Package for food product

Abstract

A package is configured for heating a food in a solid state microwave oven, and a method heats a food in a solid state microwave oven. Particularly, the package comprises includes a tray and a susceptor, and a thermal insulation is positioned between the susceptor and a food to be placed in the tray.

Claims

1. A package for heating food items in a solid state microwave oven, the food items comprising a first food item and a second food item, the package comprising a tray and a susceptor, wherein the tray comprises a first compartment for receiving the first food item and provided with the susceptor, and the tray further comprises a second compartment for receiving the second food item and not provided with the susceptor, wherein the susceptor is integrated or attached to a bottom of the tray and covers a part of a surface of the bottom of the tray, and the tray comprises a thermal insulation layer between the susceptor and the food items to be placed in the tray, wherein heating of the food items simultaneously in the tray provides a higher temperature for the second food item positioned in the second compartment of the tray, which is not provided with the susceptor, relative to the first food item positioned in the first compartment, which is provided with the susceptor.

2. The package according to claim 1, wherein the thermal insulation layer comprises a material selected from the group consisting of plastic material, paper material, and combinations thereof.

3. The package according to claim 2, wherein the thermal insulation layer comprises plastic material selected from the group consisting of polypropylene, polyethylene terephthalate, crystallized polyethylene terephthalate, and combinations thereof.

4. The package according to claim 2, wherein the thermal insulation layer is a PET laminated paperboard.

5. The package according to claim 1, wherein the thermal insulation layer is at least 0.20 mm thick.

6. The package according to claim 1, wherein the tray is not thicker than 2 mm.

7. The package according to claim 1, wherein the thermal insulation layer has a thermal resistance value R of at least 0.0004 m.sup.2K/W.

8. The package according to claim 1, wherein the part covered by the susceptor is up to 50% of the surface of the bottom of the tray.

9. The package according to claim 8, wherein the part covered by the susceptor is up to 40% of the surface of the bottom of the tray.

10. The package according to claim 1, wherein the part covered by the susceptor is at least 20% of the surface of the bottom of the tray.

11. The package according to claim 1, wherein the susceptor has the form of a horseshoe.

12. The package according to claim 1, where wherein the package is disposable.

13. A method for heating food items in a solid state microwave oven, the food items comprising a first food item and a second food item, the method comprising: (a) placing the food items into a package for heating the food items in the solid state microwave oven, the package comprising a tray and a susceptor, wherein the tray comprises a first compartment for receiving the first food item and provided with the susceptor, and the tray further comprises a second compartment for receiving the second food item and not provided with the susceptor, wherein the susceptor is integrated or attached to a bottom of the tray and covers a part of a surface of the bottom of the tray, and the tray comprises a thermal insulation layer between the susceptor and the food to be placed in the tray; and (b) heating the food items or parts thereof in the solid state microwave oven at a selected frequency between 900 and 5800 MHz, wherein the heating of the food items simultaneously in the tray provides a higher temperature for the second food item positioned in the second compartment of the tray, which is not provided with the susceptor, relative to the first food item positioned in the first compartment, which is provided with the susceptor.

14. The method according to claim 13, wherein the selected frequency is between 900 and 930 MHz or between 2400 and 2500 MHz.

15. The method according to claim 13, wherein the selected frequency corresponds to the frequency which results in the highest energy absorption of the susceptor.

16. The method according to claim 13, wherein the solid state microwave oven is operated at a power from 100 to 1600 Watts and for 1 to 30 minutes.

17. The package according to claim 1, wherein the second food item positioned in the second compartment, which is not provided with the susceptor, comprises a meat product, and the first food item positioned in the first compartment, which is provided with the susceptor, is selected from the group consisting of a vegetable product, a pasta, a noodle, a rice product, a potato product, and combinations thereof.

18. The method according to claim 13, wherein the second food item positioned in the second compartment, which is not provided with the susceptor, comprises a meat product, and the first food item positioned in the first compartment, which is provided with the susceptor,. is selected from the group consisting of a vegetable product, a pasta, a noodle, a rice product, a potato product, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Two compartment tray and defined zones containing frozen mashed potatoes (left) and infrared image corresponding to the tray indicating temperature from ‘Low’ to ‘High’.

