Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 93/01101 2 :~ ~ 2 9 0 ~ PCr/AU92/0032~
CONq ROL OF CONDENSATION
Pield of the Tn~ntion
The present invention re~a~es to a packaging material
and method for the control of condensstion within packages
of horticultural produce and other packages of other
pxoducts requiring high relatiYe humidities. The
packaging material and ~ethod of the present invention
provide a means by which condensed water is transferred to
the outside of the packag~ or into a sachet of de~iccant
without substantially depleting the water vapour content
of the atmosphere within the package.
Background of the Pre,sent Invention
1. The causes of condensation in packages requiring high
xelative humidities.
Much of the freshness of horticultural produce, such
as fruit, flowers and vegetab}es can be maintained by
packaging it in polymer films. Thi~ keeps the relati~e
humidity of the air in the package high, typically at 98%
or more of saturation. However, at a relati~e humidity of
98%, free water will condense where the temperature of any
part of the package i8 about 0.2C degrees lower than
the produce. In pxactice, it is difficult to avoid
temperature gradients of this magnitude, either because of
' small fluctuations in the temperature of storage or
because of~inadequate cooling of the produce before
packing. ~Even when;produce is adequately cooled and
temperature control is~ideal conde~sation may occur. This
is because the produce itself produces heat in proportion
to its rate of~respiration. Under equilibrium conditions,
the produce will therefore be at a higher temperature than
its surroundings. If the resulting temperature difference
exceeds the diffexence between the produce temperature and
the dew point, condensation will occur.
2. Harmful effects of condensation
Condensation is harmful when it comes into contact
W093/0110~ r~ O ~ PCT/AU92lO0325
with horticultural produce. Oxygen diffuses at a much
slower rate through liquids than through ga~es. A~ a
consequence, a film of condensed water on 60me part of the
surface of horticultural produce can impede the supply of
oxygen to that part. This may cau e a phy~iological
stress to the produce, particularly if the surrounding
atmosphere contains much less than the atmospheric level
of oxygen, a~ is the case in modified atmosphere
packaging. Solutes such as sugar~ and amino acids leak
from the plant tissue into the condensate, e~pecially
where microscopic wounds are present. Such solutes
stimulate microorganisms to grow. The microorganisms
further reduce the level of oxygen available to the
horticultural produce. The overall effect of the
condensation is to lower the resistance of the produce to
invasion by pathogenic microorganisms.
3. Previous methods used to control condensation.
The most effective method currently used to control
condensation in ho~ticultural packaging aims at cooling
2a the produce before packing. Then as long as the produce
îs never warmer~than the package walls are, the dew point
will not be reached and no water will condense.
Unfortunately this~ideal condition is often difficult to
`~ ; achieve in practice. ; ~
~ A~second~method of control involves attempting to
stop condensation;occurring by making the packaging
material so permeable~to water vapour that it is more
readily lost to the~exterior. This is done by perforating
~; the packaging with~small holes. A problem is that this
~eads to reduced~humidities within the package and
increased~weight~loss from~the commodity. This method is
not compatible with~modified atmospheric storage of
.
commodities, because the holes in the packaging allow free
diffusion of ~xygen in from the atmosphere. It does not
work if the atmosphere of the storage room is very humid.
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W093/01101 21~ 2~ PCT/AU92/00325
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A third method is to place desiccants in the
horticultural package within sachet~ that are freely
permeable to water ~apour. A problem i~ that the
differences in partial pressure for water vapour between
the desiccant and other parts of the bag are small. This
results in the transfer of water being diffusion limited
and water is preferentially removed from the produce
clo3est to the sachet. The local dehydration reduces the
life and quality of the produce.
In contrast with the methods outlined above, the
present invention allows condensation to be removed from
packages without dehydrating the produce and without
decreasing the relative humidity around the produce.
Summary of the Invention
lS In a firfit aspect the present invention consists in a
pack~ging material for use in packing produce, the
packaging mater~al comprising a sheet which is impermeable
to water characterised in that a first side of the sheet
is hydrophilic and~is provided with fibres capable of
conducting water;~by~capillary action.
In a second aspect the present invention ccnsists in
a method of packing produce compri~ing wrapping the
~; produce in a sheet,~ characterised in that a first side of
the sheet is hydrophilic and is provided with fibres
capable of conducting water by capillary action.
; In a preferred~embodiment of the present invention
the fibres pass~through~the sheet material.
~ In another preferred~embodiment of the present
;~ invention a desiccant is provided within the package and
the fibres are bought into contact with the desiccant.
The fibres~may be composed of any of a number of
materials provided~that they are capable of conducting
~; water by capillar~y action. Examples include cotton thread
and the like, highly hydrophilic super absorbent polyemrs
and polymers the sulphate of whichis highly hydrophilic.
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WO93/01101 2 1 1 .~ J ~ ~3 PCT/AU92/00325 ~..
A variety of desiccants may be used in the present
in~entio~. Any compound that is able to reduce the
relative humidity of an environment below 98% can be
used. Typical desiccants of this kind are ones made from
minerals that ab~orb water such as silica gel, or salts
such as sodium chloride. Organic msterials that absorb
water such as sugars and other polyhydroxy compounds can
be used~ Polymeric materials, such as water swellable
gels and pol ~ inyl alcohol may al~o be used. The common
feature of suitable desiccants is that they should be able
to provide local environments with a relative humidity
: lower than 98%.
In the e~bodiment where a desiccant is provided and
there is no perforation of the sheet by the fibres, the
packaging material and method of packaging of the present
~: invention may be used in modified atmosphere packages.
Detailed Description of the Invention
In order that the nature of the present invention may
~: be more clearly understood, preferred forms thereof will
now~be described with reference to some of the
~: accompanying drawings:-
Figures 1, 2 and 3 show the set up and results of
experiments to demonstrate the theory behind the pre~ent
invention.
