Note: Descriptions are shown in the official language in which they were submitted.
Vd0 92/042~G fC'f'/LJ591/06~41
~~'~~J~~
A '2ACKAGE FOFt PFFt2S~IiLE FOOD
APED HORTIC'GLTURAL FRODUCT~~
BACKGROUND OF 'fNE :INVENTION
The present invention relates to packaging for
perishable products and in particular, to packaging usable
in both cooling and protecting the: products.
Several methods are commonly used for cooling
perishable products where rapid cooling is required.
These include hydrocooling, vacuum cooling, icing and
forced air refrigeration. For. example, the so-called
"Desert Water Hag" operates on the principle that the
evaporation of water from fabric forming the bag cools the
water in the bag.
In the produce field, it is common to pick heads
of lettuce and place them in waxed boxes with the box of
lettuce then being hosed down with water either before or
after the boxes are loaded onto a truck. Although
evaporation of water from the lettuce during
transportation assists in cooling the lettuce, relatively
insignificant am~unts of water are absorbed by the waxed
boxes and cooling is limited.. Transportation of broecoli
in waxed boxes filled with ice is also known.
In addition, vacuum cooling approaches have been
used for cooling produce. sn accordance with this cooling
technique, the warm pr~duct is loaded into an air tight
chamber or tube which is su3asequen~tly evacuated my a
mechanical or steam--ejector vacuum pump to establish a
partial vacuum therein.. As the t~tal gas.pressure in the
tube is reduced below 'the saturation pressure of water at
the temperature of the warm product (the "flash point~').
watE;r on and within the product begins to evaporate
rapidly. The thermal energy reguired to provide the heat
of vaporization of.this water comes predominately from the
WO 92/0~82j6 P~1"/11591 /Ofi3A 1
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sensible heat (e.g. °'field heat°°) of the product. k~s a
result, the product temperature begins to fall as rapid
evaporation begins. Because vacuum pumps are generally
very inefficient movers of condensable gases, such as ,
water vapor, chilled coils are provided within the tube or
chamber to condense and thereby remove the liberated water
vapor. These coils are chilled usually by evaporation of
liquid ammonia within, the ammonia being supplied by a
conventional vapor-compression refrigeration unit.
In t'he absence of air or any other restriction to
water vapor movement from the product to the chilled coil,
the temperature of the product will in time equilibrate
with that of the coil (the coil temperature in fact being
commonly used as a control variable in vacuum cooling .
operations). Under these circumstances, the rate of
thermal equilibration is largely determined by product
characteristics. In general, products high in readily
evaporated moisture content, with high thermal
conductivity and high evaporative surface-to-volume ratio,
will cool more rapidly under vacuum than do other types of
products. For example, lettuce and other leafy vegetables
cool well under vacuum (high moisture content and high
surface-to-volume ratio), while melons do not (low
evaporation rate and lour surface-to-volume ratio). In
addition, strawberries have not been viewed as suitable
for vacuum cooling because of damage to the surface of the
berries under vacuum conditions and the relatively small
rise in cooling rate resulting from the vacuum conditions
a,s opposed to nonvacuum refrigeration type cooling.
pne example of a prior art vacuum cooling system
is described in U.S. Patent No. 4,576,014.to Miller, et
al.' In these approaches, water has been known to be added
to the produce by sprinkling the produce before or while
the vacuum is imposed to reduce the amount of moisture
removed from the produce during cooling with the water r
evaporated during cooling being supplied at least in part
by the water added to the system instead of entirely by
the produce. In these approaches known to the inventor,
CVO 92/04256 fC~'/U~91/Ofi341
~~'~~~9a
the vacuum cooled produce sprinkled with water has been
packed in waxed boxes which absorb very small amounts of
water. All of these methods are significantly inhibited
if product "exposure°' is restricted, a~ w h2n t h2 product
is packed in a plastic bag; such i;s the case where
modified atmosphere packaging is used.
Modified or controlled-atmosphere packaging of
fresh produce has also been heretofore utilized and offers
advantages to virtually all sectors of the industry, from
l0 grower-shipper to food service and retail consumers.
Benefits include reduced waste due to spoilage, enhanced
quality, extended shelf life and greater consumer
convenience. The essential feature of the modified-
atmosphere approach to packaging is to seal the product in
a package that restricts, to a predetermined degree, the
exchange of gases between the product and the
surroundings. Many studies have been performed on the
desired gas environments for various types of products.
In general, modified-atmosphere packaging retards the four
mayor causes of produce quality loss, namely dehydration,
respiration, microbial spoilage and enzyme attack. The
quality of cut fruits or vegetables (e. g. florets]
deteriorates much more rapidly due to these factors than
if the products remain uncut. Moisture~loss from produce
is governed by Pick's law of diffusion which states that
the rate of vapor lass increases in direct proportion to
the vapor pressure difference between the surface of the
produce and the surraunding air. since at a constant
relative humidity, vapor pressure iv the air nearly
doubles for each 10°C temperature rise, and vapor pressure
at the surface of fresh praducs is nearly 100 percent,
produce will~dehydr~te nearly four times faster. at rooan
temperature than at a temperature near freez?ng,.,when .
exposed' to ',dry" a,ir. A ~raodified-atmasphere. packaging
~ with a' lord ~ioist;ure permeability will prevent this loss. .: .
All'~produc~ continues to respire.~fter harvest.
.. ...
During normal reapiratian; internal carbohydrates ire
t'~, 1 / U~ l 1 / 1)UJ4 1
~o~~~o~ - ~ -.
converted into carbon dioxide, water and energy (heat)
according to:
(aerobic respiration) : C6HIZO6 + 602-->6C02 + 6F~z0 +
(heat) .
y
This process generally results in a, progressive
deterioration in product quality. If a harvested item is ,
stared in an oxygen depleted environment, anaerobic
respiration occurs. This latter type of respiration is
essentially a fermentation process that results in the
production of an assortment of organic conipouxlds that lead
to undesirable flavors and odors. Anaerobic respiration
is described as follows:
(anaerobic respiration) : C6H12~'6-°'~lcohOls + Acids
+ COz + H20 -~ (heat) .
Aerabic respiration rates can vary greatly among
commodities, among varieties and even among parts of the
same plant. There can be further variability due to
growing conditions and post-harvest injuries, such as
knife cuts, bruises, chill damage, etc. The most
2~ significant factors effecting respiration rate are the
stage of maturity of the produce, temperature and storage
atmosphere.
The "law of mass action" in ah~~aistry states that
the rake of a chemical reaction is proportional to the
concentration of each of the reactants. Thus, aerobic
respiration can be slowed by either decreasing the oxygen
level or increasing the carbon dioxide level of the
storage atmosphere. In practice, this relationship.:,
appears--to hold with the result that increasing the CCZ
level is-equally as effective as decreasing the 02.1.evel
and that the results are additive. Plant sens.itivitv to
COZ ranges fro~a .low tolerance, .as with 'apples., ,to, high .
tolerance, as °.~it:h. strawberries.
~nzymas ax~e.organic catalysts present in
abundance in produce. After harvest, these enzyfnes tend
to "spill°' from damaged, cut, bruised, ~etc, cells of
produce and can lead to rapid discolorization,of light
colored surfaces, such as of mushrooms and cut apples.
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There are two basic ways to combat this enzyme activity.
The first is through the reduction of the oxygen level in
a package. Enzymatic browning rate tends to vary nearly
linearly with oxygen concentration. The second approacrA
is to use enzyme inhibitors. These are components that
deactivate the browning enzyme. Svulfite, citric acid and
ascorbic acid additives have been 'used for this purpose.
In addition, carbon monoxide in concentrations of one to
ten percent is effective as an enzyme inhi.biter and as a
microbicide. Items known to benefit from small (one to
five percent) concentrations of carbon monoxide include
cauliflower, avocados, strawberries, tomatoes, cherries
and grapes. Items known to benefit from larger
concentrations (five to tan percent) include lettuce,
stone fruit, melons, cantaloupe, mushrooms and citrus
products.