(2) FIG. 2: Illustration of a design of a susceptor (left) and its placement on the outer surface of the bottom of the tray (right).

(3) FIG. 3: Samples #1-10 illustrating the different designs and forms of the susceptors attached to the trays tested.

(4) FIG. 4: Plot of a frequency scan measuring energy absorption in a solid state microwave oven.

(5) FIG. 5: Two compartment tray according to sample #4 and infrared image corresponding to the tray containing the mashed potatoes after heating in a solid state microwave oven. Temperature scale is indicated from ‘Low’ to ‘High’.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention pertains to a package for heating a food in a solid state microwave oven, the package comprising a tray and a susceptor, wherein the susceptor is integrated or attached to a bottom of the tray and covers a part of the surface of the bottom of said tray, characterized in that there is a thermal insulation between the susceptor and the food to be placed in the tray.

(7) A “solid state microwave oven” is a microwave oven delivering solid state electromagnetic energy. Typically, production of such solid state energy is transistor-based and not magnetron produced.

(8) A “susceptor” is a material used for its ability to absorb electromagnetic energy and to convert it to heat. Susceptors are usually made of metallized film or paper.

(9) A “tray” is a shallow platform for carrying or holding things such as food items. For example trays are typically used for holding food items in the area of prepared dishes and frozen meals. Trays usually have a more or less flat bottom part which allows to stably placing the tray onto a surface e.g. for heating it in an oven or for putting it onto a table for ease of consumption.

(10) “Thermal insulation” is the reduction of heat transfer between two objects of different temperatures which are in thermal contact or in range of thermal radiative influence.

(11) In the package of the present invention, the thermal insulation can for example be provided by a layer of plastic material, paper material, or a combination thereof. Thereby the plastic material can be selected for example from PP (polypropylene) or Polyethylene terephthalate (PET), or particularly from crystallized Polyethylene terephthalate (CPET). Paper material can be paperboard or cardboard. And a combination between plastic and paper material can be for example PET laminated paperboard.

(12) Preferably, the layer of plastic material, paper material, paperboard or a combination thereof, is at least 0.20 mm thick, preferably at least 0.25 mm or 0.30 mm thick, more preferably at least 0.5 mm thick. These are preferred minimal thicknesses to assure an adequate thermal insulation between the susceptor and the closest food item which can be placed into the package.

(13) In an embodiment, the tray is not thicker than 2 mm, preferably not thicker than 1.75 mm, more preferably not thicker than 1.50 mm. The tray is preferably designed for a single use application. Therefore, the tray should be thick enough to support the amount and weight of the food items to be placed therein, and to support a certain handling of the tray by the consumer such as placing it into a microwave oven, carrying it around and using it as a tray for directly eating from the package. Furthermore, the tray should not be too thick as to be not too heavy by itself, and not to require more packaging material as absolutely necessary in order to reduce production costs and environmental impact, particularly when the tray is used only once and discarded thereafter.

(14) In a preferred embodiment, the thermal insulation of the package has a thermal resistance value R of at least 0.0004 m.sup.2K/W, preferably of at least 0.001 m.sup.2K/W, more preferably of at least 0.005 m.sup.2K/W, even more preferably of at least 0.01 m.sup.2K/W. R stands for thermal resistance value R. R is measured in m.sup.2K/W, wherein K stands for Kelvin and W for Watt. Thermal conductivity (k-value) is the ability of a material to conduct heat and it is measured in W/mK. Consequently, the value R is determined by assessing the k-value of an insulating material and measuring its thickness L as follows: R=L/k. Table I provides some k-values for materials typically used for making packaging trays.

(15) TABLE-US-00001 TABLE I Material k = W/mK at ca. 25° C. Aluminum 205    Cellulose 0.23 Celluloid 0.12-0.21 Cork board  0.043 Crystallized PET (CPET) 0.15-0.4  Fiberglass 0.04 Nylon 0.25 Paper 0.05 Polycarbonate 0.19 Polyester 0.05 Polyethylene 0.33-0.51 Polypropylene (PP)  0.1-0.22 Polytetrafluorethylene (PTFE) 0.25 Polyvinylchloride (PVC) 0.19 Vinyl ester 0.25

(16) In one embodiment of the present invention, the part covered by the susceptor of the package is up to 50% of the surface of the bottom of the tray. Preferably, the part covered by the susceptor is up to 40% of the surface of the bottom of the tray. Typically however, the part covered by the susceptor is at least 20% of the surface of the bottom of the tray.

