Jung Han. Innovations in Food Packaging
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Preservative packaging for fresh meats, poultry, and fin fish
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Roberto
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Buffo and Richard
A.
Holley
Introduction
During processing and preservation, the texture, flavor, color, and fresh taste of food
are affected. Useful storage life is the time a food remains acceptable from a sensory,
nutritional, microbiological or safety perspective following its manufacture andlor
packaging. Storage life can be extended when the most probable mechanism for its
deterioration is known, and when techniques that will not affect sensory and nutritional
characteristics can be applied (Labuza, 1996).
A
variety of effective techniques have
been adopted by the food industry to extend the storage life of liquid foods (retort or
aseptic processing), liquid foods with particulates (canning and retort treatments),
dehydrated foods (freeze drying), cut fruits and vegetables (cryogenic freezing), and
meat (refrigeration or freezing). However, most of these techniques can cause a loss
of nutrients and 'freshness' (i.e. fresh taste). The value of freshness is measured by the
fact that fresh fruits, vegetables, and meats are premium-priced products in both local
and international markets (Tewari
et
al., 1999). Chilling reduces the growth of micro-
organisms and allows storage-life extension with minimal changes in the textural and
nutritional qualities of foods. If properly used, it can be considered the most conven-
ient and reliable means of providing fresh food products (Jeyamkondan
et
al., 2000).
To date, modified atmosphere packaging
(MAP)
is the only technique available that
consistently delays microbial growth, ensures freshness, and provides a long shelf-life
for fresh meat (Gill and Harrison, 1989). Nevertheless, shelf-life goals can only be
achieved with strict temperature control to achieve maximum microbial inhibition.
Innovations
in
Food Packaging
ISBN:
0-12-31 1632-5
Copyright
O
2005
Elsevier Ltd
All
rights of reproduction
in
any
form reserved
Centralized packaging
systems for meats
Introduction
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.......
. .
227
Traditional meat distribution
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228
Centralized packaging systems
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228
Individualpackages
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230
Appliedresearch
........................................................
233
Conclusions
............................................................
234
References
.............................................................
235
228
Innovations in Food Packaging
Temperatures must be controlled as closely as possible to the freezing point of meat
tissue (-2°C) in order to inhibit organisms like the pseudomonads, which can grow
at -3"C, and still avoid ice crystallization damage to the meat tissue. The rate of spoilage
in muscle foods is high because they are a protein-rich medium that encourages
microbial growth. Muscle tissue continues to metabolize just after slaughter, using
stored carbohydrates and fats. Without further processing, microbial growth occurs as
the energy stored is depleted and metabolic products, typically low molecular weight
organic compounds, accumulate in the tissues. This growth results in undesirable
odors and flavors, and eventually microbiological growth produces signs of decay on
the meat surface (Tewari
et
al., 1999).
meat
Optimized storage of fresh meat can yield 9-1 5 weeks of useful product life if meats are
held at
-
1.5
+
0.5"C in atmospheres saturated with C02 and devoid of 02. These sys-
tems are most useful for long-term storage and the intercontinental transport of primal
cuts of meat (Tewari
et
al., 1999). The current meat distribution system in North America
involves the transportation of primal and subprimal cuts in vacuum packages to retail
stores, yielding a storage life of about 42 days for pork to 45 days for beef. Due to resid-
ual O2 present in the package, some surface discoloration occurs due to the oxidation of
myoglobin to form metmyoglobin (brown). Once the primal cuts reach the retail stores,
they are trimmed to remove the surface-discolored tissue, which can carry a high micro-
bial load. The primal cuts are then reduced to consumer-size cuts and packaged in dis-
posable retail trays using 02-permeable films (Jeyamkondan
et
al., 2000). Oxygen from
the atmosphere combines with the free binding site of deoxymyoglobin to form oxymyo-
globin (a process known as oxygenation), which yields a bright red color. This reaction,
which takes place in less than 30 minutes due to the high affinity between deoxymyo-
globin and 02, is known as "blooming" in the meat industry. Because spoilage occurs
primarily on exposed surfaces, the creation of new surfaces after extended storage sets
the spoilage clock back to near zero (Seideman
et
al., 1984; Penny and Bell, 1993).