Although bacterial diseases can cause significant
decay in vegetables, most post-harvest diseases are caused
by fungi. Since these organisms respire in the:same
manner as the cut plant, their growth in general is
controlled by the same factors (e.g. high COZ
concentration, etc.). In addition, microbial decay is
dramatically accelerated under high relative humidity
conditions. There are a variety of chemical treatments
2.5 used to control these pathogens, including carbon monoxide
and sulfur dioxide: )elated to controlling ~aicrobial
decay of produce, is the control of insects, in particular
with respect to exported products which are frequently
subjected to quarantine fumigant treatments.-
It i~ also known to inject or charge modified-
atmosphere containers with gas of a desired.;~ompositi.on
for the particular products. This approach has been used,
for~example, in connection with bread.whereby brad is
placed in~plast9.c wrappers'which are injected,with gas of
the desired environment prior to sealing the bread in..the
wrappers. In audition, poultry products are packaged in
high COz environments and.red meat products are packaged
i.n high OZ and COZ environanents.
fcrrv u~9 w io~~m
Because modified-atmUSphere packaging inhibits
the action of these major causes of product quality loss,
it has recently been a focus of much activity. In this
regard, there is much data which de:~cribes the optimal ,
atmosphere for a variety of commodities. For example, the
article entitled °°Post-Harvest Technology of Horticultural
Crops°', by Kader, A. et al, special publication 3311,
published by the University of Cali:Eornia at Davis in '
1985, contains a table of optimal storage atmospheres for
l0 a wide variety of types of prod~ice. Controlled atmosphere
packaging has also been used for bakery, meat and other
perishable food products. In general, it appears that one
can deviate substantially prom an optimal atmosphere and
still benefit. Modified-atmosphere packaging is also the
subject of numerous patents, such as U.S. Patent Nos.
4,256,770 t0 Rainy; 4,515,266 to Myers; and 4,91.0,032 t0
Antoon, Jr.
Although these technologies exist, when produce
is enclosed in a modified-atmosphere package, it becomes
difficult to remove heat, such as heat in the produce and
existing at the harvest site or field. In addition to
this trapped field heat, the produce continues to warm due
to the heat of respiration. As temperature rises,
respiration increases exponentially, resulting in heat
build up. This situation can readily lead to a loss of
product quality that quickly negates 'the benefits intended
with the modified-atmosphere package.
In the prior art,, due to the fact that
controlled-atmosphere packaging involves the sealing of
products iri'a package that restricts the exchange of gases
between the''product and surroundings, conventional
techniques for fi~eld.heat removal,.such,as forced-air
cooling and hydro~cooling have been applied before the
product is~sealed in its package and palletized. Because ,
35~'tlae equipment associated with the cooling techniques is
usually-a.ocated at a central location, the use of..
modified-atmosphere packaging systems generally requires
that the product be shed-packed at a location remote from
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the picking location, in contradiction 'to recent trends in
agriculture favoring field-packing of many fresh produce
items. zn addition, if the ready escape of water vapor
from the product surfaces a:.d/or its subsequent flow to a
chilled condensing coil are restricted, the rate of
cooling under vacuum may be significantly reduced, even in
the case of otherwise readily-cooled items, such as
lettuce. By their very nature as gas--flow regulating
devices, typical modified-atmosphere packages would be
expected to inhibit the vacuum cooling process, owing to
the severely restricted rates of gas (water vapor) removal
from the package.
Thus, the standard modified atmosphere approach
far packing berries, such as strawberries, is to pick or
harvest the berries into containers; palletize the
containers of berries and refrigerate the pallets. After
the berries are cooled, the pallets of berries axe wrapped
in plastic and injected with an enriched COz mixture and
shipped. 6~hen the pallets reach the distributors or end
users, the pallets are broken apart and the benefit of the
modified atmosphere packaging is lost at that point.
For most modified at~aosphere packaged produce
other than berries, the produce is harvested and
transported to a remote shed for cooling. The cooled
produce is cut, processed and sorted. The cooled and now
processed produce is theca packaged in a modified
atmosphere container. This approach is costly and results
in damage to the produce due to multiple handling steps
and due to the delayed placement of the produce in a
modified atmosphere package.
Therefore, a need eacists for a new package and
packaging system for overcoming these and,othex
disadvantages of the prior art. :.. : .
:.' c,pg~Y OIa, TFI~ INVFNT~~3~
.. .~ In accordance with one aspect of the. present
invention, a package for perishable food. and horticultural
products includ~,s a cooling element. A c~ntainer of the
type providing a controlled flow of gas between the
fC f/U~)1 /Ofi341
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exterior and interior thereof when closed is positioned in
thermal communication, and preferably in contact with, the
cooling element. The cooling element may comprise a
temperature heat sink element in proximity tca the exterior
of the container for cooling the container. preferably,
the heat sink element is in contact with or adjacent to a
major portion of the exterior surface area of the exterior
of the containers
The heat sink element may comprise a chilled or
frozen element, such.as in the for7:n of a collar. A frozen
block of liquid, such as ice, may be used as the heat sink
element. Vacuum cooling of the package enhances the
cooling of the packaged product. Also, frozen or cooled
phase change chemicals, such as potassium nitrate as water
in a sealed container, may he used as the heat sixik.
Also, the heat sink may comprise a cooling element 'with a
liquid holding portion which contains a liquid and which
is exposed to the environment outside or exteriorly of the
container such that evaporation of liquid from the liquid
holding portion of the cooling element enhances the
evaporative cooling of the product packed in the
container. In this latter case, vacuum cooling of the
cooling element enhances the evaporation of. the liquid
from the cooling element and the gaoling of the exterior
of the container and ~f the products packed therein even
though this c~ntainer is closed to dorm a modified
atmosphere environment.
The cooling element may comprise a collar which
substantially surrounds the container. The cooling
element and container may be integral. The cooling
element cools the container such that a cold surface is
provided within the container on whiclx water vapor from
products within the container (assuming the products are
the type whicka contain.waterj may condense. This
accelerates the cooling of ahe products with or without an
applied vacuum: _~
The cowta~.nar may be of a film or films or other
material which controls the flow of oxygen and carbon
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~~'~299c~
dioxide between the interior and exterior thereof and may
also have a water permeable portion so as to permit water
vapor to pass from the interior to the exterior of the
container. .
In accordance with a specific aspect of the
present invention, the liquid holding portion of a liquid
evaporative type of cooling element may comprise a
hydrophilic material, such as a wood pulp sheet. To
increase the water holding capacity of this material, a
superabsorbent material, such as a hydrogel, may be
incorporated into the cooling element. For example, the
container may be formed of a hydrophilic material, such as
a cellulose based material with cellophane being one
example such that the container itself holds water used in
cooling the product. Similarly, the container may be
coated with wood pulp or other hydrophilic material
adhered to the container.
To enhance the bulk transfer of gas from the
interior of the closed container to the exterior: thereof,
for example when the container is placed under vacuum
conditions, a bulk gas flow mechanism is provided for this
purpose. In its simplest form, the bulk flow mechanism
may comprise an aperture which is sized to control the
flow of gas by diffusion between the interior and exterior
of the container while permitting the bulk transfer of gas
'through the aperture upon subjecting the container to a
vacuum. Typical. apertures are in the .form of a circle
with a diameter of from about twewty~five microns to about
six hundred and fifty microns per kilogram of packed
product within the container. In another form of a bulk
transfer enhancing mechanism, the container includes a
valve~which selectively enhances the bulk transfer rate of
gas from the intern.or to the exteriar of the container,
for; example, upon the application of a vacuum to,the
container .-Idiechanical valves, such as described in U.S.
Patent Noo 4,890,637 and used in connection with packaging
coffee, may be used for this purpose. However, a specific
preferred valve is formed by a flexible patch of an oxygen
w~ <~?ioa2s~ Pc-~v us~~ r io~3a ~
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and carbon dioxide gas permeable material mounted to the
container so as to overlay and close: an opening in the
container, the container being of a substantially oxygen
and carbon dioxide gas impermeable material. The patch
may also be of a water vapor permeak~le material. The
patch is mounted to the container ak:~a perimeter
surrounding and spaced from the opening in the container.
Upon the application of a vacuum to the container, the
area of the patch exposed to the interior of the container
increases due a bubbling of the ~atc:h away from the
opening so as to increase the surface area of the patch
exposed to the interior of the container through the
aperture and enhance the bulk transfer rate of gas through
the patch from the interior to the exterior of. the
container.
