U.S. patent application number 12/601920 was filed with the patent office on 2010-07-15 for packaged food products.
This patent application is currently assigned to Mars Incorporated. Invention is credited to Annica Bonna, Martijn Johannes Maria De Vries, Paul Alois Maria Otten, Cornelius Jan Van Appeldoorn, Marcel Christian Anthony Velthuis.
Application Number | 20100178401 12/601920 |
Document ID | / |
Family ID | 38289471 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178401 |
Kind Code |
A1 |
Van Appeldoorn; Cornelius Jan ;
et al. |
July 15, 2010 |
PACKAGED FOOD PRODUCTS
Abstract
A method for the production of a stabilized packaged food
product includes the steps of: filling a tray with a predetermined
quantity of a food starting material; introducing the tray into a
pressure vessel and conveying the tray through the pressure vessel
while performing the following steps in sequence inside the
pressure vessel: (i) treating the food starting material with
high-temperature pressurized steam to sterilize the material, (ii)
dosing the sterile food material inside the tray with a
predetermined amount of sterile water; and (iii) applying a lid to
the tray to seal the food product inside the tray while maintaining
the tray in a sterile environment. Also provided are an apparatus
for performing the method and packaged stabilized full moisture
food products obtainable by the process.
Inventors: |
Van Appeldoorn; Cornelius Jan;
(Oud Beijerland, NL) ; Otten; Paul Alois Maria;
(Olen, BE) ; Bonna; Annica; (Oud Beijerland,
NL) ; De Vries; Martijn Johannes Maria; (Oud
Beijerland, NL) ; Velthuis; Marcel Christian Anthony;
(Oud Beijerland, NL) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
1301 MCKINNEY, SUITE 5100
HOUSTON
TX
77010-3095
US
|
Assignee: |
Mars Incorporated
McLean
VA
|
Family ID: |
38289471 |
Appl. No.: |
12/601920 |
Filed: |
May 29, 2008 |
PCT Filed: |
May 29, 2008 |
PCT NO: |
PCT/IB2008/002120 |
371 Date: |
February 2, 2010 |
Current U.S.
Class: |
426/392 ;
53/284.5; 53/432; 53/471 |
Current CPC
Class: |
B65B 55/18 20130101;
A23V 2002/00 20130101; B65D 81/3453 20130101; A23L 3/04 20130101;
B65B 7/28 20130101; B65B 25/04 20130101; B65B 25/062 20130101; A23L
3/0155 20130101; B65B 55/10 20130101; B65B 31/028 20130101; B65B
25/22 20130101; B65B 55/025 20130101; B65B 25/065 20130101; B65B
29/08 20130101; B65B 25/001 20130101 |
Class at
Publication: |
426/392 ;
53/284.5; 53/432; 53/471 |
International
Class: |
A23L 3/02 20060101
A23L003/02; B65B 61/00 20060101 B65B061/00; B65B 31/04 20060101
B65B031/04; B65B 7/28 20060101 B65B007/28 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2007 |
GB |
0710228.8 |
Aug 9, 2007 |
GB |
0715579.9 |
Jan 21, 2008 |
GB |
0801052.2 |
Claims
1. A method for the production of a stabilized packaged food
product comprising the steps of: filling a tray with a
predetermined quantity of a food starting material; introducing the
tray into a pressure vessel and conveying the tray through the
pressure vessel while performing the following steps in sequence
inside the pressure vessel: (i) treating the food starting material
with high-temperature pressurized steam to sterilize the material,
(ii) dosing the sterile food material inside said tray with a
predetermined amount of sterile water; and (iii) applying a lid to
the tray to seal the food product inside the tray while maintaining
the tray in a sterile environment.
2. The method according to claim 1, wherein the food starting
material comprises one or more starchy food pieces having a
moisture content of less than about 30 wt. %.
3. The method according to claim 1, wherein the food starting
material is selected from the group consisting of cooked fruit or
vegetable pieces, uncooked fruit or vegetable pieces, nuts, spices,
mushroom pieces, salad pieces, herb pieces, meat and fish.
4. The method according to claim 1, wherein the food starting
material is sterilized by treatment with steam in said pressure
vessel at a temperature of from about 125.degree. C. to about
150.degree. C.
5. The method according to claim 1, wherein the step of dosing the
sterile food material with sterile water is initiated while the
temperature of the food material is from about 125.degree. C. to
about 150.degree. C.
6. The method according to claim 1, wherein the step of applying
the lid to the tray to seal the food product inside the tray is
performed in a pressurized sealing chamber in sterile communication
with the rest of the pressure vessel.
7. The method according to claim 1, wherein the step of applying
the lid to the tray to seal the food product inside the tray is
performed not more than about 3 minutes after said step of
dosing.
8. The method according to claim 1, wherein the total residence
time of each said tray inside the pressure vessel is from about 30
seconds to about 5 minutes.
9. The method according to claim 1, further including the step of
removing the packaged food product from the pressure vessel wherein
no post-processing of the packaged food product is required.
10. The method according to claim 1, wherein at least a major
portion by weight of the food starting material is not subjected to
a soaking or wetting step prior to introduction of the material
into the pressure vessel.
11. An apparatus for the production of a stabilized packaged food
product comprising: a filling device for filling individual trays
with a predetermined amount of a food starting material; a pressure
vessel having an inlet pressure lock and an outlet pressure lock
for transferring said trays into and out of the pressure vessel; a
means of supplying pressurized steam for sterilizing the food
starting material in said trays in a first zone of the pressure
vessel; a means of supplying sterile water and a dosing pump for
dosing a predetermined amount of sterile water into each of said
trays in a second zone of the pressure vessel to achieve a desired
full moisture food product in the trays; and a sealing device
located in said pressure vessel for sealing the trays following
said step of dosing.
12. The apparatus according to claim 11, wherein the pressure
vessel is divided into two or more chambers, separated by pressure
locks.
