
mishandling, abuse and resistance to sachets, scavengers can be incorporated in
labels, oxygen scavenging films or crown corks. In Finland a consumer survey
conducted in order to determine consumer attitudes towards O
2
scavengers
44 Novel food packaging techniques
revealed that the new concepts would be accepted if consumers are informed
well by using reliable information channels. When the consumers understand the
quality improvement and/or the assurance function of the scavengers, they will
have more confidence in the safety of the food they buy (Mikkola et al., 1997).
In Europe, the introduction of scavenging technologies is limited because of
legislative restrictions. Active compounds need to be registered on positive lists
and the overall and specific migration limits need to be respected. Moreover,
traditional migration testing is not always a realistic simulation of the real use of
the scavenging system and could result in a serious overestimation of the
migration of the active compound. The solution for this legislative issue is
complex and will probably require some more time.
As legislative barriers disappear and more companies become aware of the
economic advantages of using absorbent technology, and consumers accept this
approach, the technology will be very likely to emerge as an important
preservation technology.
3.7 References
ABE K and WATADA A E (1991), ‘Ethylene absorbent to maintain quality of
lightly processed fruits and vegetables’, Journal of food science, 56(6),
1589–92.
ABE Y (1994), ‘Active packaging with oxygen absorbers’, in Ahvenainen R,
Nattila-Sandholm T, Ohlsson T, Minimal processing of foods, VTT
symposium 142, Espoo, 209–33.
ABELES F, MORGAN P and SALTVEIT M (1992), Ethylene in plant biology, San
Diego, Academic Press Inc.
AGELESS
TECHNICAL INFORMATION (1994), Ageless
– oxygen absorber
preserving product purity, integrity and freshness’, Mitsubishi Gas
Chemical Company, inc., Japan, 24p.
AGELESS
TECHNICAL INFORMATION (2002), www.mitsubishiAGELESS.com.
AHVENAINEN R and HURME E (1997), ‘Active and smart packaging for meeting
consumer demands for quality and safety’, Food additives and
contaminants, 14, 753–63.
AMOCO CHEMICALS BULLETIN AS-1 (1999a), Amosorb oxygen scavenger
concentrates’, Amoco Chemicals, USA.
AMOCO CHEMICALS BULLETIN AS-3 (1999b), Freshness by Amosorb, Amoco
Chemicals, USA.
ANON. (1991), ‘Oxygen absorption reaches new plateau and provides superior
product protection’, Food engineering, 63, 50.
ATCO
TECHNICAL INFORMATION (2002), ATCO
oxygen absorbers, Standa
industrie, France.
BARKAI-GOLAN R (1990), ‘Post harvest diseases suppression by atmospheric
modifications’ in Calderon M and Barkai-Golan R, Food preservation by
modified atmospheres, Boca Raton, CRC Press, 237–64.
Oxygen, ethylene and other scavengers 45
BEN-ARIE R and SONEGO L (1980), ‘Modified-atmosphere storage of kiwifruit
with ethylene removal’, Scientia Horticulturae, 27, 263–73.
BERENZON S and SAGUY I S (1998), ‘Oxygen absorbers for extension of crackers
shelf-life’, Food science and technology, 31, 1–5.
BIOKA TECHNICAL INFORMATION (1999), Bioka oxygen absorber, Bioka Oy,
Finland.
BRODY A L, STRUPINSKY, E R and KLINE L R (2001), Active packaging for food
applications, Pennsylvania, Technomic publishing company.
CALDIC TECHNICAL INFORMATION (2002), Freshmax/Freshpax, Multiform
desiccants Inc.
CHAMARA D, ILLEPERUMA K, GALAPPATTY, P T and SARANANDA K H (2000),
‘Modified atmosphere packaging of Kolikuttu bananas at low tempera-
ture’, Journal of Horticultural Science and Biotechnology, 75(1), 9296.
CULLEN J S and VAYLEN N E (1994), Carbon dioxide absorbent packet and
process, United States Patent 5322701.
DAIFAS D P, SMITH J P, BLANCHFIELD B and AUSTIN J W (1999), ‘Growth and toxin
production by Clostridium botulinum in English-style crumpets packaged
under modified atmospheres’, Journal of food protection, 62, 349–55.
DAREX TECHNICAL INFORMATION (2002). Darex Active packaging technology
brochure.