As another aspect of the present invention, the
package includes a receptacle, which may be of a box-like
configuration, for receiving the cooling element and
container with these latter components of the package
being positioned at least partially within the receptacle.
The cooling element may also be integral with the
receptacle. In one specific form, the receptacle
comprises a fluted or corrugated core of a la.~a~.d
resistant material, such as wax impregnated medium, a
hydrophilic material at one side of the core so as to form
the interior of the receptacle and a sheet at the oppasite
side of the core which forms the exterior of the
receptacle. The hydrophilic material,, which may comprise
wood pulp or ether suitable materials contains water for
cooling the produce within the container by evaporation.
The liquid resistant core, due the corrugations or flutes,
provides a path for the flow of air adjacent t.o.the
hydrophilic materiah to aid in the evaporation of moisture
from the~hydrophilic material and thus.the cooling of the
container. The liquid resistant material also i~ibits
the transfer of water from 'the hydrophilic material, to the
cover sheet of the receptacle. The cover sheet may be
printed, far example with brand identifications or
6vV vL~u~6L~6 fLI~U~H~~Ub.i~l1
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advertising material, such that 'the entire package is
suitable for display in a retail store. In addition, the
package may be assembled in the field with the produce
being harvested directly into the container to minimize
the handling of the produce between harvest and display.
The receptacles may else be configured for
stacking in tiers with the product in containers placed in
proximity to, preferably in contact with, the cooling
elements and in the receptacles. A vacuum may be applied
to the containers so as to evaporate liquid from products
within the containers. Ti the evaporative type cooling
elements are used, liquid also evaporates from the cooling
elements to cool the products within the containers. By
making the containers of a flexible material, the
containers tend to expand against the respective cowling
elements during the application of the vacuum to enhance
the conductive cooling through the container to the
cooling elements.
Far effective cooling purposes, the liquid
absorbent material of the evaporative type cooling element
is typically designed for holding liquid, such as water,
in an amount which is at least from about forty-five to
about sixty-five grams of water for each kilogram of
product within the container. Assuming the field
temperature of the products is approximately 8~°F,
evaporation of forty-five grams of water for each kilogram
of the products within the container will cause a drop in
temperature of about 45°F in the products, or to 35°F.
The additional water included in such cooling elements
is used to assist in evaporatively cooling the products as
they are picked in the field.
...The cooking element.may include plural .
passageways open at at least-one end.to which. gas.,may pass
..
to enhance the~rate of heat transfer, for example by
enhancing the evaporative type evaporation of liquid from
cooling elements. In a specific example, the cooling
element may be formed of a corrugated board having a
1W0 92/04256
~ PC'('/~JS911063~t I-~
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fluted core and a fibrous mat on one surface thereof for
purposes of absorbing liquid.
It is accordingly one object of the present
invention to provide an improved ~:ontainer for packaging
and cooling perishable food and horticultural products.
Another object of the present invention is to
provide a package usable in field applications by which a
field-packed modified-atmosphere car other wrapped
container may still be effectively cooled, including
l0 cooling under vacuum conditions.
Still another object of the present invention is
to provide a package capable of. enhancing the
effectiveness of cooling of a wide variety of products,
including strawberries, and in which vacuum cooling may be
utilized to enhance the cooling process.
Another object of the present invention is to
provide a package which extends the duration of the peak
quality of a product for eating or other use. This allows
the picking of produce which is closer to full maturity,
an expansion of marketing opportunities in that products
may be economically shipped to more distant markets; and
an extension of the market season in that seasonal
products may beheld longer and still be at high quality
when sold.
As another object of the present invention,
efficiencies in processing the products are enhanced and
costs arm reduced. ~'or example, waste (e. g. lettuce
cores, broccoli stalks) can be removed and left in the
field so that the product arrives ready to eat without
3~ additional processing being required. This reduces waste
disposal costs and labor costs at the point of sale. In
addition, losses due to-..spoilage of.the products are
reduced. Moreaiver, transportation costs are reduced as
much 'of the r~7L:~tively heavy..ice. used Vin, the ..
.. transportation i~f many types of products, sucta as , .
broccoli, can be ~elianinated.
As another object of the present invention, loads
of various products not otherwise typically shipped
N'O 92/04256 pCT/US91/U6341
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together, may be commingled. For e~cample, ethylene
sensitive products, such as bananas, or odor absorbing
products, such as strawberries, can be shipped with odor
emitting products such as onions or ethylene emitting
products, such as apples, pears and 'tomatoes.
As another object of the present invention, the
products may be packaged and labeled in the field to
minimize the possibility of misbranding of the products '
downstream in the distribution chain.
As an advantage of the present invention, a
package is provided which increases the room temperature'
tolerance of the products and enhances the duration of
peak quality of such products even under such adverse
conditions.
As yet another object of the present invention, a .
package is provided which minimizes the possibility of
cross-contamination of products, for example pests found
in some products migrating to other products during
shipment.
2o The present invention relates to the above
features, objects and advantages both individually and
collectively. These and other objects, features and
advantages of 'the present invention will become apparent .
with reference to the following description and drawings.
~'~21EF DESCRTPT:CON of TFiE DRP~WINGS
FIG. 1 is an exploded view of one form of package
in.accordance with the present invention illustrating a
produce container, a cooling eleynent and receptacle.
FIG. 2 is a cross-sectional view of a portion of
one foz~n of cooling element in accordance with the present .
invention also showing a portion of an alterxaative form of
rec~ptacle~'i.n accordance with the present invention in the
event the cooling element and receptacle are combined.
FIG. 3 is cross-sectional view of a portion of an ..
~lternat~.ve for~rt of container-in accordance with the
present invention in which-the container and cooling
element are combined.
'WO 92/O~J2~j, r s
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FIG. 4 is cross-sectional illustration of one
form of mechanism for increasing the bulk flow of gas from
the interior to the exterior of the container when the
container is subjected to a vacuum.
FIG. 5 is an illustration similar to FIG. 4
showing the operation of the bulk gas transfer aaechanism
when subjected to a vacuum.
FIG. 5(a) is a plan view of the gas transfer
mechanism of Fig. 4.
~.0 FIG. 6 is a cross-sectional view of a portion of
a container which illustrates an alternative bulk gas
transfer mechanism.
FIG. ~ is an exploded view of an alternative form
of container in accordance with the present invention.
FIG. 8 is a plan view of a cutout blank which may
be formed into the cooling element of the package of FIG
7.
FIG. 9 is a plan view of a cutout blank which may
formed into the receptacle of the package of FIG:7.
FIG. ~.0 is a schexuatic .illustration of the use of
the package in a field packing applicati~n.
FIG. 13, is a cross-sectional view illustrating
one form of mechanical fastening mechanism suitable for
use in sealing containers of the present inventipn.
FTG. L2 illustrates palletized packages in
accordance with the present invention and also illustrates
heat sealing of the container used in such packages.
FIGS. ~.3 ° 15 are graphs illustrating the gas
transfer axed perraeance characteristics of , selected types
of media suitable for use in containers in acCOrdance with
the present invention.
FIG. 1Ev is a graph illustrating oxygen and carbon
~d~.cixid~ concentrations.achievable in containers of various
constrtactions . . . . .
w~v FIG. 1f is an explcaded view of a coxata:iner .and .
another form of cooling element in accordance with the .
present invention.
WO ~2/i)4256 pt:'T/~JSt)1/06341
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FIG. 18 is a top perspective view of another form
of receptacle and cooling element in accordance with the
present invention.
DETAILED -DES CFIPTION CF PREF;EP.~?ED E:~3CDIt~ENTS
The package, packaging system, and method of the
present invention is applicable to the packaging of a wide
variety of perishable food and horticultural products.
These products include both respiring and nonrespiring
types. Respiring products include, but axe not limited
to, cut and uncut fruits and vegetables and other
horticultural. products such as cut flowers. Nonrespiring
products include, but are not limited to, bakery products,
meats, poultry and fish. Although the invention has wide
applicability to the packaging of perishable food and
horticultural products in general, the invention offers
particular advantages in conjunction with packaging arid
cooling products, including tl2ose products benefited by a
modified atmosphere environment.
