6.1 Introduction
During recent years there has been a greatly increased consumer demand for
perishable chilled foods which are perceived as being fresh, healthy and
convenient. The major food retailers have satisfied this consumer demand by
providing an ever increasing range of value-added chilled food products. The
wide diversity of chilled foods available is accompanied by a huge range of
packaging materials and formats which are used to present attractively packaged
foods in retail chill cabinets. This chapter overviews the requirements and types
of packaging materials and formats which are commonly utilised for a broad
variety of chilled food products. In addition, established and emerging
packaging technologies for extending chilled food shelf-life, such as modified
atmosphere packaging, vacuum packaging, vacuum skin packaging and active
packaging, are described and new developments are highlighted. Process and
packaging techniques that rely on heat treatments to achieve extended shelf-
lives for chilled food products, such as hot-fill, sous-vide and in-pack
pasteurisation, are outside the scope of this chapter, but are described in
Chapter 11.
6.2 Requirements of chilled food packaging materials
Table 6.1 lists the main requirements of a chilled food package (Turtle 1988).
Depending on the type of food packaged, not all of these requirements will need
to be satisfied. The packaging material must contain the food without leaking, be
non-toxic and have sufficient mechanical strength to protect the food and itself
6
Chilled food packaging
B. P. F. Day, Campden and Chorleywood Food Research Association
from the stresses of manufacture, storage, distribution and display. Certain packs
require a degree of porosity to allow moisture or gaseous exchange to take place,
and packaging materials used in these situations should possess appropriate
permeability properties. Alternatively, most modified atmosphere packs require
moisture and gases to be retained within the pack and hence the packaging
materials used should possess appropriate barrier properties. The specific
requirements for modified atmosphere packs are described later. Depending on
the type of chilled food product, the packaging material may need to be tolerant
of high temperatures experienced during hot filling, in-pack pasteurisation or re-
heating prior to consumption. The packaging material, particularly with high-
speed continuous factory operations, may need to be compatible with form–fill–
seal machines. The pack closure must have seal integrity but at the same time
should be easy to open. There may be a need for reclosure during storage after
opening in the home. Also, with the increased incidence of malicious
contamination, tamperproof or tamper-evident packaging is desirable. The
package is the primary means of displaying the contained chilled food and
providing product information and point-of-sale advertising. Clarity and
printability are two pertinent features that require consideration in the choice
of materials. Finally, the packaging must be cost-effective relative to the
contained food. For example, a prepared ready meal retailing at a high price can
support a considerably higher packaging cost than a yoghurt dessert selling at a
fraction of that price.
6.3 Chilled food packaging materials
Once the requirements of a container for a particular chilled food product have
been established, the next step is to ascertain which type of packaging material
will provide the necessary properties. The answer is almost certain to be more
than one type. Packaging materials consisting of paper, glass, metal or plastic
Table 6.1 Main requirements of a chilled food package
? Contain the product ? Seal integrity
? Be compatible with food ? Prevent microbial contamination
? Non-toxic ? Protect from odours and taints
? Run smoothly on filling lines ? Prevent dirt contamination
? Withstand packaging processes ? Resist insect or rodent infestation
? Handle distribution stresses ? Be cost effective
? Prevent physical damage ? Have sales appeal
? Possess appropriate gas permeability ? Communicate product information
? Control moisture loss or gain ? Show evidence of tampering
? Protect against light ? Easily openable
? Possess antifog properties ? Be tolerant to operational temperatures
136 Chilled foods
have their individual advantages and these should be exploited when making a
choice. The main technical advantages of current chilled food packaging
materials are compared in Table 6.2, while the principal types of materials (and
their abbreviations) are listed in Table 6.3 (Turtle 1988). For any particular
product, a number of materials can generally be used, either as separate
components or in the manufacture of a composite.