DAY B P F (1998), ‘Active packaging of foods’, CCFRA New technologies
bulletin, 17, 23p.
DON Y S and KOO L S (1996), ‘Effect of ethylene removal and sulfur dioxide
fumigation on grape quality during MA storage’, Journal of the Korean
Society for Horticultural Sciences, 37 (5), 696–9.
EDWARDS A M (1998), ‘Striking back’, Packaging today, 5, 34–6.
ELLIS W O, SMITH J P, SIMPSON B K, RAMASWAMY H and DOYON G (1994), ‘Novel
techniques for controlling the growth and aflatoxin production by
Aspergillus parasiticus in packaged peanuts’, Food microbiology, 11,
357–68.
FLOROS J D, DOCK L L and HAN J H (1997), ‘Active packaging technologies and
applications’, Food Cosmetics and Drug Packaging, 20(1), 10–17.
GRAF E (1994), Oxygen removal, US patent 5284871.
GRAFF G (1998), ‘O
2
scavengers give ‘‘smart’’ packaging a new lease on shelf-
life’, Modern plastics, 75 (2), 69–72.
GREENFIELD P F and LAURENCE R L (1975), ‘Characterization of glucose oxidase
and catalase on inorganic supports’, Journal of food science, 40, 906–10.
HOLLAND R V (1992), ‘ Absorbent material and uses thereof, Australian Patent
Application PJ6333.
HOPKINS W G (1995), Introduction to plant physiology, New York, John Wiley
and Sons.
HOSHINO A and OSANAI T (1986), Packaging films for deodorization, Japanese
patent 86209612.
HOWARD L R, YOO K S, PIKE L M and MILLER G H (1994), ‘Quality changes in diced
onions stored in film packages’, Journal of food science, 59 (1), 110–17.
46 Novel food packaging techniques
HURME E and AHVENAINEN R (1998), ‘Active and smart packaging of food’,
Technical report VTT, Finland.
JACXSENS L (2000), ‘Application of ethylene adsorbers for the storage of fresh
fruit and vegetables’, International Conference on active and intelligent
packaging, Campden, CCFRA.
JAYARAMAN K S and RAJU P S (1992), ‘Development and evaluation of a
permanganate-based ethylene scrubber for extending the shelf-life of fresh
fruits and vegetables’, Journal of Food Science and technology India,
29(2), 77–83.
KADER A A (1985), ‘Ethylene-induced senescence and physiological disorders in
harvested horticultural crops’, Hortscience, 20(1), 54–57.
LABUZA T P (1987), ‘Oxygen scavenger sachets’, Food research, 32, 276–7.
LABUZA T P and BREENE W M (1989), ‘Applications of ‘active packaging’ for
improvement of shelf-life and nutritional quality of fresh and extended
shelf-life foods’, Journal of food processing and preservation, 13, 1–69.
LEE D S, SHIN D H, LEE D U, KIM, J C and CHEIGH H S (2001), ‘The use of physical
carbon dioxide absorbents to control pressure build-up and volume
expansion, of kimchi packages’, Journal of food engineering, 48, 183–8.
LIU F W (1970), ‘Storage of bananas in polyethylene bags with an ethylene
absorbent’, Hortscience, 5(1), 25–7.
LYVER A, SMITH J P, AUSTIN J and BLANCHFIELD B (1998), ‘Competitive inhibition
of Clostridium botulinum type E by Bacillus species in a value-added
seafood product packaged under a modified atmosphere’, Food research
international, 31, 311–19.
MATSUI M (1989), Film for keeping freshness of vegetables and fruit, US patent
4847145.
MCGLASSON W B (1985), ‘Ethylene and fruit ripening’, Hortscience, 20(1), 51–4.
MIKKOLA V, LA
¨
HTEENMA
¨
KI L., HURME E, HEINIO
¨
R, JA
¨
RVI-KA
¨
A
¨
RIA
¨
INEN T and
AHVENAINEN R (1997), Consumer attitudes towards oxygen absorbers in
food packages, VTT research notes 1858, Espoo.
MILTZ J, PASSY N and MANNHEIM C H (1995), ‘Trends and applications of active
packaging systems’, in Ackermann P, Mortimer R G (1993), Physical
chemistry, California, The Benjamin/Cummings Publishing Co.