For purposes of convenience, and not to be
construed as a limitation, the invention will be described
in an application involving the harvesting and packaging
of strawberries (a respiring product' and in which a
modified atmosphere. environment is utilized.
With reference to FCC. 1,, the illustrated package
includes a modified atmosphere container 10 enclosing
strawberries 12 therein, a cooling element in the form of
a cooling collar 3.4 within which the container 10 :is
positioned when the packaged is asseanbled, and a box-like
receptacle,l6 for receiving both the cooling collar and
~O container. The illustrated receptacle ~.6 is subdivided by
a wall 18 into a first compartment 20 and a second
compartment'22. Although only one cooling collar l4'and
container 1.0 is ,shown in FIG..,1, plural such elements are
typically provid~pd with one.containex:and collar being
positioned in co~mpartment.20 and..another such Container
and c~llax being positioned in compartment 22. As
explained.below, the receptacle 1.6 is typically of a
corrugated kraft board material assembled to provide
wc) 9zioazs~ r~~°riusd)~iob~a~
- 16 -
reinforced corners and the central wall, with upper planar
shelves, some being numbered as 26, 28, to facilitate
stacking of product containing receptacles on top of one
another.
The container has a produce containing interior
and an exterior and is preferably of the type which is
closable with product to provide a controlled flow of gas
between the interior and exterior of the container when
closed. The material used for the container is selected
l0 to provide a desirable gas environment for the particular
product being contained. Suitable environments and
storage conditions are found in the literature, for
example in the previously mentioned article by Kader, A.
et al. entitled °°Post Harvest Technology of Horticultural
Crops." The Kader article mentions that a desirable
environment for broccoli is one to two percent 02 and five
to ten percent COZ, and that a desired environment for
strawberries is ten percent OZ and fifteen to twenty
percent CO2.
l~Iost gases will dissolve in plastic films. Once
dissolved, the gases diffuse through the film and
eventually evaporate frown the opposite surface. With
films, this process has been shown to follow an
'°Arrehenius'° relationship, whereby their permeab~.lity
increases with temperature. For most non-gas°barrier
films, this temperature change a~aaounts to approximately
doubling the permeability when the temperature rises from
freezing to room temperature. The:perx~eability of a
plastic film cars-be inoreas~d with the.addition of.
plasticiz~rs. Water vapor is a strung plastici~~.ng agent
for hydrophilic polymers, such as cellophane, nylon and
ethylene vinylralcohol~.thus, permeabilities of these
films tend to be highly dependent upon relative. humidity.
Permeability is ;s~anewhat rtlifferent for each gas depending
35-upon its salubilit;~ and molecular size. , Pea-zaeabality
ratios, howev~x~ are remarkably constant across a broad
spectrum of polymers. As a rule of thumb,...O2 and nitrogen
permeabilities through film are four and eight times lower
WO 92/04256 P~ i'/U591 /()6341
_ 17
~Orl~~~
than carbon dioxide, respectively. Each gas diffuses
independent of the others in the mix so that the transfer
of a single gas through a film or membrane is dependent on
its partial pressure drop across t:he membrane.
Gas permeability of plastic films is measured in
accordance with ASTM Standard D1434, commonly referred to
as the Dow cell Method. The water vapor transmission rate
of plastic fihus is generally mea:aured in accordance with
ASTPi Standard E9fi. Typical permea~nce and water vapor
transmission data for plastic films can be obtaixled from
the suppliers of these films with one needing only to
select a film that provides the desired environment. In
general, the Higher the water vapor transmission rate, the
lower the gas permeance of a film. Typical film permeance
properties of a number of films are set forth in the table
below.
TA1BL~ I
Permeant;e (1)
Flm CO2" O' N~ , W~'I'R~~
a '
Polyethylene
(!err density) 1,500 100 ~ 1
270
Potyptopylene 350 ?3 ~G 1
100
Silicone 350,000 70,OQU30,000.d 1 .
2 5 Ceflop6ane < 1 < 1 75
.( 1
Nylon s a ~ 1 to
Polyrattronate sso ~s s
iso
styrene s~ iso 3o s
pvc s,soa sso irs is . '
30
( 1 ) mml',/hr - atm
- mZ ( 1 mm thickrae~a,
room ta~mperature
)
(2) ~en,lm~/day (1 9~~ IiFI, room temperature)
mm thickness,
35 For products which are not sensitive to the
presence of water, suck( as broccoli, a film container of a
material such as polyethylene may be selected. However,
f~r packaging praducts which are sensitive to relative
-rlumidity and the presence of water, for example fruit and
40 sugar co><ztaining produce such as apples and strawberries,
a material with a higher.-water vapor transmission,.xats,
such as cellophane is preferred., However,.a.container
entirely of cellophane or of anotl~ler gas barrier film, as
is apparent from the above table, would in most cases not
45 provide the desired controlled atmosphere environment in
W~ 92/04256 PCT/ US91 /06341
- 18 - ,
the container for respiring type products as cellophane
tends to be a gas°barrier to carbon dioxide, oxygen and
nitrogen.
It should also be noted that for nonrespiring
products, barrier type films are preferred with the
containers being charged with desired mixes of gases
during packaging.
A number of options exist for providing a
container with a modified atmosphere environment and which
l0 allows the escape of water vapor. In one basic approach,
the container may be made of more than one material, one
of the materials permitting the passage of~wa'ter vapor and
the other material controlling diffusion of gases. This
approach, which may be called a window technique, may be
accomplished by, for example, the inclusion of a section
or patch of porous or nonporous material in the container,
the patch being of the type which controls the desired
diffusion'of gas between the interior and exterior of the
container. Another approach, as explained below,: is to
include one or more apertures in the container which are
sized to control the diffusion of gases through the
aperture. As explained below, the use of a patch of
porous material or an apertured container is helpful in
vacuum cooling applications as the apertures and porous
material facilitate the bulk transfer of gas from the
container when the container is subjected 'to a vacuum.
In connection with the window approach, one
container material may be relatively water permeable and a
gas barrier, such 'as cellophane or ethylene vinyl alcohol
copolymers. Another container material may be a nonporous
material selected to control the gas transfer by diffusion
between the interior and exterior..of the container so as
to establish the desired controlled atmosphere
environment.- One approach for accomplishing this result
is to make the cowtainer 10 in the form of a bagP ~..
portion of which is indicated at-30 in FIG. 4, of a water
vapor permeable gas barrier material with an aperture 32
being provided in the bag. The aperture is covered with a
WO 92/042>~ PC1'/US9 i /06341
19
patch 34 having a permeance which establishes the desired
gas environment within the container. For example, the
patch 3~ may be of silicone such that gas diffuses through
the patcY~ unti'i the oxygen and car:aon dioxide
concentrations reach the desired relative levels within
the container. If the product is respiring, equilibrium
levels in the container will differ from air in that the
oxygen concentration is reduced and the carbon dioxide
concentration is increased. Yet, the overall bag material
30 permits the removal of water and water vapor through
this portion of the container. As another option far
removing excess water from witha.n the container,
desiccants, such as in the form of one or more package
inserts, may be included within the container.
Referring again to fIG. 4, the patch 34 is
typically sealed, as by an adhesive 36 (or mechanically,
or heat sealed,-or otherwise sealed) to the container to v.
close the aperture 32. As shown in FIG. 5A, the adhesive
36 is typically placed so as to form a perimeter:seal at a
location spaced from the boundary of the aperture 32 for
purposes explained below. '
Another window approach involves the use of a
porous patch for the window. These porous mtambranes
control the bulk diffusion of~gas between the interior and
exterior of the container so as to control the atmosphere
within the container as desired. l~xampl.es of suitable
porous patch materials and the measured gas transfer
coefficients through apertures of selected dimensions
covered with a number of such porous materials are
indicated in Table II below.
TABLE II
Diameter
ylembrane .. ~ndition fMLlhr-ahnl
. fcmL
yj
_
.
Nuclepore (3 D~ . . 695 . . .. . , . .
micron) . 0,69
.
Wet ~ 0.69 650 - -
.