6.3.1 Paper-based materials
Paper and board are widely used in chilled food packaging. They are easy to
decorate attractively and are complementary to all other packaging materials in
the form of labels, cartons, trays or outer packaging. They are available with
coatings such as wax, silicone and polyvinylidene chloride (PVDC) or as
laminates with aluminium foil or flexible plastics. Such coating or lamination
imparts heat-sealability or improves oxygen, moisture or grease barrier
properties. For example, butter is traditionally packed in waxed paper or
aluminium laminated paper.
Dual ovenable trays can be made of paperboard that is extrusion-coated with
polyethylene terephthalate (PET). They can resist temperatures up to 220oC and
Table 6.2 Comparison of chilled food packaging materials
Material Main technical advantages
Aluminium Impermeability
Lightweight
Container axial strength
Withstands internal pressure
Paper Great variety of paper grades
Ease of decoration
Adjunct to all other packaging materials
Lightweight
Semi-rigid plastics Properties variable with type of plastic
Choice of container shape
In-house manufacture
Lightweight
Flexible plastics Properties variable by combination
Very lightweight containers
Tailor-made sizing
Glass Chemical inertness
Impermeability
Product visibility
Container axial strength
Withstands internal vacuum pressure
Reuse facility
Chilled food packaging 137
hence are suitable for microwave and conventional oven heating of chilled ready
meals. Another application of paperboard in chilled food packaging is in the area
of microwave susceptors which enable the browning and crisping of meat and
dough products, e.g., pizza and pies, during microwave heating. A typical
microwave susceptor is constructed of metallised PET film laminated to
paperboard.
6.3.2 Glass
Glass jars and bottles are the oldest form of high-barrier packaging and have the
advantages of good axial strength, product visibility, recyclability and chemical
inertness. Returnable glass bottles are still used extensively for pasteurised milk
in the UK. Aluminium caps and closures make opening simple, while tamper-
evident features such as pop-up buttons provide an important consumer safety
factor. Impact breakage of glass containers is a major disadvantage, but new
glass technology and plastic sleeving with polyvinyl chloride (PVC) or
expanded polystyrene (EPS) have helped to reduce glass breakage.
6.3.3 Metal-based materials
Pressed aluminium foil trays have a long history of use for prepared frozen
meals and hot take-away food. They are also used for many chilled ready meals.
Their temperature stability makes them ideal for conventional oven heating, but
precautions should be taken to prevent arcing if used in microwave ovens.
Guidelines have been developed for the successful use of foil containers in
microwave ovens (Foil Container Bureau 1991). In some circumstances,
Table 6.3 Chilled food packaging materials
Aluminium foil EVOH (ethylene-vinyl alcohol)
Cardboard HDPE (high density polyethylene)
Cellulose HIPS (high impact polystyrene)
Cellulose fibre LDPE (low density polyethylene)
Glass LLDPE (linear low density polyethylene)
Natural casings MXDE (modified nylon)
Paper OPP (orientated polypropylene)
Metallised board OPS (orientated polystyrene)
Metallised film PA (polyamide-nylon)
Steel PC (polycarbonate)
Plastics PE (polyethylene)
ABS (acrylonitrile-butadiene-styrene) PET (polyethylene terephtlalate)
APET (amorphous PET) PETG (modified PET)
CA (cellulose acetate) PP (polypropylene)
CPET (crystallised PET) PS (polystyrene)
CPP (cast polypropylene) PVC (polyvinyl chloride)
EPS (expanded polystyrene) PVDC (polyvinylidene chloride)
EVA (ethylene-vinyl acetate) UPVC (unplasticised polyvinyl chloride)
138 Chilled foods
aluminium foil enables more uniform heating than microwave-transparent trays
(Bows and Richardson 1990). Aluminium foil or aluminium laminated paper are
also used for many dairy products, such as butter, margarine and cheese.
Aluminium foil is also used in cartonboard composite containers for chilled fruit
juices and dairy beverages. In addition, aluminium or steel aerosol containers are
used for chilled creams and processed cheeses.