NAKAMURA H and HOSHINO J (1983), ‘Techniques for the preservation of food by
employment of an oxygen absorber’, Mitsubishi Gas Chemical Co.,
Tokyo, Ageless
Division, 1–45.
NATAWA T, KOMATSU T and OHTSUKA M (1982), Oxygen and carbon dioxide
absorbent and process for storing coffee by using the same’, United States
Patent 4366179.
NIELSEN T (1997), Active packaging-a literature review, SIK-rapport n 631,
Sweden.
OXYGUARD TECHNICAL INFORMATION (2002), Oxyguard technology, Toyo
Seikan, Japan.
ROONEY M L (1981). ‘Oxygen scavenging from air in package headspaces by
singlet oxygen reactions in polymer media’, Journal of Food Science, 47,
Oxygen, ethylene and other scavengers 47
291–4, 298.
ROONEY M L (1995), ‘Active packaging in polymer films’, in Rooney M L,
Active food packaging, London, Blackie Academic and Professional, 74–
110.
ROUSSEL (1999), ‘Les emballages absorbeurs d’oxyge`ne’, in Gontard N, Les
emballages actifs, Paris, Tec and Doc, 31–7.
SALTVEIT M E (1999), ‘Effect of ethylene on quality of fresh fruits and
vegetables’, Postharvest biology and technology, 15, 279–92.
SAWADA S and TOTSUKA T (1986), ‘Natural and anthropogenic sources and fate
of atmospheric ethylene’, Atmospheric Environment, 20, 821–31.
SCOTT K J and WILLS R B H (1974), ‘Reduction of brown heart in pears by
absorption of ethylene from the storage atmosphere’, Australian Journal
of Experimental Agriculture and Animal Husbandry, 14, 266–8.
SHERMAN M (1985), ‘Control of ethylene in the post harvest environment’,
Hortscience, 20(1), 57–60.
SHORTER A J, SCOTT, K J, WARD G and BEST D J (1992), ‘Effect of ethylene
absorption on the storage of Granny Smith apples held in polyethylene
bags’, Postharvest Biology and technology, 1(3), 189–94.
SILGELAC TECHNICAL INFORMATION (1998), L’emballage actif- une technologie
innovante pour vos emballages alimentaires, Silgelac, France.
SMITH J P (1996), ‘Improving shelf life of packaged baked goods by oxygen
absorbents’, AIB research department technical bulletin, 18, 2–7.
SMITH J P, HOSHINO, J and ABE Y (1995), ‘Interactive packaging involving sachet
technology’, in Rooney M L, Active Food Packaging, London, Blackie
Academic and Professional, 143–73.
SMITH J P, OORAIKUL B, KOERSEN W J, JACKSON E D and LAWRENCE R A (1986),
‘Novel approach to oxygen control in modified atmosphere packaging of
bakery products’, Food microbiology, 3, 315–20.
SMITH J P, RAMASWAMY H S and SIMPSON B K (1990), ‘Developments in food
packaging technology, Part 2: Storage aspects’, Trends in food science and
technology, 11, 111–18.
SOARES N F F and HOTCHKISS J H (1998a), ‘Bitterness reduction in grapefruit juice
through active packaging’, Packaging technology and science, 11, 9–18.
SOARES N F F and HOTCHKISS J H (1998b), ‘Naringinase immobilisation in
packaging films for reducing naringin concentration in grapefruit juice’,
Journal of food science, 63, 61–5.
SOMEYO and NOBUO (1992), Packaging sheet for perishable goods, US patent
5084337.
SUSLOW T (1997), ‘Performance of zeolite based products in ethylene removal’,
Perishables handling quarterly, 92, 32–3.
VERMEIREN L, DEVLIEGHERE F, VAN BEEST M, DE KRUIJF N and DEBEVERE J (1999),
‘Developments in the active packaging of foods’, Trends in Food science
and technology, 10, 77–86.
WHITING R C and NAFTULIN K A (1992), ‘Effect of headspace oxygen
concentration on growth and toxin production by proteolytic strains of
48 Novel food packaging techniques
Clostridium botulinum’, Journal of foods protection, 55, 23–7.
YANG S F (1985), ‘Biosynthesis and action of ethylene’, HortScience, 20(1), 41–
5.
ZAGORY D (1995), ‘Ethylene-removing packaging’, in Rooney M L, Active food
packaging, London, Blackie Academic and Professional, 38–54.
Oxygen, ethylene and other scavengers 49