4 0 veratec Dry 1.0 1,120
58.1# Polyester
Wet 1.0 8s(1
42# Bleached Dry 1.0 155
Liner
Wet 1.0 265
~~~0 92/01256 PC'!'/U~91/06341
- 20 -
33# Kraft Liner Dry 1.0 500
Wet 1.0 480
Teslin Synthetic
Papcr (PPG) (10 mil) Dry 1.0 655
Wet 1.0 480
Tyvek #1059B Dry 5° 7,580
*Large diameter required due to rnaterial ncynuniformity.
Yet another way of achieving the desired modified
atmosphere environment within the container 10 has been
discovered. with reference to FIG. 5, perforating the
container 10 with a small aperture or hole 60 has been
found to work effectively in these applications.
Ordinary molecular diffusion occurs through
perforated or porous.membranes whose pore diameters are
large relative to the mean free path of the gas. For
atmospheric gases, relatively large pores refers to pore
sizes larger than about 0.5 microns in diameter, l~lthough
ordinary molecular diffusion increases with absolute
temperature to the 1.75 power, there is little temperature
dependence over the relatively small range of interest to
modified atmosphere packaging. There is, however, a
slight dependence on gas composition, since X32 and N2
diffuse approximately thirty percent more readily than CUZ
and H20 vapor diffuses approximately sixty percent more
readily than CO2. However, it has been found that the gas
transfer coefficient increases proportionately with the
circumference of an aperture rather than the area of the
aperture. ~'T~~. 13, 14 and 15 illustrate these
observations for 'three different types of materials. This
finding has provided a basis for selecting aperture sizes
which result in the desired gas environment while still
permitting the enhanced bulk transfer of gas under vacuum
conditions. ,apertures havzng an area of that of a circle
of a diameter of from. about.twen~,y_-five microns to about
six hundred and fifty microns per k~.logram of, packed
product have proven to maintain, the desired -aontroll~d
atmosphere with packages having,.in the range,of up to.
WO 92/04266 PCt'/U~91/06341
2l - 2~'~2~~J
about one-half to ten kilograms of packed product having
been tested to date.
Another gas transfer mechanism is Knudsen
diffusion through porous membranes whose pore diameters
are small relative to the mean free path of the gas. For
atmospheric gases, this means pores smaller than about 0.5
microns in diameter. In Knudsen diffusion, gas permeance
is related to the inverse of the molecular weight of the
gas. Thus, theoretically, Knudsen diffusion will result
in oxygen and nitrogen permeabilities twenty percent and
thirty percent higher than carbon dioxide, respectively.
It is also possible to further modify the
internal atmosphere of a modified atmosphere container
using an assortment of gas scrubbing materials. Scrubbing
products are commercially available for ethylene, carbon
dioxide, oxygen and water vapor. In particular, silica
gel and clay are commonly used to scrub water vapor, iron
oxide is commonly used to scrub oxygen, lime is commonly
used to scrub carbon dioxide, and potassium permanganate
is commonly used to scrub ethylene from the controlled
atmosphere environment. In addition, humectants are
sometimes used ~o control the humidity in a controlled
atmosphere container.
nesignia~g a modified atmosphere package simply
involves throttling the incoming oxygen and outgoing
carbon dioxide streams so that respiring produce becomes
starved for oxygen and flooded with carbon dioxide. At a
steady state, in general, all of the oxygen being consumed
by the respiring produce must pass through the package.
This oxygm will pass through at a rate dependent upon the
gas transmission rate of the film and the partial pressure
drop across it. Thus, when respiring produce is packed in
a controlled atmosphere package, the oxygen level will
continue to dre~i-and the carbon dioxide and water vapor
levels will continue to rise until.the respiration rate is
in balance with the gas transfer rate of the film.
As previously mentioned, most plastic films are
more permeable t:o carbon dioxide than they are to oxygen.
wo ~zioazs~ ~~criu~~~iob~a~
~~~~~~~7 - zz - _
In addition, respiring produce consumes approximately the
same volume of oxygen as the volume of carbon dioxide it
emits. Because of these properties, produce in a sealed
plastic film container will reach a stable atmosphere in
which the oxygen deficit is higher than the carbon dioxide
buildup. As shown in Table I, permeance ratios (COZ:oz)
for "commodity'° film materials range from about three to
one (styrene) to ten to one (polyvi.nyl chloride). With a
sealed polystyrene wrap, it is thus possible to achieve
ZO any atmosphere along the line AD of: FIG. 16. Similarly,
with a PVC wrap, one can achieve any atmosphere along AB.
Thus, using the sealed commodity films listed in Table I,
it is possible to achieve any atmosphere within the
triangle ABD of FIG. ~.6. With other materials, the area
within the triangle may be varied.
Within the ABD range of FIG. ~.6, the carbon
dioxide and oxygen levels do not add to twenty-one
percent. This means that a partial vacuum is created
within the package. As a result, any °'pin hole":leak in
such a package will result in nitrogen enrichment to make
up the pressure difference. This in effect provides the
basis for an enlargement of the design range by using
perforated barrier wraps. As previously discussed, if the
perforations are large (relative to .5 microns), bulk
diffusion dominates so that it is possible~to achieve any
internal atmosphere along AE in FIG.,16. Similarly, if
the perforations are small (relative to 0.5 microns),
~Cnudsen diffusion dominates so that it is possible to
achieve any internal atmosphere along line AC.
By combining these mechanisms, (e. g. perforating
a gas permeable film) one can obtain any. atmosphere within
tine triangle ABC of FIG. 1.6.
Thus, a mechanism is described for readily
selecting materials for obtaining a desired controlled
a°tmrisphere environment for a wide variety of products.
By'circumventing the inherent restrictions placed
on the outward water vapor flow bar modified-atmosphere
packages, affective cooling of products sealed in such
wo 9~io~2ss ~crvus~iio~~m
z3 ~~'~2~-~
packages is permitted. This cooling is accomplished by
locating a heat sink or cooling element in proximity to
the outside wall of the container 10. The heat sink is in
close enough proxiwity to the outside wall so as to
facilitate heat transfer between the exterior of the
container and the heat sink. Most preferably the heat
sink is in direct contact with such. outside wall of the
container. It is also preferred that the heat sink
contact is proximate to a major portion of the surface
area of the exterior of the container. A major portion
means for purposes of this description at least from about
thirty to about fifty percent of 'the exterior container
wall surface area.
To facilitate use of the invention in the field,
it is preferred that the package, including the cooling
element, be of a size and weight which makes them easily
manually portable. Consequently, harvesters can carry
these packages with them as they move about a field and
harvest produets. Typically, the receptacles, cantainers,
cooling elements and packed produce in a package of the
present invention weigh less than fifty pounds to
facilitate manual carrying of the package.
The cooling element may take nnany forms to
produce the desired heat sink at the exterior of. the
container. AS shown in FIG. 17, the cooling element may
comprise a collar 14b, such as of a liquid impermeable
plastic film ~e.g. polyethylene) which seals a liquid
therein,' such as water or a phase change cooling chemical,
with potassium nitrate being one example. The illustrated
collar 14b has plural liquid containing compartments 15a,
15b, 15c and 15d which are.jained 't~gether by,hinge
funning portions,-such.as indicated at 17. The components
may be formed, for.. example,.: by sealing the outer pouch
forming cover malterial together at the hinge locations, to
separate the collar 14b into the indiva.diaal cooling
material c~nthining compartments.
The collar 14b is typically frozen and placed in
a receptacle 3.~ with the container 10 opened and
AVO 92/04256 ~CT/US91/~D6341
2~'~~~~~ - 2~ -
positioned within the collar in tree Field. Produce is
harvested into the container. When the container is full,
the container is closed, as explained below, for example
in the field. The collar 14b acts as a heat sink to cool ,
the exterior wall of the container and the packed product,
which may then subsequently be vacuum cooled to
substantially accelerate the coola..ng, such as explained by
example in conjunction with Table T1T, below. The collar
14b gray be removed prior to shipment of the cooled produce
and refrazen for subsequent reaise in the field harvesting
operation. Other forms of heat sinks or cooling elements
may also be used, provided the heat sink offers a
sufficient thermal mass to accomplish the desired cooling.
preferably the thermal mass is such that it is capable of
dropping the temperature of packed produce in the field
under normal field temperatures and container filling
times from about 80° l: to about 35° F. In general, it is
preferred that the thermal mass be capable of one BTU
(British Thermal Unit) per pound of packed product in the
container per degree of cooling desired. Thus, for a
temperature drop ~f from 80° F to about 35° ~', the thermal
capacity of the collar preferably is at least about 45 BTU
per pound of packed product. By providing excess thermal
capacity (e.g. another 5 BTU per pound of packed product),
the cooling collar also compensates somewhat for the time
the container is exposed to field temperatures as the
container is being filled.
