Note: Descriptions are shown in the official language in which they were submitted.
CA 02512796 1999-03-26
MODIFIED ATMOSPHERE PACKAGE WITH ACCELERATED REDUCTION
OF OXYGEN LEVEL IN MEAT COMPARTMENT
This is a divisional application of Canadian Patent Application Serial No.
2,325,992 filed March 26, 1999.
FIELD OF THE INVENTION
The present invention relates generally to modified atmosphere packages for
storing food such as raw meat. More particularly, the invention relates to a
modified
atmosphere package having two compartments, one containing meat, separated by
a
substantially permeable partition member, and relates to techniques for
rapidly reducing
1o the oxygen level in the meat-containing compartment below pigment sensitive
levels so
that the growth of metmyoglobin is inhibited. It should be understood that the
expression
"the invention" and the like encompasses the subject matter of both the parent
and the
divisional application.
BACKGROUND OF THE INVENTION
15 Containers have long been employed to store and transfer perishable food
prior to
presenting the food at a market where it will be purchased by the consumer.
After
perishable foods, such as meats, fruits, and vegetables, are harvested, they
are placed into
containers to preserve those foods for as long as possible. Maximizing the
time in which
the food remains preserved in the containers increases the profitability of
all entities in
2o the chain of distribution by minimizing the amount of spoilage.
The environment around which the food is preserved is a critical factor in the
preservation process. Not only is maintaining an adequate temperature
important, but the
molecular and chemical content of the gases surrounding the food is
significant as well.
By providing an appropriate gas content to the environment surrounding the
food, the
25 food can be better preserved when maintained at the proper temperature or
even when it
is exposed to variations in temperature. This gives the food producer some
assurance that
after the food leaves his or her control, the food will be in an acceptable
condition when it
reaches the consumer.
Modified atmosphere packaging systems for one type of food, raw meats, exposes
3o these raw meats to either extremely high levels or extremely low levels of
oxygen (OZ).
Packaging systems which provide extremely low levels of oxygen are generally
preferable because it is well known that the fresh quality of meat can be
preserved longer
under anaerobic conditions than under aerobic conditions.
CA 02512796 1999-03-26
Maintaining low levels of oxygen minimizes the growth and multiplication of
aerobic
bacteria.
One example of a low-levehoxygen system is disclosed.in U.S. Patent No.
5,698,250 to DelDuca et al. ("DelDuca"). FIGS. 1 and 2 of DelDuca are
s reproduced herein as FIGS.1 and 2. Referring to FIGS. 1 and 2, DelDuca
discloses a modified atmosphere package IO
including an outer container 12 composed of a oxygen barrier material and an
inner
container 14 composed of a material substantially permeable to oxygen. The
inner
container I4 is preferably comprised of a polystyrene foam tray 16 and a
stretch film
~o wrapping 18. The tray 16 contains a retail cut of raw meat 26. An oxygen
scavenger
28 is located between the inner container 14 and the outer container 12.
To create a modified atmosphere in the package 10, DelDuca employs the
following method. First, the meat 26 is placed within the inner container 14,
and the
inner container 14 is then sealed. Second, the inner container 14 is inserted
into the
~ s outer container 12. Third, without using any evacuation, the outer
container I2 is
flushed with an appropriate mixture of gases, such as 30 percent carbon
dioxide and
70 percent nitrogen, to remove most of the oxygen from the outer container 12.
Fourth, the outer container 12 is sealed. Fifth, the oxygen scavenger 28 is
activated
and used to absorb any residual oxygen within the package I0. The DeIDuca
method
Zo relies upon activation of the oxygen scavenger 28 to quickly absorb the
residual
oxygen.
FIG. 2 identifies four oxygen sources, or zones, that exist within the package
10. Zone I is the oxygen volume between the outer container 12 and the inner
container 14; zone II is the oxygen volume within the inner container 14; zone
III is
as the oxygen volume within the cells of the foam tray 16; and zone IY is the
oxygen
volume within the meat 26, which is believed to be minimal with the exception
of
ground meats. The oxygen scavenger 28 is located in zone I.
In the above-described DelDuca method, the step of flushing the outer
container 14 lowers the level of oxygen within the package 10 to about 0.05 to
5
3o percent. At such oxygen levels, especially at the lower end of the above
range (0.05
to 2 percent), metmyoglobin can form very quickly. Metmyoglobin is a substance
that causes meat to change to an undesirable brown color. Metmyoglobin forms
very
CA 02512796 1999-03-26
slowly at oxygen levels above 2 percent and below 0.05 percent but very
quickly
between these oxygen levels. Accordingly, it is important to pass the meat
located in
zone II through the pigment sensitive oxygen range (0.05 to 2 percent) very
quickly,
e.g., less than about two hours. Although DelDuca contemplates flushing the
inner
s container 14, existing technology generally will not flush zone II down
below the
pigment sensitive oxygen range. Therefore, even if the inner container 14 is
flushed,
the oxygen level in zone II must still be passed quickly through the pigment
sensitive
oxygen range.