This distribution system is considered to be inefficient, based on the following
premises (Jeyamkondan
et
al., 2000):
1.
Packaging is carried out at both packer and retail levels
2. Quality control at the retail level is generally deficient
3.
Considerable floor space in retail stores is used for malung retail cuts
4. Fabrication costs of retail cuts are usually high because of the lack of specialized
labor crews and appropriate machinery at the retail level
5. By-products and edible waste are underutilized at the retail level.
Centralized packaging
sj&tems
Moving the packaging of retail-ready cuts from retail stores to the packer level or, alterna-
tively, to centralized packaging operations, eliminates the time-consuming labor required
Centralized packaging systems
for
meats
229
for cutting, trimming, and re-wrapping meat at retail stores. Higher efficiency can be
achieved at a centralized location by the incorporation of robotics, which minimizes
human handling, thus improving quality and safety (Scholtz
et
al., 1992a). Only the
saleable meat cuts are transported from the centralized operation to the retail store; fat
. .
tnmmmgs, bones, and other waste products remain at the packaging center, thus elirninat-
ing unnecessary refrigerated transport (Jeyamkondan
et
al., 2000). It should be noted that
storage life of master-packaged retail-ready meat containing O2 is considerably shorter,
typically no more
than
a week. There
are
two main reasons for this (Shay and Egan, 1987):
1.
As meat color must be red in the retail arena to attract consumers, meat must be
packaged either in an 02-permeable film or in packages containing high concen-
trations of
02.
2. No further manipulation is possible and no new surfaces are created
-
in other
words, no additional trimming is possible following initial packaging.
Nevertheless, there is presently an irreversible shift of meat distribution systems
towards centralized packaging operations, especially by large supermarket chains.
Advantages associated with the system are as follows (Quigley, 2002):
1.
A case-ready program transfers a large portion of the labor component from the
store to the packaging plant, reducing costs and adding storage space for other
merchandise at the retail point
2. A case-ready program makes it logistically possible for a retailer to keep the meat
case filled with specific cuts and concentrate on meat products that are most
in
demand throughout the day and over holiday periods, when other stores may
run
out of popular cuts
3.
A case-ready program ensures that the cuts in inventory are the exact ones most in
demand, as opposed to an in-store meat-cutting program, where a range of dif-
ferent cuts (some popular and some not) is produced and then have to be further
merchandized
4.
Case-ready programs provide uniformity in terms of product weight and quality
throughout the retain chain. Customers can expect to receive the same quality and
cut of meat or meat product, such as sausage, from every store throughout the
chain without having variations introduced by different butchers with different
meat-cutting techniques or different recipes at different stores
5.
Since store employees do not handle unpacked meat, the case-ready program reduces
the opportunity for contamination and enhances food safety assurance levels; this
removes the responsibility from the store manager and frees up his or her time
6.
Case-ready products have significantly reduced the amount of in-store shrinkage
-
according to some market analysts, by up to two-thirds
7. Since each case-ready package is completely traceable, stores can determine the
exact quantities sold; also, for quality control purposes, packages can even be
traced back to the farm level
8. Case-ready products lend themselves to the product-branding programs that are
rapidly becoming an essential part of the North American meat business, offering
consumers significantly more information about the meat they purchase.
230
Innovations in
Food
Packaging
Researchers at universities and industry scientists have developed a number of cen-
tralized packaging systems. Some of these are discussed below.
Individual Packages
High
O2
MAP
system
This type of packaging system has been known to the meat industry for many years.
It keeps the color of the meat bright red throughout the storage period. Aerobic bacte-
ria tolerate high concentrations of 02; thus, their growth can be reduced by including
C02 (typically 80% 02/20% C02) in the gas mixture (Gill and Molin, 1991). This sys-
tem is able to extend the shelf life of beef by
2
weeks while maintaining an acceptable
red color at
-
1.5OC (Gill and Jones, 1994). Yet the shelf life is considerably less than
that given by anoxic atmospheres due to the oxidative rancidity (lipid oxidation)
induced by O2 and the rapid growth of psychrotrophic bacteria (Cole, 1986).