The cooling element array also be of the type which
permits the evaporatian of ,liquid therefrom;to provide the
heat sink in this manner. Evaporation of a cooling liquid
in proximity to the exterior wall of the container x0
~~ coolsvthe contents of the container by,~v~aporation and _
tra.n~fer of heat ~ frown the . products in the ;.container.
through the container wall-a . .. Water vapor within the. .., .
package, for~~xample, from moisture containing products,
tends to coxadenw;e on the chilled inner surface of the _ .
package wall (wh.ich is also true when other types of
cooling el~ment~o are used), reducing the water vapor
WO 9/04256 fCf/US9i/06341
Z5 - .. .
pressure inside the package and promoting further
evaporation of water from the moist product. This
evaporation from both the cooling element and packed
product is enhanced under ~:~acu»m Jonditions and results in
a rapid cooling of the product. Thus, cooling, and in
particular a vacuum cooling approach can be applied to the
product within a modified-atmosphe~:°e package. Cooling is
accomplished by a series evaporation-candensation-
evaporation process that is facilitated by the moisture
l0 source in proximity to or contact with the exterior
container wall.
Although FIB. 1 illustrates one form of a
separate cooling element which is capable of holding a
volatile liquid, such as water, ethanol or the like,
against the container wall, other approaches may be used.
For example, by making the container of a hydrophilic
material, such as of a cellulose based material (e. g.
nylon, cellulose acetate, cellophane or other dissolved
cellulose based films) or other absorbent material, the .
container 10 itself may function as a cooling element with
liquid evaporating from the container to facilitate the
cooling of its contents. Polysaccharide films, hydrogels
(such as the so-called superabsorbent particles Goanmon in
the disposable diaper art) adhered to film, fibrous
materials such as wood pulp adhered t~ the film, water
pouches or pockets on the container, are yet other
examples of mechanisms for incorporating liquid into the
container for purposeswof evaporative cooling. For
example, FTC. 3 illustrates a film 30 with adhered wood
pulp particles 40, the wood pulp particles holding water
for use in evaporative cooling of the contents of the
container. " .. -
The required oapacity of the moisture source,
whether it be a substrate ors ttie coaatainer l0 or ~c~isture
holding substrate in a separate coating element such as;-
collar 14, depends Japan the mass of the product within the
package. Edith water being the cooling liquid, a rule of
thumb indicates that one percent of the product mass is
WO 92/04256. P(~'T/U~91/Ofi341
lost to evaporation for every 10°F of vacuum cooling. To
minimize evaporation of moisture from the product itself
during cooling, the moisture source is typically designed
to provide ~t least this minimum mass. In a typical field ,
packing operation, one can assume an average air
temperature of about 80°F, Therefore, to drop the ,
temperature of products from 80°F to 35°F would require
about forty-five grams of water for each kilogram of
product in the container. However, in accordance with the
method of the present invention, and to gain benefits of
cooling during harvesting of the produce, water is ,
typically added to the cooling element or package in
advance of harvesting the praduce such that the produce is
harvested into a container already provided with this
added moisture. Because evaporation can take place, and
is encouraged for cooling purposes, during actual picking .
of the strawberries or other products, excess water is
typically included so that enough water remains in the
container for purposes of subsequent evaporative: cooling,
~0 such as under vacuum conditions. Therefore, a preferable
cooling container is designed to hold an excess amount of
water, such as about sixty-five grams of water for each
kilogram of product in the container., .Also, in general,
the greater the proportion of the c~ntainer in contact
with the moisture source, the more effective the pooling.
In addition, relatively thin moisture containing
substrates offer a low resistance to the transfer of heat
from the condensing surface at the interior of the ,
container to the evaporating moisture.in the substrate and
thereby increase cooling effectiveness.
To accommodate this relatively. large quantity of
moisture, the moisture is most conveniently placed in a
substrate with the..substrate being.positioned in contact
.: With the container: wall. - ~.lso, , by utilising a container
35.:::1~ of a flexible material,-'the container expands against
the substrate during the applica~t~.on of a vacuum. This
advantage is also obtained by usa.ng a flexible container
with the other forms of cooling elements. This is due to
wo oziaazs~ ~c.-ri t ~a a
-z~-
'the delay in evacuating the air from the container and the
fact that the container tends to inflate against. the
cooling element, thereby enhancing the contact between
rheas components and enhancing the resulting heat
transfer.
Any moisture absorbing material may be utilized,'
such as blotter pads, absorbent fluff pulp, superabsorbent
polymers, paper, molded fiber and combinations thereof.
The location of the moisture containing substrate with
respect to the container 10 may be varied, such as '
underneath, along side, or on top of the container.
In the design of a cooling element such as collar
~.4 shown in FIG. 1, the substrate material is indicated at
50 and positioned at the interior of the collar 14. Zn ,.
FIG. 2, the water containing substrate 50 comprises a
sheet which is positioned at a surface of the collar 14
and which is incorporated into the collar. Again, the
sheet may be of any suitable liquid containing material,
such as wood pulp. Also as shown in FIG. 2, the:collar ~.4
may include a conventional corrugated corer indicated at
52, such as of corrugated Kraft paper. T'he corrugations
define passageways or flutes, some being indicated at 54
in FIG. 2, which permit the passage of air or otherwise
expose the back side of the sheet 50. Consequently,
evaporation of liquid from the back side of the sheet is
enhanced. This can be important, especially if the
container is pressing against the exposed surface 56 of
the sheet so as to limit evaporation at the area of
contact between the container and sheet. To limit the
possible transmission of liquid to-an exterior sheet 5~ of
the collar 14, the core 52 may be formed of a water
r~sistent or water impermeable material. Wax, impregnated
medium, such as a ~iaxed paper, is one specific.~xample of
a medium which may be utilized for this purpose. although
migration of liquid through'the liner and the.;core..52 to
the sheet 58 is~typically limited in any event, the use of
a water resistent core 52 minimizes the potential wetting
of 'the sheet 58.
WO 92/04256 fCT/iJS91/06341
' 28 -- _
The receptacle 16 may be a separate element as
indicated at FTG. 1, or may be combined with the cooling
element 14. One convenient approach for combining these
elements is to utilize the structure of FIG. 2 for the
receptacle, in which case the interior surface of the
receptacle comprises the water holding or carrying
,material, such as the sheet 50. Also, with a water
resistant core 52, the sheet 58 remains substantially dry.
Therefore, the sheet 52 may be preprinted with brand
to identification or other advertising material so that the
receptacle 16 is usable as the display container for the
produce, such as in a retail establishment. Of course, a
separate receptacle 16 may also be used for this purpose.
with the optional construction utilizing a water resistant .
core 52, the receptacle 16 remains strong enough for
stacking and carrying the products as well as for
protecting the products during shipment even though the
sheet 50 is wet.
In applications wherein the package is to be
vacuum cooled, cooling is greatly assisted if a path is
provided fox removal of air from the inside of the package
during the evacuation period. otherwise the pressure of
air within the package inhibits the condensation of. water
vapor from the product onto the cold package wall. pne
way of providing the pathway is to utilize the small
window or patch of porous filtration material which allows
the bulk transfer of air from within the container during
the application of the Vacuum while.still peranitting _.
diffus3an to control the gas balance within.the container
during storage:' However, to increase the gas transfer
rate during evaporative cooling, mechanical Valves, such
as thewvalve described in U.S. 1?atent.No. 4,890,67 or the
like;-..~a~ be included in the: wall.of the,. container, 10.
w Although suitable; mechanical valves,tend..;to add to,the ,
expenseo of the packaging.system. . . ....