13. (canceled)
14. A method for the production of a stabilized packaged food
product comprising the steps of: filling a tray with a
predetermined quantity of a food starting material, followed by
performing the following steps in sequence while maintaining the
tray in a sterile environment: (a) treating the food starting
material with high-temperature pressurized steam in a pressure
vessel to sterilize the material; (b) dosing the sterile food
material inside said tray with a predetermined amount of sterile
water; and (c) applying a lid to the tray to seal the food product
inside the tray; removing the tray from the sterile environment,
wherein the duration of the process from the start of step (a) to
the completion of step (c) is less than about 10 minutes.
15. A method for the production of a stabilized packaged food
product comprising the steps of: filling a tray with a
predetermined quantity of a food starting material, followed by
performing the following steps in sequence while maintaining the
tray in a sterile environment: (a) treating the food starting
material with high-temperature pressurized steam in a pressure
vessel to sterilize the material; (b) dosing the sterile food
material inside said tray with a predetermined amount of sterile
water; and (c) applying a lid to the tray to seal the food product
inside the tray; removing the tray from the sterile environment,
wherein the food material is not subjected to a cooking step
subsequent to step (b).
16. A method for the production of a stabilized packaged food
product comprising the steps of: filling a tray with a
predetermined quantity of a food starting material, followed by
performing the following steps in sequence while maintaining the
tray in a sterile environment: (a) treating the food starting
material with high-temperature pressurized steam in a pressure
vessel to sterilize the material; (b) dosing the sterile food
material inside said tray with a predetermined amount of sterile
water; and (c) applying a lid to the tray to seal the food product
inside the tray; removing the tray from the sterile environment,
wherein at least a major portion by weight of the food material is
not subjected to a wetting or soaking step prior to step (a).
17. The method of claim 7, wherein the step of applying the lid to
the tray to seal the food product inside the tray is performed not
more than about 2 minutes after said step of dosing,
18. The method of claim 17, wherein the step of applying the lid to
the tray to seal the food product inside the tray is performed not
more than about 1 minute after said step of dosing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national stage filing of
PCT/IB2008/002120 filed May 29, 2008 claiming priority to GB
0710228.8 filed on May 29, 2007; GB 0715579.9 filed on Aug. 9,
2007; and GB 0801052.2 filed on Jan. 21, 2008.
TECHNICAL FIELD
[0002] The present invention relates to stabilized, packaged, full
moisture food products and to methods and apparatus for the
preparation thereof. It relates in particular to stabilized,
packaged, full-moisture food products containing cereals such as
rice, wheat or pasta, and/or other ingredients such as vegetables
and meat.
BACKGROUND OF THE INVENTION
[0003] It is known to provide packaged, full-moisture precooked
food products, such as soups, stews, and rice, pasta or wheat
(bulgur) products that can be reheated in a short time, for example
in a microwave oven. These products are sometimes referred to as
"ready-to-heat" or "one-minute" products.
[0004] The high moisture content of these ready-to-heat products
requires special steps to be taken in order to render them
sufficiently stable for storage and distribution through
conventional retail channels.
[0005] U.S. Pat. No. 4,986,995 describes a process for the
preparation of shelf-stable rice. The process includes soaking dry
rice in water at 20.degree. C., introducing the rice into a
container such as a pouch together with sufficient water to hydrate
the rice to a full moisture product, sealing the pouch with a
restricted amount of oxygen in the pouch, and then cooking and
sterilizing the rice in the pouch by heating in an autoclave to a
temperature of at least 121.degree. C. The resulting shelf-stable
rice product can be microwave-heated in the pouch before serving.
Unfortunately, the time-temperature-moisture conditions required to
achieve sterility cause some chemical modification of the food
starch, resulting in a tendency of the full-moisture sterile
product to agglomerate over time. As a result of this agglomeration
the rice does not have the optimum freshly-cooked texture and
free-flowing properties. Furthermore, the autoclave cooking within
the sealed pouch can result in some undesirable aroma of the
product, especially when the pack is first opened.
[0006] EP-A-0602953 describes shelf-stable microwaveable pouches
containing full moisture precooked rice. The rice has been
acidified by the addition of enough edible acid to lower its pH to
a range of 3.5 to 4.6. This enables a shelf-stable product to be
achieved by heat treatment at lower temperatures than are needed
for a non-acidified product, resulting in improved texture and flow
properties compared to the autoclaved rice products. Further
acid-stabilized rice products are described in U.S. Pat. No.
5,702,745 and EP-A-1338209. Unfortunately, the addition of an
edible acid to the rice gives rise to acid flavor notes that reduce
consumer acceptability of the product. EP-A-0322996 teaches to
overcome this problem by packaging the stabilized rice with a
neutralising agent that can be mixed with the rice immediately
before consumption.
[0007] EP-A-0691082 describes a plant for the production of
packaged, stabilized, ready-to-heat cooked meals such as pasta. The
plant comprises an autoclave body defining a food-processing
chamber having a conveyor therein for conveying open trays
containing a food product from an inlet end of the autoclave to an
outlet end thereof. The autoclave comprises, in succession, between
the inlet and outlet ends: a) a first region which includes means
for dispensing steam for the heat stabilisation and/or
sterilisation of the food and of the open trays, b) a second region
which includes a spray for delivering boiling water for cooking the
food in the respective trays, c) a straining region which includes
a device for inverting the trays for removing the excess cooking
liquid from the cooked food while retaining the cooked food in the
respective containers. The system includes a sealing assembly for
hermetically sealing the trays. The sealing assembly is located in
a sterile environment communicating with the sterile cooking
chamber.
[0008] U.S. Pat. No. 5,860,356 describes a system for providing a
sterile, full-moisture packaged rice product. The system includes a
rice filling device that fills individual trays with a
predetermined quantity of washed and soaked rice. The trays are
then conveyed through a sterilization chamber that substantially
air-tightly contains one or more of arrays of the trays for
sterilizing the rice with high-temperature pressurized steam
introduced into the chamber. The trays are then transferred to a
steaming chamber separate from the sterilization chamber and at
ambient pressure, where a water filling device fills the trays
containing the sterilized rice with a predetermined quantity of
water necessary for steam rice-cooking, and the rice is cooked with
steam for a suitable period, for example 30 minutes. The trays
containing the cooked rice are then conveyed to a sealing device in
a clean booth that applies an air-tight lid to the trays containing
the cooked rice. Since the clean booth does not completely prevent
contamination of the rice before sealing, the packaged products are
subjected to a final steaming step to achieve the desired rice
quality and stability. Processes of this type are also described in
US-A-20040219267.
