Note: Descriptions are shown in the official language in which they were submitted.
MODIFIED_ATMOSPHERE PACR
The present invention relates to a modified
atmosphere pack, principally for food packaging, in which a
food whose shelf life is limited when in contact with oxygen
can be enhanced by storing it in an atmosphere which has a
constituency carefully chosen to maintain the appearance of
the food over an extended period.
It is a known problem of meat packaging that when
the product is packed under vacuum or in any other oxygen-
free environment such as in an inert gas, the meat loses itsoxy-myoglobin colour and can become red/purple in
appearance, thereby losing its attractiveness to the
consumer.
It is an object of the present invention to
endeavour to maintain the oxy~myogl~bin red colour of fresh
red meat while packaging the meat for an extended shelf life
of, say, 7 to 10 days.
One form of modified atmosphere pack which has been
used for extending the shelf life of meat is that disclosed
in EP-A-02s2477 and EP A-0316329 in which a support tray has
a meat product placed therein and covered by a gas permeable
film by a VSP (vacuum skin pack) process. The pack is
completed by the attachment of a sealed closing lid which
maintains the space above said VSP-enclosed product filled
with either atmospheric air, or nitrogen, or carbon dioxide.
When the pack is ready to be displayed for
retailing, the lid can be removed, thereby allowing normal
atmospheric air to contact the exterior of the gas permeable
VSP, allowing the atmospheric air to permeate into the VSP
and to restore the colour of the meat product.
The present invention provides a simplified form of
pack which nevertheless enables a modified atmosphere
environment to be applied over a pack to preserve its shelf
li~e until such time as it is required to be used. In
particular, the pac~ in accordance with the present
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invention is to be easier to handle at the point of sale.
Accordingly, the present invention provides a focd
pack comprising a food product between a support and a semi-
permeable (as herein defined) skin covering web attached to
the product and the support by a vacuum skin packaging (VSP~
process, and a sealed outer enclosure substantially
completely surrounding the vacuum skin packed assembly of
support, product and covering web and filled with a
conditioning atmosphere which has a composition different
from that of atmospheric air.
A second aspect of the present invention provides a
method a method of packaging a food product, comprising
vacuum skin packaging the product on a support using a semi~
permeable (as herein defined) web, surrounding the vacuum
skin packed assembly of the support and the food product
thereon within an outer enclosure of a film which has a
lower permeability to gas than said semi-permeable web, and
sealing said outer enclosure about bu., not io, the vacuum
skin packed assembly to maintain it exposed to the modified
atmosphere enclosed within said outer enclosure, said
modified atmosphere having a composition other than that of
atmospheric air.
In order that the present invention may more
readily be understood the following description is given,
merely by way of example, reference being made to the
accompanying drawings, in which:-
FIGURE 1 is a top plan view of a pack in accordancewith the present invention; and
FIGURE 2 is a transverse sectional view taken on
the line 2-2 of Figure 1.
Figure 1 shows a meat product 1 placed on a
thermoformed tray 2. The tray has a central floor area 6
which is optionally raised to define therearound a channel 3
at the foot of an upstanding rim 10 of the tray. The rim 10
preferably has a height at least as great as that of the
product for which the tray 2 is intended.
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Figure 2 shows that the meat product 1 is covered
with a semi-permeable film 4 by means of a VSP process,
preferably in accordance with our GB-A-1307054. With such a
VSP covering the juices of the meat are prevented from
escaping and causing an unsightly product in the pack. The
term semi-permeable as used herein in relation to film webs
denotes a film web whose permeability is such that the
oxygen transmission under atmosphere pressure will allow a
partial (ie. not full) blooming of a fresh red meat product
enclosed in the film web. Such film webs may have a
permeability of from 500 to 5000 cc. 02 /24 hour/atmos./m2 at
23C and at 0% R.H. Preferably ~he semi-permeable films
used with this invention have their permeability in the
range 1000 to 5000 cc0~/24 hour/atmos./mZ.
The film web 4 used for the VSP envelope is
preferably the one available from W. R. GRACE & CO.-CONN.,
and known by the Trade Mark DARFRESH, having a limited
permeabili~y to oxygen, carbon dioxide and nitrogen.
Although for the purposes of illustration in Figure
2 the VSP web 4 is shown as separate from the product
article 1, in practice the VSP process results in the VSP
web 4 constituting a skin of the meat product so that there
will be intimate contact with the meat product over the
whole of the area of the product which is exposed.