6.3.4 Plastics
Plastics are the materials of choice for the majority of chilled foods. Chilled
desserts, ready meals, dairy products, meats, seafood, pasta, poultry, fruit and
vegetables are all commonly packed in plastics or plastic-based materials. Semi-
rigid plastic containers for chilled foods are predominantly made from
polyethylene (PE), polyproplyene (PP), polystyrene (PS), PVC, PET and
acrylonitrile-butadiene-styrene (ABS). Other plastics such as polycarbonate
(PC) are used in small quantities. Containers are available in a wide range of
bottle, pot, tray and other shapes and thermoforming, injection moulding and
blow moulding techniques give food processors the option of in-house
manufacture. Flexible plastics offer the cheapest form of barrier packaging
and may be used to pack perishable chilled food under vacuum or modified
atmosphere. Multilayer materials are typically made by coextrusion or coating
processes, using sandwich layers of PVDC or ethylene-vinyl alcohol (EVOH) to
provide an oxygen barrier. Alternatively, plastics such as PE or PP may be
metallised or laminated with foil to provide very high-barrier materials. The
required technical properties and pack size and shape may be matched to a
desired specification, thereby ensuring cost effectiveness. The oxygen and water
vapour transmission rates of aluminium foil and selected monolayer plastic films
are compared in Table 6.4.
Most polymers used for chilled food packaging are thermoplastics, i.e., they
are reversibly softened by the application of heat, provided that no chemical
breakdown occurs. PE is derived from the polymerisation of ethylene, whereas
other thermoplastics such as PP, PVDC, PS, PVC, ethylene-vinyl acetate (EVA)
and ABS are similarly polymerised from ethylenic monomers. In contrast,
plastics such as polyamide (PA), PC and PET are manufactured by condensation
reactions. For example, PET film is produced from PET resin, the
polycondensation product of ethylene glycol and terephthalic acid, by a
stretching process known as biaxial orientation.
6.4 Packaging techniques for chilled food
6.4.1 Modified atmosphere packaging (MAP)
MAP is an increasingly popular food preservation technique in which the
gaseous atmosphere surrounding the food is different from air (Day 1989). The
consumer demand for fresh, additive-free foods has led to the growth of MAP as
Chilled food packaging 139
a technique to improve product image, reduce wastage and extend the quality
shelf-life of a wide range of foods (Day 1992). Established chilled products now
available in MAP include red meats, fish, seafood, poultry, crustaceans, offal,
cooked and cured meats and fish, pasta, pizza, kebabs, cheese, cooked and
dressed vegetable products, dairy and bakery goods, ready meals, and whole and
prepared fresh fruit and vegetables (Day and Wiktorowicz 1999, Air Products
Plc 1995).
Gases
The gas mixture used in MAP (see Table 6.5) must be chosen to meet the needs
of the specific food product, but for nearly all products this will be some
combination of carbon dioxide (CO
2
), oxygen (O
2
) and nitrogen (N
2
) (Day and
Wiktorowicz 1999). Carbon dioxide has bacteriostatic and fungistatic properties
and will retard the growth of mould and aerobic bacteria. The combined
negative effects on various enzymic and biochemical pathways result in an
increase in the lag phase and generation time of susceptible spoilage
microorganisms. However, CO
2
does not retard the growth of all types of
Table 6.4 Oxygen and water vapour transmission rates of selected packaging materials
Packaging film Oxygen Water vapour
(25C22m) Transmission rate transmission rate
(cm
3
m
C02
day
C01
atm
C01
)(gm
C02
day
C01
)
23oC: 0% RH 38oC: 90% RH
Al foil neg.
a
neg.
a
EVOH 0.2–1.6
b
24–120
PVDC 0.8–9.2 0.3–3.2
MXDE 2.4
b
25
PET 50–100 20–30
PA6 80
b
200
PETG 100 60
MOPP 100–200 1.5–3.0
UPVC 120–160 22–35
PA11 350
b
60
PVC 2000–10 000
c
200
OPP 2000–2500 7
HDPE 2100 68
PS 2500–5000 110160
OPS 2500–5000 170
PP 3000–3700 10–12
PC 4300 180
LDPE 7100 16–24
EVA 12 000 110–160
Microperforated 20 000–2 000 000
d
–
a
Dependent on pinholes.
b
Dependent on moisture.
c
Dependent on moisture and level of plasticiser.
d
Dependent on degree of microperforation.