In DeIDuca, after the outer container 12 is sealed, oxygen remaining in zone
II
~o (within the inner container 14) passes through the substantially, but not
100 percent,
permeable material of the inner container 14 and is rapidly absorbed by the
activated
oxygen scavenger 28 in zone I. The faster the rate of oxygen egress from zone
II into
zone I, the faster the oxygen level in zone II can be passed quickly through
the
pigment sensitive oxygen range. The present invention is directed to
techniques for
~s improving the rate of oxygen egress from zone II into zone I. In addition,
the present
invention is directed to techniques for directly absorbing oxygen in zone II
before the
oxygen passes into zone I.
SUMMARY OF THE INVENTION
zo In accordance with one embodiment of the present invention, a modified
atmosphere package includes first and second compartments separated by a
partition
member that is substantially permeable to oxygen. The first compartment
contains an
oxygen scavenger activated with an oxygen scavenger accelerator. The second
compartment contains a retail cut of raw meat.
zs More specifically, the present invention provides a modified atmosphere
package comprising first and second compartments separated by a partition
member
substantially permeable to oxygen, the first compartment containing an oxygen
scavenger activated with an oxygen scavenger accelerator, the second
compartment
containing a retail cut of raw meat, and permeability enhancement means for
3o increasing a permeability rate of the partition member to a rate in excess
of about
7,000 cubic centimetres per 100 square inches in 24 hours so that formation of
metmyoglobin in the raw meat is inhibited.
CA 02512796 1999-03-26
The present invention also provides a modified atmosphere package
comprising first and second compartments separated by a partition member
substantially permeable to oxygen, the first compartment containing a first
oxygen
scavenger activated with an oxygen scavenger accelerator, the second
compartment
containing a cut of raw meat, and further including a second oxygen scavenger
for
absorbing oxygen within the second compartment.
To improve the flow of any oxygen in the second compartment from the
second compartment to the first compartment, one or more features can be
incorporated in the partition member to improve its permeability. For example,
if the
partition member is partially comprised of a stretch film wrapping such as
polyvinyl
chloride (PVC.), the stretch film wrapping can be provided with a plurality of
holes in
the form of relatively large holes, pin holes, or microperforations. If the
holes are
relatively large holes, e.g., having a diameter ranging from about 0.125 inch
to about
0.75 inch, the holes are preferably covered with a label composed of TYVEK~
3a
CA 02512796 1999-03-26
spunbonded olefin or paper to prevent meat juice from leaking out of the
second
compartment through the holes and to prevent desiccation and contamination of
the
meat. The label is adhered to the stretch film wrapping in areas around the
holes.
TYVEK spunbonded olefin is entirely permeable to oxygen, so no additional
holes are
s formed in the TYVEK label. If, however, the label is composed of paper or
plastic,
which are somewhat-impermeable to oxygen, pin holes or microperforations are
formed in the label.
Various other features can be incorporated in the partition member to increase
its permeability, including a snorkel or straw; embossments; a self sealing
film or
io coating to allow for the creation of temporary holes in the partition
member; a
Landec-type film having a permeability that can be controlled by heat, light,
or some
other energy source; and two layers of perforated stretch film wrapping. If
the
partition member includes a stretch film wrapping wrapped about a foam tray, a
section of the tray wall can be composed of open-cell or perforated foam. This
~s section of the tray wall is left uncovered by the stretch film wrapping to
allow oxygen
from the second compartment to readily pass through both the stretch film
wrapping
and through the exposed section of the tray wall.
Other techniques for rapidly reducing the oxygen level in the second .
compartment
zo pertain less to changing the structure of the partition member. For
example, a second
oxygen scavenger can be placed inside the second compartment away from the
meat,
or scavenging material can be dispersed in the tray wall. Alternatively,
carbon
dioxide pellets can be placed inside the second compartment away from the
meat.
The pellets serve as a flushing agent that forces oxygen out of the second
z> compartment. Also, the finished package can be irradiated to create ozone
(03) within
the package. Ozone is more readily scavenged by the oxygen scavenger.
The above summary of the present invention is not intended to represent each
embodiment, or every aspect of the present invention. This is the purpose of
the
figures and detailed description which follow.
