GB2421937A

GB2421937A - Water vapour generating device for use with packaged food when microwaved

Info

Publication number: GB2421937A
Application number: GB0500166A
Authority: GB
Inventors: Nigel John Brace Parker
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-01-05
Filing date: 2005-01-05
Publication date: 2006-07-12
Anticipated expiration: 2025-01-05
Also published as: GB2421937B; GB0500166D0

Abstract

A device to prevent drying out of packaged food when microwaved comprises hydrated Bentonite clay within a permeable container such as a sachet to release water vapour when exposed to microwave radiation. The fully hydrated clay may correspond to one part by weight in the dry form thereof per at least five parts of water. Hydration of the clay may occur by adsorption of drip loss fluid from the food in the package prior to microwaving; and/or by previously placing the sachet in water for at least 30 minutes. The sachet is liquid and gas permeable and may also contain polyacrylate beads and flavourings. The food packaging may be self-venting when microwaved.

Description

A WATER VAPOUR GENERATING DEVICE TO IMPROVE THE QUALITY OF

PREPARED FRESH PRODUCE, COOKED IN MICROWAVE OVENS. WITHIN SELF-

VENTING RETAIL PACKAGING

Introduction to the invention

1. FIeld of the Invention

2. This invention relates to a. water vapour generating food packaging inclusion, in the form of a sachet, both liquid and gas permeable, containing of a mixture of readily hydrated, highly adsorbent, powdered compounds.

3. This device has been designed as an active inclusion, within microperforated, self- venting retail packs, to provide a significant sacrificial contribution to the saturated water vapour content of the pack atmosphere during the microwave-ovening of prepared fresh produce and other foods, with the aim of improving the cooked quality of the same.

4. Description of the Related Art

5. The extension of retail convenience foods into the area of prepared, fresh fruit and vegetables is a relatively recent and rapidly growing market. There is now available a wide range of ready to cook', prepared fresh produce in packaging suitable for microwave ovening.

6. The weight of the product contained within this packaging can range from less than bog to 10009, about the maximum mass that can be satisfactorily cooked within a microwave oven.

7. Many of these products require the consumer to puncture the packaging before cooking, but a number of products are already available in selfventing, microwaveable, laser perforated or un-perforated, plastic polymer packaging, generally polypropylene or polyester - both CPET and APET, in which an aperture, of predetermined dimensions, will open at a certain point in the cooking cycle.

8. This aperture prevents the packaging rupturing under the increasing pressure within the pack, caused by an expanding volume of water vapour, but provides sufficient restriction to the escape of the latter, to limit, but not prevent, accelerated dehydration of the cooked product.

9. When compared to conventional cooking methods, such as boiling or steaming, the microwave-ovening of prepared fresh produce, even within specialised packaging, can still produce an inferior cooked product 10. With prepared fresh produce cooked by these conventional methods, heat is transferred from the water, or water vapour, to and through the product by conduction. This means that the food is first of all cooked on the outside before it is cooked on the inside.

I

11. in a microwave oven, food is cooked by radiation generated at a frequency of 2.45 gigahertz - 2.50 gigahertz. Microwave radiation in this frequency range is absorbed by water fats and sugars where it is converted to kinetic energy, manifested by the oscillation of the molecules of these substances about a mean position, causing collisions with neighbouring molecules and resulting in the generation of heat. Food suitable for microwave cooking generally has a high water content and as a consequence, all of the food material is cooked at the same time, having the overall effect of cooking the product from the inside.

12. Food cooked in a microwave oven, especially prepared fresh produce, can lose well in excess of 20% of its pre-cooked weight as water. This water loss is rapid, one result of which can be marked textural changes within the product, typically presented as a toughening or a fibrousness of the outer layers, which can seriously diminish eating quality.

13. Under microwave cooking conditions, the pre-hydrated sachet is designed to lose water at a rate faster, and as a greater proportion of its mass, than does the product. This rapidly establishes a pack atmosphere saturated with water vapour, which inhibits water loss from the product and reduces, or eliminates, differential dehydration within the product tissue - achieving a much more uniform texture and improved eating quality.

14. The criteria, which this device has had to meet to be effective, are as follows: - * to be discrete and unobtrusive within the retail pack * the contents and the materials from which the sachet is fabricated to be stable and safe under microwave radiation * the retention of fill material pre-hydration * tohydraterapidly * the retention of fill material post-hydration * a clearly observable hydrated end-point * a ready release of adsorbed/absorbed water as water vapour during microwave ovening * the retention of adsorbed water to maintain the fully hydrated state, within the self- venting retail pack with the product, throughout the shelf life of the product.