140 Chilled foods
microorganisms. For example, the growth of lactic acid bacteria is improved in
the presence of CO
2
and a low O
2
content. CO
2
has little effect on the growth of
yeast cells. The inhibitory effect of CO
2
is increased at low temperatures
because of its enhanced solubility in water to form a mild carbonic acid. The
practical significance of this is that MAP does not eliminate the need for
refrigeration. The absorption of CO
2
is highly dependent on the water and fat
content of the product. Excess CO
2
absorption can reduce the water-holding
capacity of meats, resulting in unsightly drip. In addition, some dairy products
can be tainted, and fruit and vegetables can suffer physiological damage owing
to high CO
2
levels. If products absorb excess CO2, the total volume inside the
package will be reduced, giving a vacuum package look known as pack collapse.
In MAP, O
2
levels are normally set as low as possible to inhibit the growth of
aerobic spoilage microorganisms and to reduce the rate of oxidative
deterioration of foods. However, there are exceptions; for example, O
2
is
needed for fruit and vegetable respiration, colour retention in red meats or to
avoid anaerobic conditions in white fish MA packs.
Nitrogen is effectively an inert gas and has a low solubility in both water and
fat. In MAP, N
2
is used primarily to displace O
2
in order to retard aerobic
spoilage and oxidative deterioration. Another role of N
2
is to act as a filler gas so
as to prevent pack collapse. Other gases such as carbon monoxide, ozone,
ethylene oxide, nitrous oxide, helium, neon, argon, propylene oxide, ethanol
vapour, hydrogen, sulphur dioxide and chlorine have been used experimentally
or on a restricted commercial basis to extend the shelf-life of a number of food
Table 6.5 Gas-mix guide for MAP of retail chilled food products
Chilled food item % CO
2
%O
2
%N
2
Meat (red) 15–40 60–85 0–10
Meat (cured) 20–35 – 65–80
Meat (cooked) 25–30 – 70–75
Offal (raw) 15–25 75–85 –
Poultry (white) 20–50 – 50–80
Poultry (reddish) 25–35 65–75 –
Fish (white) 35–45 25–35 25–35
Fish (oily) 35–45 – 55–65
Crustaceans and molluscs 35–45 25–35 25–35
Fish (cooked) 25–35 – 65–75
Pasta (fresh) 25–35 – 65–75
Ready meals 25–35 – 65–75
Pizza 25–35 – 65–75
Quiche 25–35 – 65–75
Meat pies 25–35 – 65–75
Cheese (hard) 25–35 – 65–75
Cheese (mould-ripened) ––100
Cream 100
Fresh fruit/vegetables 3–10 210 80–95
Vegetables (cooked) 25–35 – 65–75
Chilled food packaging 141
products. For example, carbon monoxide has been shown to be very effective at
maintaining the colour of red meats, maintaining the red stripe of salmon and
inhibiting plant tissue decay. However, the commercial use of most of these
other gases is severely limited owing to safety concerns, regulatory constraints,
negative effects on sensory quality or economic factors (Day 1992).
Argon (Ar) and nitrous oxide (N
2
O) are classified as miscellaneous additives
and are permitted gases for food use in the European Union. Air Liquide S.A.