[0009] The overall processes of EP-A-0691082 and U.S. Pat. No.
5,860,356 are capital intensive because of the multiple process
steps. The total time/temperature/moisture exposure of the products
is considerable, and in the case of starchy products these
processes can result in products that are sticky, not free-flowing,
and not ideal texture.
BRIEF SUMMARY OF THE INVENTION
[0010] In a first aspect, the present invention provides a method
for the production of a stabilized packaged food product comprising
the steps of: filling a tray with a predetermined quantity of a
food starting material; introducing the tray into a pressure vessel
and conveying the tray through the pressure vessel while performing
the following steps in sequence inside the pressure vessel: (i)
treating the food starting material with high-temperature
pressurized steam to sterilize the material, and (ii) dosing the
sterile food material inside said tray with a predetermined amount
of sterile water; and (iii) applying a lid to the tray to seal the
food product inside the tray while maintaining the tray in a
sterile environment.
[0011] The feature of steam sterilizing and water dosing the food
product sequentially under sterile steam conditions, followed
promptly by sealing the trays under sterile conditions in the steam
pressure vessel, provides a very rapid route to commercially
sterile products with minimum capital assets. It has been found
that extended cooking of the food product following the dosing step
is not needed in order to achieve a stable, full moisture,
ready-to-heat product. Further advantages of the process are
discussed below.
[0012] The initial step of the process comprises filling trays with
a predetermined quantity of food starting material. The trays may
be formed of any suitable material that is sufficiently heat
resistant to keep its shape in the subsequent steps of the process.
Thermoformed polypropylene (PP), polyethylene terephthalate (PET)
or CPET trays may be suitable, preferably with an ethylene vinyl
alcohol (EVOH) oxygen barrier layer. For example a PP-EVOH-PP
laminate may be suitable, with the PP selected to provide the
necessary heat resistance at 135.degree. C. The laminate thickness
is suitably from about 0.8 mm to about 1.5 mm, for example about 1
mm to about 1.2 mm. The tray suitably has a bottom, straight or
tapered side walls, and a flange (lip) at the top for sealing. The
bottom and/or the side walls may be profiled in various ways for
decorative or structural reasons. In certain embodiments, the tray
may be substantially in the shape of a bowl to assist consumption
of the food product directly from the tray. Metal foil or
metal/polymer laminate trays could also be used, but are not so
suitable for subsequent microwave reheating of the food product
before consumption. The tray may include metallised susceptor
regions to provide localized heating in a microwave oven.
[0013] The depth of the tray and quantity of starting material are
normally selected so as to produce a substantially filled tray when
hydration of the contents is complete. The starting material is
filled into the trays in a layer (bed) that is preferably not more
than about 3 cm deep, for example from about 0.2 to about 2 cm
deep. A uniform bed of food product is desirable, and accordingly
the bed height is preferably equalized before performing subsequent
steps of the process.
[0014] The food starting material in the processes of the present
invention may be any dry or wet solid food material. The process is
applicable to both human foods and animal (pet) foodstuffs. The
overall moisture content of the starting material is suitably less
than the overall moisture content in the packaged product, but in
certain embodiments a full moisture starting material or materials
may be used. For example, the food starting material may comprise
partially or completely dehydrated food ingredients such as
freeze-dried meat or vegetable ingredients, or dehydrated milk or
sauce components.
[0015] The food starting material may alternatively or additionally
comprise cooked or uncooked fruit or vegetable pieces, mushroom
pieces, nuts, salad pieces, herb pieces, whole herbs such as
cloves, anise or cardamom, meat or fish. The starting material
pieces may be chilled or even frozen. Suitably, vegetable starting
materials (including potato) are substantially full-moisture. In
certain embodiments, the food starting material consists of solid
soup components, such as meat, vegetable and/or cereal pieces. In
these embodiments, a larger amount of sterile liquid is dosed in
the dosing step of the process to result in a sterile, liquid soup
or sterile soup concentrate containing the solid pieces. It is an
advantage of the present process that the relatively brief heat
treatment to which the products are subjected causes relatively
little deterioration of the appearance and texture of fresh food
pieces compared to a conventional autoclaving process.
[0016] In certain embodiments, the food starting material comprises
or consists essentially of at least one dry starchy component, such
as rice, wheat, pulses (e.g. beans or lentils), or pasta pieces. In
certain embodiments, at least 10% by weight of the food starting
material is made up of such starchy components, suitably at least
about 50% thereof, for example 90% or more of the food starting
material is made up of such starchy components. The remainder of
the material may be made up of sauce components and vegetable, meat
or fish components as described. Typically, the non-starchy
components are deposited on a bed of the starchy component in the
tray.
[0017] The term "dry starchy component" refers to a starchy food
starting material having a moisture content below the full moisture
content for consumption of starchy food materials of that type.
Suitably, the dry starchy component has a moisture content less
than about 30 wt %, for example less than about 20 wt. %, suitably
less than about 16 wt. %. The dry starchy material typically has a
moisture content of about 10-15%, whereby it is storage-stable. The
starting material may comprise whole or comminuted food grains such
as rice or wheat grains, couscous, bulgur, or pulses such as beans
or lentils. The food grains may be fully milled (white), or they
may have part or all of the bran layer still attached. The grains
may suitably be parboiled. In certain embodiments, the starting
material may comprise or consist essentially of dried pasta pieces.
In other embodiments, the starting material comprises or consists
essentially of dry, milled, parboiled rice having a moisture
content of about 10% to about 15%. Long-grain rice, basmati rice,
Thai rice, wild rice and Arborio rice are all suitable for the
process of the present invention.