* the retention of fill material during microwave ovening and post-cook phases * an opaque outer surface which will allow print of high definition * the packaging and fill materials to meet permitted food contact regulations 15. The device meets these criteria.

18. In the device, the sachet contents are a mixture of Bentonite clay in the form of a granulated powder and a polyacrylate in the form of fine beads.

17. The Bentonite clay, as a finely particulate material, has a very large capacity for water adsorption, with no readily defined saturation point as it changes, with the addition of water, from a dry powder to a paste and then to a sluny.

18. Bentonite clays, when hydrated, become hydrophobic cofloids, the particles of which have negatively charged surfaces and form an elect double-layer that holds them in Suspension by the electrostatic interaction between the negative surface charge and the positive charges from cations in the water. This form of bonding can allow enormous degrees of hydration causing the hydrated Bentonite clay to become extremely fluid, but with unstable water retention. Under microwave radiation, this instability of the electrostatic bonding between the clay particle and water allows the bonds to break very readily allowing the water to be released rapidly as water vapour.

19. To achieve an easily observable end-point in the form of a fully turgid sachet, a small quantity of polyacrylate has been added to absorb that water not securely adsorbed on to the Bentonite clay particles.

20. In use, the sachet is placed in potable or sanitised water for a minimum of 30 minutes to ensure full hydration. By the end of this period, the sachet will be fully hydrated and turgid, with the fabric of the envelope tightly stretched, at which point it can be removed from the water and allowed to drain for another 30 minutes, to ensure the dispersal of any free water on its surface. The sachet is now ready to be placed and sealed within in the packaging, together with the product.

21.As the Bentonite clay, although supplied in a granular form, is finely particulate, with a mean particle size of O.2p - 1.Op, the sachet is designed to retain fully this powder, despite being both liquid and gas permeable, especially to water in both its liquid and gas phases.

22. To achieve this, the material from which the sachet is fabricated, comprises a three layer laminate, where the middle layer is a dense nonwoven fabric, adhesive bonded on both its outer and on its inner surface to perforated films.

23. This construction, when fabricated into a sachet, successfully retains the Bentonite clay powder, when both dry and hydrated, avoiding contamination of the food the device is in contact with, while allowing the inward passage of water, and subsequently, the outward passage of water vapour, the fatter at both a relatively high rate and high pressure.

24. The porosity of the three layer laminated material, as determined using a Gurley densitometer spot tester, was not less than 850ml of water vapour/mm/sq. in, a minimum permeability which is essential for the device to be effective.

25. The fact that water is adsorbed on to the Bentonite clay particles, rather than being absorbed, not only allows water to be taken up very readily, resulting in rapid hydration of the device, but also allow water to be released equally readily as water vapour, when exposed to microwave radiation. In practice, in excess of 80% of the adsorbed water can be released from the hydrated mass during the microwave ovening of food within self-venting packaging.

26. This means that the hydrated mass of the fully hydrated device can be kept relatively small, allowing it to be discrete and unobtrusive within the retail packaging.

27. In this regard, this device compares favourably with those other devices, based on hydrocofloids, which are also designed to release water vapour with the aim of improving the cooked quality of microwave ovened foods. Hydrocofloids, especially super absorbents, such as polyacrylate acid salts, on which these devices are generally based, are hydrophilic colloids, which form a relatively stable hydrogen bond with water molecules. They are extremely efficient at absorbing water, sometimes at up to 50 times its original dry mass. They are, however, because of their hydrophilic hydrogen bonding, also extremely effective at retaining absorbed water, even under microwave ovening conditions, losing only a very small percentage of the hydrated mass as water vapour when compared to that lost by the food product being supported. To be at all effective therefore, such products require a substantial hydrated mass, causing the devise to be relatively large and thus somewhat intrusive within retail packaging.

28. The high water content of the hydrated BentonIte clay, due to adsorption, rather than absorption, makes the device very susceptible to heating by microwave radiation, allowing the rapid generation of water vapour.

29. The use of Bentonite clay allows the addition to the device of volatile, oil based, odours or flavours, typically those of herbs or spices, both natural and synthetic, by adsorption on to the clay particles at the time of sachet filling. By this means, the concentration of the odour or flavour can be precisely controlled, allowing, at the time of microwave ovening, the concentration of the volatile addition to provide either an attractively appetising odour or to actually impart a flavour to the cooking food.

30. Odours and flavours can also be added to the device in the form of a powder of modified starch, on to the particles of which these volatile, oil-based compounds have been adsorbed.

31 Again the concentration of the fragrance or flavour can be precisely controlled, by regulating the quantity of treated modified starch powder in the formulation.