4
CA 02512796 1999-03-26
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading the following detailed description and upon reference to the drawings
in
which:
s FIG. 1 is an isometric view of a modified atmosphere package;
FIG. 2 is a section view taken generally along line 2-2 in FIG. 1;
FIG. 3 is an enlarged view taken generally along circled portion 3 in FIG. 2;
FIG. 4 is a diagrammatic side view of a system for making the modified
atmosphere package;
~o FIG. 5a is a top view of a section of the modified atmosphere package with
a
portion of the outer package broken away to reveal an inner package having
stretch
film wrapping with a hole covered by a TYVEK patch;
FIG. 5b is an enlarged section view taken generally along line Sb-Sb in FIG.
5a;
~s FIG. 6a is a top view of the modified atmosphere package with a portion of
outer package broken away to reveal an inner package having perforated stretch
film
wrapping;
F1G. 6b is an enlarged section view taken generally along line 6b-6b in FIG.
6a;
2o FIG. 6c is an enlarged view similar to FIG. 3 but showing pin holes formed
in
a tray wall;
FIG. 7a is a top view of a section of the modified atmosphere package with a
portion of the outer package broken away to reveal an inner package having
stretch
film wrapping with a hole covered by a perforated paper or plastic patch;
is FIG. 7b is an enlarged section view taken generally along line 7b-7b in
FIG.
7a;
FIG. 8 is an enlarged view similar to FIG. 3 but showing an inner package
having stretch film wrapping comprised of two layers of perforated film;
FIG. 9 is an enlarged view similar to FIG. 3 but showing a straw mounted to
3o the inner package of the modified atmosphere package;
FIG. 10 is an enlarged view similar to FIG. 3 but showing an inner package
having an embossed stretch film wrapping;
CA 02512796 1999-03-26
FIG. 11 a is an enlarged side view similar to FIG. 3 but showing holes punched
through an inner package wrapping comprised of standard stretch film coated
with a
self sealing layer of low molecular weight wax or polymer;
FIG. llb is an enlarged side view similar to FIG. I la but showing the holes
s plugged by the self sealing layer;
FIG. 12 is an enlarged side view similar to FIG. 3 but showing an unwrapped
section of the tray wall formed from open cell or perforated foam;
FIG. 13 is an enlarged side view similar to FIG. 3 but showing an oxygen
scavenging packet affixed to the tray wall and oxygen scavenging material
dispersed
io within the tray wall;
FIG. 14 is an enlarged side view similar to FIG. 3 but showing carbon dioxide
pellets along the tray wall; and
FIG. 1 ~ is a top view of a section of the modified atmosphere package with a
portion of outer package broken away to reveal an inner package having stretch
film
is wrapping with a hole covered by a Landec-type film patch.
While the invention is susceptible to various modifications and alternative
forms, certain specific embodiments thereof have been shown by way of example
in
the drawings and will be described in detail. It should be understood,
however, that
the intention is not to limit the invention to the particular forms described.
On the
zo contrary, the intention is to cover all modifications, equivalents, and
alternatives
falling within the spirit and scope of the invention as defined by the
appended claims.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Turning now to the drawings, FIGS. 1-3 depict a modified atmosphere
zs package 10 including an outer package 12 and an inner package 14. The term
"package" as used herein shall be defined as any means for holding raw meat,
including a container, carton, casing, parcel, holder, tray, flat, bag, film
envelope, etc.
At least a portion of the inner package 14 is permeable to oxygen. The inner
package
14 includes a conventional semi-rigid plastic tray 16 thermoformed from a
sheet of
3o polymeric material which is substantially permeable to oxygen. Exemplary
polymers
which may be used to form the non-barrier tray 16 include polystyrene foam,
cellulose
pulp, polyethylene, polypropylene, etc. In a preferred embodiment, the
polymeric
6
CA 02512796 1999-03-26
sheet used to form the tray 16 is substantially composed of polystyrene foam
and has
a thickness ranging from about 100 mils to about 300 mils. The use of a common
polystyrene foam tray 16 is desirable because it has a high consumer
acceptance. The
inner package 14 further includes a stretch film wrapping or cover 18
substantially
s composed of a polymeric material, such as polyvinyl chloride (PVC), which is
substantially permeable to oxygen. Like a foam tray, a PVC stretch film
wrapping has
a high consumer acceptance. In a preferred embodiment, the stretch film used
to form
the cover 18 contains additives which allow the film to cling to itself, has a
thickness
ranging from about 0.5 mil to about 1.5 mils, and has a rate of oxygen
permeability
io greater than about 1000 cubic centimeters per 100 square inches in 24
hours.