[0018] It is an advantage of the present invention that the food
starting material generally does not require soaking or wetting
before introduction into the pressure vessel. Indeed, at least a
major portion by weight of the starting material is generally not
soaked or wetted before introduction into the pressure vessel,
since the sterilization step is preferably carried out on a dry
product in order to minimize heating time, and to minimize thermal
damage to the food components such as starch. This is a
simplification over the process described in U.S. Pat. No.
5,860,356.
[0019] The trays containing the food starting material are
introduced into a pressure vessel, for example through a suitable
pressure lock. Preferably the pressure lock permits continuous
feeding of the trays to the pressure vessel. Exemplary pressure
locks and tray conveyors are described in EP-A-0691082.
[0020] The pressure vessel may consist of a single pressure
chamber, or it may comprise two, three or more pressure chambers
separated by pressure locks. The use of multiple pressure chambers
to form the pressure vessel enables process parameters to be
controlled further by varying the steam pressure and temperature
between the chambers. In addition, it allows individual pressure
chambers to be isolated for cleaning or maintenance. The pressure
vessel (or chamber thereof) is suitably in the form of a tube
having a conveyor therein for conveying the trays along the tube.
The diameter of the tube is typically about 30 cm to about 100 cm,
for example about 50 cm. The total length of the pressure vessel
(i.e. the sum of the lengths of the pressure chambers) is typically
about 10 m to about 50 m, for example about 15 m to about 40 m. The
pressure vessel is thermally insulated to minimise heat loss and
steam condensation within the vessel. The pressure vessel is
pressurized with steam, optionally mixed with other gases. The
steam may be saturated or superheated. The steam temperature is
suitably from about 100.degree. C. to about 160.degree. C.,
preferably from about 125.degree. C. to about 150.degree. C., for
example about 135.degree. C. The temperature inside the pressure
vessel (or each chamber thereof) is thereby maintained
substantially at the steam temperature. Suitably, the gauge
pressure in the pressure vessel (or each chamber thereof) is from
about 0.05 MPa to about 1.0 MPa, preferably from about 0.1 MPa to
about 0.5 MPa, for example about 0.3 MPa to about 0.4 MPa. The
temperatures and pressures in each chamber of the pressure vessel
may be the same or different within the above ranges.
[0021] The steam is may be injected through suitable nozzles. In
certain embodiments, the steam impinges directly onto the top
surface of the food bed as the trays move through the tube. In
other embodiments, the steam in injected below and/or laterally to
the trays. Steam injection may be intermittent or continuous.
Improved energy efficiency is achieved by using intermittent
injection of (preferably saturated) steam, preferably with forced
flow inside the pressure vessel to circulate the steam. The forced
flow can be achieved, for example, by providing fans within the
vessel. The high temperature of the steam causes the core
temperature of the food to rise quickly to a value sufficient to
cause rapid sterilization. Uptake of water by the food in this
stage of the process is minimal. Typically, with steam at about
135.degree. C., trays containing only rice or wheat are exposed to
the steam for a period of from about 20 seconds to about 1 minute,
for example about 20 seconds to about 1 minute. Longer steam
sterilization, typically about 3 to about 4 minutes, is needed if
the trays contain larger pieces, such as vegetable pieces, meat
pieces, or large pasta pieces, or if lower steam temperatures are
used. The duration of the steam sterilization step is typically
regulated by moving the location of the water dosing point in the
pressure tube, as described further below. Alternatively or
additionally, the duration of the steam sterilization step may be
regulated by varying the speed of the conveyor.
[0022] The sterilization time and temperature are suitably selected
to provide a reduction of 12D (i.e. 12 orders of magnitude) of the
population of the microorganism clostridium botulinum. The minimum
lethality factor F.sub.o (equivalent to number of minutes of
treatment at 121.1.degree. C.) needed to achieve 12D reduction is
2.4 minutes. In practice, a higher lethality factor, generally of
at least about 3, for example about 5, is applied in order to
provide a safety margin and optionally to inactivate other, more
resistant spores, such as B. Stearothermophilus.
[0023] It is an advantage of the present invention that the
sterilization step may be performed on the food while the food is
still dry. This avoids many of the problems caused by prior art
processes in which the sterilization temperatures are applied to
hydrated cereal grains, or to cereal grains in contact with liquid
water. In particular, the present invention results in a more
free-flowing final product exhibiting less damage to the starch
structure, for example exhibiting less de-retrogradation of the
starch and less extrusion of soluble starches from the product
grains. Furthermore, the time required to heat the food particles
to sterilization temperatures is greatly reduced, thereby further
reducing the process time and damage to the starch and other
ingredients as compared to prior art processes.
[0024] The food product in the trays is conveyed from the steam
sterilization zone of the pressure vessel to a dosing station (or
separate dosing chamber) inside the pressure vessel, where a
predetermined amount of liquid water is dosed into each tray. The
pressure and temperature conditions at the dosing station are
suitably within the ranges specified above for the steam
sterilization step, but need not be the same as those in the steam
sterilization step. In particular, the water dosing may be
performed in a chamber that is maintained at a low overpressure
(e.g. about 0.01-0.3 bar) to maintain sterility. The liquid water
is sterile, and is dosed by means of a suitable pump at a
temperature suitably of from about 5.degree. C. to about
150.degree. C., preferably about 25.degree. C. to about 99.degree.
C.
[0025] The term "liquid water" refers to a sterile aqueous liquid.
The liquid may further comprise additives, such as herbs, salt,
flavorings, nutrients, acidulents, edible oil and/or edible fat.
For example, the liquid may comprise or consist of a stock, a
bouillon or a soup base. It will be appreciated that the water
supply to the dosing nozzles is normally intermittent, so that
water is supplied only to the trays in the specified amount and no
water is wasted. The duration of the water dosing step is short.
Suitably, the liquid water dosing step takes less than about 60
seconds, for example less than about 20 seconds, and typically less
than about 10 seconds, for example from about 1 to about 5 seconds.