(Paris, France) has stimulated recent commercial interest in the potential MAP
applications of using Ar and, to a lesser extent, N
2
O. Air Liquide’s broad range
of patents claim that in comparison with N
2
, Ar can more effectively inhibit
enzymic activities, microbial growth and degradative chemical reactions in
selected perishable foods. Although Ar is chemically inert, Air Liquide’s
research has indicated that it does have biochemical effects, probably due to its
similar atomic size to molecular O
2
and its higher density and solubility in water
compared with N
2
and O
2
(Brody and Thaler 1996). Hence, Ar is probably more
effective at displacing O
2
from cellular sites and enzymic O
2
receptors with the
consequence that oxidative deterioration reactions are likely to be inhibited. In
addition, Ar and N
2
O are thought to sensitise microorganisms to antimicrobial
agents. This possible sensitisation is not yet well understood, but may involve
alteration of the membrane fluidity of microbial cell walls, with a subsequent
influence on cell function and performance (Day 1998). Clearly, more
independent research is needed to better understand the potential beneficial
effects of Ar and N
2
O.
Packaging materials
Specifically with regard to MAP, the main characteristics to consider when
selecting packaging materials are as follows:
Gas permeability. In most MAP applications, excluding fresh fruit and
vegetables, it is desirable to maintain the atmosphere initially incorporated into
the package for as long a period as possible. The correct atmosphere at the start
will not serve for long if the packaging material allows it to change too rapidly.
Consequently, packaging materials used with all forms of MA-packed foods
(with the exception of fresh fruit and vegetables) should have barrier properties.
Typically, the lidding film consists of 15C22 PVDC-coated PET/60C22 PE and the
tray consists of 350C22 PVC/PE (see Fig. 6.1). Alternatively, PA/PVDC/LDPE,
PA/PVDDC/HDPE/EVA, OPP/PVDC/LDPE or PC/EVOH/EVA may be used
for the lidding film, and HDPE, PET/EVOH/LDPE, PVC/EVOH/LDPE or PS/
EVOH/LDPE used for the tray (Air Products Plc 1995).
The permeability of a particular packaging material depends on several
factors such as the nature of the gas, the structure and thickness of the material,
the temperature and the relative humidity (RH). Although CO
2
,O
2
and N
2
permeate at quite different rates, the order CO
2
C62O
2
C62N
2
is always maintained
and the permeability ratios CO
2
/O
2
and O
2
/N
2
are usually in the range 3 to 5.
Hence, it is possible to estimate the permeability of a material to CO
2
or N
2
142 Chilled foods
when only the O
2
permeability is known. As a general rule, packaging materials
with O
2
transmission rates less than 100 cm
3
m
C02
day
C01
atm
C01
are used in MAP.
Packaging materials are usually laminated or coextruded in order to have the
necessary barrier properties required (Roberts 1990).
In contrast to other perishable foods that are packed in MA systems, fresh fruit
and vegetables continue to respire after harvest and any packaging must take this
into account. The depletion of O
2
and the accumulation of CO
2
are natural
consequences of the progress of respiration when fresh fruit or vegetables are
stored in a sealed package. Such modification of the atmospheric composition
results in a decrease in the respiration rate, with a consequent extension in the
shelf-life of fresh produce. However, packaging film of the correct permeability
must be chosen to realise the full benefits of MAP of fresh produce (Day 1998).
Typically, the key to successful MAP of fresh produce is to maintain an
equilibrium MA (EMA) containing 2–10% O
2
/CO
2
within the package. For
highly respiring produce such as mushrooms, beansprouts, leeks, peas and
broccoli, traditional films like LDPE, PVC, EVA, OPP and cellulose acetate (CA)
are not sufficiently permeable. Such highly respiring produce is most suitably
packed in highly permeable microperforated films. However, microperforated
films are relatively expensive, permit moisture and odour loss, and may allow for
the ingress of microorganisms into sealed packs during wet handling situations
(Day 1998). A very interesting development for the packing of fresh prepared
produce involves the use of high O
2
(70–100%) MAP which has been recently
shown to overcome the many disadvantages of current air packing and low O
2
MAP. High O
2
MAP has been demonstrated to inhibit enzymic discolorations,
prevent anaerobic fermentation reactions and inhibit microbial growth with the
result of extending prepared produce shelf-life (Day, 1998; 1999a).