Preferably, the film has a rate of oxygen permeability greater than about
7,000 cubic
centimeters per I 00 square inches in 24 hours and, most preferably, has a
rate of
oxygen permeability greater than about 10,000 cubic centimeters per 100 square
inches in 24 hours. One preferred stretch film is ResiniteTM meat film
commercially
~ s available from Borden Packaging and Industrial Products of North Andover,
Massachusetts.
The tray 16 is generally rectangular in configuration and includes a bottom
wall 20, a continuous side wall 22, and a continuous rim or flange 24. The
continuous
side wall 22 encompasses the bottom wall 20 and extends upwardly and outwardly
zo from the bottom wall 20. The continuous rim 24 encompasses an upper edge of
the
continuous side wall 22 and projects laterally outwardly therefrom. A food
item such
as a retail cut of raw meat 26 is located in a rectangular compartment defined
by the
bottom wall 20 and continuous side wall 22. The raw meat may be any animal
protein, including beef, pork, veal, lamb, chicken, turkey, venison, fish,
etc. Prior to
is fully wrapping the tray 16 with the cover 18, the partially formed inner
package 14
may be flushed with an appropriate mixture of gases, typically a mixture of
about 30
percent carbon dioxide and about 70 percent nitrogen, to lower the oxygen
level in the
inner package 14 to about 1.5 to 5.0 percent. The foregoing mixture of gases
displaces the oxygen within the inner package 14 during the flushing
operation. After
3o flushing the inner package 14, the tray 16 is manually or automatically
wrapped with
the cover 18. The cover 18 is wrapped over the retail cut of raw meat 26 and
about
both the side wall 22 and bottom wall 20 of the tray 16. The free ends of the
cover 18
7
CA 02512796 1999-03-26
are overlapped along the underside of the bottom wall 20 of the tray 16, and,
due to
the cling characteristic inherent in the cover 18, these overlapping free ends
cling to
one another to hold the cover I 8 in place. If desired, the overwrapped tray
16, i.e., the
inner package 14, may be run over a hot plate to thermally fuse the free ends
of the
s cover 18 to one another and thereby prevent these free ends from potentially
unraveling.
The outer package 12 is preferably a flexible polymeric bag composed of a
single or multilayer plastics material which is substantially impermeable to
oxygen.
The polymeric bag I2 may, for example, include a multilayer coextruded film
to containing ethylene vinyl chloride (EVOH), or include an oriented
polypropylene
(OPP) core coated with an oxygen barrier coating such as polyvinylidene
chloride and
further laminated with a layer of sealant material such as polyethylene to
facilitate
heat sealing. In a preferred embodiment, the polymeric bag 12 is composed of a
coextruded barrier film commercially available as product no. 325C44-EX861B
from
is PrintPack, Inc. of Atlanta, Georgia. The coextruded barrier film has a
thickness
ranging from about 2 mils to about 6 mils, and has a rate of oxygen
permeability less
than about 0.1 cubic centimeters per 100 square inches in 24 hours. Prior to
sealing
the peripheral edges of the polymeric bag 12, the inner package I 4 is placed
within
the polymeric bag 12. Also, the bag 12 is flushed with an appropriate mixture
of
zo gases, typically about 30 percent carbon dioxide and about 70 percent
nitrogen, to
lower the oxygen level in the bag 12 to about 0.05 to 5.0 percent. After
flushing the
bag 12, but still prior to sealing the bag 12, an oxygen scavenger/absorber 28
is placed
in the bag 12 external to the sealed inner package 14. The bag 12 is then
sealed.
The oxygen scavenger 28 is designed to reduce the oxygen level in the bag 12
is at a rate sufficient to prevent discoloration (e.g., browning) of the raw
meat 26. Many
factors influence the color stability of raw meat, but it has been found that
the
reduction of the oxygen level from the 0.05 to 5.0 percent level described
about to less
than about 0.05 percent within 90 minutes works for all types of raw meat. If
there is
still oxygen in the bag 12 after this time period, the oxygen scavenger 28
absorbs any
3o remaining oxygen in the bag 12 and any oxygen which might still be trapped
within
the inner container 14 so as to lower the oxygen level in the bag 12 to about
zero
percent within 24 hours. The oxygen scavenger 28 also absorbs any oxygen which
CA 02512796 2006-05-29
might permeate into the bag 12 from the ambient environment. To increase the
rate of
oxygen absorption, the oxygen scavenger is activated with an oxygen uptake
accelerator in the form of a predetermined amount of activating agent or by
other
means just prior to being placed in the bag 12. The oxygen uptake accelerator
is
preferably selected from the group consisting of water or aqueous solutions of
acetic
acid, citric acid, sodium chloride, calcium chloride, magnesium chloride and
copper.