~:~ 25 Fi~ures 4, 5 and 6 show various embodiments of the
: present invention.
In Fig. lA a glass bottle is shown that contains
liquid water. The lid of the bottle îs pierced by a hole
of diameter lmm. In Fig. B the weight of water lost
through the hole to the atmosphere (relative humidity 55~,
~: temperature 21C):is plotted as a graph against time
.~
: over 25 minutes. ~he result indicates that the loss of
~ater as vapour through the hole was too small to be
mea~ured over the tLme scale u~ed.
~; 35 Fig. 2A ~hows a sLmilar set up except that a cotton
WO93/01101 2 1l ~ g 0 6 PCT/AU92/0032
~ewing thread has been passed from the liguid xeservoir
through the hole fiO that liguid water may be transferred
to the out~ide by capillary action and ~e evaporated
there. Fig. 2B shows the plot of weight water 103t. ~n
5 this case, there was a constant rate of water loss through
the cotton capillary of about 0.B micrograms per minute.
The principles demonstrated by Figs. l and 2 are u~ed
in the invention described below. A material capable of
conducting water by capillary action is used to transfer
condensed water from a region in equilibrium with a high
relative humidity of the gas phase or high water
potential, to a region in equilibrium with a lower
relative humidity of the gas phase, or lower water
potential.
The setup in Fig. 3 i8 similar except that the
~ contact of the cotton thread with the water reservoir has
: : been broken. The graph shows that this stops the transfer
~: of water.
The results of Figs. 1 to 3 illustrate how capillary
flow along a wick can transfer water only when it is in
contact with liquid:water. ~hi~ principle is uæed in the
invention described bélow.:
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One configur~tion of the invention is shown in
Fig. 4. A package is made;of a material l0 that restricts
2~ water 108s from the~horticultural produce 12. ~he inner
: ~surface~of the packaging materlal l0 is hydrophilic. ~hat
is, water in contact with~the inner surface will spread
and not form discrete:droplets. In addition, the inner
surface of the packaging material is contacted by or
lami~ated with fibres or threads 14 capable of conducting
water by capillary;~action. An example of such a material
is cotton thread. ~The material conducting water passes at
a point Qr at several points through the packaging
material 10, to be exposed on îts oute~ surface. In this
: ~ 35 configuration of the in~entio~, the average relative
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wog3/0l10~ 1 ~ 2 ~ ~ 6 PCT/AU92/00325
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humidity outside the package is assumed to be
substantially less than 98%, as is typical of refrigerated
stores. Under these conditions, any condensation on the
inner surface of the package spreads and i8 ab~orbed by
cotton thread 14. It i8 transferred by capillary action
to ~he outside of the package which is at a lower water
potential and where it evaporates. Once the condensate
has been totally removed in this way, there is no further
transfer of liquid~water. Net transfer of water will be
reduced to that through the gas phase. The rate at which
this occurs is small and the produce is therefore not
desiccated.
Fig. 5 shows a second configuration of the invention
which is suitable for use in modified atmosphere
packages. A package is made of a material 16 that
restricts the transfer of oxygen, carbon dioxide and water
to and from the atmosphere surrounding horticultural
produce 12. The inner surface of the material 16 i~
hydrophilic and is;contacted by or laminated with fibres
or threadt 14 that are capable of conducting water by
capillary action.~ ~A desiccant 18 is contained in a
water-impermeable sachet~or pouch 20. The cotton thread
14 t~ae contacts the~inner surface of the packaging
material pa~ses~through the wall of the desiccant sachet
or pouch 20. Any condensate is conducted along the fibres
or threads 14 to~the désiccant 18 where it evaporates.
When horticultural~produce 12 is placed within the package
it can be sealed~hermetically to form a modified
atmosphere package. In this case, the permeation of
oxygen into the package is balanced by the respiratory use
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of oxygen by the;horticultural produce. This balance is
achieved at some reduced level of oxygen typically between
1 and 10%. In an analogous way, the level of carbon
dioxide within the package is elevated, typically between
1 and 15%. This is achieved by the rate of respiratory
WO 93/01101 2 11 2 ~ ~ ~ PCT/AU92/00325
production of carbon dioxide being equal to the rate of
permeation of the carbon dioxide out of the package. A
substantial barrier to the permeation of ga~es is
necessary for modified atmosphere packaging to work. This
mean~ that holes to allow the exit of nny condensation
water must not be pre~ent. This requirement is met by
this configuration of the invention, as the water is
removed by a desiccant within the package. Because the
desiccant is contained within a package impermeable to
water it does not dry out the produce.
Another configuration of the invention is shown in
Fig. 6. It takes the form of a condensation control
flake, in which a de~iccant 22 is sealed within two leaves
of water impermeable polymer 24. Fibres or threads 26 are
capable of tr~nsferring water by capillary action traverse
the walls of impermeable polymer 24. Flakes made in this
way may be scattered in packages where condensed water is
likely to accumulate. The flakes will absorb any liquid
water that they contact, but will not appreciably lower
levels of relative humidity.
As can be seen from the above the packaging material
:. ~
and method of the present invention provide a means by
which produce may be~ packaged without dehydrstion o the
produce. The packaging material and method of packaging
~;~ 25 of the present invention also substantially ameliorates
the problem with~the prior art of water condensing on the
surface of the horticultural produce.
; It will be appreciated by persons skilled in the art
that numerous variations and/or modifications may be made
to the invention as shown in the specific embodiments
without departing from the spirit or scope of the
invention as broadly described. The present embodiments
~; are, therefore, to be considered in all respects as
strative and not restrictive.
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