Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1253028
Field of Invention
This invention re]ates to the preservation of fresh fruit
and veqetables. In particular, this invention relates ~o an
improved process Eor prolonginq the storaqe life of fre~sh fruit and
veqetables at ambient storage temperatures without deterioration of
freshness, 1avour and texture..
Background of _v ntion
Despite the fact that fresh Eruit and veqetables have been
preserved by many methods, the systems which have been developed to
date all tend to result in a loss of ~reshness durin~ processing or
a loss of freshness aEter a short period of storage. In addition,
the texture and ~lavour of the fruits and vegetables which are
preserved by present methods is also signiEicantly changed.
It is well known to reErigerate or freeze fruit and
vegetables in an attempt to prolong storage liee of these products.
It is also well known to use hermatic seal film, bags, packages or
containers, with our without inert gases, to increase the storage
life of Eresh Eruit and vegetables. In addition, attempts have heen
made to increase storage life by subjecting the Eruits and
veqetables to irradiation. While each of these techniques provides
an improvment over the mere storing of the fruits and vegetables at
ambient temperature, the systems have serious limitations whether
used individually or in combination.
Some fruits such as papaya and manqo and the like cannot be
frozen without destroying the texture and flavour. Furthermore,
without the deactivation of enzymes, ethylene qas is produced and
the flavour and texture of the products deteriorates rapidly, even
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when refrigerated. Radapperation has proven to be the most
effective long range chemical free way of preservin~ food such as
fruit and vegetables. In this proces.s, the fruits and vegetables
are cooked and are then placed in a hermatic sealed container which
is then sterilized by an irradiation process. This process is not
suitable for ~resh fruit or vegetable preservation because the
texture of the flavour is destroyed.
Enzymes are a qroup of proteins found in living plant cells
which catalyze a variety of chemical reactions. Over one thousand
such enzymes have been discovered in fruits and vegetables~ When
fruits and vegetables are harvested, it is normal for senescence to
set in. During this period ethylene ~as is formed within the fruit
or vegetables. This gas triggers the activation of the enzymes,
e.~. breakdown of pectin, protein, etc., which causes a breakdown of
the fruit or vegetables.
Enzymes are deactivated by heat to coa~ulate or denature at
temperatures over 50C.
The freshness, texture and flavour of many fruits and
vegetables will be adversely affected if the fruit or vegetable is
held at the enzyme deactivating temperature beyond a critical dwell
time which varies with different fruits or ve~etables. Generally,
if a fruit or vegetable is heated to a temperature of 90C and is
held at this temperature for ten minutes, the naturally occurring
enzymes will be deactivated.
It is known that fruits and ve~etables can be damaged if
subjected to excessive irradation and consequently it is desirable
to minimize the radiation dosa~e used for the purpose of sterilizing
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fruits and vegetables.
Research and reports from medical authorities .show that
many people are allergic to sulphur dioxide. Sickness and death
have resulted from consumption of sulphur dioxide. Sul~hur dioxide
is used in fruit and vegetable salads, dried fruits, etc. to retain
freshness, colour and to partially preserve.
The present process allows cut fruits and vegetables, e.g.
fresh fruit salad and fresh vegetable salad to be prepared, hold and
eaten without the need to use sulphur dioxide as a preservative.
Summary of Invention
It is an object of the present invention to provide a
process which will substantially increase the storage life of fresh
fruits and vegetables without destroyinq their freshness, texture or
flavour.
Accordinq to one aspect of the present invention, a process
for preserving the freshness, flavour and texture of fresh fruits or
veqetable products comprisinq the steps of heating the fruit or
vegetable product rapidly and uniformly by means of a microwave
heatinq system to a temperature and retaining the product at the
enzyme deactivating temperature for a dwell time sufficient to
deactivate all of the natural enzymes which are present in the
product without cooking the product, and immediately thereafter,
cooling said ~roduct rapidly to a sufficient extent to remove the
enzyme deactivating heat before any cooking of the product can
occur, and to cool the product to a temperature which will inhibit
deterioration of the freshness, flavour and texture thereof and
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shortly thereafter, while the product remains in said cold
condition, packa~ing and hermetically sealing the cooled product in
a container which contains an inert gas, irradiating the packaged
product, using a food sterilizing form of radiation to an extent
sufficient to sterilize the product and prevent the formation of
degenerative qas in the product, without damaqing the product to
thereby provide an enzyme-free, sterile and hermetically packagea
fruit or vegetable product which has its fresh flavour and texture
characteristics substantially unaltered and which can be stored
without deterioration of freshness, flavour or texture for a long
time.
The invention will be more clearly understood after
reference to the following detailed specification read in
conjunction with the drawinqs wherein:
Figure 1 is a diagram illustrating the various steps of the
process of the present invention.
