Packaged food products

Abstract

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. Suitable food starting materials comprise starchy food products, such as rice, wheat or pasta, and/or meat or vegetable pieces. Also provided are an apparatus for performing the method and packaged stabilized full moisture food products obtainable by the process.

Claims

1. A method for the production of a stabilized, full moisture, ready-to-heat packaged food product comprising the steps of: filling a tray with a predetermined quantity of food starting material comprising at least 90% by weight of a dry starchy component, wherein the dry starchy component comprises whole rice grains selected from the group consisting of long-grain rice, basmati rice, Thai rice, wild rice, Arborio rice, and combinations thereof that are fully milled or have part or all of a bran layer attached, wherein the dry starchy component has a starting moisture content of less than 30 wt %; 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 at a temperature of from about 125 C. to about 150 C. immediately before a dosing step in order to sterilize the food starting material; (b) in the pressure vessel at a pressure of from about 0.5 Mpa to about 1.0 Mpa and at a temperature of from about 125 C. to about 150 C., dosing the sterile food starting material inside said tray with a predetermined amount of sterile water to provide the food starting material with a final moisture content of 50 to 75% wherein the food starting material is dosed such that there is no excess water in the tray; (c) in the pressure vessel, after step (b), applying a lid to the tray to seal the food starting material inside the tray wherein the pressure vessel having a pressure of from about 0.5 Mpa to about 1.0 Mpa and at a temperature of from about 125 C. to about 150 C., and then cooling the food starting material to a temperature less than 100 C. in the pressure vessel; and (d) after step (c) removing the sealed tray of food starting material from the pressure vessel and holding the sealed tray at atmospheric pressure and in an environment at 25 C.-80 C. for a period of from about 20 minutes to about 4 hours, thereby producing the stabilized full moisture, ready-to-heat packaged food product, wherein the duration of the process from the start of step (a) to the completion of step (c) is less than about 10 minutes.

2. A method for the production of a stabilized, full moisture, ready-to-heat packaged food product comprising the steps of: filling a tray with a predetermined quantity of food starting material comprising at least 90% by weight of a dry starchy component, wherein the dry starchy component comprises whole rice grains selected from the group consisting of long-grain rice, basmati rice, Thai rice, wild rice, Arborio rice, and combinations thereof that are fully milled or have part or all of a bran layer attached, wherein the dry starchy component has a starting moisture content of less than 30 wt %; 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 at a temperature of from 125 C. to about 150 C. immediately before a dosing step in order to sterilize the food starting material; (b) in the pressure vessel at a pressure of from about 0.5 Mpa to about 1.0 Mpa and at a temperature of from about 125 C. to about 150 C., dosing the sterile food starting material inside said tray with a predetermined amount of sterile water to provide the food starting material with a final moisture content of 50 to 75% wherein the food starting material is dosed such that there is no excess water in the tray; (c) in the pressure vessel, after step (b), applying a lid to the tray to seal the food starting material inside the tray wherein the pressure vessel having a pressure of from about 0.5 Mpa to about 1.0 Mpa and at a temperature of from about 125 C. to about 150 C., and then cooling the food starting material to a temperature less than 100 C. in the pressure vessel; and (d) after step (c) removing the sealed tray of food starting material from the pressure vessel and holding the tray of food starting material at atmospheric pressure and in an environment at 25 C.-80 C. for a period of from about 20 minutes to about 4 hours, thereby producing the stabilized full moisture, ready-to-heat packaged food product, wherein at least a portion by weight of the food starting material is not subjected to a wetting or soaking step prior to step (a).

3. The method of claim 1, wherein the step of applying the lid to the tray to seal the food starting material inside the tray is performed not more than about 2 minutes after said step of dosing.

4. The method of claim 1, wherein the step of applying the lid to the tray to seal the food starting material inside the tray is performed not more than about 1 minute after said step of dosing.

5. The method of claim 1 or 2, wherein the whole rice grains are the long-grain rice and wherein the removing of the sealed tray of food starting material from the pressure vessel and the holding of the tray of food starting material at the atmospheric pressure and in the environment is at 55 C. for the period of 30 minutes followed by 15 minutes at 45 C., thereby producing the stabilized, full moisture, ready-to-heat packaged food product.

6. The method of claim 1 or 2, wherein the whole rice grains are the basmati rice and wherein the removing of the sealed tray of food starting material from the pressure vessel and the holding of the tray of food starting material at the atmospheric pressure and in the environment is at 75 C. for the period of 30 minutes followed by 30 minutes at 45 C., thereby producing the stabilized, full moisture, ready-to-heat packaged food product.

7. The method of claim 1, wherein a total residence time of said tray inside the pressure vessel is from about 30 seconds to about 5 minutes.

8. The method of claim 2, wherein a total residence time of said tray inside the pressure vessel is from about 30 seconds to about 5 minutes.

9. The method of claim 2, wherein the step of applying the lid to the tray to seal the food starting material inside the tray is performed not more than about 2 minutes after said step of dosing.

10. The method of claim 2, wherein the step of applying the lid to the tray to seal the food starting material inside the tray is performed not more than about 1 minute after said step of dosing.

Description

(1) An embodiment of the present invention will now be described further, with reference to the accompanying drawing, in which:

(2) FIG. 1 shows a schematic sectional view of an apparatus according to the invention;

(3) FIG. 2 shows a detail of the dosing and sealing regions of the apparatus of FIG. 1; and

(4) FIG. 3 shows a perspective view of a packaged food product according to the invention.

(5) 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.

(6) 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.

(7) 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.

(8) 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 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.

(9) 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 C. to about 140 C., for example from about 25 C. to about 100 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.

(10) 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 C. is needed. It is merely necessary to store the products at an environmental temperature typically in the range 40 C.80 C. for a few hours to achieve a stable, packaged, ready-to-heat rice and vegetable product.

(11) 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

(12) 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 1 cm 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 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 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 C. to 80 C.

(13) 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 chromatographymass 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.

(14) 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.