There may be more than one water dosing step, optionally separated
by re-heat steps, especially when a substantial amount of water
must be dosed, for example in the preparation of soup products.
[0026] It is a feature of the present invention that the water is
dosed in an amount that is just sufficient to provide a product
having the desired final moisture content, i.e. typically about 50
to about 75% moisture for food grains and pasta. There is
substantially no addition or loss of water from the product after
the dosing step, other than a small amount of condensation from
steam in the pressure vessel. This eliminates any need to invert
the trays in order to drain off excess water. The amount of water
dosed is typically from about 0.01 to about 5 g of water per gram
of food starting material, for example about 0.01 to 3.5 g/g for
rice, and 0.01 to 4 g/g for pasta and couscous. A substantially
larger amount of water is dosed for soup products. The measured
dosing of water inside the pressure vessel provides a number of
advantages over the process of EP-A-0691082, in which the trays are
simply sprayed with excess boiling water. These advantages include
reduced energy consumption, reduced waste water, reduced loss of
nutrients, and reduced capital cost as it is no longer necessary to
provide a mechanism to drain the excess water from the product.
Likewise, the process of the present invention eliminates the need
for a separate steaming chamber and prolonged cooking step as
described in U.S. Pat. No. 5,860,356. The present inventors have
made the surprising finding that simply dosing the precise amount
of water required onto the hot food product, followed directly by
sealing under sterile conditions, results in an excellent, stable,
full-moisture product after a suitable period for moisture
equilibration of the product at ambient or moderately elevated
temperature, as explained further below.
[0027] Suitably, directly following the sealing step, the product
cooled to a temperature less than about 100.degree. C., is
transferred to atmospheric pressure and stored in an environment
maintained at less than about 80.degree. C., for example about
25.degree.-80.degree. C., and tempered at this temperature for a
period of from about 20 minutes to about 4 hours, for example about
30 minutes to about 150 minutes, to achieve the desired product
characteristics. Suitable long-grain rice tempering conditions are
30 minutes in an environment maintained at 55.degree. C. followed
by 15 minutes in an environment maintained at 45.degree. C.
Suitable basmati rice tempering conditions are 30 minutes in an
environment maintained at 75.degree. C., followed by 30 minutes in
an environment maintained at 45.degree. C. In certain embodiments,
tempering may be achieved by stacking the trays and allowing them
to cool to ambient temperature over a period of at least about 1
hour, for example 3-4 hours. Certain embodiments, such as soups, do
not require any tempering.
[0028] Suitably, the temperature of the food bed is at least about
120.degree. C., for example from about 125.degree. C. to about
150.degree. C. immediately before the water is dosed. As noted
above, it is an advantage of the present invention that an extended
cooking step is not needed in order to achieve complete hydration
of the food. Suitably, the interval between the water dosing and
sealing of the trays is less about 2 minutes, preferably less than
about 1 minute, and more preferably less than about 30 seconds
Likewise, the interval between the liquid water dosing and removal
of the trays from the pressure vessel is suitably less than about 2
minutes, preferably less than about 1 minute, and still more
preferably less than about 30 seconds.
[0029] The food product immediately following the dosing and
sealing steps may not be ready to consume, since not all of the
water may be absorbed instantly and the water distribution in the
food pieces is not initially uniform. Nevertheless, it has been
found that the moisture distribution in the food pieces (such as
rice grains) becomes uniform within a few hours at ambient
temperature, or after tempering as described above, to give a
highly satisfactory product.
[0030] The trays containing the hydrated food are sealed by
application of a lid to the trays while maintaining the trays in
the sterile environment of the pressure vessel (or separate sealing
chamber thereof) following the dosing step(s) and any optional
reheat step(s) following the dosing step(s). The lid is suitably
formed of a film or foil sheet that is stable at the temperature
inside the pressure vessel. The cover sheet (lid) may be formed of
a suitable heat-resistant laminate comprising a sealing layer such
as PP and a barrier layer such as EVOH. The thickness of the cover
sheet is suitably from about 50 .mu.m to about 250 .mu.m, for
example from about 100 .mu.m to about 150 .mu.m. The trays are
suitably maintained continuously in a sterile environment between
the dosing step and completion of the sealing step in an atmosphere
of steam at a temperature and pressure within the ranges specified
above for the steam sterilization and dosing steps. This ensures
that sealing is performed under fully sterile conditions, thereby
eliminating the need for subsequent heat treatment steps to achieve
a shelf stable product.
[0031] In certain embodiments, the film or foil sheet is fed
continuously (as a continuous strip) into the pressure vessel
through a suitable pressure lock. The pressure lock may, for
example, comprise a series of rollers or belts between which the
sheet is pinched, whereby the pressure applied across the sheet at
any point does not cause permanent compression of the sheet. The
film or foil sheet may be releasably laminated to a continuous
support strip (e.g. a release-coated paper) to provide the
necessary tensile strength after sealing for the residue of the
film or foil sheet to be wound up. The support strip also enables
the continuous film or foil sheet to be die-cut with appropriate
lid shapes before feeding to the pressure vessel. In other
embodiments, pre-cut film or foil lids are fed to the sealing
apparatus inside the pressure vessel.
[0032] The temperature inside the pressure vessel is sufficient to
sterilize the lid before it is applied. The lid can be attached to
the tray in airtight fashion by means of ultrasonic or thermal
sealing. Ultrasonic converters suitable for sealing trays inside
sterile enclosures are described, for example, in WO96/09932.
[0033] In any event, the hydrated food product inside the trays
preferably exits from the pressure vessel at a temperature
sufficiently low to avoid the risk that steam pressure inside the
sealed package could cause the package to burst. For example, the
food product may return to ambient pressure at a temperature less
than about 110.degree. C., suitably about 100.degree. C. or less.
For this purpose, the outlet pressure lock may comprise a cooling
stage.