. '~s another approach for increasing the bulk.
transfer ~f hir fxom the interior of .a container under
vacuum conditions, reference should be made to FIGS. 4, 5
WO 92/04256 PL f/1JS91 /Ofr3A l
- 29 -
2~N~~~9
and 5a. As previously explained, the patch 34 is
typically secured, as by adhesive, to the container wall
30 about a perimeter 35 which is spaced from 'the boundary
of the aperture 32. Under vacuum conditions, the patch 34
tends to form a bubble, as shown in FIG. 5, whereas in the
absence of the vacuum, the patch tends to lay flat against
the container wall as shown in FIG.. 4. In comparing FIGS.
4 and 5, it is apparent that the area of the underside of
the patch 34 exposed to the aperture 32 is increased under
l0 vacuu~a conditions as opposed to the case when a vacuum is
not being applied. Due to the increase in exposed area of
the patch 34, the gas transfer rate through the patch 34
is increased under vacuum conditions. Consequently, a
more rapid escape of air fram within the container is
permitted when a vacuum is applied and, as a result, more
effective cooling of the product contained therein takes
place.
Also, the use of an aperture in the container
(See FIG. 6) enhances the bulk gas flow under vacuum
conditions.
In connection with bulk flow of gases, gases are
transferred from the high pressure side of the package to
the low pressure side independently of the partial
pressure differences of each gas component. For example,
if air is bulk transferred from the outside of a package
to the inside, enrichment is in the constant ratio of
seventy-nine parts nitrogen to twenty-one parts oxygen
(the composition of air), regardless of what the internal
partial cancentrations of these gases are.
As previously mentioned, the package of the
present invention can be utilized in conjunction wit?a
various means of achieving evaporative co~la.ng. For
example, water vapor may siaaply be allowed to evaporate
from an ewapora~:ive type Gaoling collar. ~an:addi~tion,
~ offirmative waX>orative cooling rnay be accomplished: by .
moving air acro~a~such a cooling collage pressure cooling
may also be utilized, involving use of dry air at a higher
temperature. In addition, and offering particular
wo 9zionzs~ ~c rvus~ r io~3~ l
~~~~~)~~3 - 30 - -
advantages, vacuum cooling may be employed to cause the
flashing of water vapor from the produce and from an
evaporative type cooling collar when air is removed as a
vacuum is applied. ' .
It is also possible to charge the package with a
desired gas environment. For example, the vacuum may be'
relieved by charging the vacuum chamber with a desired gas
atmosphere having a gas balance wr;~ich differs from air.
For a nonrespiring product in a gas barrier film, the
l0 modified atmosphere within the container remains at the
charged gas composition for a substantial period of time. .
For example, the atmosphere may be enriched in carbon
dioxide. This charging gas will pass into the container
and effectively precharge the container with gas of the
25 desired environment. The charging gases may include a
fumigant for destroying fungi, bacteria, insects and other
pests that might otherwise damage the packaged product. A
number of known fumigants can be used, such as methyl
bromide gas for mite control to satisfy export
20 requirements, such as the case for strawberries being
shipped to a number of foreign countries. In addition,
gases such as carbon monoxide may be used to inhibit
enzymes responsible for browning of lettuce, mushrooms and
other products. Again, any number of suitable fumigants
25 may be utilised, with other examples indluding sulfur
dioxide and sulfite based materials. Other chemicals for
these purposes may be added in liquid or solid fore.
FIG. 7 illustrates another form of package in
accordance with the present invention with corresponding
30 elements being assigned the same numbers as in ~'IG. 1, but
with the added subscript '°a". In this case, a ,omewhat
smaller container 10a, in comparison to the container 10
~~ FIG. 1,' is shown with strawberriesl2a therein. .The .
cooling cellar W4a in this case is formed.into a box-like
35 configuratio~i with.a water absorbi~g.:s~bstrate a~a at one
surface of this form of cooling element. ~n the FIG. 7
package,.the receptacle 1~ is comprised of a first
receptacle ~.6a for receiving the container 10a and cooling
- ~1 ~ ~~i'~~~~~
collar 14a therein and a larger receptacle 16b for
receiving plural, in this case four, of the containers 16a
and contents.
FIG. 8 illustrates a corrugated board blank used
in forming the cooling collar 14a o:f FIG. 7. When folded
along perforations 60, 62, 64, 66, 68 and '70, the cooling
collar 14a takes the form of a box 'which may include the
water holding substrate 50 on all of its interior
surfaces. During use, the collars 14a, as well as collars
of the form 14 shown in FIG. 1,'and 14c in FIG. 18,
are typically inverted (substrate 50, 50a, 50c side down]
and floated in a pool of liquid, such as water, so that
these collars become at least partially saturated. To
expedite this wetting procedure, the blanks used to form
the collars 14, 14a and 14c may be carried by a~cOnveyer
across the surface of a pool of water with the substrate
50 in contact with the water so as to wet the substrate
without wetting the remaining surfaces o~ the collar,
However, the entire collar nay be wetted if desired.
FIG. 9 illustrates a corrugated board blank for
one of the receptacles ~.6a which, if folded along
perforations 80 - 94 forms another box-like structure for
receiving the cooling collar and container.
With reference to FIG. 10, a typical method in
accordance with the present invention will be described.
In this case, at a location x.00 a cooling lic~uuid, such as
water, is added t0 the cooling collar. This x~ay be
accomplished by at least partia~.ly saturating the
Substrate 50 Of the cooling Collars 1.4, lea, Or 3.4c (FIGS.
1, 7, 18). Liquid is typically added to the cooling
collars in the field, that is at the location where the
products are to be harvested. Following the addition of
the cooling liquid,"~(or in the case. of the collar 14b.
~foll.ing the chilling 'or freezing;-Of the collar) the- .:.
35. packages are typically assemblede' That is,.;open-..
containers 10, l.Oa are placed a.n respective cooling
collars 14, 14a, 14b, 14c and in the receptacles 16 ar 16a
and 16b. The assembled containers, one being indicated at
~'O 92/0d256 fCT/1hi91 /~)6:~A i
32
102 in FTG. 10, are 'then taken by the produce harvesters
and filled with produce, such as strawberries from a row
104. The strawberries are sorted by the picker and placed
directly into ~,he open containers 10, 10a. Evaporation of
liquid from the cooling collars 14, 14a, 14c (and heat
transfer to the chilled collar 14b if this 'type of collar
is used) helps to cool the berries as they are being
harvested.
In a typical commercial strawberry field, plastic
or other ground covering 106 is placed on the ground
between the plants so that the berries are clean. Thus,
the berries being placed in the containers 10, 10a are
clean and attractive for marketing purposes. The picker,
when containers 10 and ~.oa are full, typically takes the
filled package to a sealing location, indicated at 108, at
which time the controlled atmosphere packages 10, 10a are
closed.
The containers may be provided with mechanical
fastening mechanisms for use in sealing the containers.
One such mechanism is shown in FIG. 1.1 and is indicated by
number 110 as comprising a common "zip-lock" type
mechanism having an elongated bead 112 which fits within
and mates with an elongated groove 3~.4 formed in the
container 10. This mechanism may be provided in a strip
of material secured to the container. Although mechanical
seals may provide the sole sealing for the containers 10,
10a, films of this type are typically of a heat sealable
material. .."Consequently, as shown. in FIG. 1.2, a filled
package x.02 may simply be placed on a table l~.s with the
open end af'the container 10, 1.0a being exposed,for
positioning between heating elements x.20, 122 of an
j
electrically powered heater a24. With the end 118 of the
bag clasped betweenwthe bars,120,and..122, the bag is '
closed by'heat s~ealing~:..Of course,:.~~trasonic and other .
sealing approach~eswmay;alsp be.used. For example,
commercially available cable ties, such as Part No. X54?6~
ties~from Consolidated Plastics Comgany of Twinsburg, Ohio
have proven suitable. In addition, the mechanical
WC) )2/04256 PC.'C/U~91/063~i
fastening mechanism 110, although helpful in preliminarily
closing the bags so that ends 118 may be oriented easily
for heat sealing, is not necessary. After sealing, the
now sealed end of the bag 118 is typically tucked into the
receptacle.