(17) In one embodiment, the susceptor of the package of the present invention has the form of a horseshoe. As substantiated in the examples as provided here below, the form of a horseshoe proved very efficient for some specific applications, for example for use in a two compartment tray.

(18) In one embodiment of the present invention, the tray of the package is a two-compartment tray or a multi-compartment tray. A multi-compartment tray may have three, four, five or even more compartments in one tray. One of the advantages to using a two- or multi-compartment tray is that it allows to easily separate individual different food items from each other. In this way and in combination with a use and design of one or more specific susceptor(s), the bundled energy of a solid state microwave application can be very clearly and local specifically be directed and targeted to the appropriate food item(s) to be heated.

(19) In one embodiment, only one of the compartments of the tray of the package is provided with a susceptor. However, preferably, at least one of the compartments of the tray is not provided with a susceptor. A further possibility may be that at least one of the compartments of the tray is shielded from microwaves in the solid state microwave oven. This would allow to include a food item into a multi-food item dish which will not be heated in the solid state microwave application. This food item may be for example a salad, a pastry, a dessert, or an ice cream.

(20) The package of the present invention is suitable for being used for heating a food. In one embodiment of the present invention, the package is suitable for being used where the food is frozen or chilled. For example the package of the present invention can be frozen and kept frozen for a long time, e.g. several months, without cracking or deteriorating. And on the other hand, this same package can also be used to be heated in a solid state microwave oven without cracking or deteriorating, and with withstanding the generated heat.

(21) A second aspect of the present invention relates to a method for heating a food in a solid state microwave oven comprising the step of placing a food into a package according to the present invention, and heating the food or parts thereof in a solid state microwave oven at a selected frequency of between 900 and 5800 MHz. Preferably, the selected frequency is between 900 and 930 MHz or between 2400 and 2500 MHz.

(22) Solid state microwave ovens have a degree of heating process control unavailable with classical magnetron driven microwave ovens. With this additional control and feed-back from the heating cavity of the oven, these solid state microwave ovens can determine how much power is reflected back and adapt the heating process accordingly. In some cases, those new ovens can sweep phase and frequency of the applied microwave wavelengths methodically over a wide range and determine the highest return loss modes. This allows then to set frequency and phase in such a way to ensure that the maximum microwave energy is retained within the cavity of the oven, where it is available for an optimal preparation of the food product. Therefore a preferred embodiment of the present invention pertains to a method of the present invention, wherein the selected frequency corresponds to the frequency which results in the highest energy absorption of the susceptor. Thereby, the solid state microwave oven is then preferably operated at a power from 100 to 1600 Watts and for 1 to 30 minutes.

(23) Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the product of the present invention may be combined with the method of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined.

(24) Further advantages and features of the present invention are apparent from the figures and examples.

EXAMPLE 1

(25) Reference Sample Before Microwave Heating.

(26) Equal quantities of mashed potato (132 g±2 g) were placed in a two compartment tray and frozen to −18° C. The two compartment tray was a common tray as used commercially for frozen meals and did not comprise any susceptor. It had a dimension of ca. 18.4 cm to 14.6 cm and a height of ca. 3 cm. It was made of Crystallized Polyethylene terephthalate (CPET) and had a material thickness of 0.5 mm. FIG. 1 shows the nomenclature used for the two zones/compartments of mashed potato and their corresponding infrared images taken using a FLIR Infrared Camera. It can be seen that the mashed potatoes are about equally well frozen in both compartments.

EXAMPLE 2

(27) Test Samples with a Susceptor Fixed at the Bottom of the Tray in Zone 2.