[0034] An important advantage of the processes according to the
present invention is the short processing time. The total residence
time of the trays in the pressure vessel is typically from about 20
seconds to about 6 minutes, for example from about 30 seconds to
about 4 minutes. The total treatment time of the trays from entry
into the pressure vessel to exit of the sealed trays from the
pressure vessel (or the sealing chamber, when sealing is performed
in a separate chamber) to the ambient atmosphere is typically from
about 20 seconds to about 6 minutes, for example from about 30
seconds to about 5 minutes. The total treatment time depends
primarily on the recipe. The processing time for plain rice
products is at the low end of the above ranges. The processing time
for more complex recipes containing vegetable pieces is at the long
end of the above ranges.
[0035] For example, a typical protocol for the preparation of a
sterile full-moisture rice product from parboiled long-grain rice
comprises steam sterilization for 24 seconds (excluding a few
seconds for in-feed and out-feed time), followed by dosing (about 2
seconds). In some cases, e.g. for basmati rice, the dosed rice is
held for a further 30 seconds in the pressure vessel to heat up the
mixture of liquid and solids prior to sealing.
[0036] No pre-processing of the food by soaking or wetting is
required for most ingredients (pulses and mushrooms may benefit
from a preliminary soak). No post-processing of the packaged
product by steaming or cooking at environmental temperatures above
about 80.degree. C. is normally required. As well as giving a less
thermally degraded product, the present high-speed process requires
less capital for equipment than most previous processes, and less
energy. It can be seen that a further advantage of the process
according to the present invention is that it generates only
minimal quantities of waste water. A further advantage of the
present process is that it is a robust aseptic process that
normally does not require the use of a clean room or booth.
[0037] Accordingly, in a further aspect, the present invention
provides a method for the production of a stabilized packaged food
product comprising the steps of: filling a tray with a
predetermined quantity of a food starting material, followed by
performing the following steps in sequence while maintaining the
tray in a sterile environment: (a) treating the food starting
material with high-temperature pressurized steam in a pressure
vessel to sterilize the material; (b) dosing the sterile food
material inside said tray with a predetermined amount of sterile
water; and (c) applying a lid to the tray to seal the food product
inside the tray; followed by removing the tray from the sterile
environment, wherein the residence time of the tray in the sterile
environment is less than about 10 minutes. Suitably, the residence
time is less than about 6 minutes, for example from about 20
seconds to about 6 minutes, typically from about 30 seconds to
about 5 minutes.
[0038] In a further aspect, the present invention provides a method
for the production of a stabilized packaged food product comprising
the steps of: filling a tray with a predetermined quantity of a
food starting material, followed by performing the following steps
in sequence while maintaining the tray in a sterile environment:
(a) treating the food starting material with high-temperature
pressurized steam in a pressure vessel to sterilize the material;
(b) dosing the sterile food material inside said tray with a
predetermined amount of sterile water; and (c) applying a lid to
the tray to seal the food product inside the tray; followed by
removing the tray from the sterile environment, wherein the
duration of the process from the start of step (a) to the
completion of step (c) is less than about 10 minutes. Suitably,
said duration is less than about 6 minutes, for example from about
20 seconds to about 6 minutes, typically from about 30 seconds to
about 5 minutes.
[0039] In a further aspect, the present invention provides a method
for the production of a stabilized packaged food product comprising
the steps of: filling a tray with a predetermined quantity of a
food starting material, followed by performing the following steps
in sequence while maintaining the tray in a sterile environment:
(a) treating the food starting material with high-temperature
pressurized steam in a pressure vessel to sterilize the material;
(b) dosing the sterile food material inside said tray with a
predetermined amount of sterile water; and (c) applying a lid to
the tray to seal the food product inside the tray; followed by
removing the tray from the sterile environment, wherein the food
material is not subjected to a cooking step subsequent to step
(b).
[0040] The term "cooking step" in the above aspect refers to a heat
treatment of the product by exposure of the product to an
environmental temperature above about 80.degree. C. for a period
greater than about 10 minutes. Suitably, the product according to
this aspect is transferred to an environment held at a temperature
less than about 80.degree. C., for example less than about
60.degree. C., within about 10 minutes, preferably within about 5
minutes of the completion of the water dosing step (b).
[0041] In a further aspect, the present invention provides a method
for the production of a stabilized packaged food product comprising
the steps of: filling a tray with a predetermined quantity of a
food starting material, followed by performing the following steps
in sequence while maintaining the tray in a sterile environment:
(a) treating the food starting material with high-temperature
pressurized steam in a pressure vessel to sterilize the material;
(b) dosing the sterile food material inside said tray with a
predetermined amount of sterile water; and (c) applying a lid to
the tray to seal the food product inside the tray; followed by
removing the tray from the sterile environment, wherein a major
portion by weight of the food material is not subjected to a
wetting or soaking step prior to step (a). The term "a major
portion" refers to at least about 50%, for example at least about
75%.
[0042] All of the various features described above in relation to
the first aspect of the present invention are likewise applicable
to the methods according to the further aspects of the
invention.
[0043] In methods according to the further aspects of the
invention, sealing may be performed either in the pressure vessel,
or the trays may be transferred from the pressure vessel to a
separate sealing chamber or clean booth in sterile communication
with the pressure vessel for the sealing step, for example as
described in EP-A-0691082. The film or foil sheet may be fed to the
sealing chamber or clean booth, with suitable sterilizing means
(e.g. steam, UV or peroxide) provided as appropriate. The sealing
chamber or clean booth may suitably be maintained at substantially
ambient pressure or a slight overpressure (e.g. about 0.01 bar to
about 0.3 bar) with sterile filtered air or steam.
[0044] In a further aspect, the present invention provides an
apparatus for the production of a stabilized packaged food product
comprising: a filling device for filling individual trays with a
predetermined amount of a food starting material; a pressure vessel
having an inlet pressure lock and an outlet pressure lock for
transferring said trays into and out of the pressure vessel; a
supply of pressurized steam for sterilizing the food starting
material in said trays in a first zone of the pressure vessel; a
supply of sterile water and a dosing pump for dosing a
predetermined amount of sterile water into each of said trays in a
second zone of the pressure vessel; and a sealing device located in
said pressure vessel for sealing the trays following said step of
dosing.