Further information concerning the oxygen scavenger 28, the oxygen uptake
accelerator, and the means for introducing the oxygen uptake accelerator.to
the
oxygen scavenger 28 may be obtained from U.S. Patent 5,928,560 filed
May 14, 1997, entitled "Oxygen Scavenger Accelerator ", In FIGS. 1-3,
the oxygen scavenger 28 is illustrated as a packet or label which is inserted
into the bag
12 prior to sealing the bag 12. Alternatively, an oxygen scavenging material
may be
added to the polymer or polymers used to form the outer package 12 so that the
oxygen
scavenging material is integrated into the outer package 12 itself.
The retail cut of raw meat 26 within the modified atmosphere package 10
takes on a purple-red color when the oxygen is removed from the interior of
the
package 10. The meat-filled modified atmosphere package 10 may now stored in a
refrigeration unit for several weeks prior to being offered for sale at a
grocery store.
A short time (e.g., less than one hour) prior to being displayed at the
grocery store, the
inner package 14 is removed from the polymeric bag 12 to allow oxygen from the
ambient environment to permeate the non-barrier tray 16 and non-barrier cover
18. .
The purple-red color of the raw meat 26 quickly changes or "blooms" to a
generally
acceptable bright red color when the raw meat 26 is oxygenated by exposwe to
air.
FIG. 4 illustrates a modified atmosphere packaging system used to produce the
modified atmosphere package 10 in FIGS. 1-3. The packaging system integrates
several disparate and commercially available technologies to provide a
modified
atmosphere for retail cuts of raw meat. The basic operations performed by the
packaging system are described below in connection with FIG. 4.
The packaging process begins at a thermoforming station 30 where a tray 16 is
thermoformed in conventional fashion from. a sheet of polystyrene or other non-
barrier
polymer using conventional thermoforming equipment. The thermoforming
9
CA 02512796 1999-03-26
equipment typically includes a male die member 30a and a female die cavity
306. As
is well known in the thermoforming art, the tray 16 is thermoformed by
inserting the
male die member 30a into the female die cavity 30b with the polymeric sheet
disposed
therebetween.
The thermoformed tray 16 proceeds to a goods loading station 32 where the
tray 16 is filled with a food product such as a retail cut of raw meat 26. The
meat-
filled tray 16 is then manually carried or transported on a conveyor 34 to a
conventional stretch wrapping station 36 where a stretch film I8 is wrapped
about the
tray 16 to enclose the retail cut of meat 26 therein. The overwrapped tray 16
forms
io the inner package 14. Just prior to sealing the meat-filled tray 16 at the
stretch
wrapping station 36, the tray 16 is flushed with a mixture of carbon dioxide
and
nitrogen to reduce the oxygen level in the tray 16 to about 1.5 to 5.0
percent. The
mixture of carbon dioxide and nitrogen emanates from a conventional gas supply
hollow tube or rod 40 fed by a gas tank (not shown). The stretch wrapping
station 36
is may be implemented with a compact stretch semi-automatic wrapper
commercially
available from Hobart Corporation of Troy, Ohio.
Next, the flushed and sealed inner package 14 proceeds to a high speed form,
fill, and seal station 42 which may be implemented with a Fuji-Formost high-
speed
horizontal form-fill-seal machine commercially available as model no. FW-3700
from
zo Formost Packaging Machines, Inc. of Woodinville, Washington. The inner
package
14 may be transported to the form, fill, and seal station 42 by a conveyor 44.
At the
form, fill, and seal station 42, a web 46 of oxygen barrier film from a roll
47 is
arranged to run along the direction of movement of the inner package 14. The
web 46
of film is fed to a conventional forming box which forms a section 48 of the
web 46
is into a tube configuration encompassing the inner package 14. The tube-
shaped
section 48 of the web 46 is thermally sealed along a lower fin 50 and is
thermally
sealed at one end 52 by a pair of vertically-oscillating heated sealing bars
54 or the
like.
Just prior to sealing the other end 56 of the tube-shaped web section 48 to
3o complete formation of the polymeric bag 12, the web section 48 is flushed
with an
appropriate mixture of gases, typically about 30 percent carbon dioxide and
about 70
percent nitrogen, to lower the oxygen level in the bag 12 to about 0.05 to 5.0
percent.