There have been successful applications of this system. For example, Tesco, a large
British supermarket chain, converted its entire fresh meat operation into a high
02
MAP centralized operation (Brody, 1996). Another British chain, Marks
&
Spencer,
has combined vacuum-skin packaging (VSP) and high O2 MAP for the delivery of
fresh meat cuts. Each cut is first vacuum-skin packaged in an 02-permeable film, and
then bagged in an 02-impermeable nylon pouch with a gas mixture of 80% O2 and
20% C02 (Anonymous, 1989).
Cryovac peeling
Cryovac (Sealed Air Corporation, Duncan, SC, USA) developed the Darfresh peel-
able VSP system for retail-ready meat cuts.
In
this system, cuts
are
first vacuum-packaged
in a transparent 02-permeable
film
and then vacuum-skin packaged in a transparent
02-impermeable film. Just before the retail cut is displayed
in
the corresponding case,
the outer impermeable film is removed and meat blooms on exposure to air. A similar
technique can be applied to retail-ready cuts in flexible plastic trays. However, these
double-film systems are expensive (Jeyamkondan
et
al.,
2000).
Flavaloc fresh
This system was developed by Garwood Packaging, Inc. (Indianapolis,
IN,
USA) and
AS1 Plastic Solutions (Moorabbin, Victoria, Australia). The package has three parts: a
shallow, white base tray made of polyethylene terephthalate plastic, Estapac 992
1,
in
which the retail cut is placed; a transparent polyvinyl chloride (PVC), 02-permeable
film being stretched across the cut; and a transparent 02-impermeable lid or dome,
made of polyethylene terephthalate G 6763 polyester (Eastrnan Chemical Company,
Kingsport,
TN,
USA), which is sealed on top. Retail cuts are prepared at a centralized
packaging operation, and placed in the preformed trays together with pads to absorb
drip that may form. Air is then evacuated and back-flushed with a gas mixture at
atmospheric pressure containing at least 30% C02 with the remainder N2, which
Centralized packaging systems
for
meats
231
yields less than 300ppm of residual O2 (Zhao
et
al., 1994). The meat is purple when
the dome is in place. Once the package reaches the store, the dome is removed and the
meat blooms within 20 minutes. The company claims a storage life of 21-40 days in
the dome, and subsequently
4
days of retail display (Jeyamkondan
et
al., 2000).
Windjammer case-ready packaging system
In
this system, retail cuts are first individually packed in MAP with high 02-barrier
films to give a storage life of up to 21 days. Before retail display, a gas-exchange
machine is used to evacuate the anoxic atmosphere. The package is then back-flushed
with high O2 modified atmosphere containing 80% O2 and 20% Cozy which allows
blooming of the meat. This technology has been characterized as a "dynamic gas-
exchange system" (Zhao
et
al., 1994).
Master packaging (multiple packages)
In
this technique, four to six conventional retail packs, wrapped in 02-permeable films,
are placed within a large pouch made of an aluminum laminate with negligible
02
trans-
mission, known
as
the master pack. This pack
is
evacuated to remove O2 and
back-
flushed with a desired gas mixture, typically 100% C02. When C02 is introduced, meat
absorbs it, reducing the atmospheric volume. Thus, a sufficient amount of C02 (about
2 litreskg of meat) must be used in order to maintain a 100% concentration throughout
the storage period. Needle holes are burned in at least two different locations of the
02-
permeable films to allow the meat rapidly to come in contact with the modified atmos-
phere. As needed, according to consumer demands, master packs are opened, the holes
sealed with a label, and the retail cuts placed in the retail display case. Blooming takes
place
within
30 minutes penny and Bell, 1993; Gill and Jones, 1994).
Master packaging is more economical than the previous systems because of the
grouping of the individual packs under a common master bag. It differs from the
Flavaloc Fresh system in that it uses an opaque aluminum laminate film as the outer
barrier rather than a transparent dome. The aluminum laminate has an O2 transmis-
sion rate near zero, thereby substantially reducing the formation of metmyoglobin.