[0045] Suitably, the apparatus according to this aspect of the
invention comprises a conveyor for conveying the trays through the
pressure vessel. The pressure vessel may comprise two or more
pressure chambers, as described above. Suitably, the apparatus
according to this aspect of the invention is adapted for operation
of a process according to the first aspect of the invention. All
optional features described above in relation to the first aspect
are likewise applicable to the apparatus according to the present
aspect.
[0046] The term "dosing pump" refers to any pressurizing and dosing
apparatus for supplying predetermined doses of liquid to the trays
inside the pressure vessel. The dosing pump is suitably adapted for
intermittent operation, whereby the pump is operated intermittently
to dose water into the trays in the pressure vessel. The apparatus
may comprise a plurality of dosing pumps for sequentially dosing
each product more than once.
[0047] Suitably, the outlet of the pressure vessel or of the
separate sterile sealing chamber, communicates in airtight fashion
directly with the ambient atmosphere or with a tempering chamber
for tempering the product at an environmental temperature below
about 80.degree. C. That is to say, the said outlet does not
communicate with a further cooking or steaming chamber.
[0048] A further advantage of the processes of the present
invention is that the resulting stable, packaged ready-to-heat food
products do not exhibit the undesirable aroma that can be
experienced with in-pouch sterilized precooked products. This
advantage could be due to the fact that the present process
performs the high-temperature and short-time sterilization on open
trays of the products, whereby undesirable aromas evaporate from
the product before sealing. Alternatively or additionally, the low
moisture content of the product during the high-temperature and
short-time sterilization step will reduce the development of the
undesirable aroma compounds. In particular, gas chromatography of
rice products made according to the invention show lower levels of
odorous aldehydes, in particular heptanal and 2,4-decadienals, than
were found in pouched ready-to-heat rice products.
[0049] Accordingly, in a further aspect, the present invention
provides a stabilized, packaged, full-moisture food product
obtainable by a process according to the invention.
[0050] The term "stabilized" signifies that the product exhibits
reduced spoilage upon storage under ambient conditions as compared
to a product that has been cooked and packaged under ambient air.
Suitably, the food products are shelf-stable or ambient-stable. The
term "shelf stable" refers to a product that can be stored at
typical chill cabinet temperatures of about 7.degree. C. for a
period of at least 1 month, preferably at least 3 months, more
preferably at least 6 months and most preferably 1 year, without
unacceptable deterioration of organoleptic properties or
appearance, or without developing microbiological activity outside
regulatory limits. By "ambient stable" is meant a product that can
likewise be stored at typical ambient temperatures, such as
20-25.degree. C. at 60% relative humidity, with similar
stability.
[0051] In certain embodiments, the food products are commercially
sterile. Commercial sterility is defined as freedom from viable
forms of micro-organisms having public health significance, as well
as any micro-organisms of non-health significance capable of
reproducing in the food under the normal non-refrigerated
conditions of storage and distribution. In yet other embodiments,
the food products may be sterile, that is to say completely free
from viable microorganisms.
[0052] The term "full-moisture" implies that the moisture content
of the food product is sufficient to produce a normal, edible
product without further hydration. For food products such as rice,
wheat or pasta the full moisture content is in the range of from
about 50 wt. % to about 75 wt. % moisture. The full moisture
products may therefore be ready-to-heat products. In other
embodiments, such as salads, the products may be ready to consume
directly at ambient temperature, without reheating. In yet other
embodiments, such as soup concentrates, the products are fully
hydrated but may be suitable for dilution by addition of water to
produce a more palatable product.
[0053] The food product obtainable by the invention may optionally
be acidified, for example salad products (e.g. pasta salad, rice
salad) may be acidified to achieve the desired flavor. However, the
products are usually sufficiently sterile to be ambient
shelf-stable without any need for added acid. Suitably, the pH of
the packaged stabilized food product is greater than about 5, for
example greater than about 5.5. The pH is determined by liquidising
the food product with an equal weight of distilled water in a
blender to form a slurry, and measuring the pH of the slurry with a
conventional pH electrode.
[0054] The packaging is normally in the form of a tray having a
bottom, side walls, a flange (lip) extending around the top of the
side walls, and a flexible sheet lid bonded to the flange to form a
microorganism-impermeable closure. The packaging is substantially
impermeable to microorganisms, and it is also substantially
impermeable to gases such as oxygen, in order to maintain the
freshness of the product. Preferably, the packaging is
substantially oxygen-impermeable. Suitable packaging materials have
an oxygen permeability at 23.degree. C./50% relative humidity less
than about 2 cm.sup.3/m.sup.2/day at 1 atm pressure. Suitably, the
lid has been bonded to the flange by ultrasonic bonding. Suitably,
the packaging is substantially free of metallic material so that it
can be reheated in a microwave oven. In certain embodiments,
metallised susceptor regions may be provided to enhance microwave
heating. Suitably, all components of the packaging have a softening
temperature greater than about 120.degree. C., preferably greater
than about 125.degree. C., for example greater than about
140.degree. C.
[0055] The components of the food product and packaging are
suitably as described above in relation to the first aspect of the
invention. Accordingly, the packaged product preferably comprises
or consists essentially of full moisture starchy pieces, such as
rice grains.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] An embodiment of the present invention will now be described
further, with reference to the accompanying drawing, in which:
[0057] FIG. 1 shows a schematic sectional view of an apparatus
according to the invention;
[0058] FIG. 2 shows a detail of the dosing and sealing regions of
the apparatus of FIG. 1; and
[0059] FIG. 3 shows a perspective view of a packaged food product
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0060] Referring to FIG. 1, the apparatus comprises a tray filling
zone 1, an inlet pressure lock 2, a pressure vessel 3, and an
outlet pressure lock 4.