32. Because the odours and flavours are oil based and adsorbed on to the clay or modified starch particles, they are not removed during the process of hydrating the sachet and its contents.

33. In another aspect of this invention, the device, in its un-hydrated state, can also be introduced into and sealed within self-venting, microwaveabje packaging with foods, other than prepared fresh produce, such as precooked ready meals.

34. In another aspect of this invention, the device can, in its unhydrated state, be introduced into and sealed within self-venting, microwaveable packaging with such foods as fresh fish, in which the driploss' of significant levels of tissue fluids is common. In these products, the device is employed both to adsorb the aqueous and oil based components of the leached-out fluid and dunng subsequent microwave cooking use the adsorbed water to generate water vapour to enhance the cooked textural quality of the product.

35. In another aspect of this invention, the device can, in its hydrated state, be introduced into and sealed within conventIonal, laser perforated, modified atmosphere packaging (MAP), containing whole or prepared fresh produce, such as fresh leaf salads. In these products, the device is employed to allow a controlled and limited release of water vapour in order to maintain an elevated relative humidity (RH) within the pack, where there is continuous water vapour loss due to the perforations, and thus limit dehydration by the product and a consequent loss of turgor, leading to wilting and a reduced shelf-life.

36. In the above application, the hydrated Bentonite clay is a particularly suitable material in the provision of a controlled, maintained elevated RH, as it will allow evaporative water loss in unsaturated pack atmospheres. By contrast, hydrophilic hydrocolloids, especially super absorbents, are not practically effective in this role as they do not allow levels of evaporative water loss significant enough to elevate the RH of the pack atmosphere.

Summary of the Invention

37. The device in this invention consists of an outer envelope, in the form of a sachet, which has a dual function of both retaining fully the contents, in all states of its use, and of being readily permeable to water vapour, even when the latter is generated at a relatively high pressure.

38.The sachet contains a mixture of two powders, the major component being a Bentonite clay, which comprises at least 97% by weight of the fill' mass. This is in the form of a granulated powder, with granule dimensions in the range of 1.0mm - 1.5mm. The actual particle size of the clay, however, is 2p, a state it reverts to when hydrated.

39. The minor component within the sachet contents is a permitted, food contact grade polyacrylate, super-absorbent, which comprises no more than 3% by weight of the fill' mass. This is in the form of fine beads, with dimensions, when not hydrated, in the range of 0.6mm - 1.0mm. When hydrated these dimensions can increase by a factor of three.

40. ln order to retain fully the contents, both dry and hydrated, when in contact with food, the sachet is fabricated from a tn-laminated material, consisting of an outer, reverse printed, clear l2p polyester (APET) film, adhesive bonded to middle layer of a non-woven 50g/m2 fabric, adhesive bonded in turn to and inner layer of a cast 25p polypropylene copolymer. The tn-laminate, as a complete material, is then cold- needle perforated at a grid density of 3mm x 3mm.

41. The sachet is formed with internal dimensions of 74mm x 34mm and has a fill mass of 33g and a gross mass of 3.7g.

42. The sachet, when fully hydrated, has a gross mass of 16g - 19g, providing a free- water availability for water vapour generation of 12g 15g.

43.The sachet, when fully hydrated, has a generous surface area to volume ratio for evaporative water loss, ranging from 1:2.2 to 1:3.0.

44. The sachet with these dimensions and hydrated mass forms a relatively discrete an unobtrusive food packaging inclusion.

45. The sachet, when fully hydrated, is able to retain the adsorbed water allowing it to maintain the fully hydrated state, within the self-venting retail pack with the product, throughout the shelf life of the product.

46. The contents and the materials from which the sachet is fabricated are stable and safe under microwave radiation.

47. The materials from which the sachet is fabricated are transparent to microwave radiation 48. The sachet, with its contents fully hydrated, readily absorbs radiation, causing the adsorbed water to heat up rapidly and generate water vapour.

49. The sachet, when fully hydrated and exposed to microwave radiation and depending on power output and exposure period, will yield up to 90% of its free-water availability as water vapour.

50. The size and hydrated mass of this device, when included within sealed food packaging, will generate sufficient water vapour to provide a significant improvement in the cooked quality of up to 10009 of microwave ovened, fresh prepared produce.

51. In another aspect of this invention, natural volatile, off-based, aromatic extracts from herbs and spices, or synthetic equivalents, can be added to the Bentonite clay, in precise amounts at the time of formulation and mixing, in order to create specific predetermined concentrations of odour or flavour during microwave cooking, which remains unaffected by subsequent hydration of the sachet and its contents.