Water vapour transmission rate. Water vapour transmission rates are quoted in
gm
C02
day
C01
at a given temperature and RH. Similar to gas permeabilities, there
Fig. 6.1 Construction of a typical tray and lidding film MA pack.
Chilled food packaging 143
is a wide variation between different packaging materials (see Table 6.4).
However, there is no correlation between what is a good barrier to gas and what
is a good barrier to water. A further complication is that some materials (e.g.
nylons and EVOH) are moisture-sensitive and their gas permeabilities are
dependent on RH (Day 1992).
Mechanical properties. Packaging materials used for MAP must have sufficient
strength to resist puncture, withstand repeated flexing and endure the
mechanical stresses encountered during handling and distribution. Additionally,
if trays are to be thermoformed, the web must draw evenly and not thin
excessively on the corners. Poor mechanical properties can lead to pack damage
and leakage (Day 1992).
Sealing reliability. It is essential that an integral seal is formed in order to
maintain the correct atmosphere within a MA pack. Therefore, it is important to
select the correct heat-sealable packaging materials and to control the sealing
operation. For example, in high-speed form–fill–seal operations, it is important
to consider the hot tack of the material. Additionally, there is often a
requirement for a peelable seal so that the consumer can gain easy access to the
contents. However, the balance between peelability and integrity of the seal
must be determined (Day 1992).
Transparency. For most MA packed foods, a transparent package is desirable so
that the product is clearly visible to the consumer. However, high-moisture
foods stored at chilled temperatures have the tendency to create a fog on the
inside of the package, thereby obscuring the product. Consequently, many MAP
films are treated with coatings or additives to impart antifog properties so as to
improve visibility. These treatments only affect the wetability of the film and
have no effect on the permeability properties of the film (Roberts 1990).
For some MA packed foods (e.g. green pasta and cured meats), it may be
desirable to exclude light in order to reduce undesirable light-induced oxidation
reactions. In these cases, light barriers such as colour-printed or metallised films
may be used. Another influence of light is the possibility of a ‘greenhouse
effect’ causing a temperature rise within chilled food packs (Malton 1976).
However, Gill (1987) concluded that this effect was not an important factor in
increasing temperatures of products displayed in chilled cabinets.
Type of package. The type of package used will depend on whether the product
is destined for the retail or the catering trade. Popular options include flexible
‘pillow packs’, ‘bag-in-box’ and semi-rigid tray and lidding film systems (see
Fig. 6.1).
Microwavability. The ability of MAP materials to withstand microwave heating
is important, particularly in the case of ready-to-eat food products. For example,
the low softening point of PVC makes the popular PVC/LDPE thermoformed
144 Chilled foods
trays unsuitable for microwave oven heating. Hence, materials with greater heat
resistance, such as CPP, CPET and polystyrene-high temperature (PSHT) are
used for MA-packed food products intended to be heated in a microwave oven.
6.4.2 Vacuum packaging (VP)
Vacuum packaging is an established technique for packaging chilled foods such
as primal red meats, cured meats and cheese. Similar to MAP, VP extends shelf-
life of food by removing O
2
and thus inhibiting the growth of aerobic spoilage
microorganisms and reducing the rate of oxidative deterioration (Yamaguchi
1990).
Packaging materials
In order to maintain a vacuum around the food, high oxygen barrier materials are
required. Although the requisite O
2
barrier for VP depends on the type of food
packaged, O
2
transmission rates of less than 15 cm
3
m
C02
day
C01
atm
C01
are
generally required. Also, packaging materials with low water vapour transmis-
sion rates must be used. Typical VP materials consist of coextruded or laminated
films such as OPP/EVOH/PE, PA/PE, PET/PE, OPP/PVDC/PE, OPP/ PVDC/
OPP and PVC/EVOH/PVC (Yamaguchi 1990).