CA 02512796 1999-03-26
The mixture of carbon dioxide and nitrogen emanates from a conventional gas
supply
hollow tube or rod 58 fed by a gas tank (not shown). After flushing the web
section
48, but still prior to sealing the end 56, the oxygen scavenger/absorber 28 is
placed in
the web section 48 external to the sealed inner container 14 and the oxygen
scavenger
28 is activated with an oxygen uptake accelerator. The end 56 is then conveyed
between and sealed by the heated sealing bars 54 to complete formation of the
bag 12.
In addition to thermally fusing the web section 48 at the end 56, the heated
sealing
bars 54 sever the web section 48 at the end 56 to separate the bag 12 from the
next
upstream web section being formed into another bag. The sealed bag 12 is
io substantially in the form,of a sealed bubble or envelope loosely containing
the inner
package 14 and providing a sealed modified atmosphere surrounding the inner
package 14.
The oxygen scavenger 28 lowers the oxygen level in the package 10 from the
previously described 0.05 to 5.0 percent oxygen level to less than about 0.05
percent
~s within a time period of about 90 minutes. Although the oxygen scavenger 28
is
depicted in FIG. 4 as a packet or label inserted into the polymeric bag 12, an
oxygen
scavenger may alternatively be integrated into the polymers used to form the
bag 12.
One preferred oxygen scavenger is a FreshPaxTM oxygen absorbing packet
commercially available from MultiSorb Technologies, Inc. (formerly Multiform
zo Desiccants Ine.) of Buffalo, New York.
The modified atmosphere packaging system in FIG. 4 can produce the
modified atmosphere packages 10 at cycle rates ranging from about 1 to 60
packages
per minute. The maximum cycle rates which can be attained by the system in
FIG. 4
are significantly higher than the cycle rates which can be achieved by prior
art
zs systems. The attainment of high cycle rates is largely due to the fact that
the
packaging system in FIG. 4 relies upon the use of simple, commercially
available, and
high-speed form, fill, and seal equipment, as opposed to the slower evacuation
equipment employed by prior art systems. Reducing oxygen levels in the
modified
atmosphere package 10 by first flushing the package 10 and then subsequently
3o introducing the activated oxygen scavenger 28 into the package 10 is
significantly
faster and more cost-effective than the reliance upon slow evacuation
techniques.
CA 02512796 1999-03-26
Referring to FIG. 2, the region outside the inner package 14 and inside the
outer package 12 defines a first compartment or zone I, while the region
inside the
inner package 14 defines a second compartment or zone II. The inner package 14
itself forms a partition member between the first and second compartments. As
s discussed above, after the outer package 12 is sealed during the
manufacturing
process, it is desirable to improve the flow of oxygen from the second
compartment to
the first compartment so that any oxygen in the second compartment can be
rapidly
absorbed by the activated oxygen scavenger 28 in the first compartment. The
improved flow of oxygen, in turn, minimizes the amount of time that the meat
in the
~o second compartment is exposed to oxygen levels in the pigment sensitive
range (0.05
to 2 percent). Minimizing the exposure of the meat to oxygen levels in the
pigment
sensitive range inhibits the formation of metmyoglobin, which can cause the
meat to
change to an undesirable brown color.
The present invention provides various features that can be incorporated in
the
is inner package 14 to increase its oxygen permeability to rates in excess of
about 7,000
cubic centimeters per 100 square inches in 24 hours and, most preferably, to
rates in
excess of about 10,000 cubic centimeters per 100 square inches in 24 hours.
Such
high rates of oxygen permeability allow the activated oxygen scavenger 28 in
the first
compartment to lower the oxygen level in the second compartment (inner package
14)
zo to less than about 0.05 percent within a time period of less than about two
hours and
typically about 90 minutes after the package 10 is sealed. The permeability-
increasing features can be employed separately or in combination. In addition
to
increasing the oxygen permeability of the inner package 14, the present
invention
addresses other concerns such as preventing meat juices (purge) from escaping
the
zs inner package 14, preventing desiccation of the meat, and preventing
bacterial
contamination of the meat. Leakage of juices from the inner package is a
significant
drawback of the system proposed by U.S. Patent No. 5,667,827 to Breen et al.
Referring to FIGS. Sa-b, 6a-b, and 7a-b, if the inner package 14 is partially
comprised of a stretch film wrapping 18 such' as polyvinyl chloride (PVC), the
stretch
so film wrapping 18 can be provided with one or more relatively large holes 60
(FIGS,
5a-b and 7a-b) or a plurality of pin holes or microperforations 62 (FIGS. 6a-
b). The
holes 62 in FIG. 6a can represent either pin holes or microperforations. In
order for
12
CA 02512796 1999-03-26
the holes to be effective, they must communicate with the interior of the
package 14.