52. In another aspect of this invention, natural volatile, off-based, aromatic extracts from herbs and spices, or synthetic equivalents, preabsorbed on to modified starch powder, can be added, in precise amounts, to the sachet fill material at the time of formulation and mixing in order to create specific, predetermined concentrations of odour or flavour during microwave cooking, which remains unaffected by subsequent hydration of the sachet and its contents.

53. In another aspect of this invention, the device, in its un-hydrated state, can be introduced into and sealed within self-venting, microwaveable packaging with such foods as fresh fish, where it is employed to adsorb drip-loss' fluid and during subsequent microwave cooking use the adsorbed water to generate water vapour.

54. in another aspect of this invention, the device can, in its hydrated state, be introduced into and sealed within conventional, laser perforated, modified atmosphere packaging (MAP), containing whole or prepared fresh produce, such as fresh leaf salads, where it is employed to allow a controlled and limited release of water vapour in order to maintain an elevated relative humidity (RH) within the pack.

Claims

Claims 1. A water vapour generating device configured to produce

additional water vapour within self-venting packaging, when microwave cooking of foodstuffs, comprising packaging fabricated from a composite material, penneable to both liquid and gas, and a Bentonite clay contained within the packaging, the said clay being capable of readily adsorbing water, prior to employment, and rapidly releasing the same, as vapour, when exposed to microwave radiation, the fully hydrated clay corresponding to one part by weight in the dry form thereof per to at least 5 parts of water. In another aspect of this invention, the device, in Its unhydrated state can, in the same packaging context, be employed to adsorb dnp.loss' fluid from particular fresh foods and during subsequent microwave cooking, use the absorbed water to generate water vapour. In another aspect of this invention, the device can, in its hydrated state and within conventional, laser perforated, modified atmosphere packaging (MAP), be employed to allow a controlled and limited release of water vapour in order to maintain an elevated relative humidity (RH) within the pack.
2. The water vapour generating device according to claim 1, wherein the Bentonite clay is selected from purified, naturally occurring compounds.
3. The water vapour generating device according to claim 1, wherein the Bentonite clay can be supplemented by a minority addition of a hydrocollojtj selected from a group synthetic super-absorbents
4. The water vapour generating device according to claim 1, wherein the Bentonite clay can be supplemented by the surface adsorption of natural, aromatic, oil-based, volatile herb and spice extracts, or synthetic equivalents.
5. The water vapour generating device according to claim 1, wherein the Bentonite clay can be supplemented by modified starch powders, on to which have been adsorbed natural, volatile herb and spice extracts, or synthetic equivalents.
6. The water vapour generating device according to claim 1, wherein the packaging is a sachet, the sachet being constituted of an hydrophihc, nonwoven material based on polypropylene
7. The water vapour generating device according to claim 1, wherein the packaging is a sachet, the sachet having both an outer and inner membrane of a perforated, non- hydrophilic material based on polyester (APED and polypropylene respectively
8. The water vapour generating device according to claim 7, wherein the sachet is produced from an hydrophijic, non-woven material laminated to a perforated, non- hydrophilic film on both its surfaces, which is adhered to itselt
9. The water vapour generating device according to claim 1, wherein the packaging is a sachet, the sachet being produced from a complex, which is adhered to itself and whsch is Constituted of an outer layer of a non- hydrophilic perforated material, a middle layer of an hydrophilic, non-woven material and an inner layer of a non- hydrophilic, perforated material.
10. The water vapour generating device according to claim 1, wherein the water used to hydrate the clay is spring water, mains supply water or additionally sanitised mains supply water.
11. The water vapour generating device according to claim 1, wherein the sachet when containing the fully hydrated clay, form only a minor inclusion in any food packaging, representing a total mass of less than 20g.
12. The water vapour generating device according to claim 1, wherein the fully hydrated clay, when exposed to microwave radiation, is capable of releasing water vapour equal to 80% of its original hydrated mass.
13. A food packaging system, including a water vapour generating device according to claim 1, the food packaging system being configured to facilitate the cooking of food by microwaves, the system further comprising a primary packaging; and at least one foodstuff contained in the primary packaging.
14. A food packaging system, according to claim 1, wherein the primary packaging is constituted by either thermo-formed trays with lidding film or both horizontal and vertical, form, fill and seal pouches, which are thermo-stable under microwave radiation.
15.A food packaging system, according to claim 11, wherein the primary packaging is transparent to microwave radiation.
16.The water vapour generating device according to claim 3, wherein the day is selected from the naturally occurring Bentonite clays, which are complex alumina silicates.
17. The water vapour generating device according to claim 4, wherein the minority addition of a hydrocolloid selected from a group of synthetIc, super-absorbents Consisting of polyacrylic acid salts.