Fruits and vegetables which can be processed by the present
invention include: apples, oranges, grapefruit, lemon, grapes,
peaches, nectarines, olives, cherries, elderberries, avocado, mango,
gooseberries, strawberries, raspberries, boysenberries,
youngherries, bana~as, tomatoes, guava, pineapple, soursop,
jackfruit, broccoli, cauliflower, carrots, peas, potatoes, french
fries, oka, beets, onions and peppers.
Various other fresh fruit and vegetables are capable of
beinq processed hy the present invention and the above list is
intended to be representative rather than limiting.
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DS4-4198-7
Refore a particular type of fruit or vegetable is processed
it is necessary to carry out some preliminery enzymic testing to
determine~ its optimum enzyme deactivating dwell time. The optimum
enzyme deactivatinq dwell time is the maximum time for which a
particular type of fruit or vegetable may be maintained at the
enzyme deactivating temperature without adversely affecting its
freshness, texture and flavour. The temperature of the product
should be controlled by suitable sensor devices to maintain the
product at an even temperature. Samples of the particular fruit or
vegetable which is to be processed should be heated to the required
enzime deactivating temperature and held at this temperature for
various time periods and then subjected to laboratory and taste
tests to determine an appropriate dwell time. Periodic tests should
also be carried out during production runs to ensure the the dwell
time is correct. It is desirable to maximize the enzyme
deactivating dwell time to thereby permit the sterilizing
irradiation dosage to be minimized. If the product is overheated it
will soften or rupture the cell walls of teh product and give the
product a cooked flavour and texture.
As illustrated in Fiqure 1 of the drawings, the fruit or
vegetable products are sorted as soon as possible after harvesting.
The products which contain rot or which are diseased or off-colour,
deformed or irregular in shape or subject to other defects are
rejected. The products are then graded for size or weight and
products of a substantially uniform grade are transferred to a
heating unit which is preferably in the form of a microwave unit.
The products are then subjected to a high speed uniform heating to a
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temperature of approximately 50 to 85 C to deactivate the
enzymes.
Testinq must be carried out in order to determine the
amount of heating required in order to heat a particular fruit or
vegetable product to the required temperature ran~e. In a
particular microwave unit it will be apparent that the amount of
enerqy required to heat products of one grade may be siqnificantly
different from that required to heat products of another grade of
the same product and it is ~or this reason that gradin~ is carried
out before heatin~. Havin~ predetermined the settings required in
the microwave unit to obtain the required heatinq for a particular
grade of a particular product, it is possible to process all of the
product of the particular qrade and then adjust the settings of the
microwave unit when product of a different grade is supplied from
the grader. In order to achieve a uniform heatinq of the fruit or
veqetable product, the product is preferably caused to rotate in the
microwave heating unit. This can be achieved by providing a simple
rotating or tumbling mechanism which will cause the items to be
rotated as they are advanced continuously through the microwave
unit. Screw feeding devices suitable for this type of rotation are
available in many mechanisms in which rotation of a fruit or
vegetable product is required and will not therefor be described.
Mechanisms which will handle cut fruit, fruit salad and the like,
without any loss of juice, are also available.
When the fruit or veqetable product has been heated in a
microwave unit to a temperature of about 50 to 85C, it is removed
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from the microwave unit and is then held at a temperature of about
70C for the appropriate predetermined dwell ~ime. When cut fruit
or cut vegetables are being processed, a predetermined quantity of
the product is placed in a container to ensure that co~plete
deactivation of the enzyme and complete cooling is achieved.By
ensuring that the fruit or vegetable product is held at the
appropriate enzyme deactivating temperature ~or the appropriate
dwell time complete deactivation of the enzymes is achieved.
Immediately after enzyme deactivation, the product is submerged in
cold water at a temperature of about 1 to 5 C and cooled to the
water temperature of about 1 to 5C and is retained in this body of
water at this temperature for about thirty minutes.
In the case of cut fruits and vegetables, care must be
taken to prevent water absorption into the product.
Cooling is preferably carried out by immediately submerging
the fruit or vegetable products in cold water. The cooling water is
preferably agitated to obtain rapid cooling. When the fruit or
vegetable products are cooled to a substantially uniform temperature
of about 1C, it is then removed from the cooling water and without
allowing it to be reheated, it is then packaged in a hermetic sealed
inert ~as filled Package. The packages in which the product is
sealed may contain an ethylene absorbing chemical. After cooling,
the fruit or vegetable product may be dried before packa~ing.
Alternatively, the fruit or vegetable product may be packaged with
some water remaining therein. In either case, the fruit or
vegetable product is packaged before it is allowed to warm up to any
siqnificant extent from the temperature achieved in the coolinq
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stage. The package which is used is preferably in a form suitable
for use in subsequent display of the fruit or vegetable product for
sale. It is important to note that the packaging must be capable of
providing a hermatic seal which will not permit air, water,
bacteria, yeast, mold, or the like, to enter the package.