Accordingly, the holes should be located along the portion of the stretch film
wrapping 18 generally above the tray bottom wall 20 and inside the continuous
tray
side wall 22. The holes may be made during the manufacture of the stretch film
s wrapping 18 or just prior to covering the tray 16 with the wrapping 18.
If the holes are relatively large holes 60 as in FIGS. 5a-b and 7a-b, e.g.,
having
a diameter ranging from about 0.125 inch to about 0.75 inch, the holes are
preferably
covered with a patch or label 66 composed of TYVEK~ spunbonded olefin, paper,
or
plastic to prevent meat juice from leaking out of the second compartment
through the
to holes and to prevent desiccation and contamination of the meat. TYVEK
spunbonded
olefin is commercially available from DuPont of Wilmington, Delaware. The
holes
are punched in the stretch film wrapping 18 before the label 66 is applied.
The label
66 could be decorative or could provide pricing information. Using a food-
grade
adhesive, the label 66 is adhered to the stretch film wrapping 18 in areas
around the
is holes. In one embodiment best shown in FIG. 5b, the label 66 is circular,
has an outer
diameter of 0.75 inch, and has adhesive applied to an area bound by the outer
diameter
of 0.75 inch and an inner diameter of about 0.375 to 0.5 inch. The area within
the
inner diameter is free of adhesive. With respect to a TYVEK label (FIGS. 5a-
b), since
TYVEK spunbonded olefin is entirely permeable to oxygen, no additional holes
are
Zo formed in the TYVEK label. When attaching the TYVEK label to the stretch
film
wrapping, the food-grade adhesive is not applied to the portion of the label
covering
the holes so that the oxygen permeable pores in the label are riot plugged by
the
adhesive. With respect to a paper or plastic label (FIGS. 7a-b), which is
somewhat
impermeable to oxygen, additional pin holes or microperforations 70 (FIG. 7b)
are
is formed in the label. Although a label 66 over the relatively large holes in
the stretch
film wrapping 18 is preferred, the label is not absolutely necessary so long
as care is
taken to avoid tilting the package 10 to a degree that allows meat juices to
leak out of
the inner package 14.
If, on the other hand, the holes are pin holes or microperforations 62 (FIG.
6a)
3o having a diameter ranging from about 0.004 inch to about 0.030 inch, a
label is not
preferred because the holes are sufficiently small in diameter that surface
tension
prevents meat juice from passing through the holes. In the illustrated
embodiment,
13
CA 02512796 1999-03-26
the small holes 62 are applied to most of the portion of the wrapping 18
located inside
the tray side wall 22 and are arranged in a rectangular grid. Adjacent ones of
the
holes are spaced approximately one inch from each other. Alternatively, as
shown in
FIG. 6c, pin holes 64 can be formed in an unwrapped section of the side wall
22 of the
s tray 16. As shown in FIG. 8, if larger perforations are desired, the stretch
film
wrapping 18b may be comprised of two perforated layers in which the
perforations
62a of one layer are offset from (not aligned with) the perforations 626 of
the other
layer. The offset perforations create a tortuous path that prevents leakage of
meat
juices from the inner package 14.
io Experiments have found that all of the above options concerning the
application of holes and labels to the stretch film wrapping 18 successfully
increase
the oxygen permeability of the inner package 14 to rates that allow the
activated
oxygen scavenger 28 in the first compartment to lower the oxygen level in the
second
compartment (inner package 14) to less than about 0.05 percent within a time
period
~s of less than about two hours after the package 10 is sealed. Specifically,
the
experiments tested the following options: one hole having a diameter of 0.125
inch,
one 0.25 inch hole, one 0.375 inch hole, four 0.125 inch holes with TYVEK
label, one
0.25 inch hole with TYVEK label, one 0.375 inch hole with TYVEK label, one
0.75
inch hole with TYVEK label, one 0.75 inch hole with paper label having 15 pin
holes,
20 one 0.75 inch hole with paper label having 12 pin holes, 6 pin holes, 12
pin holes, and
microperforations throughout the stretch film wrapping. Each of the above
options
helped the stretch film wrapping attain acceptable high rates of oxygen
permeability.
Various other features can be incorporated in the partition member to increase
its permeability. FIG. 9 depicts a snorkel or straw 72 inserted through the
stretch film
is wrapping 18 and the side wall 22 of the tray 16 and into the interior of
the tray. FIG.
depicts embossments 74 formed in the stretch film wrapping 18. The embossed
areas of the stretch film wrapping are thinner than other areas of the stretch
film
wrapping and, therefore, exhibit higher oxygen permeability rates. FIGS. 11 a
and 11 b
depict a stretch film wrapping 18a including a PVC layer 67 and a thin self
sealing
30 layer 68 of food-grade wax or polymer having a low molecular weight. The
self
sealing layer 68 can be applied to the PVC layer 67 by conventional spraying
techniques or by conventional application and metering rollers of a printing
press.