- The tray 2 is in this case thermoformed from a
semi-rigid support web. It may or may not be semi-
permeable. For example a gas permeable tray or other
support of cardboard or foamed polystyrene may be used,
provided it is not too permeable to permit the VSP operation
to be carried out. For this purpose it may have a surface
layer of semi-permeable (as herein defined) or impermeable
(ie. less permeable than "semi permeable) film thereon. A
gas impermeable tray 2 may be used, if required, in which
case the optional venting slots 5 shown in Figure 1 may be
present in order to ensure that the atmosphere both above
and below the cen~ral floor area 6 of the tray is of the
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same compcsition and pressure.
As indicated above, the VSP web 4 intimately
adheres to the sur~ace of the meat product 1, but also
adheres intimately to the upper surface of the tray 2, so as
to define therewith an envelope which has substantially no
gas space around the surface o~ the meat product 1.
The tray with the VSP-enveloped product thereon is
then subjected to a subsequent packaging operation using a
horizontal form-fill-seal (HFFS) process in which a modified
atmosphere may be introduced into the outer enclosure formed
by a film 7 which is, during the HFFS process, shaped as a
tube which is then sealed at its ends 8 in order to define
an enclosed gas space 9 retaining the modified atmosphere
which may be a mixture of oxygen with carbon dioxide and
nitrogen, in proportions which may be tailored to suit the
particular meat type constituting the product 1.
By increasing the oxygen content in the gas space 9
over ihe normal oxygen content of a-mospheric air, i~ is
possible to ensure that the semi-permeable (as herein
defined) VSP web allows sufficient oxygen from the modified
gas atmosphere to permeate into the meat product 1 through
the semi-permeable VSP web, during the storage and possible
transportation of the pack from the production site (for
example a slaughter house) to the re ~i~ outl~et~
Oxygen contents of between ~ and ~ % are -founcl to
be particularly useful for meat products. S~e U,~
For red meats, it is advantageous for substanti.ally
all the rest of the atmosphere to comprise carbon dioxide,
with substantially no nitrogen.
For poultry, the residue of the modified atmosphere
may comprise a mixture of carbon dioxide and nitrogen with
the carbon dioxide amounting to up to 40% of the total. One
particularly desirable atmosphere for poultry may comprise
20% oxygen, 40% carbon dioxide and 40% nitrogen.
Increasing the carbon dioxide content has the
advantage o~ inhibiting bacterial growth, although this
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promotes the release of juices. Since the juices provide a
culture medium for bacteria, it is advantageous not ~o
employ too high a carbon dioxide content for those meats
which will tend to release juices readily.
In order to achieve adequate exposure of the meat
product within the VSP to the oxygen of the modified
atmosphere within the external covering web for "blooming"
the meat, it is advantageous for the permeability of the VsP
web 4 to be at least 1000 cc.02/24 hour/atmos./m2. Equally,
10 it is felt that if the permeability exceeds 5000 cc.02/24
hour/atmos./m2 this will give too free an exchange of the
oxygen into the product, to cause the oxygen of the modified
atmosphere above the VSP web to be consumed too soon for
achieving optimum shelf life.
Because there is no seal between the outer
packaginy film 7 of the HFFS enclosure and the rim 10 of the
tray 2, the gas space 9 also extends around the underneath
or the tra~, thereby allowing ~or slightly more gas volume
than would arise if the tray were to form the lower boundary
~0 of the gas space 9.
The film 7 used for the HFFS enclosure is a so-
called barrier film which is substantially impermeable to
gas and hence ensures that the chosen proportions of the
modified atmosphere in the gas space 9 will be varied only
as a result of permeatlon of one or more of the constituents
of that atmosphere through the VSP web 4 into the meat
product 1, and not by loss to the surrounding atmosphere
outside the enclosure 7.
Finally, in order to improve the appearance of the
pack and to make lt more readily stackable with other
similar such packs for storage and/or transportation
purposes, the outer H~FS film 7 is subjected to a heat
shrinking operation, causing it to pull taut over both the
upper and lower surfaces of the tray 2.
A further advantage of carrying out the heat
shrinking operation is that this will increase the pressure
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in the modified atmosphere in the gas space 9 between the
VSP web 4 and the film 7 for the outer enclosure, thereby
providing a cushion which will prevent the product from
being crushed when stacked for storage.
Furthermore, the increase in pressure in the gas
space 9 serves to enhanc~ the efficiency oE transfer of the
oxygen from the space 9 into the product, through the VSP
web 4.