[0061] The tray filling zone 1 comprises filling stations for
loading the trays 5 before they are introduced into the pressure
vessel 3. The filling stations comprise a rice filling station 21
and a non-rice filling station 22 for depositing non-rice food
pieces such as carrot or mushroom on top of the rice bed. Each
filling station comprises a hopper 23, a feeding device 24 and a
dosing device 25. Trays 5 are fed from two stacks 26 to two
conveyors 27,28 for filling and supply to the inlet pressure lock
2. It will be appreciated that the apparatus may comprise further
filling lanes, for example 6, 8 or 12 filling lanes, in order to
achieved the desired filling rate of the trays.
[0062] The pressure vessel 3 is in the form of a tube of length up
to 50 m and diameter approximately 50 cm. The tube is thermally
insulated to minimize heat losses. The tube may be subdivided into
two or more chambers by pressure locks (not shown) to assist with
maintenance and to provide better control of process
conditions.
[0063] A conveyor 10 is provided within the tube to move trays 5
containing the food product from the inlet to the outlet thereof.
The pressure vessel comprises a sterilization zone 7, a water
dosing zone 8, and a sealing zone 9. The sterilization zone 7 of
the tube 1 proximate to the inlet end is provided with steam spray
nozzles 6 for spraying hot steam onto the product bed in trays 5.
The steam is supplied from a suitable steam generator 11 through a
manifold to the nozzles 6. The temperature of the steam is about
135.degree. C., and the pressure is about 0.3 MPa gauge. Fans (not
shown) may be provided to circulate the steam inside the pressure
vessel. It has been found that a sterilization time of about 24-30
s is sufficient for dry parboiled long-grain rice, and a
sterilization time of about 120 s or more is necessary for 1
cm.sup.3 pieces of fresh vegetables such as carrot.
[0064] The conveyor 10 extends from the sterilizing zone 7 of the
pressure tube to the water dosing zone 8. Referring to FIG. 2, the
water dosing zone of the apparatus comprises a water supply 13,
pump 14 and water sterilizer 15 for dosing predetermined amounts of
sterilized aqueous liquid from a nozzle into the trays containing
sterile dry rice in the dosing zone. It will be appreciated that
more than one dosing apparatus may be provided in the dosing zone
to sequentially dose larger quantities of liquid, for example when
making soups, with re-heat zones between the dosing apparatuses.
The water supplied may contain additional ingredients such as salt,
oil, herbs, spices, vegetable particles, bouillon or flavorings.
The location of the dosing zone 8 may be moved, depending on the
time required for the sterilization step. That is to say, the
dosing zone is moved further down the tube if a longer
sterilization step is required assuming constant conveyor speed.
Alternatively or additionally, the conveyor speed may be adjusted
to vary the duration of the steam sterilization step. Just
sufficient water is added in the dosing step to increase the
moisture content of the rice to about 65-67 wt. %. The temperature
of the liquid is adjusted within the range about 5.degree. C. to
about 140.degree. C., for example from about 25.degree. C. to about
100.degree. C. depending on the parameters of the system. The water
dosing zone 8 is shorter than the sterilizing zone 7, since the
time taken to dose the water is very short. The conveyor then
extends to a sealing zone 9. The apparatus further comprises an
ultrasonic or thermal sealing tool 17 for sealing a plastics foil
lid to the trays in the sealing zone. The trays in the sealing zone
are lifted into contact with the ultrasonic sealing tool by movable
anvil 18. The foil lid is cut from a continuous web 19 of the
plastics foil that is fed through a suitable pressure port 20 in
the pressure tube. In alternative embodiments, the sealing is
performed in a separate sealing chamber in sterile communication
with the pressure vessel 3, i.e. downstream of, and in sterile
communication with, the pressure lock 3.
[0065] The apparatus does not comprise any steaming or cooking
equipment downstream of the outlet port. It is an advantage of the
apparatus and method of the present invention that no cooking of
the packaged products at environmental temperatures above about
80.degree. C. is needed. It is merely necessary to store the
products at an environmental temperature typically in the range
40.degree. C.-80.degree. C. for a few hours to achieve a stable,
packaged, ready-to-heat rice and vegetable product.
[0066] Referring to FIG. 3, the packaged food product 30 according
to the invention comprises full-moisture shelf-stable long-grain
rice packaged in a thermoformed tray 32 having a flanged top 34, to
which is hermetically bonded a film lid 36.
Reference Example 1
[0067] A bench-top simulation of the method according to the
invention was performed as follows. A polypropylene tray was filled
to a depth of about 1cm with dry, milled, parboiled long-grain rice
having moisture content about 14 wt. %. The tray was introduced
into a modified small retort and treated with steam at 135.degree.
C. for a time sufficient to achieve F.sub.o of 5 minutes. The tray
was then removed from the retort and liquid water at 100.degree. C.
was immediately added in an amount just sufficient to bring the
total water content of the rice up to 65 wt. %. The tray was then
immediately sealed by ultrasonically bonding a polypropylene film
over the top of the tray. The tray and contents were then left to
equilibrate for 30 minutes to 150 minutes at temperatures in the
range 40.degree. C. to 80.degree. C.
[0068] The packaged rice product obtained by this method was
ambient stable and had a natural, freshly cooked appearance. It
could be reheated for immediate consumption. The reheated product
was completely free-flowing. None of the undesirable aroma of prior
art ready-to-heat pouched rice was detected. Analysis of the rice
aroma by gas chromatography--mass spectrometry (GCMS) showed
reduced levels of certain aroma aldehydes relative to conventional,
ready-to-heat pouched rice. In particular, levels of heptanal and
2,4-decadienals were reduced. These aldehydes are produced
primarily by fat oxidation. The analysis also revealed the absence
of certain hydrocarbon (alkane) components that are present in the
conventional pouched ready-to-heat rice products. It is thought
that these alkane components may be derived from the packaging
material under the conventional high-temperature sterilization
conditions.
[0069] The above embodiment has been described by way of example
only. Many other embodiments falling within the scope of the
accompanying claims will be apparent to the skilled reader.
* * * * *