6.4.3 Vacuum skin packaging (VSP)
Vacuum skin packaging is a technique which was developed to overcome some
of the disadvantages of the traditional vacuum pack and MAP (White 1990). The
VSP concept relies upon a highly ductile plastic barrier laminate which is gently
draped over a food product, thereby moulding itself to the actual contours of the
product to form a second skin. The product’s natural shape, colour and texture
are highlighted and, since no mechanical pressure is applied whilst drawing the
vacuum, soft or delicate products are not crushed or deformed. Successes of
VSP in the UK market include sliced cooked and cured meats, pa?te′ and fish
products (e.g. peppered mackerel). Unlike VP, VSP and MAP allow pre-sliced
meats to be easily separated after pack opening. In VSP, the appearance of the
product is enhanced and the wrinkle-free skin prevents product movement,
thereby enabling vertical retail display. Also, since the bottom and top web films
are sealed from the edge of the pack to the edge of the product, pack integrity is
maximised and juice exudation is limited. Finally, VSP saves space in domestic
refrigerators compared to MA packs and is ideally suited for freezing since the
second skin prevents formation of ice crystals on the product surface, thereby
eliminating freezer burn and dehydration (White 1990).
6.4.4 Active packaging
Active packaging refers to the incorporation of certain additives into packaging
film or within packaging containers with the aim of extending product shelf-life
Chilled food packaging 145
(Day 1999b, Rooney 1995, Labuza and Breene 1989). Such additives or
‘freshness enhancers’ are capable of scavenging O
2
,CO
2
and/or ethylene;
releasing preservatives; emitting ethanol or CO
2
; and absorbing moisture and/or
flavours and odours (see Table 6.6). Many of the freshness enhancers claimed to
extend shelf-life of food products (many of which are chilled foods) have yet to
be approved for use with foods (Day 1999b, Rooney 1995).
Active packaging is an emerging and exciting area of food technology that is
developing owing to advances in packaging technology, material science,
biotechnology and new consumer demands. This technology can confer many
preservation benefits on a wide range of ambient-stable and chilled food
products. The intention is to extend the shelf-life of foods, whilst at the same
Table 6.6 Selected examples of active packaging systems
Active packaging Mechanisms Actual and potential
system food applications
O
2
scavengers 1. Iron based Bread, cakes, cooked rice,
2. Metal/acid biscuits, pizza, pasta, cheese,
3. Metal (e.g. platinum) catalyst cured meats and fish, coffee,
4. Ascorbate/metallic salts snack foods, dried foods and
5. Enzyme based beverages
CO
2
scavengers/ 1. Iron oxide/calcium hydroxide Coffee, fresh meats and fish,
emitters 2. Ferrous carbonate/metal halide nuts and other snack food
3. Calcium oxide/activated charcoal products and sponge cakes
4. Ascorbate/sodium bicarbonate
Ethylene 1. Potassium permanganate Fruit, vegetables and other
scavengers 2. Activated carbon horticultural products
3. Activated clays/zeolites
Preservative 1. Organic acids Cereals, meats, fish, bread,
releasers 2. Silver zeolite cheese, snack foods, fruit and
3. Spice and herb extracts vegetables
4. BHA/BHT antioxidants
5. Vitamin E antioxidant
Ethanol emitters 1. Encapsulated ethanol Pizza crusts, cakes, bread,
biscuits, fish and bakery
products
Moisture absorbers 1. PVA blanket Fish, meats, poultry, snack
2. Activated clays and minerals foods, cereals, dried foods,
3. Silica gel sandwiches, fruit and
vegetables
Flavour/odour 1. Cellulose triacetate Fruit juices, fried snack
adsorbers 2. Acetylated paper foods, fish, cereals, poultry,
3. Citric acid dairy products and fruit
4. Ferrous salt/ascorbate
5. Activated carbon/clays/zeolites
146 Chilled foods
time maintaining nutritional quality and assuring microbial safety (Labuza and
Breene 1989). The use of active packaging is becoming increasingly popular and
many new opportunities will open up for utilising this technology in the future
(Day 1999b).
Apart from the active packaging systems listed in Table 6.6, many other
systems have been and are being developed by utilising a combination of various
ceramics, enzymes, chemicals and materials to control in-pack atmospheres.