Today there are transparent, non-metallized, laminated films with no measurable
02
transmission rates (Winpak, Winnipeg,
MB,
Canada) that can be used instead. Master
packaging differs from the Windjammer system in that it relies on atmospheric air for
bloom development, which eliminates the need for expensive gas-exchange machines
at retail stores (Jeyamkondan
et
al., 2000).
There are three essential requirements for achieving the maximum storage life of
master-packaged meat (Jeyamkondan
et
al., 2000):
1. Superior initial microbial quality of the meat
2.
A consistent storage temperature of
-
1.5"C throughout the distribution period
3. Headspace gas composition consistently maintained at 100% C02 during the dis-
tribution period without any residual
02.
"32
Innovations in Food Packaging
By following good manufacturing practices, and adoption of an appropriate HACCP
program for production and distribution, the first condition may be satisfied. With
regard to the second, there have been a number of studies recommending a cryogenic
fluid, liquid N2, as a refrigeration system in portable containers for storage and distri-
bution of retail-ready meats. It is reported that liquid N2 can control the temperature of
meat in a narrow range
(-
1.5
+
0.5"C) (Bailey
et
al., 1997; Habok, 1999; Jeyamkondan,
1999). The third condition is the most problematic, because during storage of meat the
headspace gas composition changes dynamically. Change depends on the gas trans-
mission rate of the packaging film, the respiration rate of meat tissues and microflora,
the absorption of gases by meat tissues, and the initial gas composition. The respira-
tion of meat tissues and microflora contributes in a negligible manner to the total C02
present, although the capacity of meat to absorb C02 has to be taken into account to
prevent collapsing of the package after initial packaging.
An
important issue is that
most commercial machines presently available are not capable of evacuating O2 com-
pletely from the package. Even a small amount of residual O2 is conducive to the for-
mation of metmyoglobin, which is stable and undesirable. Because meat has only a
limited capacity to reduce metmyoglobin to deoxymyoglobin, from which oxymyo-
globin can form, a large amount of the former in the package may prevent develop-
ment of the desirable red color when the retail-ready pack is displayed (Jeyamkondan
et
al.,
2000).
There is a packaging system developed at the New Zealand Meat Research Institute
(Hamilton, New Zealand) called CAPTECH (chilled atmosphere packaging technol-
ogy) capable of creating a C02 atmosphere with <300ppm of residual
02.
In
this
process, the meat is packaged in a triple-laminated pouch consisting of high-strength
plastic film, aluminum foil, and a low-strength plastic film (SecureFresh Pacific Ltd,
Auckland, New Zealand). The aluminum foil is a good gas barrier and, together with
the high-strength plastic film, provides enough mechanical strength to avoid puncture
during transportation and handling. The inner low-strength film is helpful in heat-
sealing the package. The volume of C02 added to the package in relation to the mass
of meat is metered by a packaging machine (CAPTRON, Secure Fresh Pacific,
Auckland, New Zealand). As the packaging material has a negligible, non-measurable
O2 transmission rate, the O2 remaining in the package is at a sufficiently low concen-
tration to be converted to C02 through meat respiration. In addition, metmyoglobin
formed due to these small amounts of residual O2 is small enough to be reduced to
deoxymyoglobin and later converted to oxymyoglobin during display (Zhao
et
al.,
1994; Varnam and Sutherland, 1995; Jeyarnkondan
et
al., 2000).
As mentioned previously, headspace composition within a package changes
dynamically during the distribution period, and must be controlled continuously in
order to achieve the desired food quality and safety. These packaging techniques are
known as active or intelligent packaging (Labuza and Breene, 1989). Among them,
02-scavenging systems to remove residual O2 from the package atmosphere are of
central importance with regard to successful master packaging. The Japanese were the
forerunners in the development of this technology. 02-scavenging ageless sachets,
named Ageless FX-100 and manufactured by Mitsubishi Gas Chemical Co., Inc. (Tokyo,
Japan), are now used in the food industry around the world. These sachets contain
ferrous iron powder sealed in a moisture- and gas-permeable package. The ferrous