14
CA 02512796 1999-03-26
Since the layer 68 is self sealing, holes 76 formed in the wrapping 18a are
only
temporary and are plugged by the self sealing layer 68 over time (FIG. 11 b).
The
holes 76 are formed in the wrapping 18a during the manufacturing process prior
to
sealing the package 10 and are exposed long enough to allow the oxygen
scavenger 28
s to lower the oxygen level in the inner package 14 to less than about 0.05
percent in
less than about two hours after the package 10 is sealed. As shown in FIG. 11
b, the
holes 76 are preferably plugged prior to shipping the meat-filled package 10
to
eliminate the possibility of leakage of meat juices from the inner package 14.
In another embodiment, the stretch film wrapping 18 in FIGS. 1-3 is
io composed of a Landec-type film, produced by the so-called Intellimer
process, having
a permeability that can be controlled by heat, light, or some other energy
source. The
film is normally in a substantially impermeable amorphous state and can be
temporarily switched to a highly permeable crystalline state by application of
the
energy source. The energy source is applied to the Landec-type film during the
is manufacturing process and for a long enough time period after the package
10 is
sealed to allow the oxygen scavenger 28 to lower the oxygen level in the
second
compartment (inner package 14) to less than about 0.05 percent in less than
about two
hours. Alternatively, as depicted in FIG. 15, the stretch film wrapping 18 can
be
composed of conventional polyvinyl chloride and include a hole 73 covered by a
label
zo 75 composed of a Landec-type film.
In yet another embodiment depicted in FIG. 12, the inner package 14 includes
a stretch film wrapping 18 wrapped partially about a foam tray 16a having an
exposed
(unwrapped) section 77 composed of open-cell or perforated polystyrene foam.
The
open-cell or perforated foam section 77 of the tray 16a is highly permeable to
oxygen
zs and helps the inner package 14 to attain a higher rate of oxygen
permeability than an
inner package composed entirely of a close-cell foam. To take advantage of the
highly permeable open-cell or perforated foam section 77 of the tray 16a, the
coverage
of the stretch film wrapping 18 on the tray bottom is partial to allow oxygen
from the
inner package 14 to pass through the open-cell or perforated foam section.
so Other possible techniques for rapidly reducing the oxygen level~in the
second
compartment (inner package 14) pertain less to altering the structure of the
tray 16 or
the stretch film wrapping 18. For example, as shown in FIG. 13, a second
oxygen
CA 02512796 1999-03-26
scavenger 78 can be placed inside the inner package 14 away from the meat 26.
Alternatively or in addition, oxygen scavenging material 79 can be dispersed
in the
wall of the tray 16. Like the oxygen scavenger 28, the oxygen scavenger 78 is
preferably activated with an oxygen scavenger accelerator just prior to
sealing the
inner package 14 during the manufacturing process. To keep the oxygen
scavenger 78
separated from the meat 26, the oxygen scavenger 78 can be adhered by a food-
grade
adhesive to one side of the tray 16 or can be housed in a highly permeable
enclosure
along one side of the tray 16. The oxygen scavenger 78 directly absorbs any
oxygen
present in the second compartment (inner package 14) and does not require the
lo oxygen to pass from the second compartment to the first compartment in
order to be
absorbed.
Alternatively, as shown in FIG. 14, carbon dioxide pellets 80 (dry ice) can be
placed inside the inner package 14 away from the meat 26. The pellets 80 serve
as a
flushing agent that forces oxygen out of the inner package 14 even after the
package
is 10 is sealed. In yet another embodiment, the sealed package 10 is
irradiated to create
ozone (03) within the package 10. Ozone is more readily scavenged than oxygen
(02)
by the oxygen scavenger 28, and therefore oxygen levels within the second
compartment (inner package 14) holding the meat 26 are reduced more rapidly.
In
effect, the carbon dioxide pellets 80 and the creation of ozone each increase
the rate of
zo oxygen egress from the second compartment (inner package 14) to the first
compartment.
While the present invention has been described with reference to one or more
particular embodiments, those skilled in the art will recognize that many
changes may
be made thereto without departing from the spirit and scope of the present
invention.
zs Each of these embodiments and obvious variations thereof is contemplated as
falling
within the spirit and scope of the claimed invention, which is set forth in
the following
claims
16