These include photosensitive dyes which indirectly scavenge O
2
and antimicro-
bial packaging films and materials. Perhaps one of the most interesting
developments involves the bringing together of packaging engineering and
enzymology so that the package can actually change the chemical composition of
packaged liquid foods (Brody 1990). For example, PharmaCal Ltd of California
developed immobilised enzyme packages that are capable of removing lactose
and cholesterol from milk (see Fig. 6.2).
6.5 Future trends
The following trends are likely to influence the chilled food packaging industry
during future years:
Fig. 6.2 In-package immobilised enzyme cholesterol removal from milk.
Chilled food packaging 147
6.5.1 Environmental factors
The packaging industry is going to face an increasing burden which has been
placed on it by Packaging Waste legislation throughout Europe. The need to
meet recycling and recovery targets is resulting in short term packaging
solutions which may not be in the best interest of long-term sustainability. The
legislation requires more packaging to be designed for reuse or recycling, yet
under certain circumstances these may not be the most environmentally friendly
solutions. Further more, the additional requirement for packaging minimisation
may work against design for recycling since the lightest-weight materials may
not be the easiest to recycle. Finally, future Packaging Waste legislation is likely
to increase recycling and recovery targets, with the possibility of reuse targets
being introduced (Stirling-Roberts 1999).
6.5.2 Consumer-driven packaging innovation
The increased focus on consumer needs provides the packaging industry with
opportunities to innovate. Consumers respond well to added-value packaging
innovations that improve the functionality and design of packaging, e.g. easy to
open and resealing devices, easy to pour bottles, tamper-evident features, time/
temperature indicating labels and microwave ‘doneness’ indicators. Packinging
is increasingly being viewed as a strategic marketing tool. The retail supply
chain is becoming more responsive and consumer-driven, and the effect on the
packaging industry is that demand is for increasingly smaller quantities of
consistent quality packagings delivered against tight schedules. In response to
consumer demand, a wider range of packaging formats is now on offer and this
range is likely to expand even wider in the future. For example, fresh chilled
soups can be bought in glass bottles, plastic tubs, laminated paperboard cartons
and flexible pouches, each of which has different technical and marketing
advantages. Consumers have also responded well to convenient food packages
and this trend will undoubtedly continue in the future, e.g. prepared fruits,
vegetables and salads which are ready to eat or ready to heat in microwaveable
packaging (Stirling-Roberts 1999).
6.5.3 New materials and technology
Driven by both environmental concerns and economics, new lighter-weight
packaging materials are being developed throughout Europe and around the
world. Examples include the introduction of superior performance plastics using
metallocene catalysts and micro-flute corrugated paper and board materials.
Research and development in the fields of edible and biodegradable packaging
continues to expand as well as methods of reducing the cost of packaging
recycling. Also, more strategic developments in the areas of barcode tagging,
active and intelligent packaging and digital printing will continue to expand in
the future (Stirling-Roberts 1999, Pugh 1998, Anon. 1998).
Regarding new materials, the invention of advanced catalyst technologies,
such as metallocene technology, has enabled the design of new plastic resins,
148 Chilled foods
many of which allow for thinner, high-performance packaging materials which
can be tailored for specific application requirements. Technical advantages
claimed for metallocene plastic resins include improved rigidity, clarity and
gloss; excellent heat seal and hot tack strength and puncture resistance; and
light-weight or downgauging opportunities that were not previously available
with traditional plastic resins (Pugh 1998, Anon. 1998).
6.6 Sources of further information
ROBERTSON G L, (1993). Food Packaging – principles and practice. Marcel
Dekker, Inc., New York, USA.
KADOYA T, (ed.) (1990). Food Packaging. Academic Press, London, UK.
BRODY A L and MARSH K S, (eds) (1997). Wiley encyclopaedia of packaging
technology, 2nd edn, J. Wiley and Sons, Inc., New York, USA.
6.7 References
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