Furthermore, the packaging material must be selected to ensure that
it will not deteriorate under normal storage conditions. In
addition, a blanket of nitrogen, carbon dioxide or any food approved
inert gas may be provided in the package to ~urther inhibit
deterioration during storaqe. Oxygen in the air causes oxidatior of
many natural chemicals within the fruits and vegetables and for this
reason air must be replaced by an inert gas.
The packaged fruit or vegetable products are then
irradiated in an irradiation chamber of an irradiation device. The
radiation dosage will vary depending upon the type of fruit or
vegetable product which is to he processed. I have found that when
using gamma wave radiation a dosage higher than 0.85 kgy. tends to
damage to centain fruit. In addition in fruit/vegetables such as
onions and garlic, internal discolouration (browning) takes place in
the growth zones.
Any one of the microwave heating ovens which are presently
available on the market may be used to heat the fruit or vegetable
products. A suitable gamma wave food irradiation unit is
manufactured by Atomic Energy of Canada ~td. and is identified by
Model No. Js-8~00. Many other suitable units are available from
other sources.
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A 1965 report issued by the surgeon general oE the U.S.A.
army indicates that foods irradiated up to absorbed doses of 5.6 KGY
with a cobalt 60 source of gamma irradiation or with electrons with
enerqies up to 10 million electron volts have been found to be
wholesome, i.e. safe and nutritionally adequate. In November, 1980
in Geneva the ~oint FAO/IAEA/Who expert committee on wholesomeness
of Irradiated Foods concluded that the irradiation of any food
commodity, up to overall, average dose of 10 KGY presents no
toxicological hazard; hence toxicological testing of ~oods so
treated is no lon~er reauired. Irradiation of foods up to an
overall average dose of 10 KGY introduces no special nutritional or
microbiological problems.
EXAMPLE 1
An apple wei~hing lfi5.4 grams taken from cold stora~e at
4.5 C (40 F) was placed in a microwave unit. The microwave was
activated to emitt 750 watts for 95 seconds and as a result the
apple was heated to an interior temperature of 71.1 C.
The apple was then submerged in a body of water which is at
a temperature o~ 70 C and it is held in the water to ensure that
it remains at a temperature of 70C about two minutes to ensure
complete deactivation of the enzymes. The apple was then removed
from this body of water and is immediatly submerged in cold water at
a temperature of about 1~1 C and is retained in this body of water
for about thirty minutes. The internal temperature of the apple was
as a result cooled to a temperature of about 3.6 C.
After removal from the water the apple was placed in a
plastic ba~. The bag was then flushed with nitrogen gas. The ba~
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was then sealed and the ba~ and its contellts were then irradiated
with 0.70 KGY.
After irradiation the bag and its contents were stored at
room temperature.
EXAMPLE 2
A tomato weiqhing 153.9 grams was used instead of an
apple. The initial temperature to of the tomato was 4.5 C.
The tomato was heated to 71.1 C for 93 seconds as in
Example 1. All other treatment was the same as ~or the apple in
Example 1.
EXAMPLE 3
A pepper (red bell) weighing 200.4 grams was used instead
of an apple. The initial temperature of the pepper was 4.5C.
The pepper was heated to 71.1C (160F) for 115 seconds in
the microwave as in Example ]. All other treatments and results
were the same as for the apple in Example 1.
Example 4
Cut chilled (4.5C - 40F) fruit salad (1/2" cut)
consisting of melon, pineapple, apple, peaches, weighing 165.0 grams
was placed in a glass beaker size 42 mm x 90 mm and placed in a
microwave unit.
The microwave unit was activated to emitt 750 watts for 96
seconds. The fruit salad had an interior temperature of 72.0C
(162F).
The beaker was removed from the microwave unit and held for
about 2 minutes.
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The beaker and contents were placed in cold water (not to
allow water to enter the top of the beaker) for 35 minutes where it
reached a temperature of 4.0C (39F.).
The fruit salad was placed into a hermetic sealed plastic
container, flushed with nitrogen qas and sealed.
The package was irradiated with 0.7 KGY.
After irradiation the package and its contents were stored
at room temperature.
After storing the products produced in Examples 1 to 4 at
room temperature for , the packayes were opened and the
products were found to have retained most, if not all of their
original freshness, flavour and texture.
Example 5
Example 4 was duplicated but neither heating nor enzyme
deactivation was done.
The 165 qrams o fruit salad was placed in a hermetic
sealed plastic container and flushed with nitrogen gas and sealed.
The package was irradiated with 1.2 KGY hefore complete
sterility (as compared to 0.7 KGY with microwave). Further the
enzymes were not deactivated. The product did not have the
freshness, flavour or texture of the original fruit.
Combined microwave and irradiation have a synergistic
effect on sterilization requiring less irradiation doseage.