The seal at the ends of the HFFS film 7 is a so-
called fin seal which involves flattening the tube of the
film 7 and then sealing the flattened area and cutting off
the excess using a hot wire knife.
Having thus sealed one end, the chosen modified gas
atmosphere mixture is introduced through the still open
opposite end until eventually the interior of the tubular
HFFS enclosure is charged with the appropriate atmosphere,
following which the second end of ~he tubular enclosure can
he sealed in the manner just described, and the pack then
subjected to the final heat-shrinking operation to shrink
the film 7.
If desired, the introduction of the modified
atmosphere to the gas space 9 may involve the extraction of
atmospheric air by a vacuum step, followed by introduction
of the appropriate conditioning atmosphere.
The above-mentioned channel 3 formed in the tray
defines a ridge on the underside of the tray, to hold the
outer HFFS film 7 clear of the underside of the tray even
after the shrinking operation. This ensures that the
modified atmosphere within the HFFS pack is able to contact
all sides o~ the VSP pack, in order to allow permeation of
the modified atmosphere through the tray where the tray is
not of impermeable form.
EXAMPLE
A batch of 50 packages was prepared using the tray
confisuration illustrated in Figures 1 and 2, with the tray
formed of a 240 micron thick laminate based on
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thermoformable polyvinyl chloride sheet laminated to a
coextruded multilayer easy opening sealant. This laminate
had a permeability of from 5 to 10 cc 02/24 hour/atmos./m2
at 23C and at 0% RH.
Some of these trays were then covered, by use of a
VSP process, with a covering film which was 100 microns
thick and was a seven layer coextruded film containing six
different polyolefin resins.
Both of these films are available from W. R. GRACE
~ CO.-CONN. as Darfresh films, the tray material being
identified as VGEV 243X and the VSP covering film identified
as ELDX 256. The oxygen permeability of the covering film
is 2000 cc 02/24 hour/atmos./m~ at 23 C and at 0% R.H.
The VSP operation was carried out on a VS 44 vacuum
skin packaging machine available from W. R. GRACE & CO.-
CONN.
The product was a set of 50 beef loin steaks, one
packed in each tray.
Both the VSP packs resulting from the above steps,
and the xemaining stack-carrying trays without the VSP cover
film, were then all packaged individually in a pillow
packaging which contained a modified atmosphere consisting
of 70% 2~ 20% cO2 and 10% N2, using a five layer coextruded
shrinkable barrier shrink film containing ethylene vinyl
~lcohol (EVOH) as a gas barrier layer, and having a total
thickness of 25 microns. This film is readily available
from W. R. GRACE ~ CO.-CONN. identified as BDF 2001 and has
a permeability of 5 cc 02/24 hour/atmos./m2 at 23C and at
0% RH.
Some other of the non-VSP covered packs were
packed, again in the BDF 2001 pillow packaging, but with
atmospheric air instead of the modified atmosphere.
The pillow packaging for all of these types of
packs was carried out on a Ilapak Delta P machine available
from Ilapak 4P, Lugano, Switzerland.
A11 of these pillow packages were then subjected to
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a hot air shrink operation to shrink the outer barrier film
on to the loaded tray or the VSP pack and thexeby to raise
the gas pressure within the pillow pack.
The three batches of pillow packs were stored in
dark conditions under temperatures of from o to +2C. The
packs were checked daily for appearance, colour and odour by
an evaluation panel experienced in such a task.
The two types of modified atmosphere packages
displayed the normal behaviour expected of such packs in
that the colour was bright red until after eight days of
storage, but by the eleventh day of storage discoloured
areas were no~iceable. The odour of the packs was
acceptable until after five days of storage, and then a sour
and sweetish odour was noticed, which was considered close
to borderline acceptability of the packs. After eleven days
of storage, off odours were present. In many samples the
product wzs observed as exhibiting in the centre of the
underside a colour behaviour typical of vacuum packaged meat
in that it was deep purple in colour, turning to bright red
when the meat was exposed to air on opening of the pack.
As expected the air-filled packages displayed
unsatisfactory behaviour in that visible discolorations were
present after four days of storage, and after the fifth day
the samples were heavily discoloured.
The VSP-packed products had a superior appearance
in that the meat juices were held in by the VSP covering
film, whereas the non-VSP pacXed modified atmosphere packs
showed signs of exudation of juices which gave the pack a
less attractive appearance vis-à-vis customer appeal at the
point of retail sale.
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