As shown in FIG. 12, the receptacles may be
printed with brand identifying indicia or advertising
material, as indicated at 130, so that the produce can be
displayed at its end destination, such as at retail
stores, in these receptacles. As also shown in FIGS. 10,
12, following sealing, the packaged products may be
palletized, that is, stacked in tiers on a pallet 138 as
shown in FIG. 12. fihis approach minimizes the number of
times that the produce is handled following harvest. mhat
is, the only direct handling of the produce occurs at the
time it is picked and initially placed in the container
and then again at the restaurant or other end location
when the produce is actually used. Also, the modified
atmosphere container typically remains in tact until the
individual containers of produce are used. Although the
produce has been placed in modified atmosphere containers,
evaporation of liquid from the form of cooling collars 14,
lea coxttinues to cool the produce. In a like manner, heat
transfer to the FIG. 17 form of cooling collar 14b also
continues to cool the produce.
Following the optional palletizing step, the
packaged product is moved to a vacutam cooler of a
conventional type. The vacuum cooler may be located at
the field, that is in proximity to the location where the
product is harvested, ox at a remote site. I'he packaged
product is subjected to vacuum cooling to further cool the
prodixct until tr=msported, as indicated by vehicle 142 in
F"IG.~10, during distribution of the product.
~:.. . ~: F~.~$llyo to provide a further explanation the.
present invention; a"specific example is_described below.
In connection with this example, a four~unit retail flat
of the type showrnvin FIG. ~' was used. Each container 10a
of this flat was packed with approximately one thousand
WO 92/0d256 fL t'/U~91/06341
- 34 -
grams of strawberries. The film utilized in 'the container
10a was ethylene vinyl alcohol (EVO~) having a twelve
micron thickness and being approximately of a twelve inch
by five and one-half inch by six inch size. The patch 34
(FIG. 4) comprised forty-two pound bleached liner paper in
the form of a one and one-fourth inch by one and one-
fourth inch label with a one-quarter inch diameter
adhesive-free circular area applied positioned over a one-
sixteenth inch diameter perforation in the film (the
l0 perforation corresponding to aperture 32 in FIG. 5). Over
the aperture, the gas transfer coefficient (diffusion) was
measured as 80 mL/hr/atm while the Gurly (bulk flow) was
measured at 560 sec/100mL. In addition, the cooling
collar 14a (FIG. 7) was partially saturated with
approximately 100 grams of water with the assembly being
placed in one of the containers 16a. Testing revealed the
steady-state internal atmosphere of this container was
approximately seven percent COZ and sixteen percent 02 at
~0°F.
When a package of this type including a cooling
collar is stored in a well-ventilated area, tae
temperature of the cooling collar approaches the wet bulb
temperature of the surrounding air. For example, in
Watsonville, California, where the average high
temperature in June is 70°F and the average relative
humidity is fi.a~ty percent, the wet bulb temperature is
approximately 60°F. It has been found that after two
hours under these conditions, strawberry packages with a
cooling collar as described above are on the average 3.5°F
cooler than those without collars.
When subaected to a vacuum, to minimize bursting
problems of the container 10a, the. porous membrane
typically has aw~Gt~rly flow of greater than-0.2 mL~/sec (100
mL/560 sec). This Gnarly flow is also achieved by placing
an oversized porous~label,:for example one-quarter inch in
diameter, over a one-sixteenth inch diameter perforation
in the film. As previously explained, under vacuum
conditions this label bubbles out to expose the entire
WO 92/092~i6 PC'r/U~9H/f163~S1
2~~~~~9~
one-quarter inch diameter porous material, but then
returns to a flat position under ambient conditions.
Also, as previously explained, a small aperture may be
used for this purpose.
In a conventional vacuum cooling process (e.g. no
cooling collar or other cooling element), all of the heat
removed from a product is contained in the water vapor and
is removed from the product or from any water sprayed onto
the product. With: a modified atmos;~here package, ttae
removal rats of heat from the product would therefore be
limited by the rate at which water vapor would pass
through the porous membrane, which in turn is related to
its Gurly number, or to the rate water vapor is otherwise
collected within the container. If a cooling collar is
used, a condensing surface is created on an interior
surface of the modified atmosphere container. This allows .
the water vapor inside the container to give up its heat
(while condensing) to the cooling collar sa as to enable a
much ars~ore rapid heat transfer. In addition, the cooling
collar removes heat by conduction at points of contact
with the container. Tt has been observed that after
either a fifteen minute or thirty minute vacuum cycle, tile
temperature drop of a package which comzbines a modified
atmosphere container with a cooling dollar is three to
2~ four times greater than the case sai.thout a cooling collar.
Iw addition, it has been observed that this method of
cooling (utilizing a cooling eleanent in coanbination with a
modified atmosphere package) appears to be gentler on
strawberries than a conventional vacuum cooling process.
Although the reason is not entirely clear, it is quite
possible that evacuation shock and cell rupture of the
berries is reduced and that freezing is minimized since no
berry can be colder than the coating collar.
Also, after about fifteen ~ainutes in a vacuum
tube,.(an open, e.g. conventional modified atmosph~re~
package) would be approximately 6° cooler if a cooling
collar is used than if one is not used. Thus, a cooling
collar may be used to speed up the cycle time of vacuum
~vo ~2ioazsrs ~cPrius~~io63a~
- 36
~~~~JJ
cooling. In~~addition, with such a cooling collar, cooling
has been observed to continue for several hours after
removal from the vacuum tube as heat continues to transfer
to the collar. Early observations suggest that the
equilibrium (two-hour) temperature drop using a liquid
evaporative type cooling collar in combination with a
fifteen minute vacuum cycle is com~aarable to that from the
use of a thirty m'z.nute vacuum cycle without a cooling
collar.
~.0 Mature (full color) strawberries packaged in this
manner have maintained their peak quality for eating up to
three weeks from packaging. Presently, the maximum
strawberry life is about seven to ten days even if the
berries are less mature when picked (green). Although
this example has been described in connection with
strawberries, the invention is not limited to this
particular type of produce. ~s another specific example,
broccoli packaged in this manner has maintained its
quality and freshness for the duration of a twenty-one day
test period, with the maximum duration not yet having been
determined.
To provide further evidence ~f the effectiveness
of the present invention, room te~tperature strawberries
were placed in a xnodif led ataaosphere container and the
container was closed. The container was then subjected to
cooling for thirty minutes under conditions indicated by
Table I~T belaw and with the results being set forth in
this table. '
:. T~I"E Iu
3 0 STItAVJ~BERRY COOLING IN A
CLOSED MODIFIED ATMOSPFIERE CONTAINER
(EVOII F">lm with an Aperture)
Cooling Elcmtnt Vacuum Applied ' ' Average Packed Strawberry
3 5 Type Area' During Cooling Temperature
. .. , ,. . : Initial Fenal C2Sange ..
Frozen .Scale! Cooling ' .. - . .
Collar (14b type)°° 120 ~ No ,' 66.6 52.0 14.6
4A ~ - .... . .... , ,. . , .
Froaen Sealod Cooling _ _...
Collar (14b type)°° 120 Yes . 65.1D 36.8 , . 28.2
Wet yber Cooling
~ 5 Collar (14a type) 50 Yes ' . 67.8 ~ 37.2 30.6
WO 9?/042Sfi fC'f/US91/()f>34i
- 37 --
~~'~Z~~~
None Yes 66.9 59.6 7.3
In square inches per pound of packaged fruit
~' Commercially a~railablc Blue lca"' packaged sealed cooling elemeW s
frozen at a tamperalure of 15° F.
From the above table i.t~iu apparent that vacuum
cooling of room temperature strawberries is simply
ineffective without a cooling collar. Also, the use of a'
sealed cooling element without vacuum cooling of the
strawberries offered an improvement over the cooling
element-less vacuum cooling approach. Moreover, the
combination of vacuum cooling with a cooling element (of
either the sealed or evaporative cooling type) was
extremely effective in cooling the strawberries. Also,
the evaporative cooling type of cooling element required
far less surface area than the sealed type cooling element
to accomplish the substantially same result.
FIaving illustrated and described the principles of
our inventian with reference to several preferred
embodiments, it should be apparent to those of ordinary
skill in the art that the invention may be modif~.ed in
arraaigement and detail without departing from such
principles. We claim as our invention all such
modifications which fall within the scope of the following
claims.