(28) Susceptors used in this study were of a very thin metal layer applied to the non-food contact side of the film and laminated to a paper based substrate (from Lorence & Pesheck, 2009). Susceptors in certain selected designs were then fixed to the outer bottom at zone 2 of same CPET trays as described in Example 1 (FIG. 2). The susceptors were fixed to the trays in such a way that the metal part of the susceptor faced the surface of the tray.

(29) Different designs and forms of the susceptor as shown in FIG. 3 were used and tested in a solid state microwave oven. For this, each sample tray was filled with mashed potatoes as described in Example 1 and thereafter frozen at −18° C. Thereafter, the samples were put into a solid state microwave oven, where the oven system identified first the frequency with the highest energy absorption, i.e. the highest return loss. One example is shown in FIG. 4 where a highest absorption peak was observed at 2483 MHz. The highest absorption peak is related basically only to the energy absorption by the susceptor as frozen food does not absorb microwave energy well because of its low dielectric loss.

(30) The obtained frequency of the absorption peak depends on the susceptor, its form and design, and its ultimate location within the cavity of the microwave oven.

(31) The trays were then heated in a solid state microwave oven operating at the determined frequency with the maximum energy absorption at 500 Watts for 5 minutes. Infrared images were then captured at the end of the heating and the temperatures along the edges and centre of the mashed potatoes placed in the two zones were recorded. The results are shown in the Table II here below.

(32) TABLE-US-00002 TABLE II Peak Suscept. Temp. Zone 1 Temp. Zone 2 Sample Freq. area *.sup.) Edge Centre Edge Centre Nr. [MHz] [%] [° C.] [° C.] [° C.] [° C.] #1 2450  0% 38 0 53 0 #2 2423 50% 40 10 16 −1 #3 2451 20% 61 4 27 −1 #4 2409 30% 49 28 20 0 #5 2417 25% 58 9 10 2 #6 2451 20% 60 3 27 −1 #7 2408 30% 62 11 33 1 #8 2471 80% 31 2 36 0 #9 2457 50% 62 7 50 1 #10 2452 100%  51 0 62 1 *.sup.) Total bottom area of the tray covered by the susceptor in percent of total bottom surface of the tray.

(33) Sample #1 is a control sample having no susceptor. As can be seen from the results, heating of the food is about identical in both zones (see temperature in Centre). Heating at the edges is pretty inconsistent and variable.

(34) Samples #2-#7 are working examples of the present invention. Particularly when looking at the temperatures in the Centre of the food there is clear evidence that heating in Zone 1, not having the susceptor, is superior to heating in Zone 2, having the susceptor. Temperatures measured at the edges of the food confirm this as well.

(35) Samples #8-#10 are again control examples. Those samples have susceptors in both zones and cover 50% or more of the bottom surface of the tray with susceptor. As can be seen from the results, there is no or much less targeted heating of only one zone. Particularly, the result of #10 (with 100% coverage of susceptor) is very similar to the result of #1, which has no susceptor at all.

(36) Conclusion:

(37) As shown in the examples presented, the invention allows to specifically target heating to e.g. only one specific compartment of a multi-compartment tray. Particularly sample #4 gave a very good result as also shown in FIG. 5. Hence, it will now be possible with the teaching of the present invention to design new packages for food products which can be used to for example to cook in one compartment a meat item which needs to be cooked very well, and in another compartment a vegetable or salad item which does not need to be heated as much.

EXAMPLE 3

(38) Further packages according to the present invention can be produced with using trays having for example the following thermal resistance value R of the package tray between the susceptor and the food to be placed therein as specified in Table III.

(39) TABLE-US-00003 TABLE III Type of package tray: R value of package tray CPET Tray + PET film of 0.001232-0.000462 Susceptor PP Tray + PET film of Susceptor 0.001316667-0.000594773 Pressed Paper tray + PET film 0.002697102-0.002667935 of susceptor CPET Tray + Paperboard of  0.00273142-0.001990587 Susceptor PP Tray + Paperboard of 0.002816087-0.00212336  Susceptor Pressed Paper Tray + Paperboard 0.004196522 of Susceptor

(40) PET films typically used in the prior art on the surface of susceptors to protect for example the food product and/or the susceptor have an R value ranging from 1.75 E-05 to 4.7E-05. This R value is not sufficient to provide thermal insulation as claimed in the present invention.